Parasites, bacteria, and viruses have been the scourge of humanity as long as we have been here, but disease has reshaped our history and influenced our evolution. Parasites helped give our immune systems the boost it needed to get up and running, and the humble bacterium has helped dictate the form this planet has taken. Sometimes, it seems that we humans are simply playthings in their hands, but they haven’t just been capricious forces that toss us around like rag dolls. These microorganisms have also done incredible things to help humanity.

10The Viruses We Carried Out Of Africa Helped Us Survive

Thanks to the science of viral molecular genetics, we now know quite a bit about the bugs that infected us along our evolutionary path, and we have found that these hitchhikers have done quite a bit to help us along the way. For example, it was the evolutionary pressure they placed upon our immune system that made it as robust as it is today. Additionally, viruses may have played a role in the loss of specific receptors that we once possessed on the surface of our cells that infectious agents could latch onto and use to cause disease. By ridding the human body of this source of disease, viruses created a safer environment for themselves, benefiting everybody involved.

But they may have also played a role in ensuring that, among competing hominid species, it was Homo sapiens that came out on top. While our species was developing, disease and parasites encouraged genetic diversity and weeded out the unfit. Once the first Homo sapiens left the continent, they brought their infectious agencies and parasites with them. If you’ve read about North American and European smallpox, you know how this goes.

While it wouldn’t have been the only factor, viral parasites would spread to other hominids like Homo neanderthalensis (Neanderthals), who wouldn’t have had any previous exposure to the new bugs and possessed a nasal structure that was less efficient at filtering air and keeping new viruses at bay. They would have devastated other hominid species, because the bugs were primed to live in similar environments, but the hominids were not primed to receive them. Models have shown that if Neanderthals had a mortality rate only 2 percent higher than humans, it would have been sufficient to cause their extinction after 1,000 years of competition. While disease was doubtless not the only factor, it would have certainly played a large role.

Most models of human disease evolution claim that they mainly evolved during the Neolithic era, after man moved out of Africa and populations increased, so there is some evidence of this selective viral pressure. Many of these early viruses have even been so successful that their genes have literally become a part of our DNA. For example, the human genome has been found to contain genes from the borna virus that were gained about 40 million years ago. In fact, scientists have isolated about 100,000 elements of human DNA that have come from viruses, mostly within what is called our “junk DNA.” The viruses that make up the majority of our junk DNA are called endogenous retroviruses, and they are so much a part of us that a scientist recently brought one “back to life” and even infected hamsters and cats with it.

9Modern-Day Medical Uses Of Leeches And Maggots

For thousands of years, the European leech (Hirudo medicinalis) was used in medicine for bloodletting purposes, treating a wide range of disorders from hemorrhoids to ear infections. The practice goes so far back in time that an Egyptian painting from 1500 B.C. depicts their use. While some nations have never stopped using them, the practice fell out of favor in the Western world with the knowledge of bacteria and subsequent focus on the germ theory for medical treatment.

In the 1970s and 1980s, though, leeches made a comeback. Cosmetic and reconstructive surgeons found that they were an effective method for draining blood from swollen faces, black eyes, limbs, and digits. They are also helpful for reattaching small body parts like ears and flaps of skin, because they draw away blood that could clot and interrupt the healing process. Leeches have saved people from amputations and may even relieve the pain of osteoarthritis. Even veterinarians sometimes use them.

Maggots, on the other hand, are nature’s clean-up crew. They’re great for eating away dead or infected flesh, revealing the healthy tissue below in a process called debridement. They have also been found to be an effective treatment for ulcers, gangrene, skin cancer, and burns, among other things.

Maggots and leeches, as gross as they may be, are so effective that the FDA classified them as the first “live medical items” in 2010, paving the way for an entire industry called biotherapy. An organization called Biotherapeutics Education and Research Foundation (BTERF) has even sprung up to raise awareness of the new uses for these old critters, and there are several companies that sell them.

8Parasites And Our Immune Systems May Have Co-Evolved To Protect Us From Allergies

Researchers studying the effects of gastrointestinal parasites have come up with an astonishing theory: After parasites first colonized our gastrointestinal systems, they evolved over millions of years the ability to suppress our immune systems. At the same time, our own bodies evolved to partially compensate for the effect.

The astonishing part, and what this means for human health, is that once parasites and harmless microorganisms present in water and soil have been largely removed from their natural environment inside of us in developed nations through the use of modern medicine, our immune systems actually overcompensate for their loss, leading to allergies and even increased chances for asthma and eczema.

This “old friends” hypothesis (sometimes referred to as the “hygiene hypothesis,” though it’s actually more of a complementary theory) has gained more support in recent years as we identify new ways microorganisms have helped us survive over the eons. Clinical trials have been conducted using worms to test against multiple sclerosis, IBD, and allergies.

The main proponent of the old friends hypothesis is Graham A.W. Rook of University College London. He first proposed it in 2003, and since then, it has also been proposed as a possible cause of some forms of stress and depression.

Some people have taken the old friends hypothesis to its ultimate logical conclusion that if removing our parasites from society has led to health problems, we should put them back. In 2008, University of Wisconsin professor of neurology John Fleming conducted a clinical study in which he infected multiple sclerosis patients with parasitic worms to test their effectiveness against the disease. Over a period of three months, patients who had an average of 6.6 active lesions around their brain’s nerve cells were reduced to an average of two. When the trial was over, the number of lesions shot back up to 5.8 within two months. In earlier trials, the parasites appeared to have positive effects upon ulcerative colitis and Crohn’s disease as well.

Parasite therapy is still in the experimental phases, however, and probably has negative effects that outweigh the positive ones. As of now, the FDA has classified the worms as biological products that cannot be sold until proven safe. Only one species, Trichuris suis, has been approved for testing under Investigational New Drug (IND) status.

7Virotherapy

One of the most exciting and promising branches of medicine in recent decades is virotherapy, a biotechnology technique to reprogram viruses to treat disease. In 2005, researchers at UCLA announced that they had turned one of humanity’s deadliest enemies into a cancer-killer when they reprogrammed a modified strain of HIV to hunt down and destroy cancer cells. Around the same time, researchers at the Mayo Clinic in Rochester, Minnesota modified the measles virus to do the same.

The technique is similar to the one used to breed genetically engineered plants, in that a virus is used as a gene-delivery vehicle. It has long been recognized as the most efficient means of gene transfer. This system is used for the production of useful proteins in gene therapy and has great potential for the treatment of immunological disorders such as hepatitis and HIV.

Viruses have been known to have the potential to treat cancer since the 1950s, but the advent of chemotherapy slowed its progress. Today, virotherapy is proving to be extremely effective against tumors without harming the healthy cells around it. Clinical trials of oncolytic virotheraphy have shown low toxicity and promising signs of efficacy. In 2013, a drug called talimogene laherparepvec (TVEC) became the first drug based on a tumor-killing virus to succeed in late-stage testing.

One of the biggest challenges facing researchers is how to deliver the virus where it will do the most good before the body recognizes it as an intruder and mounts a defense. Current research is looking into finding natural tumor-targeting “carriers,” cells that can deliver the virus without either the cell or the virus losing its normal biological functions.

6Using Viruses To Cure Bacterial Infections

Bacteriophages are viruses that specifically attack bacteria. First recognized by Frederick Twort in 1915 and Felix d’Herelle two years later, they have been used to study many aspects of viruses since the 1930s. They are especially common in soil, where many species of bacteria make their home.

Because phages disrupt the metabolism of bacteria and destroy them, it has been long recognized that they could play a role in treating a wide range of bacterial diseases. Because of the innovation of antiobiotics, though, phage therapy was mostly shelved until the rise of antibiotic-resistant bacteria generated a renewed interest in the field.

An individual phage species is generally only effective against a small range of bacteria or even one specific species (its primary host species), which was originally seen as a disadvantage. As we have learned more about the beneficial aspects of our natural flora, though, it has come to be recognized as the advantage that it is. Unlike antibiotics, which tend to kill bacteria indiscriminately, bacteriophages can attack the disease-causing organisms without harming any other bacteria living inside us.

While bacteria can develop resistance to both antibiotics and phages, it only takes a few weeks rather than a few years to develop new strains of phages. Phages can also have an easier time penetrating the body and locating their target, and once the target bacterium is destroyed, they stop reproducing and soon die out.

5Vaccines

Beginning in the 1790s, when Edward Jenner developed the world’s first vaccine against smallpox using a less virulent strain called cowpox to inoculate patients, vaccines have saved countless millions of lives. Since then, several different types of vaccines have been developed. Attenuated or “live” vaccines use live viruses that have been weakened or altered so that they do not cause illness, while inactivated or “killed” vaccines contain dead microorganisms or toxins that are usually used against bacterial infections. Some vaccines—including subunit and conjugate vaccines, as well as recombinant and genetically engineered vaccines—only use a segment of the infectious agent.

When a vaccine is injected, the pathogen goes to work, but there is not enough of it to replicate at the rate it needs to in order to take hold. The body mounts an immune response, killing the pathogen or breaking down the toxin responsible for disease. The body’s immune system now knows how to fight the disease and will “remember” if it comes across it again. In other words, scientists have figured out how to get a pathogen to help its own target defend itself against it. They have even taken the first steps toward developing vaccines for several forms of cancer, with three vaccines approved by the FDA for the hepatitis B virus (which causes liver cancer), human papillomavirus types 16 and 18 (which cause cervical cancers), and metastatic prostate cancer in some men.

Thanks to vaccines, several diseases have been driven to virtual extinction. Smallpox is the most famous example, but polio, though not totally eradicated, comes in at a close second. Several other diseases might be gone by now if vaccines weren’t so hard to come by in the underdeveloped nations that still struggle with them. Things are getting worse instead of better, with diseases coming in from an unexpected source: affluent, educated Westerners who should know better.

Unfortunately, the anti-vaccination movement is making a comeback in regions where these diseases were once under control. Before the introduction of the measles vaccine in 1963, approximately 500,000 people per year were infected in the US, 500 of whom—mostly children—ended up dead. By 1983, there were only 1,497 cases reported, and after a brief resurgence in the ’80s and ’90s, reported cases were down to just 37 in 2004. After the anti-vaccination movement began gaining traction, 118 cases were reported in the US alone in 2011. That number keeps growing, fed by travelers coming in from areas with higher rates and finding less resistance. Whooping cough, once thought to be gone forever in the US, is also on the rise.

4Bacterial Waste Breakdown

Some of the smallest and simplest of creatures on Earth play some of the most important roles in safeguarding all of life. Bacteria have perhaps the most important role of all: breaking down and recycling waste.

The dead remains of animals and plants, along with the excrement of all organisms, contain vital nutrients and stored energy. Without a way to reclaim these nutrients, though, the available sources would be quickly depleted. Luckily, many bacterial species feed upon these energy sources, breaking them down to their smallest molecules and returning them to the soil, where they reenter the food chain.

As helpful as this process already is, humans have found many ways to exploit it for a variety of even more advantages. Bacteria are used in sewage treatment, industrial waste management, and the clean-up of oil spills, leaked pharmaceuticals, and wastewater. They have also been useful in the development of aqua-farming, algae control, and waterless toilets. Researchers and engineers are currently looking into their potential use in the production of environmentally friendly bioplastics, glues, and building materials. They may even be used to break down plastic waste.

3We Would Quickly Die Without Our Gut Bacteria

Poorly understood until recently (and there is still quite a bit of research to be done), the natural bacteria that lives in our guts works with our immune system to drive out pathogens, produce vitamin K, stimulate peristalsis, and perhaps most importantly, digest our food. Without our gut bacteria, we wouldn’t be able to perform any of these functions, and we would quickly die.

The more we learn about beneficial strains of gut bacteria, the more we can incorporate that knowledge into healthy living. After it was determined that certain gut bacteria can play a role in obesity, probiotics became all the rage. Probiotics are the bacteria that reside in fermented foods and are now sold as supplements. Bacteria like some species of bifidobacteria, found in most yogurts, can create a highly acidic environment in which less-beneficial microorganisms cannot survive. Fatty foods and stress can also play a role in the health of our stomach flora, killing beneficial bacteria while favoring the more harmful kind that cause gas, bloating, and “leaky gut syndrome.”

In a huge breakthrough in the study of our gut bacteria and what they do, a team of Chinese and Danish researchers have recently developed a new way to identify these microorganisms using DNA sequence data. They identified over 500 species of benign bacteria and 800 new species of viruses that could live off them, providing hope for new ways to treat diseases associated with them, such as diabetes, obesity, and asthma.

2Skin Bacteria Serve As Our First Line Of Immune System Defense

The moment you emerged from your mother’s womb, you were set upon. They ambushed you in mere moments and colonized every inch of your skin, and they have been with you ever since. They are prokaryotes and other bacteria, and without the evolutionary partnership humans forged with them millions of years ago, you would have been dead soon after being born.

One of the most common skin bacteria is Staphlococcus epidermis, a bug that we now know plays a role in fighting off Leishmania major, the cause of a nasty disease called leishmaniasis that results in skin boils and open sores that don’t heal. The good bug triggers an immune response called IL-1 that the body can’t produce on its own, making Staphlococcus a necessary part of the human body, as vital to our existence as any organ.

Prokaryotes, which also colonize the digestive tract, cover every exterior surface on the skin. Along with the rest of our beneficial skin microbiota, they became a part of us when they started competing against less-benevolent microorganisms for real estate. Along with the immune cells in our skin, they protect us against both pathogenic bacteria and opportunistic fungi that try to invade. This allows our bodies to spend less energy defending our exteriors and focus more on things like fighting viruses and precancerous cells.

While there is still much to learn before we can really use this knowledge in our health regimens, we are already looking to a future that involves the purposeful use of skin bacteria. A start-up based in Massachusetts called AOBiome, for example, has created a body spray made of live cultured chemoautotrophic bacteria called Nitrosomonas. They claim that their spray can “replenish healthy skin bacteria” and even replace showering, as the bacteria live off the ammonia in our sweat.

1Life As We Know It Wouldn’t Be Here Without Cyanobacteria

Cyanobacteria, or blue-green algae, are possibly the oldest still-living species on Earth, with fossils dating back 3.5 billion years. They are unicellular bacteria that grow in colonies, and if it weren’t for them, you wouldn’t be here, and neither would nearly every other form of life.

Cyanobacteria were the world’s first photosynthesizers. They used energy from the sun along with chemicals in primordial oceans and inert nitrogen in the atmosphere to make their food. As a waste product, they generated oxygen, a poison to virtually every other form of life at that time and the cause of early mass extinction events. Over a period of roughly 300 million years, all this oxygen generation helped form the atmosphere as we know it, during the Archaean and Proterozoic eras.

That wasn’t the only way this bacteria kick-started life as we know it. Sometime during the Proterozoic or early Cambrian era, they formed a symbiotic relationship with certain eukaryote cells, making food for the cell in return for a stable environment to call home. These were the first plants, as well as the origin of eukaryotic mitochondria, which is essential for animal life. This truly titanic event is now known as endosymbiosis.

While several forms of cyanobacteria are toxic, a species named Spirulina was an important food source for the Aztecs and eaten regularly by many Asian nations. Today, it is often sold in powder or tablet form as a health food supplement.

Lance LeClaire is a freelance artist and writer. He writes on subjects ranging from science and skepticism to religious history and issues to unexplained mysteries and historical oddities, among other subjects. You can look him up on Facebook.

You are not going to make it through life without getting sick. It happens to the best of us. What kind of sickness you end up with depends on a number of factors. Some illnesses are far easier to get over than others. Some are pretty much death sentences the moment you’re diagnosed.

The cause of your illness can also vary greatly. Did you eat something that had gone bad? Chances are you picked up some kind of bacteria. Did you get sick after going swimming in some polluted water? You might have got a parasite. Did somebody sneeze on your bagel? You might have a virus. And let’s not forget that, if there’s mold growing in your house, you could be infected with a deadly kind of fungus. What a fun group!

In an ideal world, you’ll just avoid every kind of dangerous bacteria, parasite, fungi, and virus. But the world is rarely ideal. So what’s the most dangerous one of them all? If an evil wizard trapped you in a room with four doors, which would be the one that you’d be most likely to survive a walk-through? Let’s look!

The Basics

In general, a virus is more dangerous than a bacterium. Take that with a grain of salts, of course, because circumstances will vary. The virus that causes a cold is probably not going to be as dangerous to you as botulism.

Bacteria are single cells, and they’re able to survive on their own. Most bacteria are harmless, some are even helpful. Your gut has 100 trillion bacteria in it right now to help you digest your food. Only a small number of them are actually going to cause you any harm. Bacteria can be 10 to 100 times larger than viruses, or about one to three microns in length. Salmonella is a common bacterium.

On the other hand, viruses don’t do well on their own. They have a parasitic nature and require a host to help them survive. They need your body to reproduce and proliferate the cost of which is you getting sick and maybe dying. Viruses may be as small as 20 to 200 nanometers in diameter. 

Parasites, part of a group called eukaryotes (meaning their cells have a nucleus and internal structures) are larger than viruses and often bacteria as well. Some parasites can be whole, living organisms, like a tapeworm. 

Fungi are most often found in the form of spores and molds. Athlete’s foot is a kind of fungal infection.

Bacteria Breakdown

A single bacterium is a single cell. It is one complete little microorganism all on its own and can live outside of a human body. In fact, many bacteria happily reproduce in the soil, in rotten food, on your skin and anywhere else the conditions are right.

The dangerous kinds of bacteria can affect your body in a number of ways.  Many dangerous bacteria are able to produce toxins which can be deadly and are what lead to serious infections in the body. The toxins can paralyze the cells in your body or even destroy them, disrupting normal cell function and causing serious damage. Others can reproduce so prolifically that they crowd out your normal, healthy cells.

Thanks to antibiotics, medicine has been able to save countless lives by treating bacterial infections. Antibiotics can either kill or slow the growth of bacteria. They do this by either destroying the bacteria cell wall or limiting its ability to grow and reproduce.

Because bacteria are able to reproduce very quickly, some every 20 to 30 minutes, they’ve also been able to mutate quickly. This has given rise to antibiotic-resistant bacteria. Over time, the bacteria that has survived has mutated to develop various defense mechanisms against antibiotics. Some may produce enzymes that destroy antibiotics, and others have ways of removing the antibiotic before it can reach its target.

Some more common bacteria, like salmonella, gonorrhea, and campylobacter, have developed strains that are resistant to antibiotics. This means that any infection that may have been considered easily treatable could become far more dangerous and deadly as it evolves. 

Because of the ever-changing nature of bacteria, it’s hard to choose the “worst” of them all. In 2024, the World Health Organization issued a list of dangerous, drug-resistant bacteria and there were 15 chosen. Near the top of the list were bacteria that cause tuberculosis, called mycobacterium tuberculosis. This is potentially the deadliest bacterium in the world and is responsible for 1.7 million deaths per year. 

Virus Breakdown

Viruses are not cells or living organisms on their own. Instead, a virus is a small amount of genetic material that is encased in protein. A virus can only work if it’s inside a living organism. On its own, it’s nothing, it has no function or purpose. 

Once inside a host organism, the virus uses the cells of that living organism to replicate. This process can end up destroying cells and leading to infections. Because viruses are so small, they can even infect bacteria and fungi. You can breathe them in or contract them through things like mosquitoes in ways that bacterial, parasitic, and fungal infections can’t because they are larger.

While a host body will try to produce antibodies to fight off a virus, if they get overwhelmed, and the virus can replicate faster than the host organism can fight it off, that’s when sickness takes over and the potential outcome is death. The viruses need your cells to reproduce because they don’t have the material or energy to do it on their own. This process destroys your cells.

Your body will fight back by raising the temperature. That’s what a fever is. Viruses tend to need a very delicate balance of temperature to survive and even a few degrees too warm can kill them. Unfortunately, a prolonged fever is dangerous for you as well. 

In addition, your immune system will try to use antibodies to fight the virus if it can. It needs to be exposed to a pathogen before it can make antibodies, however. If the virus is something you have never experienced, you will have no antibodies at first and your immune system may not be able to fight back. 

A virus like Ebola is extremely deadly. Up to 90% of people who contract Ebola will die from it. While that’s terrifying, it also ends up being one of Ebola’s weaknesses. Because it kills so quickly, the disease is not able to spread as well as others that don’t have such a high, swift mortality rate. Outbreaks, once isolated, tend to burn themselves out before they spread too far from the source. 

Judging the danger of a particular virus can be tricky. While Ebola kills up to 90% of people who contract it, it’s not widespread. However, HIV has spread all over the globe and is arguably one of the deadliest diseases in history. As many as 32 million people have died from HIV. That said, new treatments have greatly reduced the overall mortality rate, and the odds of dying from HIV now, with treatment, are very low.

In 1918, a flu pandemic killed somewhere between 50 million and 100 million people. 

Rabies is another virus that can seem quite common but is exceedingly dangerous. Without proper treatment, the mortality rate for humans infected with rabies is nearly 100%.

Viruses we have mostly eradicated were far deadlier than what most modern people can understand. Smallpox, for instance, killed about 300 million people. 

Fungi Breakdown

Thanks to pop culture, most people are familiar with just how terrifying a fungal infection can be. What first gained attention as quirky articles on the internet were then made into a worldwide phenomenon in the game and subsequent TV show called The Last of Us.

In The Last Of Us, much of mankind has been wiped out by a fungal cordyceps infection. Cordyceps is a real thing that has been seen infecting far less complex organisms like ants. The fungus grows inside of them, literally breaks through their bodies, and forces them to keep moving like zombies even when they should be dead. Fascinating stuff, but not applicable to humans. Our immune systems are vastly more complex than an insect’s and, as a result, we are immune. Unless it mutates one day. 

While cordyceps won’t kill you anytime soon, it doesn’t mean other fungi aren’t a danger. In 2023, the CDC warned about the rapid spread of Candida Auris. The fungus is resistant to most antifungal medications and was putting people in the hospital on ventilators. The infection can spread into your heart, lungs, blood, eyes, bones and organs.

Another fungus, cryptococcus neoformans, has a mortality rate between 41% and 61% and is especially dangerous to those with an already compromised immune system. The fungus, a kind of yeast, is found all over the world in soil. It can cause a kind of meningitis.

Aspergillus fumigatus is a kind of mold and has a mortality rate as high as 90%. You can find it almost anywhere that leaves fall on the ground and start to rot. Estimates suggest all of us inhale between 10 and 100 Aspergillus spores every day. 

The problem with Aspergillus and other fungal infections is they receive less attention and fewer resources than bacteria and viruses. Also, fungi are quick to adapt to medications and become resistant. Nevertheless, as many as 1.7 million people per year die from fungal infections, which is more than malaria and twice the number who die of breast cancer. There are over 150 million severe infections reported that are damaging but not fatal, as well.

Parasite Breakdown

Parasites are, hands down, the creepiest and most disturbing things that can infect you. Even if they aren’t as deadly as other infections, they tend to be more off-putting if for no other reason than many of them are big. These are living organisms that take up residence inside of you. The way they get inside of you can be just as disturbing as the fact they are inside you.

Take Strongyloides, for instance. This parasite transmits through feces but can live in soil for weeks. If you walk barefoot across it, they will burrow through the flesh of your foot. They’ll ride your bloodstream all the way to your lungs and then cause you to cough. Coughing brings them to your mouth where they get swallowed into your gut, right where they want to be. They can live for years in there and may turn deadly depending on the medications you take.

Giardia, a small parasite, is transmitted most often through feces or things contaminated with it. You can get it on your hands or in the food you eat and ingest it without realizing, as it’s a small, one-celled organism. 

Tapeworms, which can infect you if you accidentally ingest their eggs in undercooked meats, or from meat handled unhygienically, can grow to be up to 12 feet long in your gut, but some have been reported to be over 50 feet. They can live for 30 years.

Brain-eating amoebas have been contracted by people swimming in still, warm bodies of water like ponds in the US. They enter through the nose and infect the nervous system with a near 100% mortality rate. 

Parasitic infections can lead to sepsis among numerous other symptoms. One of the most well known and deadly parasites is the malaria parasite, transmitted by mosquitoes, which caused over 600,000 deaths in 2022. 

As disgusting as parasites can be, many of them will not actually kill you. It’s not in a parasite’s interest to kill its host, after all. It’s estimated about one in seven people in the world currently have an intestinal parasite. Some estimates boost that to about half the world’s population. 

So Which is Worst?

You can’t make a strong claim that any one of these deadly pathogens is better than another. There is far too much variety among each category to conclude one is preferable to another. In addition, there are so many mitigating factors that can alter just how dangerous an infection from one of these pathogens could be.

It’s much easier to state that you really don’t want to get an infection of any kind, be it parasitic, fungal, viral or bacterial. None of these are going to be a good time for you, and all should be avoided or treated quickly if they ever come up.

Viruses challenge our definition of life. Neither dead nor alive, they are simply functional or not. Viruses do not possess the machinery to replicate themselves. Yet you can even argue that they are more evolved than us. With each discovery about viruses, we realize there is so much more to learn.

10Black Widow Virus

Scientists have recently discovered a virus containing the gene for black widow poison.

The WO virus specifically targets Wolbachia bacteria in arthropods. Latrotoxin kills by poking holes in cell membranes. It is believed that the venom genes allow the WO virus to break through cells and evade the host’s immune system. This is the first time animal genes have been seen in bacteriophages—bacteria-targeting viruses.

Experts hypothesize that the virus picked up the genetic material after breaking out of a Wolbachia bacterium into a black widow cell. However, it is possible the spider stole the gene from the WO virus.

9Infertility Virus

A mysterious viral infection may be the cause of half of unexplained cases of infertility. In one-quarter of infertility cases—roughly one in 70 women under the age of 44—doctors cannot find a cause. An Italian research team discovered that a virus in the herpes family is to blame. It causes immune reactions that make the womb inhospitable for an embryo. Customized anti-viral treatment could offer help.

The team studied 30 mothers and 30 women with unexplained infertility. 13 of the infertile women were infected with HHV-6A. None of the mothers had it. This herpes variety was discovered over 30 years ago but remains a mystery. HHV-6A infection releases estradiol hormone, which triggers ovulation and prepares a womb for fertilization.

8Survivor Virus

Scientists have recently unlocked the secrets to a virus that can survive boiling acid.

The SIRV2 virus infects a microbe called Sulfolobus islandicus, which lives in acidic hot springs where temperatures top 80 degrees Celsius (175 °F). Using a Titan Krios electron microscope to examine the specimens in previously unimaginable detail, scientists have unlocked the basic mechanism of resistance to heat, desiccation, and ultra-violet radiation.

SIRV2 forces genetic material into a protective structural state called A-formation to survive extreme conditions. The mechanism is remarkably similar to the spores bacteria form to survive such environments. These spores are known to cause hard to combat diseases like anthrax. Scientists plan on using these survival mechanisms to design a DNA package for gene therapy.

7Multicomponent Virus

Normal viruses have all their genes in one viral particle. This viral ball attaches to a cell, opens, and injects its genetic material inside. The host cell begins replicating the virus. Once enough copies are made, they kill the cell, break free, and infect more.

The Guaico Culex virus is different. To become infected, a cell needs to be exposed to four varieties of packages. A fifth appears optional.

Named after the region in Trinidad it originated, Guaico Culex was discovered during a comprehensive study by the US Army Medical Team to isolate mosquito-borne viruses around the globe. While researchers do not believe Guaico Culex virus can infect mammals, they recently discovered a closely related variety in Uganda’s red colobus monkeys.

6Human Endogenous Retrovirus

Roughly 8 percent of the human genome comes from ancient viruses. Retroviruses reproduce by inserting their genetic material into a host and hijacking its replication machinery. Occasionally, these viruses infect sperm and egg cells. If these cells survive, they go on to create an organism containing the virus’s DNA in every cell. These are referred to as endogenous retroviruses—in humans, HERVs. The vast majority are considered non-functional “fossils.” However, a small portion are still intact and can make infectious particles.

Despite being millions of years old, the HERV-K group of viruses appears capable of replicating. Researchers recently discovered a variant that contains no mutations that would downgrade its function. It is believed that this HERV-K remained “alive” within humans until recently. Scientists are unsure whether the dormant virus could reemerge. There is speculation that HERV-K might have been selected for a survival advantage it offered.

5Bourbon Virus

A Kansas farmer recently died from a mysterious tick-borne viral infection. The man’s symptoms began with nausea, weakness, and diarrhea. Lung and kidney failure followed. Doctors treated him with antibiotics, the standard course of action for tick-borne illness. Nothing worked. After 10 days in the hospital, he was dead.

With only one confirmed case, doctors are clueless about the disease’s full spectrum. It might be a killer. Or this might be a rare case in which a mild disease became deadly. The best defense is to avoid tick contact by wearing long pants, using insect repellent, and performing frequent tick-checks.

4Siberian Giant Virus

A French research team recently unearthed a 30,000-year-old giant virus from the Siberian permafrost—and it’s still infectious. The virus was discovered in a soil sample from 98 feet beneath the ground. It is wider than other giant viruses, and large enough to be seen through a standard microscope.

The team fished for viruses using amoebas, their target hosts, as bait. The amoeba starting dying, and researchers discovered they were laden with these ancient giants. Unlike most viruses, which attack the nucleus, sibericum sets up replication factories in the host’s cytoplasm. Although sibericum only targeted amoeba, another giant virus dubbed Marseillesvirus recent infected an 11-year-old boy in France. It is possible that dangerous viruses also lurk deep underground. More than any other factor, human activities like drilling and mining are likely to unearth these slumbering monsters.

3Deep-Sea Virus

Researchers now believe there is more biomass inside earth’s dark, nutrient-deprived depths than anywhere else. In the ocean depths off California, they recently made a remarkable discovery into that mysterious biomass: a virus that infects methane-eating archaea, small bacteria-like organisms, on the ocean floor. Samples were collected from a deep methane seep by pushing tubes into the ocean sediment. Back in the lab, the sediments were fed methane, which triggered archaea growth—along with their viral parasites.

The virus selectively targets one of its own genes for mutation. So do the archaea. The target of the mutations are the tips of the virus, which come into contact with their host. It is a countermeasure against tarchaea’s own selective mutation defenses. This has led to a deep-sea arms race. Partial genetic matches between the California deep-sea viruses and ones discovered around Norway suggest global distribution.

2Mysterious Paralysis

In 2015, a wave of American children suffered from acute flaccid paralysis. The outbreak coincided with the flaring up of another respiratory disease caused by the enterovirus EV-D68, a relative of poliovirus. Many suspected a correlation. However, EV-D68 is not known for causing systemic problems like paralysis, and it was only found in 20 percent of the cases. A case from Virginia led some to believe that the cause might be from another virus called C105.

Before the Virginia case, C105 had only been identified in Peru and the Republic of Congo. The disease is associated with respiratory problems. However, a few African cases were linked with paralysis. The C105 theory could explain why 80 percent of the patients tested negative for EV-D68. Yet none of the patients were found to have enterovirus in their spinal fluid, which would account for the neurological symptoms. The cause of the outbreak remains a mystery.

1Undiagnosed Hemorrhagic Fever Syndrome

South Sudan is plagued by violence, hunger, and now a mysterious viral outbreak. So far, 10 people have died from Ebola-like symptoms of bleeding, fever, and vomiting. However, Ebola is not the culprit. Doctors have dubbed the disease “undiagnosed hemorrhagic fever syndrome.” Last year, Darfur in Sudan had 129 fatalities from an unidentified illness. It is not yet known whether they are the same disease.

Blood samples for infected patients have revealed a host of viruses: onyong-nyong, chikungunya, and dengue fever. However, none explain the 10 deaths, and none contained Ebola. Most believe this is a virus spread by ticks or mosquitoes, but some are not ruling out the possibility of a bacteria or parasitic origin. So far, there is no evidence of person-to-person transmission, and 75 percent of the victims are under 20. Violent civil war and underdevelopment in the region prevent effective research into the disease’s origins.

Abraham Rinquist is the Executive Director of the Winooski, Vermont, branch of the Helen Hartness Flanders Folklore Society. He is the coauthor of Codex Exotica and Song-Catcher: The Adventures of Blackwater Jukebox.

Virus. The word is usually met with fear and understandably so. These microscopic collections of biological chemicals have been responsible for countless cases of death and sickness. The very mention of a deadly viral pandemic can send entire neighborhoods, cities, or even geographic zones into a state of sheer, frenzied panic.

Viruses are invisible to the naked eye, and they exist almost everywhere on Earth. They can infect fungi, plants, animals, and yes, humans. Some people have even speculated that viruses could pose a grave threat to the future of humanity.

However, not all viruses are bad. In fact, as we learn more about them, we are discovering that some viruses are actually quite beneficial. They have helped us in ways that we didn’t realize at first, and others pose interesting but positive possibilities for our future.

10 Bacteriophages

Bacteriophages are viruses that infect bacteria. They are found almost everywhere—in soil, in water, and even in the human body (mostly in our gut and mucus).

They were originally discovered in 1915 by Frederick Twort and have since become relatively famous in the field of microbiology as a therapeutic tool to help control bacterial infections.

While “phage therapy” is still under development, it is possible that it could be used in several different applications. It has already been used to treat some different types of ailments, and it shows great promise for the treatment of conditions ranging from cystic fibrosis to cancer. Some say that phage therapy also offers a viable replacement for traditional antibiotics in our age of antibiotic-resistant bacteria.^[1]

9 There Is a Virus That Gives Plants Extreme Heat Resistance

Tropical panic grass has always had the ability to grow in soil with an unusually high temperature. Researchers have since discovered that the cause behind this unique ability seems to be a virus. A fungal endophyte grows on this grass, and a virus that infects this fungus seems to be the source of this heat-resistant power.

Even more interesting, scientists attached the virus to other plants, giving them the same ability. The researchers even managed to grow tomatoes in soil as hot as 60 degrees Celsius (140 °F) without killing them.^[2]

But what happens if you remove the virus? They discovered that plants “cured” of the virus lost the ability to grow in extreme heat. Maybe that’s how the Human Torch does it.

8 Oncolytic Virus

Cancer—a word that causes dread in nearly every person affected by this potentially life-threatening disease. Doctors have sought different treatments and cures for the disease for more than 100 years; however, new interest has shifted focus to using viruses to treat cancer. And in recent years, a small but growing number of patients have begun to benefit from this approach. Research has shown that some viruses can infect and kill tumor cells. These viruses are known as oncolytic viruses and include viruses found in nature and viruses modified in the laboratory to reproduce efficiently in cancer cells without harming healthy cells.

Oncolytic viruses have long been viewed as tools for directly killing cancer cells. But a growing body of research suggests that some oncolytic viruses may work—at least in part—by triggering an immune response in the body against the cancer. When a virus infects a tumor cell, the virus makes copies of itself until the cell bursts. The dying cancer cell releases materials, such as tumor antigens, that allow the cancer to be recognized or “seen” by the immune system. For this reason, some researchers consider oncolytic viruses to be a form of immunotherapy—a treatment that harnesses the immune system against cancer.^[3]

7 Adenoviruses

Adenoviruses are a group of fairly common viruses. They are extremely contagious, usually cause only mild symptoms, and generally go away within a few days.

Some of them are actually quite well known. Bronchitis, pneumonia, many stomach infections, colds, croup, and even meningitis can all be found within the adenovirus family.

But researchers have also learned that one particular strain of the virus, type 52 (HAdV-52), binds to a particular type of carbohydrate found in cancer cells. This creates some interesting possibilities for virus-based cancer therapy.

There is obviously more studying to be done. But in the future, scientists might be able to arm viruses with genes to help fight cancer. They may also be able to use viruses to activate the body’s own immune system to fight the cancer itself.^[4]

6 Norovirus

Virologists have become especially interested in noroviruses. These particular micro life-forms are well known for their ability to cause epidemics of diarrhea on cruise ships. They are also infamous for their ability to ravage laboratory mice colonies with the disease.

But as it turns out, some strains of the virus have proven useful—especially for their role in helping to “normalize” mice that have grown in sterile environments. These mice don’t make enough T cells, which hurts their gut bacteria and immune response.

To fix the problem, researchers have shown that giving bacteria to the mice can help to rebalance their immune cells, but adding a norovirus to the mix can actually solve the same problem. Researchers also found that some norovirus strains helped lessen the effects of pathogens that usually cause weight loss, diarrhea, and other related symptoms in mice.

This makes for an exciting discovery as researchers unveil new ways to use viruses for good. Giving strains of the norovirus to humans to treat other diseases would be seen as highly controversial, but much evidence says that it could actually help.^[5]

5 Ancient Retroviruses

Ancient retroviruses may be the reason we don’t lay eggs.

Scientists have yet to unravel the entire part that ancient retroviruses have played in human development. But some of them, technically referred to as “endogenous retroviruses,” are believed to have helped in the evolution of the placenta in mammals.

To put it in super simple terms, some scientists believe that a primitive human ancestor contracted an endogenous retrovirus that caused mutations in the genetic code. This eventually led to mammals being capable of live birth.^[6]

The formation of the placenta was a huge step in the evolutionary process because it allowed mammals to give birth to live young. But when you take a really close look at the relationship between a mother and a fetus, it is not surprising that it shares many of the same characteristics you would expect to see in the relationship between a host and a parasite.

The work is ongoing. But don’t be surprised if we discover someday that the reason human females give birth to live babies instead of laying eggs is thanks to an ancient virus that altered our DNA.

4 Gamma-herpesviruses

This one is fairly technical, but it is no less amazing.

The Gammaherpesvirinae is technically a subfamily of herpesviruses that includes several different viruses. There are actually many different types of herpes viruses, with the best-known examples probably being herpes simplex virus type 1 and herpes simplex virus type 2, which cause cold sores and genital herpes.

As it turns out, latent infection with one type of gammaherpesvirus (type MHV-68) has been shown to increase resistance to infection with Listeria monocytogenes—the bacteria best known for food poisoning.

Who would have thought that herpes would help to fight food poisoning?^[7]

3 Cowpox

This story actually begins with a dangerous virus called smallpox. Nobody is sure where it came from. But it is believed that even as early as the third century BC, it was afflicting the Egyptian empire. Records of it have been discovered in China from the fourth century, and it has basically shown up everywhere since.

It was a devastating disease that killed about 30 percent of infected people. Even those who survived were often left with terrible scars as a result of the ordeal.

But in 1796, an English doctor named Edward Jenner made a discovery. He noticed that milkmaids tended not to contract smallpox as often as everyone else. Soon, he realized that a similar virus called cowpox often spread from cows to the milkmaids and may have had something to do with it.

He tested his theory by inoculating a boy with material from a cowpox sore and exposing him to smallpox. Although it may sound like a shocking experiment, it was actually successful. This led to the practice of vaccination that ended up eradicating the smallpox virus two centuries later.^[8]

2 GBV-C

HIV is probably one of the most terrifying and infamous viruses of the 21st century. Nevertheless, another virus, GBV-C, has been getting some attention from scientists for its effect on those who are HIV positive.

GBV-C is a member of the Flaviviridae family of viruses and can also be referred to as hepatitis G. The interesting aspect of this virus is its effect on the progression of HIV.

To put it simply, people who have both HIV and GBV-C tend to display a slower progression to AIDS and improved odds of survival—which is pretty amazing.^[9]

Who would have imagined that the existence of another virus could possibly slow down a virus as dangerous as HIV?

1 The Arc Gene

Did you know that human consciousness may have originally been caused by a virus? Yes, it is possible, and here is why.

Researchers believe that a virus attached itself to the genome of one of our ancestors long ago—probably even before we walked on two legs. But they also believe that a tiny bit of the genetic coding contained within the virus still exists within our brains today and may be responsible for some serious “brainpower,” including consciousness itself.

The Arc gene is essential for the learning process in humans. Weirdly enough, it communicates by sending genetic material from one neuron to another using a process that is commonly seen in viruses.^[10]

Further research must be done to determine exactly what this means. But right now, it looks as though it is very possible that we inherited our ability to learn and form conscious thoughts from the genetic material of some ancient brain virus!

Yes, the universe is definitely a weird and mysterious place.

Joshua Sigafus is just a writer who is trying to make the world a better place.

Scientists are at it again. This time, they’re creating new viruses and bacteria in their laboratories. Scientists usually prefer altering already-existing or extinct bacteria and viruses to produce new strains that will defeat our immunity, vaccines, and drugs.

Sometimes, they prefer creating new viruses and bacteria from scratch. However, these strains are not always dangerous to humans even though they could be deadly to animals like mice and even to other bacteria.

SEE ALSO: 10 Viruses That Actually Help Humankind

10 Horsepox

Scientists at the University of Alberta have created horsepox, a lethal virus closely related to the equally deadly smallpox. Unlike smallpox, horsepox does not affect humans and is only fatal to horses. The scientists created the virus during a six-month study sponsored by pharmaceutical company Tonix. The researchers purchased DNA pieces via mail order and arranged them to form the virus. The entire project was not expensive. The DNA pieces used to create the virus cost just $100,000.

The study caused a dilemma at the time it was revealed. Other scientists were concerned that governments or even terrorists could use the knowledge to create smallpox virus for biological weapons. A smallpox epidemic could become deadly for us today. We no longer get vaccinated for it because we eradicated the disease in 1980.

The researchers clarified that they created the virus because they wanted to develop improved smallpox vaccines. Tonix later revealed that it had produced a smallpox vaccine with the horsepox virus. Other scientists say that the researchers could have extracted horsepox from wild horse populations instead of creating it from scratch. Tonix said they would have done just that if they had known they had natural access to the virus. However, lead researcher David Evans said they recreated the virus because Tonix would have been unable to commercialize the horsepox virus taken from the wild.^[1]

9 Black Death

Between 1347 and 1351, millions of Europeans were afflicted with a mysterious disease that killed over 50 million people. Today, we know this disease is the Black Death, which is caused by the Yersinia pestis bacteria. Although the Black Death is still around, it is not as potent as it used to be.

A few years ago, researchers from several schools, including the University of Tubingen in Germany and McMaster University in Canada, recreated the deadly bacteria from DNA samples extracted from the teeth of a victim who died during the plague. They got only 30 milligrams of the bacteria from the teeth, but that was enough to recreate it.

As a result, researchers confirmed the original bacteria’s relationship to the Black Death around today. Some scientists had claimed that the bacteria were of different strains, but they are now confirmed to be the same. The one we have around today only became less deadly after it mutated.^[2]

8 Polio

Like their counterparts at the University of Alberta, scientists at the State University of New York have created a deadly artificial virus by buying DNA pieces via mail order. This time, it is polio, and it is as potent as the natural one. Mice exposed to the artificial polio got sick just as they would have if exposed to natural polio.

The laboratory-created polio was controversial among scientists. The researchers who produced it had taken its code from databases available to almost anybody. Other researchers fear that people with ulterior motives could develop their own artificial polio, which is much easier to make than other dangerous viruses like smallpox.

Smallpox’s genetic code is 185,000 letters long while polio’s is just 7,741 letters long. Although we are already at the brink of eradicating polio, scientists fear that we will still need to be vaccinated against the disease because it could be recreated.^[3]

7 Mousepox

A few years ago, researchers at the Australian National University and the Commonwealth Scientific and Industrial Research Organization (CSIRO) produced a deadly mutated strain of mousepox by mistake. Mousepox is another lethal virus that belongs to the same family as horsepox and smallpox.

The researchers were trying to develop birth control for mice at the time that they mistakenly created the virus. They inserted a gene that promoted the creation of interleukin 4 (IL-4) into mousepox, which they injected into some mice. The mice were vaccinated and were not supposed to be harmed by the mousepox.

Instead of making the mice infertile as researchers had expected, the weakened virus turned lethal and destroyed the immune systems of the mice, killing them in nine days. The new mousepox was so dangerous that it was resistant to vaccination. Half of the other vaccinated mice exposed to the mutated mousepox also died.

The researchers were so scared by their invention that they did not want to publish their findings. They even met with the Australian military to confirm if it was safe to publish.^[4] Scientists fear that human smallpox could also mutate and become deadlier if injected with IL-4. However, they are unsure because no one has tried it yet. We know it’s only a matter of time before some scientist does.

6 SARS 2.0

Severe acute respiratory syndrome (SARS) is a lethal virus. More than 700 people were killed during a SARS epidemic that infected 8,000 people in 29 countries between 2002 and 2003. Now, scientists have made it deadlier.

The new mutant SARS virus was created by a group of researchers led by Dr. Ralph Baric of the University of North Carolina. They call it SARS 2.0. The researchers developed the virus by adding some protein to the naturally occurring SARS. SARS 2.0 is immune to vaccines and treatments used to cure the naturally occurring SARS virus.^[5]

The team said that the research was necessary because the natural SARS virus could mutate and become immune to our vaccines. By creating a deadlier and mutated virus, we could develop stronger vaccines that will save us from a more lethal SARS epidemic. That is, if the natural SARS ever mutates.

However, other scientists are concerned because the SARS 2.0 that is supposed to save us from a deadly SARS epidemic could start that epidemic if it ever escapes from the lab.

SEE ALSO: Top 10 Mysterious Viruses

5 MERS-Rabies Virus Hybrid

Scientists have created a MERS-rabies hybrid virus. The idea is to use the virus to develop a vaccine that will protect us from both viruses. Rabies is a deadly disease that can be transmitted to humans through the bites of infected dogs that usually have the virus in their saliva.

Middle East Respiratory Syndrome (MERS) is a new virus that appeared in Saudi Arabia a few years ago. It is closely related to SARS and is spread from bats to camels and, finally, to humans. MERS infected 1,800 people at the time of its first epidemic and killed over 630. Its fatality rate is around 35 percent.

As we mentioned in the previous entry, SARS infected over 8,000 people during a 2003 epidemic but killed just over 700. Although SARS caused more deaths in absolute terms, it has a lower fatality rate than MERS. Only about 10 percent of SARS victims died. And for now, we do not have any vaccine for MERS.

To create the MERS-rabies hybrid, researchers took some proteins from the MERS virus and added it to rabies. They used the new virus to develop a new vaccine that made mice resistant to rabies and MERS. They believe that the vaccine can also be used for humans and camels at risk of getting MERS.^[6]

4 Phi-X174

Phi-X174 is another artificial virus we have produced in laboratories. It was created by researchers at the Institute of Biological Energy Alternatives in Rockville, Maryland. The researchers modeled the artificial virus after the natural phiX virus. PhiX is a bacteriophage, a category of viruses that infect and kill bacteria. However, it has no effect on humans.^[7]

The researchers created the artificial virus in 14 days, yet it resembles the natural virus so much that it is impossible to tell them apart. The researchers hope that the new virus is the first step in developing mutant and artificial bacteria that can be used for the benefit of man.

3 Unnamed Virus

Researchers from University College London and the National Physical Laboratory have created an unnamed virus that kills bacteria and behaves like a real virus. Like phi-X174, it is a bacteriophage but deadlier.

The unnamed virus attacks any bacteria around it. Within seconds, it breaks into smaller parts that attach and create holes on the bodies of the bacteria. The holes quickly become larger, forcing the bacteria to leak their contents. The bacteria die soon after.

Despite its scary potency, the unnamed virus is not dangerous to humans and did not attack human cells during tests. However, it could enter human cells just like natural viruses. Researchers hope the results will be used to treat and study bacterial diseases in humans. The virus could also be used to alter the human gene.^[8]

2 Bird Flu

Some Dutch scientists have created a mutant and deadlier version of the already-lethal bird flu. Natural bird flu is not easily transmitted among humans. However, the researchers altered it so that it could be. To test their new virus, the researchers exposed some ferrets to it. Ferrets were chosen because they had similar bird flu symptoms to humans.

Ten generations later, the already-changed virus mutated again and became airborne. Natural bird flu is not an airborne disease. The study was controversial in the science community. It became even more so when the Dutch researchers attempted to publish the process to create the deadly virus.^[9]

Although scientists fear that terrorists could use the study to produce a deadly biological weapon that could kill half the people in the world, the researchers involved say that the study was necessary to allow us prepare for a mutated bird flu epidemic.

1 H1N1 Virus

In 1918, the world witnessed the arrival of a deadly flu epidemic. This was the H1N1 virus. By the time it was over, up to 100 million people were dead. The flu caused blood to seep into the lungs of victims. They released blood from their noses and mouths before drowning in the blood inside their lungs.

The flu returned in 2009. But it was less lethal even though it was mutated and deadlier than it should have been. Scientist Yoshihiro Kawaoka took samples of the mutated strain that caused the 2009 epidemic and used it to create a deadlier strain that was resistant to vaccines. This strain was similar to the one that caused the 1918 epidemic.^[10]

Kawaoka was not planning to produce a more lethal version of the flu at the time. He only wanted to create the original version of the flu so that he could study how it mutated and was able to bypass our immunity. The deadly virus is stored in a lab and could become fatal if ever released.

In a world full of extraordinary things viruses might just be the strangest. They are intimately involved in the lives of all organisms but they may not technically be alive themselves. Yet, as the last year has proved, they can have dramatic effects on living things. A single virus can grow exponentially into a world changing event.

Here are ten big facts about these tiny, infectious things.

Top 10 Mysterious Viruses

10 Are Viruses Alive?

You might think that the debate on what constitutes life is settled. Generally we know whether something is alive or not just by looking at it but viruses blur the lines. They are made of the things we associate with life: proteins, lipids, and nucleic acids. They even do things we associate with life: they replicate and evolve. But the key fact is that they cannot do it on their own. For a virus to replicate it must infect a host cell and hijack their metabolism. Most scientists think of viruses as non-living assemblies of chemicals that are very good at making copies of themselves.

There are some researchers though that think of viruses as very much alive. They cite the complexity of their genomes and the speed of their evolution. They say that when we picture viruses in their complete form – as little capsules of DNA or RNA – we can imagine they are dead. But only in the same way a bacterial spore is dead when it is inactive. Once a virus enters a cell and begins the complex task of making more copies of itself they think it is perfectly correct to think of them as living organisms.

Whichever side of the debate you take the “life” cycle of a virus is a fascinating one.

9 Viruses may be the origin of life

Evolution is the best way of understanding how life on Earth has changed and developed but many people claim that evolution cannot tell us anything about the origin of life itself. One hypothesis however uses evolution to explain how life as we know it may have come into existence.

In the beginning there was RNA, a molecule closely related to DNA. Crucially though RNA is able to twist and form molecular machinery that can make copies of itself. Once the first RNA molecule that could do this formed it would rapidly proliferate. If mutations developed that made it better at making more copies then it would outcompete other RNA strands. In this way inanimate molecules can evolve.

What are the simplest things that use RNA and DNA to replicate? Viruses. In the Virus World hypothesis it was viruses that came first – and those that could infect cellular organisms are the ones that have survived until today.

8 You are mostly virus

Viruses are everywhere. Wherever there is life there are viruses that are associated with them. While some are very noticeable through their effects on us many are so harmless that we never know they are on us. And there are a lot on us at any one time.

We tend to think of humans as a mass of our tissues and cells – the bits that share our DNA. In the human body there are around 10,000,000,0000,000 cells that are human. This number is tiny however compared to the bacteria that live inside us and on us. There are ten times as many bacterial cells in any human as there are human cells. Then there are the viruses. Each human carries a hundred times more viruses than they do human cells.

While some of these viruses will target human cells many of them want nothing more than to infect the bacteria we share our bodies with.

7 Viral Antibiotics

One of the greatest threats in modern medicine is antibiotic resistance in bacteria. When our antibiotics fail to kill bacterial infections we are pretty much back in the pre-modern age when a simple scrape could lead to your death. Viruses may be our saviours.

Bacteria are prey to viruses just like we are. Phages are viruses that infect bacteria. Once a phage has infected a bacterium it replicates hundreds or thousands of copies of itself and splits the bacterium open, spewing out more viruses to infect more bacteria. If you can find a phage that hunts and kills a dangerous bacterium they you may just have found a solution to antibiotic resistance.

Lots of research is being done on phage therapy, as these treatments are called, and many scientists are excited by the possibility of novel cures for bacterial infections. But the idea of using phages is not entirely new. When a cholera epidemic struck India in 1926 doctors took stool from people who had unexpectedly recovered from cholera and gave it to the sick. Many of those treated by this somewhat gruesome method recovered. Likely the answer lay in phage viruses that targeted the cholera germs.

6 Nobel Prizes

If you want a Nobel Prize then one of the best places for you to start your work might be on a virus. In 2020 researchers were award Nobel Prizes in Medicine for their discovery of the Hepatitis C virus. The awarding of Nobel Prizes for Virology goes back much further however.

Viruses were first discovered in 1892 when Dmitri Ivanovsky found that tobacco plants could be infected by disease when injected with a fluid that had been passed through a filter much too small for any bacteria to pass through. The unseen infectious agent was soon named a virus – from the Latin for poison, or a slimy liquid. Some thought that a virus was a liquid thing but Wendell Stanley managed to isolate the tobacco mosaic virus and purify it into crystals for study, proving viruses were particles. He won the Nobel Prize for his work in 1946.

Since then viral research has won the Nobel Prize dozens of times for either curing a viral infection, such as the creation of the Yellow Fever vaccine, or working out how viruses like papillomavirus causes cervical cancer.

5 Mind-boggling Numbers

It is impossible to count the number of virus particles on Earth at any one time. By the time you counted them they would have multiplied and been destroyed many times over. Scientists can however make a good estimate. These range from 10 to the power 30 to 10 to the power 32, so many would say there are around 10 to the power 31 on Earth. That is 1 with 31 zeroes after it. To put it in perspective there are a mere 10 to the power 21 stars in the observable universe.

All of these are on the planet yet we can’t see them. This makes it clear just how small viruses actually are. So what would happen if you took some very fine tweezers and lay all these viruses end to end? A good average size of a virus is around 125 nanometres – billionths of a metre. So divide the number of viruses by their average size to find out how far our chain of viruses would stretch.

The answer is that our viral chain would be 800 million light years long. This would pass well beyond the nearest galaxy, and passed the neighbouring clusters of galaxies.

4 Tiny Viruses

We’ve seen that viruses can be small, but just how small can they go? That depends on their nucleic acids. A virus is, basically put, just a fancy shell around some DNA or RNA. The shell helps the DNA or RNA get into a host cell and the nucleic acids force the host cell to make more shells so the virus can spread. How many genes can that take?

For the Circoviruses that infect pigs all they require are three genes. The entire length of their genome is just 1726 base pairs long, compared to a human’s genome of over 3 billion base pairs. With just three genes the virus is able to invade a cell and replicate. With such a short genome it only needs a small coat to house it. The circoviruses are only 17 billionths of a metre across.

Some researchers are trying to get even smaller. One group has announced they made an artificial virus from bits of protein and DNA that is 12 billions of a metre long. It is hoped that more artificial viruses may have a role in advanced medical treatments.

3 Giant (Reanimated) Viruses

Not all viruses are content to stay tiny however. Some of them can get pretty big – if you consider bacteria large. When researchers went looking for bacteria in a cooling tower they collected what they thought were bacteria but they could not identify them. It was only much later that they were discovered to be an entirely new type of giant virus. They called it a Mimivirus as it was a MIcrobe-MImicking virus. Its genome is over 12 million base pairs long and the virus is larger than the smallest bacteria.

Since then other giant viruses have been discovered, some of them in unlikely places. In 2014 the largest ever virus was discovered in the frozen tundra of Russia. The samples it was found in were over 30,000 years old. Then they did the obvious thing and tried to reanimate them.

The scientists exposed amoebae to the defrosted viruses as they know other giant viruses infect these single-celled organisms. Despite being from the Stone Age the viruses successfully invaded the cells and replicated. The ability of viruses to remain active after so long has led to some speculation that melting permafrost may release long-forgotten human pathogens.

2 Viruses on Viruses

Mamavirus is another giant virus that was discovered in a cooling tower, infecting amoebae, but what most excited scientists was the discovery of another virus associated with it. This much smaller virus targets mamavirus and preys on it like a parasite. Because of this researchers named it Sputnik and the other viruses that attack viruses are known as satellite viruses.

Sputnik is not able to infect an amoeba on its own and reproduce. It can only replicate in amoebae that have already been infected by a mamavirus. Instead of directly hijacking the cell’s own machinery Sputnik uses the virus’ replication proteins to make copies of itself.

Not even viruses are immune to the insidious and ingenious methods of viral invasion.

1 You are part virus

Humans all carry viruses of some type or other inside us – but we also have viruses trapped within our genome. Some viruses are not content to simply replicate in our cells. Some use molecular machines to cut our DNA and insert their own into it. If they do this in a sperm or egg then their DNA can be passed down the generations. Over millions of years this has happened so often that around 8% of any person’s entire genome is made of these viruses that have become fossilised inside us.

The viruses in genomes can even be used to track evolution. If two species have evidence of the same virus infecting them then it can be a clue that the common ancestor of both was infected before they evolved into separate species.

Once the viruses become stuck in our genome however genome and passed on they can have big effects on evolution. The viruses mostly become inactivated and reshuffled across the genome and sometimes this mixing can be advantageous. Some human genes use the promoter regions of viral DNA to be activated. Some have even been co-opted into the human immune response system – a case of viruses fighting viruses.

Top 10 Viruses That Actually Help Humankind

Viruses are a particularly fearsome “germ.” Though viral infections may resemble bacterial infections, antibiotics are useless against viruses. There are very few dedicated antivirals to kill them off. But who even knows if ‘kill’ is the right word to use for something that stretches the definition of ‘alive’? Viruses: they’re like microscopically tiny zombie-robots, hijacking cells and turning them into factories for themselves. But humanity can exploit viruses’ supremely odd workings and sneaky ways for their own purposes.

10. Blue Eggs

If you’ve ever wanted to find some green eggs for some Dr. Seuss-style green eggs and ham, you’re in luck. Thanks to a virus, you don’t even need the eggs of some exotic wild bird.

Most chicken eggs are white or brown, but a few chickens lay eggs that are green or blue. These breeds include the Chilean Mapuche breed, its descendant breed, the Araucana, and the Chinese Dongxiang and Lushi breeds.

Two things are responsible for the colorful eggs: viral infections and blood. Long ago, a Mapuche fowl was infected by a retrovirus, a virus which can insert its genetic code into the host’s. The retrovirus’s effect was to trigger the buildup of biliverdin in the eggshell, a breakdown product from a part of hemoglobin that can cause a greenish tint to bruises.

The Dongxiang and Lushi breeds developed their colorful eggs independently, but from the same viral cause. According to historical evidence, the Dongxiang breed has had the bluish-greenish egg mutation since at least 500 years ago, and the Mapuche fowl since between 200 and 500 years ago. The trait is autosomal dominant, so chickens need only one parent with the mutation to lay the colorful eggs. However, those who have both copies of the gene variant lay darker-colored eggs.

9. Tulip-breaking virus

For the beauty of a virus-infected egg, one only has to pay a little more than usual. But for a beautiful virus-infected tulip in the Netherlands of the 17th century, one had to pay a lot more.

Back then, some tulips mysteriously had beautiful streaking and feathering patterns. These are called “broken” tulips. They were so expensive, they could leave their owners “broke” too, as well as the whole Dutch economy.

In 1623, some bulbs were sold for 1,000 florins, when the average annual income was 150 florins. Due to their high price, it cost less for some citizens to get still-life paintings of “broken” tulips than the tulips themselves.

Their beauty was short-lived, as the broken tulips’ bulbs shrank over successive generations. Eventually, it could no longer flower, and soon died. No one knew what caused tulips to break. People turned to all sorts of odd things, such as pigeon dung, to try to reproduce the pattern.

It was later discovered a virus called a potyvirus made the tulips break. The infection spread through aphids or by contact with an infected tulip.The virus worked by affecting the distribution of the pigment anthocyanin.

Today, such tulips are still costly, but for the damage potyvirus poses to gardens rather than their beauty. Potyvirus-infected tulips, once so valuable, are now carefully weeded out of gardens. Now there are specially-bred tulips that mimic the patterns of a “broken” tulip, without the virus.

8. Electricity-Making Virus

Computer viruses were named after their biological counterparts. Now, biological viruses lead back to electronics.

Some solids build electric charges when compressed. This is called the piezoelectric effect, and it’s most well-known in quartz watches. The piezoelectric effect has several applications, but materials used to make piezoelectric devices are toxic and difficult to work with. This limits the widespread use of the piezoelectric effect.

Berkeley Lab scientists could change that with a virus. They used the M13 phage virus, which targets bacteria and is harmless to humans. It’s useful for several reasons: it multiplies itself by the millions, naturally arranges itself into orderly films like chopsticks in a box, and is easy to genetically engineer. The ease in genetically engineering it helps scientists boost its voltage, and its self-arrangement helps with the goal of self-assembly in nanotechnology.

The Berkeley Lab scientists tested their approach by making a generator. The generator works by tapping a finger on a stamp-sized electrode patch coated with viruses. The viruses then turn the force of the tap into electricity, producing enough current to operate a liquid-crystal display (LCD).

With this technology, future devices could be charged from the vibrations of everyday tasks, such as climbing stairs or shutting doors.

7. Battery Virus

Some computer and smartphone owners worry about viruses that can overclock their devices’ batteries and leave them with a useless metal brick. But biological viruses could do the opposite: make batteries better.

In 2006, scientists at the University of Massachusetts (MIT) used a virus called M13 to make part of a battery. This part, the anode, is part of a pair of poles in the battery with opposite electrical charges. In 2009, the scientists completed the tricker task of making the anode’s counterpart, the cathode.

To make it work, the scientists had to tweak two of the virus’s genes. The first gene made proteins in the virus’s coat. The modifications allowed bits of iron phosphate to stick to it and bulge “like tiny fists all along the length of the virus,” in the words of study co-author Angela M. Belcher. The second gene let carbon nanotubes attach, forming a network of millions of electricity-conducting viruses.

To make similar technologies, extremely high temperatures of about 660 degrees Fahrenheit (350 degrees Celsius) were needed. However, the researchers could turn M13 into a battery-making tool at or below room temperature.

According to Belcher, a third of an ounce (10 grams) of the virus battery could power an iPod for 40 hours. However, she believes it is more suitable for large, high-power things like electric cars.

In 2013, progress was made on that goal. With viruses, lithium-air batteries of electric cars could be greatly improved. The M13 virus was used to make manganese-oxide nanowires for lithium-air batteries. Unlike typically-made nanowires of the metal, the virus-made wires had a rough, spiky surface, which greatly increased the wires’ surface area. The increase in surface area could be a big advantage in the batteries’ charging rate. The process has other benefits, too, such as increased electrode stability and less need for expensive metals like palladium for the batteries.

6. Cancer-Fighting Viruses

Herpes and cancer: two diseases people really don’t want to talk about. But using herpes to fight cancer is definitely worth discussing.

Imlygic is a new anti-cancer drug. On average, it extends melanoma patients’ lives by less than four and a half months. This is barely statistically significant, but Imlygic is special: it’s made using a virus. To be specific, it is a live, infectious, modified version of HSV-1, the herpesvirus variety that’s the usual cause of cold sores.

Though Imlygic is not especially effective by itself, its flu-like side effects are mild compared to chemotherapy. When cells turn cancerous, their virus-fighting machinery breaks down. Herpesvirus prefers to attack cancer cells. When it attacks, the debris of burst-open cells alerts the immune system, and the immune system then targets the cancer cells.However, it is unclear whether the immune system targets all the cancer cells of the body, or only those infected by the virus.

Though Imylgic is the first to get approval in the US as a cancer treatment, it is not the only one in development. Tumor-killing viruses are a popular topic among scientists, and the idea has been around for decades. More virus-based cancer treatments may join Imlygic in the future.

5. Orange Virus Vaccine

It’s tradition to treat colds (which are caused by a virus) with orange juice. But, using viruses, the orange trees themselves can fight off bugs spread by bugs.

Citrus greening (or huanglongbing, to use the Chinese name) is a deadly disease for citrus trees. It is caused by the bacterium C. liberibacter, which is spread by sap-sucking insects.

Before citrus greening came around, the most devastating orange virus was the citrus tristeza virus. (or CTV) The virus was named after tristeza, a Portuguese word meaning “sadness”, for the sadness that came from the virus’s arrival.

Now these two major citrus pests will be pitted against each other, with the fate of the USA’s orange juice hanging in the balance.

Bill Dawson, a plant pathologist from the University of Florida, modified a local strain of CTV. With this, anyone could insert new bits of DNA into the virus’s genome and make it a protein factory. One of the world’s largest orange juice manufacturers, Southern Gardens Citrus, licensed the viral vector from Dawson’s lab. With the virus as a needle, all Southern Gardens needed was something to inject. The company chose genes from spinach, which coded for antibacterial proteins called defensins.

Southern Gardens plans on infecting trees with a harmless strain of CTV. Branches from CTV-infected trees would then be grafted onto other trees to spread the virus. As the virus copies itself, it becomes a spinach defensin factory, and the defensins destroy C. liberibacter.

Since the biology of the tree is not modified, orange juice from these plants would not have to carry a genetically-modified label. This makes getting regulatory approval much easier, sidestepping the issue of distrust of genetically-modified plants.

4. Food Poisoning Protection

It’s terrible to hunch over a toilet, waiting to throw up, and idly wonder which of the things you ate was germ-filled. Intralytix, founded in 1998, has a plan to give germs a taste of their own medicine, so to speak: it uses viruses to infect (and kill) bacteria that cause food poisoning.

Each of its products has a mix of viruses that target the same bacteria species.The company’s first product, ListShield, was approved in 2006. It is aimed at Listeria bacteria, which cause listeriosis, a kind of food poisoning with a death rate of about 20%.  ListShield is meant to be applied to ready-to-eat meats, such as deli meats and hot dogs. To kill off Listeria, ListShield is sprayed on meat and the drains, floors and other surfaces of a food processing plant.

Intralytix’s second product, EcoShield, is for the O157:H7 strain of E.coli. EcoShield is sprayed on meat before it is ground into hamburger to kill E. coli. In studies with government investigators, Sulakvelidze showed the product killed 95-100% of the E.coli strain within 5 minutes.

The two treatments are odorless, tasteless, invisible and non-corrosive. The concentration of phages in the liquid spray is 0.001%, making the product as harmless as water to anything but target bacteria.

Later, another company, Micreos BV, made its own phage treatments, Listex (P100) and Salmonelex. Listex (P100) targets a Listeria species, while Salmonelex targets Salmonella.

3. Antibiotic Viruses

Bacteriophages (or “phages”) are the natural enemy of bacteria. They copy themselves inside bacteria, and the bacteria eventually burst open with viruses.

In the 1920s and 1930s, doctors treated a variety of infections with phages. However, phage therapy had some problems. Scientists at the time did not know phages had to be matched precisely with bacteria targets to work, which made phage treatments unreliable. In addition, people sometimes became sick from the treatments because they were not purified properly.

After World War II, antibiotics were mass-produced. They were more reliable than phages, so interest in phages declined. Though phages were mostly forgotten in the United States, they weren’t forgotten in the Soviet Union. Due to the Iron Curtain blocking access to some of the best antibiotics of the West, the Soviets made do with phages and made phage therapy more effective. In the modern day, phage therapy administered in several forms, such as tablets, liquids, and injections, and remains a standard treatment in Poland, Georgia and Russia.

Unlike antibiotics, phages are very precise and leave the “good” bacteria of the body alone. With the rise of antibiotic resistance, phages might make a comeback in the English-speaking world.

2. Viruses killing other viruses

Ever heard the expression “fighting fire with fire”? Well, in this case it works, if by “fire” one means HIV.

In 2011, scientists at the University of California-San Diego and UCLA made a harmless version of HIV that relies on HIV to reproduce. This virus was called a therapeutic interfering particle, or TIP. By slowing the replication of the HIV virus, TIPs might give someone five to ten extra years before AIDS sets in.

The TIP’s genetic code was stripped to one-third of its original size, and it lacks important pieces needed to copy itself. The TIP can only copy itself by sneaking into HIV’s genetic code and copying when it does. TIPs also contain HIV-inhibiting sequences and compete for the same proteins as HIV. Leor Weinberger, the leader of the team that made TIPs, likens it to a “virus of a virus.”

According to Weinberger, TIPs could help with HIV “superspreaders.” These people, such as drug users, are responsible for a disproportionately large amount of HIV infection.

In 2016, scientists orchestrated another virus-on-virus match, this time between reovirus and hepatitis C. During childhood, reovirus can cause colds, but by adulthood most have been exposed to it and are immune. It’s like an early-game enemy: inconvenient at first, but a piece of cake once one’s gotten stronger.

In comparison, hepatitis C is like a final boss, one some find unbeatable. Hepatitis C is a common cause of liver cancer, and cancers originating from the liver is the third-highest cause of cancer deaths worldwide.

When this early-game enemy is pitted against the final boss…well, it’s the player (or rather the patient) who wins. When introduced to the body, reovirus stimulates a signal protein called an interferon, which activates a kind of white blood cell called a Natural Killer cell. In experiments on human cancer samples and mice, the Natural Killer cells then kill the tumor and cells infected with hepatitis C. The reovirus therapy could also be used for other cancers associated with virus infections, like Epstein-Barr virus-associated lymphoma.

1. Humans Made by Viruses

In The Matrix, bad guy Agent Smith likens humanity to a virus, a disease of the planet. In real life, he’s right… to a degree.

More than 45 million years ago, a mammal was infected by a retrovirus. By turning their RNA-based code to DNA, retroviruses such as HIV can sneak their instructions into the host’s genome. Whenever the host’s cell copies itself, it also copies the virus. This ancient retrovirus happened to infect a germ line cell and so could be spread to the primate ancestor’s offspring.

17 years ago, in 2000, a team of Boston scientists discovered a strange gene in humans. This gene, called syncytin, coded for a protein made only by cells in the placenta.

The two events are related: syncytin comes from the virus.

While the virus used that gene to fuse with a host cell, a developing fetus uses the gene to fuse some placental cells into one single-celled layer. This layer is essential for the fetus to draw nutrients from its mother.

The syncytin protein comes in two varieties, the previously mentioned being syncytin 1. Reflecting its viral heritage, syncytin 2 tamps down the mother’s immune system and prevents the immune system from attacking the developing fetus.

HERV-K inserted itself as recently as 200,00 years ago, making it the newest of all retrovirus genes in humans. It activates important genes that help with embryo development, and its viral particles and proteins help protect very young embryos from infection by other viruses.

It is estimated that over 8% of human DNA came from viruses.