One out of four humans will die due to a sexually transmitted disease. It’s something that we’ve all been taught to protect ourselves from, even if everyone isn’t as diligent as they should be.

However, while many sexually transmitted illnesses are commonly known to affect humans, we aren’t the only species on the planet that can contract them. From HIV to herpes to brucellosis, the animal kingdom has its own fair share of problems when it comes to sexually transmitted infections (STIs).

10 Papillomavirus

Some mammals of the sea are known for their vast intelligence and for saving humans from sharks. But they also have the ability to contract genital warts through papillomavirus. Most commonly found in Atlantic bottlenose dolphins, genital warts are caused for the same reason that STIs are seen in humans: unprotected sex.

Mammals are most likely to be hosts of STIs, and bottlenose dolphins are not an exception. Increased contaminants in the water have compromised dolphins’ immune systems, making them more likely to contract STIs. While this has become a problem for bottlenose dolphins, learning from them has helped humans because dolphins and humans have similar types of papillomaviruses.

This is beneficial because dolphins have contracted these infections—and the resulting genital warts. But they have not developed cancer, one of the main results for human women with HPV.

Though there isn’t an indication that genital warts have been spread from bottlenose dolphins to humans, different types have been shown to exist and are being monitored by scientists.^[1]

9 Syphilis

Cute, fluffy, and able to multiply prodigiously, bunnies are adorable creatures that can often be found as pets. They are also carriers of an STI which is shared with humans: syphilis.

With almost 12 million new cases appearing each year in humans, understanding how syphilis spreads and what vaccines can aid in preventing and treating this infection will be beneficial for humans and rabbits. Treponema paraluiscuniculi, the bacteria associated with syphilis in rabbits, is different from that found in humans and cannot be spread from rabbit to human.

Still, a large population of rabbits has already contracted syphilis. According to researchers, syphilis in rabbits cannot be contracted in vitro. However, it can be spread from mother to child during pregnancy or at birth. In New Zealand, syphilis is a growing problem for humans and white rabbits.

In the late 20th century, Africa saw a syphilis epidemic in their baboon species, both in the wild and in captivity. The strain was different than the one contracted by humans but spread rapidly before treatment could be given in some cases.

However, the reason for the outbreak was unknown and the levels seen during this period have dropped dramatically. Only a few cases of baboons have tested positive for the infection since then.

As with humans, antibiotics can help to treat syphilis in animals if it’s caught in time.^[2]

8 Herpes

Herpes is not just a disease transmitted by humans. Many cases of herpes have been found in the animal kingdom—from elephants to reptiles to fish and even oysters. Herpes has a long history of infecting primates . . . and rabbits.

Rabbits can host the herpes virus and infect humans the same way that other primate species do: through bites or scratches. It can also be done the other way around. One study found that an owner gave his rabbit a human strain of herpes virus through saliva contact.

The herpes simplex virus in baboons varies from the kind seen in humans and can also be transmitted to humans from other primate species through a bite or scratch. Due to the differences in strains, the results can be deadly if not treated properly.

The types of herpes virus seen in various primates differ. For example, the one in baboons is similar to the kind in monkeys rather than chimpanzees or gorillas. Each primate species has its own strain of the herpes virus. Some researchers speculate that the herpes virus seen in humans is so similar to the chimpanzee virus because there was a common ancestor millions of years ago.

Baboons in Africa are battling a herpes strain that has scientists baffled. They are unsure where it originated or how it manages to spread so quickly. A total of 200 baboons have been infected. Although there have been no cases of human infection with this strain, the possibility of transmission may exist.^[3]

7 HIV

HIV is found in humans and other primate species. In fact, a recent discovery has shown that chimpanzees and gorillas may have been the original hosts of HIV.

As HIV spreads one million times faster than DNA can adapt, knowing where to look is key. Gorillas and humans share 98 percent of their DNA as well as the origins of HIV. Around 20 million people are affected by a type of HIV found in gorillas from Cameroon. Although HIV is usually spread from primate to primate through sexual intercourse, it’s speculated that the type given to humans came from eating infected meat.

HIV can be given to humans from other primate species through blood-to-blood contact, such as bites or ingesting infected meats. A study found that a specific group of chimpanzees in West Africa tested 90 percent positive for having a virus similar to the HIV found in humans and that it was only spreading.^[4]

While chimpanzees are known to have HIV, none of them demonstrate an illness similar to AIDS, which is an oddity as humans and chimpanzees share similar genetic structures.

6 Brucellosis

One of the most common sexually transmitted diseases in the animal kingdom is brucellosis (aka undulant fever), which can affect animals from livestock to those in the wild. Brucellosis is dangerous to animals due to its prevalence, but it also poses a threat to humans with possible long-term effects.

Brucellosis appears often in livestock and other domesticated animals as well as in deer. This disease is usually sexually transmitted among animals, but it can be shared between species by coming into contact with an infected animal or their infected meat.

Humans can contract brucellosis similarly—through ingestion of infected meat or cheese, contact with an infected animal, or drinking infected milk. While around 100–200 cases are seen yearly in humans, the results are rarely deadly. However, animals that aren’t treated quickly are not always as lucky. Symptoms range from the signature fever to vomiting, fatigue, diarrhea, and blurred vision.

Although few cases of brucellosis are spread from human to human through sexual contact, individuals who have had sexual intercourse before realizing they’ve contracted the illness are more likely to spread it to their partners. Studies have also found that when people are infected with brucellosis, medical follow-ups may be required to ensure that the virus hasn’t developed into a chronic condition.^[5]

5 Feline Immunodeficiency Virus

In 2017 alone, 940,000 humans died from AIDS-related illnesses. Although new treatments have become available, why AIDS affects humans and not other primate species is a question that is being asked. However, cats are not always so lucky.

Feline immunodeficiency virus (FIV) targets only cats and can be transmitted through bites and scratches, birth, and even semen. This virus comes from the same strain as HIV. However, we don’t know why FIV is the only non-primate virus to produce AIDS-related illnesses. With both HIV and FIV, the resulting AIDs-related illnesses can end in death.^[6]

While FIV does have a vaccine, HIV does not. This is because HIV goes through multiple mutations while FIV has only five known strains that result in AIDs-related illnesses.

4 IIV-6

Although this STI renders the host infertile, it also increases the host’s desire to mate. The infection known as IIV-6 affects cold-blooded insects, mostly crickets.

This sexually transmitted disease has become a particularly bad problem for cricket colonies. As the infected male hosts experience an increased need to mate, they spread the infection from partner to partner. The disease renders the infected males and females infertile, making it impossible for the crickets to continue breeding. The longer the host is infected, the higher the likelihood that the cricket will eventually die from this infection.

As IIV-6 is a DNA-based infection, the mutation of the disease is a possibility that many scientists are trying to stop. While the disease has existed for around a decade, the infection has increased in different colonies of crickets, spreading in a way that may start to affect other invertebrates.^[7]

3 Chlamydia

Chlamydia is an infection often seen in humans, affecting both women and men equally via sexual intercourse. Although over one million people have been diagnosed with chlamydia, it is one of the most easily treatable STIs seen in humans. For the animal kingdom, however, the disease is not as curable.

Chlamydia affects a variety of animals, from birds to mammals to reptiles. However, its strain is different than the one seen in humans, making it harder to treat. This has become a major problem in koalas, whose numbers are already dwindling due to hunting and loss of habitat.

Up to 50 percent of koalas under care in Queensland and New South Wales have tested positive for chlamydia. The rapid spread of the disease in koalas has become a major point of concern. It can quickly affect the mammals, but they don’t show any outward symptoms.^[8]

Once the symptoms progress to coughs and respiratory complications, chlamydia can result in infertility in koalas and even in death. Although the infection isn’t usually fatal, it can have serious negative effects on the koala’s health.

While the strain of chlamydia in koalas is quite different from that in humans, the possibility of a vaccine for koalas can be helpful for the development of a model to vaccinate humans.

This is especially crucial because chlamydia can spread from birds to humans in addition to human-to-human transmission. When the infection is spread from bird to cat, it mutates and turns into a feline-specific version.

This also happens when humans come into contact with infected birds. The specific infection is called psittacosis. Rare occurrences of bird to cat to human transmission have also been found.

2 Venereal Tumors

Although humans don’t “catch” cancer from one another, the ability to sexually transmit cancer does occur in the animal kingdom. Mammals are the most vulnerable to venereal tumors. Currently, the number of Tasmanian devils is dwindling due to the rapid rise in venereal tumors that have spread during mating.

Tasmanian devil facial tumor disease (DFTD) has been affecting these creatures for 20 years. It happens when Tasmanian devils bite one another during mating, resulting in cancerous facial tumors which have killed off almost 95 percent of the population since 1996.

As scientists tried to develop a vaccine to combat this, a second strain appeared. These two strains are two of the four transmissible cancers, three of which are transmitted through sexual intercourse in the animal kingdom.

The third venereal tumor is found in dogs, affecting both males and females equally and occurring naturally. Although HPV can lead to cancer in human women if not treated, canine transmissible venereal tumor (aka CTVT or Sticker’s sarcoma) is a cancer that is passed between dogs only. It has not mutated to affect humans or other animals.^[9]

CTVT has developed a way to adapt dogs’ genes to survive in almost a parasitic form. Even though this disease has several mutations, each variation includes the same gene from the original dog that was first infected. CTVT can be treated with chemotherapy.

1 Gonorrhea

Many people have speculated as to how gonorrhea, one of the oldest and most rampant STIs, came to be shared by cows and humans. One of the most prominent and unsettling theories focuses on an interspecies relationship that might be plausible but is more unnerving than anything else.

Due to the nature of gonorrhea, it’s unlikely that humans would have contracted the illness by eating infected meat. Cows aren’t the only animals affected by gonorrhea, either. Sheep, dogs, and even chimpanzees are susceptible to contracting gonorrhea.^[10]

However, with millions of people worldwide diagnosed with gonorrhea each year, understanding the illness is important for developing vaccines. Due to its adaptability and means to cross species, gonorrhea has been a difficult disease to fight.

With more antibiotics fed to sheep, pigs, and cows, the various strains of the disease have also become resistant to vaccines that are being created. Gonorrhea can mutate and adapt, which makes it harder to treat in both humans and animals. In turn, this can create a larger outbreak.

Prior to the discovery of antibiotics, severe bacterial infections were one of the major causes of human deaths throughout the developed world. We all have probably used antibiotics at some point in our lives to treat an infection.

Before the discovery of penicillin by Alexander Fleming, people died from otherwise small scrapes and cuts through complications of infection. In the modern antibiotic era, being sick is now seen as an inconvenience. Really, who wants to be ill longer than necessary?

But bacteria do more than cost us sick days. They can still kill us despite the discovery of these modern drugs. Bacteria are smart and are figuring out ways to resist antibiotics. There are many infections that currently cannot be treated with any antibiotic, killing tens of thousands of people each year in the United States alone.

Even knowing that unpleasant fact, some bacteria go overboard, not content to give us a flu-like illness. These are the artists of death. So read on . . . because that dirty door handle in the public restroom will never seem the same again.

10 E. coli Hemorrhagic Colitis

E. coli are bacteria that can really make for a crappy day. These bugs usually live in the intestinal tract, minding their own business. They are excreted in fecal matter. One exceedingly bad breed of E. coli makes a chemical called “Shiga toxin.” This is not a character that anyone wants hanging around in his guts.

A human might pick up these bacteria by consuming poorly treated food or water contaminated by excrement. In countries that lack proper water sanitation facilities, this is definitely a problem.

Once in the body, Shiga toxin–producing E. coli get to work causing a lovely disease known as hemorrhagic colitis. Essentially, this means the bacteria will cause such bad, bloody diarrhea that the victim, if untreated, can poop himself to death through severe dehydration, kidney damage, and blood loss.

Treatment includes rehydration with oral and intravenous fluids until the body rids itself of the bacteria.^[1]

9 Scarlet Fever

A common killer in the 18th and 19th centuries, scarlet fever still makes its rounds today. It terrorized centuries of humans and was known to kill entire groups of children in families. Many well-known individuals throughout history lost loved ones to this disease, including Charles Darwin, who lost at least one child to scarlet fever.

This disease is caused by a group of bacteria known as group A beta-hemolytic streptococci. Scarlet fever often begins with a sore throat and a fever, commonly known as strep throat. As it progresses, it causes a red, bumpy rash that spreads in a head-to-toe manner, causing the victim to have a red, or scarlet, appearance. In addition, it causes a red, bumpy, strawberry-appearing tongue.^[2]

Scarlet fever can cause throat abscesses, heart problems, and kidney problems, leading to death. It is easily treated today with antibiotics but still causes death and long-term injury to victims who do not receive adequate and early treatment.

8 Tuberculosis

If there was one disease that evoked fear in our ancestors at the turn of the 19th century, it was pulmonary tuberculosis, the most common form of the disease. However, it is an ancient sickness, with Egyptian mummies having been found with tuberculosis lesions on their skeletons. This disease has killed quite a few famous people, including Franz Kafka and Henry David Thoreau.

The microorganism Mycobacterium tuberculosis is the cause of all forms of tuberculosis. The most common form, pulmonary tuberculosis, involves a bacterial infection of the lungs. Untreated, the bacteria become walled off in the lungs and can remain dormant for years.

Active infections may lead to a wide variety of pulmonary symptoms, including a bloody cough, weight loss, and trouble breathing. The most severe infections allow the bacteria to spread to other body parts, including the kidneys and skeletal system.^[3]

Acutely and chronically ill individuals lost large amounts of body weight fighting this infection, leading to a frail and wasted appearance. As a result, tuberculosis was also known as “consumption” and “the white death.” Treatment includes anywhere from six months to years of antibiotics.

7 Tetanus

Also known as “lockjaw” or “the grinning death,” tetanus is a dramatic illness to behold. It was a noted complication of infected wounds in the Napoleonic Wars. Spread via dirt or contaminated soil, tetanus is caused by the bacterium Clostridium tetani.

This bacterium earns its specialization in death and destruction via its neurotoxin called tetanus toxin. This toxin binds irreversibly at the junction between nerve cells and muscles, which results in the characteristic and dramatic muscle spasms of the disease.

Individuals affected with tetanus undergo severe whole body muscle spasms strong enough to cause locking of the jaw, grinding of teeth, an involuntary smile, and involuntary muscle spasms strong enough to break bones, including the spine. Death can result from paralysis of the respiratory muscles, making breathing impossible, or secondary infections.^[4]

Without proper medical care, tetanus is a deadly disease. Treatment includes medications such as skeletal muscle relaxers, antibiotics, antitoxins, immune globulins, and supportive care to survive this deadly infection. A tetanus infection is considered a medical emergency.

6 Meningococcal Meningitis

A nervous system infection is never fun. In meningococcal meningitis, the lining of the brain or spinal cord becomes infected with a bacterium known as Neisseria meningitidis. It still occurs today throughout the world but is most common in sub-Saharan Africa.^[5]

Meningococcal meningitis commonly presents as a nervous system infection or as a blood infection. In the former case, the person may have fevers, headaches, neck stiffness, visual changes, and vomiting. In the case of blood infection, the person may develop a purple rash and bleeding into the skin and organs. This infection is deadly, but vaccines have made this disease much less of a threat than it once was.

5 Anthrax

It may surprise many readers to know that anthrax is not just the name of a heavy metal band but also a disease and potential weapon of bioterrorism. Anthrax (caused by the bacterium Bacillus anthracis) is not content to be limited to one body system. Instead, it can be found in three main infectious forms: inhalational, cutaneous (infecting the skin), and gastrointestinal.

Anthrax is considered to be a potential biological weapon because its spores can be transmitted through the air and inhalational anthrax is deadly. It was used in 2001 to contaminate US mail envelopes.

In the cutaneous form of anthrax, an ulcerating lesion develops. As long as it is contained and treated without spreading, this is a milder form of the disease.

The inhalational form, however, is a bigger problem. Once inhaled, anthrax first causes flu-like symptoms. Later, the victim begins to feel chest pain and shortness of breath. Within days, almost all patients who progress with this form of the disease die of blood infections. If caught early enough, the disease can be treated with antibiotics.^[6]

The gastrointestinal form of anthrax is not pleasant, either. It is obtained from eating undercooked meats. In this type of anthrax, ulcers can form anywhere in the infected portion of the gastrointestinal tract—from the mouth to the anus—which can lead to serious bleeding.

Anthrax can also infect the brain and spinal cord. Due to its many potentially deadly forms, anthrax has set a high bar of expectations for any band bearing its name.

4 Leptospirosis

Unlike other diseases, leptospirosis can be unassuming in terms of its symptoms. Coiled and spiral types of bacteria called Leptospira cause leptospirosis. It is rare in the United States and can be spread from animals to humans, often through animal urine.^[7]

The symptoms of leptospirosis are vague. An infected person can have no symptoms at all. In other cases, symptoms include yellowing of the skin and kidney failure, leading to death. The latter form of the disease is more severe, and the syndrome of this infection was described as Weil’s disease.

3 Syphilis

Sexually transmitted infections are becoming more common in the United States. Whether dating apps or changing culture is to blame, there’s no doubt that we all need to be careful in our sexual encounters.

As a sexually transmitted disease, syphilis (aka the “great imitator” for its wide variety of presentations) has a long history of shame. Countries often blamed each other for the disease, attributing it to the “other” population. Outbreaks in wartime decades were common across populations. Famous figures were not spared, and it is suspected that Vincent van Gogh and Beethoven may have contracted this sickness.

Syphilis is caused by the bacterium Treponema pallidum and occurs in three stages, known as primary, secondary, and tertiary. In the primary phase, an ulcerating lesion (chancre) appears, usually on the genitals. The lesion may resolve or may never be noticed.^[8]

As the disease progresses, the patient will develop flu-like symptoms and enter into the secondary stage. A widespread rash may appear, along with hair loss, headaches, and liver inflammation. The disease may lie dormant for up to 30 years, in which the late or tertiary phase will develop.

In this final phase, the patient may develop disfiguring lesions, heart problems, a central nervous system infection, and even insanity in a condition known as “general paresis of the insane.”

2 Toxic Megacolon Associated With Clostridium difficile Colitis

Diarrhea is not just an embarrassing reason to miss work. While most of us have probably had a passing case of diarrhea from a number of causes, it’s safe to say that many people have not had the sort of intestinal infection that causes a condition known as toxic megacolon.

In this condition, the intestines become infected and swollen and the patient becomes very ill. In the most serious cases, the intestines can become so swollen that they burst, requiring emergency surgery. Although many different bacteria can cause toxic megacolon, Clostridium difficile is a deadly cause of toxic megacolon.

Infection with Clostridium difficile occurs when the deadly bacteria overwhelm the normal bacteria in the gut of a person. If left untreated, it can cause serious intestinal inflammation and swelling. Severe cases of toxic megacolon, even without perforation, have been known to result in almost total intestinal resection to save the life of the patient.^[9]

1 Necrotizing Fasciitis

Also known as “flesh-eating bacteria,” necrotizing fasciitis is nothing to laugh about. Although the bacteria do not actually eat the flesh, they do infect the tissue and underlying structures which leads to tissue death and sloughing. Many different types of bacteria can cause necrotizing fasciitis.^[10]

It was first described during the US Civil War in a rapidly progressive series of cases in which individuals had necrotizing fasciitis of the genital region. A multidisciplinary team, including a surgeon to cut away the infected tissue, is almost always necessary, and amputations may occur.

I am a healthcare provider and an entrepreneur. In my free time, I like to exercise and enjoy the outdoors.