The phrase “flesh-eating” is nightmarish enough to stop anyone dead in their tracks, conjuring up images of flesh falling off of the bone, deep black necrosis, or perhaps a zombie apocalypse in which the undead are biting flesh from bone. Be it flesh-eating zombies, flesh-eating animals, or, even more terrifying, flesh-eating microscopic organisms, the idea of being eaten alive is downright terrifying, and when it comes to the latter, it’s more frightening to think of something you can’t see that slowly eats away at you.

The world of pathogens is a strange world indeed, and there are some pretty nasty critters out there that would love nothing more than to take a bite out of your flesh—and sometimes bone. Some pathogens hijack the minds of their human hosts, controlling their behavior, their thought patterns, and even their actions. Others lodge themselves inside you and consume you from the inside out. Here are ten nightmarish flesh-eating pathogens and their destructive ways.

10 Necrotizing Fasciitis

Necrotizing fasciitis deserves an honorable mention here at the top of the list, as it’s the result of several infections on this list. Necrotizing fasciitis is caused by the presence of pathogens which cause the skin to rot, especially when they become entrenched into the inner layers of the flesh. If it isn’t treated right away, necrotizing fasciitis can kill you, with anywhere from 25 to 30 percent of the cases being fatal.

Necrotizing fasciitis has earned the moniker “flesh-eating disease,” which is quite the terrifying name. While the infections that cause it vary, the pathogens don’t literally eat the flesh but rather excrete toxins that destroy tissue, causing the condition.^[1] Drug and alcohol users as well as diabetics and those who are immunocompromised are particularly at risk for necrotizing fasciitis.

9 Vibrio Vulnificus

Vibrio vulnificus is often found in a place that’s a perfect climate for the bacterium to grow and also possesses the large bodies of water which it likes to flourish in: Florida. A person can become infected either by going into the water with an open cut or wound or consuming undercooked or uncooked seafood, as it lives and thrives in salt water. Vibriosis, the disease spawned from the Vibrio genus of bacteria, can be fatal. It should be noted, as alluded to above, that V. vulnificus causes the flesh to rot rather than eating it, but that difference is quite irrelevant when you see chunks of your arm missing.

Even more terrifying is that V. vulnificus not only attacks the surface flesh but can bury itself and get underneath the top layer of tissue. It can even seep in and cause the internal organs to rot away and even eventually shut down. Sometimes, people lose limbs to the disease.^[2] Again, the immunocompromised are much more likely to contract this flesh-rotting bacterium, as well as people with liver problems. The Centers for Disease Control in the United States suggests not eating raw or undercooked fish if you’re trying not to catch this, and 80 percent of cases come between May and October, when the water is warmer, so these are the best times to avoid the water to avoid the disease.

8 Donovanosis

Donovanosis, also known as granuloma inguinale, is a disease that comes from the bacterium Klebsiella granulomatis. It’s relatively new on the scene, and it may very well be the scariest thing on this list. Why? Because it’s an STD. That’s right, donovanosis is a flesh-eating STD.^[3] The bacteria can destroy the flesh in, around, or on the genitals and can do more damage if they spread to other parts of the body. The damage to the exterior flesh can cause large, red, vascular lesions, and these holes in your flesh bleed.

This disease typically makes its initial home at sites in and around the pelvis but can work its way up inside of you and get into your organs, damaging them, too. If that wasn’t bad enough, in extreme cases, Klebsiella granulomatis can get into your bones as well if not treated promptly. Fortunately, the treatment is rather simple, with broad-spectrum or targeted antibiotics. But imagine waking up one day to find your genitals and the surrounding areas slowly rotting—even if it’s treatable, this is a day that nobody wants to see.

7 Pseudomonas Aeruginosa

Pseudomonas aeruginosa is a bacterium that grows pretty much everywhere and on pretty much everything, though it doesn’t always infect us—instead, it waits for an opportune opening, such as a cut or scrape, and when the conditions are just right, it will seep into the wound and multiply. P. aeruginosa can cause necrotizing fasciitis. The good news is that healthy people generally have a very low risk of becoming infected by this particular bacterium, but as is often the case, those who have immune system deficiencies can experience problems with it.^[4]

If left untreated, Pseudomonas aeruginosa can reach the internal organs and cause death. If left alone, it will eat all the way down to the bone. As with other Pseudomonas species, some of the more severe cases invole infections in the blood or the lungs. What’s really the most terrifying thing about Pseudomonas is the fact that many strains of it have developed antibiotic resistance and are quite difficult to treat, meaning that P. aeruginosa could eat away at you while doctors attempt to find an antibiotic regimen that will work to eliminate the bacteria.

6 Staphylococcus Aureus

Yes, as freaky as it sounds, the common staph infection can become necrotic and flesh-eating. Methicillin-resistant Staphylococcus aureus (MRSA) is Staph aureus with additional antibiotic resistance, making infections rather difficult for modern medicine to treat. Fortunately, not all cases of staph and MRSA turn into flesh-eating necrosis, but doctors can’t actually tell which strains and cases will eventually turn into a condition that eats away at the flesh, so it’s better to treat all situations involving these bacteria as if they were about to become necrotic.^[5]Staph aureus and its antibiotic-resistant counterpart both present with a nasty, thick pus which can get deep into the skin, working its way into muscles and ultimately into the bloodstream—once these infections seep into the blood, a powerful and brutal sickness ensues, and death is a likely possibility. On top of that, if the condition brings about necrotizing fasciitis, you’ll have some serious decay and blackening of the tissue layers as the excreted toxins from the bacteria wreck havoc.

5 Naegleria Fowleri

Naegleria fowleri is an amoeba that severely affects the brain on the rare occasion that it inhabits a human host—these dangerous critters love to hang out and reproduce in fresh water, making them ample under the right climate conditions, though they need to travel up the nose and into the brain in order to “hijack” your mind. How do they do that? By reproducing and spreading quickly and then slowly eating away at your brain, that’s how.

Under certain conditions, the amoeba just forms into a cyst that’s inactive and doesn’t do much of anything, but when conditions become right, they become active and begin to feed. The Centers for Disease Control says about the mechanism of death from this particular amoeba: “The infection destroys brain tissue causing swelling and death.”^[6] This is definitely not a fun pathogen to catch by any stretch of the imagination.

4 Clostridium Perfringens

Clostridium perfringens is another nasty one. It can be found in soil, water, and the human intestinal tract. This bacteria can cause a specific kind of gangrene called gas gangrene, and it definitely does not at all look very fun. The toxins which are excreted by the bacteria travel through veins, blood vessels, and other bodily systems, and they kill off the flesh inside of the body by poisoning it.^[7]

This causes massive distention, huge pockets of bloating gas that come from the bacteria feeding and releasing of gasses inside the body. Massive bulbs of purple and red swelling show up on the outside of the body as the internal gasses protrude and push outward.

3 Streptococcus Pyogenes

Possibly the best-known cause of necrotizing fasciitis is Streptococcus pyogenes, also referred to as “Group A Streptococcus.” This bacterium also causes strep throat, which many people, even in the developed world where antibacterial everything is prevalent, end up catching at one point, often as children. Like the others on this list, Streptococcus pyogenes produces toxic byproducts which cut through tissue layers of fat, muscle, and skin like butter. This infection starts off rather mild, most commonly presenting as a sore throat, but it can progress and eat away at the tissue of the infected and even cause toxic shock syndrome, a condition that comes with headache, nausea, vomiting, and much more and is also definitely no fun to get.

While most cases of strep throat don’t turn into “the flesh-eating disease,” some of them do, and the effects can be both long-term and devastating.^[8] This happens when the body’s immune response isn’t quick or powerful enough to fight off the invasive strep, and the results can be deadly. Yes, the common strep throat can actually eat your flesh until you die.

2 E. Coli

Escherichia coli is a relatively well-known bacterium which is often responsible for the common food poisoning we all miserably endure every so often. This is the usual E. coli infection, and it’s nothing to shake a stick at, but sometimes, E. coli can go above and beyond the usual case of what we know of as “food poisoning” and become catastrophically worse. As with most bacteria, the body’s immune system as well as antibiotics have fought off the invaders for a very long time, causing variations in the strains which possess radically different traits and can have radically different outcomes upon infection. Some strains of E. coli can cause the death and decay of the skin cells also as they slowly eat away at your flesh.

These strains prey upon people with limited or suppressed immune systems, which can’t fight off the infection—all cases in some studies have been fatal. A specific gene called the cnf1 toxin gene is possessed by the flesh-eating variations of E. coli, which causes them to emit a toxin which destroys flesh like an acid. Animal studies have shown that the presence of this gene in the bacteria causes the toxin to be excreted when animals are infected as well. These E. coli strains are the stuff that nightmares are made of.^[9]

1 Mycobacterium Ulcerans

Mycobacterium ulcerans is a bacterium which is the cause of a disease called buruli ulcer, which causes, you guessed it, ulcers to appear within the skin. But much more than this, buruli ulcer is also a flesh-eating condition. Prolonged infection will cause ulcers on the arm and legs typically, and the chunks of flesh which have been eaten away will usually worsen over time. Only ten percent of cases present with flesh-eating ulcers in other parts of the body outside of the limbs, but that’s still a scary ten percent. As the bacteria spread, they produce a toxin called mycolactone, which is responsible for the destruction of flesh in patients who’ve contracted the bacterial infection and allowed it to progress to the disease of buruli ulcer.

Even more terrifying than having this bacterium secrete toxins which eat away at your flesh while you wait helplessly for it to go away, or for your treatments to work, is that beyond just skin, ligament, muscle, and other soft tissues, the disease can eventually spread down to the bone and begin to eat away at that, too.^[10] And what’s even more nightmarish than that? They have no idea how this bacterium spreads. Very little is known about how M. ulcerans transmits from one person to the next, so we don’t really know what any of us can do to avoid becoming its next target—yet. Hopefully someday, science will develop methods to eradicate these bacteria as well as new and unique treatments, but for now, we’re stuck with limited knowledge and treatment options.

I like to write about the dark, strange, macabre, and unusual.

The idea of being devoured alive by an unseen nemesis is the most terrifying thing imaginable. Not only do these diseases cause fevers, nausea, and excruciating pain; they disfigure their victims, sometimes beyond recognition. With all victims have to deal with, death can seem a blessing.

10Bairnsdale Ulcer

Bairnsdale ulcer is terrorizing Australia. It begins as a mosquito bite and soon spreads to gaping wounds that devour flesh, fat, tendons, nerves, and even bone. Epidemiologists believe it spreads to humans via mosquitoes on possums. They are uncertain whether the possums are the cause or just another victim. The disease incubates slowly, often emerging four months after the initial bite. The elbow, back, calf, and ankle are the most common areas targeted.

Bairnsdale ulcer has been known for decades. However, in the past three years, the number of cases in Australia has doubled. This year, Victoria has had 45 cases alone. Fortunately, a quick and effective test is available. If caught early, ulcers are easily treated. If not, it can lead to extreme pain and possibly amputation.

9Missouri’s Mucormycosis Outbreak

In 2011, a tornado ravaged Joplin, Missouri. The high winds carried more than destructive power. After the storm, several individuals were diagnosed with a rare and deadly flesh-eating fungal infection. Mucormycosis fungus is most commonly found in wood and soil and is a key component in the cycle of decay. The virulent fungus infects the walls of blood vessels. Filaments form, resulting in clots. The clots block blood flow, leading to necrosis of the flesh and even a coating of mold.

Known as a “lid-lifter,” the fungus grows so fast in lab environments it will literally lift the lid off a Petri dish. It grows just as fast in humans, eating into tissue and even bone. Only 74 cases of this disease had ever been recorded. 13 people in Joplin had the disease. Five died. The only treatment is powerful antifungal drugs and debridement, where dead flesh is sliced away.

8Diseased Deer

After being eradicated for nearly 30 years, screwworm flies have return to the Florida Keys. It’s victim: the endangered key deer. The deer currently have a population between 1,300 and 1,500. So far, 102 animals have been euthanized after developing untreatable infections. Screwworms lay eggs in broken skin, and their maggots feed on living flesh. All but seven of the infected deer have been bucks. With open wounds from fighting over females, they are more susceptible to infection.

Federal officials began to sterilize male flies on Big Pine and No Name Key, the worst affected areas. The strategy worked in the 1950s and 1960s, leading to an eradication of the disease in Florida. Biologists and volunteers have begun to feed the key deer food laced with doramectin, a powerful anti-parasitic drug.

7Aleppo Evil

Cutaneous leishmaniasis is a disfiguring disease spread by sand flies. Known as “Aleppo Evil,” the disease has been endemic to Syria for centuries. Horrible open sores emerge around the bite site. The disease can be deadly if left untreated or if it destroys the mucus membranes.

Once contained in Syria, the disease broke out in refugee camps in Lebanon in 2012. The disease is now found in Turkey, Lebanon, Jordan, and even southern Europe. The Kurdish Red Crescent reported that ISIS spread the disease by dumping festering bodies in the streets. The School of Tropic Medicines has refuted this primitive biological warfare claim. Sand flies feed on the living, not rotting corpses. The rise is due to a collapsed health care system.

6Eczema Herpeticum

Owen Richards, seven, developed eczema when he was just six weeks old. It began as redness on his cheek and soon spread to his legs and stomach. The condition worsened, leaving the boy covered in weeping, bloody sores. The eczema grew so bad that his family could not even hug him. The scratching and bleeding fits made even simple tasks like going to the bathroom and dressing an exercise in agony. Painful cysts developed under his fingernails.

In 2013, Owen was hospitalized with eczema herpeticum, a rare flesh-eating bacterial infection. It began looking like chicken pox, but within 24 hours, the flesh-eating disease began to devour his face. It looked like he suffered from burns. Owen was initially placed on intravenous antiviral drugs. However, fearing the impact of harsh treatment on the young boy, his mother soon explored herbal alternatives. Shulan Tang, a professor of Chinese medicine in Manchester, prescribed an herbal mixture. Within four weeks, Owen was healthy enough to run, play, and even attend school.

5Alabama Rot

Alabama Rot, also known as cutaneous and renal glomerular vasculopathy, was first spotted among greyhounds in the United States. The disease causes festering skin lesions and can lead to kidney failure if untreated. Dog owners are becoming terrified to take their pets anywhere.

The first case in the UK appeared in 2012. Since 2014, a full-blown outbreak has begun across all breeds and ages, with at least 78 cases since 2012. Lesions typically appear around the face, abdomen, and legs. These are followed by nausea, fatigue, high fever, and eventual renal failure. The origins of the disease are unknown. There is no evidence of virus, fungus, bacteria, or toxins. Some suspect that a rare form of E. coli bacteria might be the culprit.

4Necrotic Spider Bites

Brown recluse bites are rare. They are not aggressive and lack the ability to pierce clothing. Bites usually only occur when the arachnids are accidentally trapped against the skin. Even without treatment, most bites heal within three weeks. However, in some cases the venom destroys the surrounding tissue.

In 2013, Jeff Hanneman, the guitarist from shred-metal band Slayer, died of liver failure. Nearly every news outlet reported that he died from complications of necrotizing fasciitis he received from a spider bite in 2010. It took several operations to remove the dead tissue. He was even placed in a medically induced coma and had to learn to walk again. A coroner ruled alcohol-induced cirrhosis was the culprit. It is likely that this liver disease preceded the spider bite.

3Sepsis’s Second Act

In 2012, John Middleditch thought he had the flu. A purple rash spread across his body. His limbs turned black and filled with fluid. Multiple internal organs failed. The diagnosis was sepsis. His forearms and both legs were amputated. Against the odds, the quadruple amputee survived. Doctors fitted him with prosthetic limbs, and Midleditch was even back at his beloved gardening.

Four years later, the disease struck again. Within weeks, Middleditch was dead.

44,000 people die of sepsis each year in the UK alone. It is more common than heart attacks and kills more people per year than cancer. Also known as “blood poisoning,” the condition is almost always triggered by another common infection. The body overreacts, and the immune system devours tissue and organs.

2Buruli Ulcer

Buruli ulcer is spreading across West Africa. So far, this flesh-eating disease has infected 40,000 people. It leaves its victims with festering wounds and swollen ulcers. In extreme cases, amputation is needed. Experts are uncertain how the disease spreads. Most suspect contact with an opening in the skin.

A huge number of West African cases go unreported because of illiteracy, poverty, and reliance on traditional healing techniques. Many sufferers believe they are under the influence of witchcraft. The World Health Organization reports that a vaccine offers short term defense against the bacteria that causes the disease, Mycobacterium ulcerans. Long-term vaccines and effective diagnosis techniques are in the works.

1Chesapeake Killer

On September 11, 2016, Michael Funk was cleaning crab pots in the Chesapeake Bay. Four days later, he was dead. A flesh-eating bacteria known as Vibrio vulnificus devoured him alive. He soon fell ill with ferocious pain in his legs and was hospitalized. A doctor removed dead tissue, but the disease spread to his bloodstream. There was nothing anyone could do.

Vibrio bacteria thrive in warm, coastal waters with low salinity. There are 85,000 cases per year in the United States. Eating tainted crabs and fish is the most common mode of infection. Funk contracted his infection through a cut in his leg. There may be pressure from the tourist industry to downplay the significance of these flare-ups.

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.