Top 10 Grossest Parasites (And What They Do To Your Body)

Teamwork makes the nightmare work with this parasite. A botfly resembles a bumblebee, and its larvae act as internal parasites for mammals. Their eggs are laid on blood-sucking species such as mosquitoes, and if you happen to be bitten by one of these, you have more than just itchiness to worry about. Botflies can also lay eggs on you directly. An infestation of fly larvae in this manner is known as Myiasis. While botflies themselves are usually not fatal for hosts, the resulting skin irritation can be deadly. Although these parasites can be removed, prevention is always better than cure. If you are unable to avoid being around botflies, always keep insect repellent handy, and wear clothes that will protect your arms and legs.

The most common parasitic infection in humans is schistosomiasis, which is typically transmitted by Schistosoma haematobium, also known as urinary blood fluke. Evidence of this parasite, which has only been found in Africa and the Middle East, goes back to at least Ancient Egypt. The organism infects human hosts through their urinary tracts, leading to urinary schistosomiasis. This is also the second leading cause of bladder cancer in humans. The resulting disease is brought about by the fluke's eggs, and this can be avoided through proper wastewater treatment and water purification. Some of the symptoms of schistosomiasis include bloody urine, chest pain, and seizures. Praziquantel is a drug used for treatment, though it's not guaranteed to cure the disease.

Scientists have identified more than 100 species of Babesia, a type of parasite that is transferred through tick bites, leading to red blood cell infections. The resulting disease is known as babesiosis, which presents symptoms that are similar to those of malaria. Treatment methods for babesiosis include antibiotics, antimicrobials, and exchange transfusion, in which affected red blood cells are replaced with safe ones. While there are more than 100 types of Babesia, not all of them are dangerous to humans. Keep in mind that it can take several weeks after infection for symptoms to arise. As long as you stay away from ticks, you can stay away from Babesia.

This species of roundworm earns its name from its long and skinny appearance. When a whipworm makes it into your large intestine, it can lead to trichuriasis, or “whipworm infection.” Often, hosts stand a greater risk of this by consuming items contaminated by the parasite’s eggs, such as water or vegetables. Whipworms can bring about intense diarrhea, anemia, and further problems through coinfection, where their effects are amplified by another parasite. Estimates put the number of infections around the world at 600-800 million. To reduce the prevalence of this, it is imperative that everyone has access to clean water and is well-informed on basic hygiene habits, such as hand-washing before eating.

There's nothing simple about this parasite, otherwise known as a herring worm. These nematodes infect hosts, resulting in a condition known as Anisakiasis or herring worm disease. Though direct herring worm infections often occur in marine animals, such as sea lions, they spread easily among other species. Humans can contract these parasites from eating seafood that hasn't been properly cooked. To prevent anisakiasis, it’s important to stay away from raw or undercooked seafood. If infection does occur, the host could present with symptoms such as diarrhea, nausea and sometimes, anaphylaxis. However, these are typically relieved within hours, if the worms are removed through an endoscopy.

You might have heard about guinea-worm disease and how prevalent it’s been in certain parts of the world. Also known as Dracunculiasis, this condition occurs when a host ingests drinking water contaminated by larvae which eventually grow in their body. As these worms develop, they cause harrowing blisters which burst open and could lead to potentially fatal bacterial infections. While guinea-worm disease once affected millions of people each year, improved water sanitation methods have reduced the number of annual cases to just 13, in 2022. Through continued education and awareness, that number could one day become zero. Anyone living with guinea-worm disease needs to have the parasite properly removed to avoid any further infections or damage from the wound.

This parasite didn't get its name because it has particularly good vision. Rather, it's because it travels - among other places - through the eyes of its hosts. Mango fly and deer fly bites introduce these nematode worms to human bodies, and cause a nasty condition known as Loa loa filariasis. Although a host's eyesight usually isn't compromised by eyeworms, it is incredibly uncomfortable to have one wriggling around up there. Hosts can start to feel itchy, sore, and exhausted, though it can take months for symptoms to arise, and it's possible to be completely asymptomatic. The worm can be surgically removed, but medication is also recommended to ensure the parasite is gone for good.

Consuming raw or otherwise undercooked pork can have consequences far beyond just some indigestion. It can also lead to contracting a pork tapeworm. When these parasites enter a host's body, they cause Taeniasis, an infection that can also bring about what is known as cysticercosis. Sufferers of this condition typically experience seizures. Doctors can treat taeniasis by prescribing oral medication, but it's fairly easy to avoid these parasites. Make sure all meat you consume - pork or otherwise - has been cooked at the proper temperature. Look for any signs of undercooking and when in doubt, use a food thermometer to confirm if the heat is just right.

Botflies aren’t the only parasites that infect their hosts via myiasis. One other culprit is the screw-worm fly, often just called a screw-worm. These flies lay hundreds of eggs inside open wounds of humans and other warm-blooded species, providing a safe place for the larvae to feed. They get their name from how they screw themselves into a host's flesh. The screw-worm was thought to have been eliminated in the U.S. in 1982, but in 2016, a Florida county experienced an outbreak. Since contracting this parasite can be fatal, it’s vital to continue research and prevention efforts. Currently, there are no FDA-approved medications for screw-worms, but they can be surgically removed, and antibiotics can be used to avoid any secondary infections.

Anything that starts with “brain-eating” has to be bad news. Known scientifically as Naegleria fowleri, these parasites are present in water, and they gain entry into a host’s body through the nose. Once inside the host, these amoebae make their way up to the brain. They then cause an infection known as primary amebic meningoencephalitis or PAM, which presents symptoms such as intense nausea, seizures, and hallucinations, before proving fatal in as little as one day. Though infection is not common, survival rates are incredibly low, with more than 97 percent of cases being fatal. For the greatest harm reduction, avoid getting freshwater or water from potentially contaminated sources up your nose.