Top 10 Most Nightmarish Parasites

They’re small, they’re sneaky, and they’re utterly terrifying. Welcome to WatchMojo.com, and today we’ll be counting down our picks for the Top 10 Most Nightmarish Parasites Around The World.

For this list, we’ll be looking at some of the most upsetting, unpleasant and nasty parasites found around the globe that affect either humans or animals.

According to some estimates, this microscopic organism already has infected up to 50% of the population. Sweet dreams! Don’t worry though, this parasite isn’t poised to take over the world and enslave the human race. When people talk about mind control, what they really mean is that Toxoplasma gondii has the ability to impact behavior. Research has suggested that its presence may play a role in mental illness, or erratic behavior in humans, but such findings are far from conclusive. In rats however, the impaired judgement is significantly more pronounced. Studies have found that infected rats are significantly less fearful, even around cats, forcing scientists to reconsider how it might be affecting our choices.

This particularly nasty little creature, found from Mexico down into central and south America, might not pose a serious threat to your health, but it’ll make your skin crawl - literally. Just thinking about bot flies is enough to turn your stomach. The bot fly lays its egg on mosquitos; and from there, the eggs snuggle into the tiny wound left in a human’s flesh when said mosquito bites. From there, they hatch and grow, eating the flesh and creating painful, pus-filled sores, eventually working their way out of the skin as full grown larva. When infected, if you look close enough, you can actually see them moving around under the skin. Good times!

Sleeping sickness, caused by two types of this extracellular parasite, is a devastating condition that has wreaked havoc in Sub-Saharan Africa. This parasitic disease, spread via the bite of tsetse flies, is particularly insidious, as it often shows little sign of its presence until it has reached an advanced stage of infection; by which point, the host’s central nervous system has been compromised. Though easy to treat in the early stages, it is often mistaken for a common cold or flu. After it reaches the central nervous system, convulsions, confusion, and erratic behavior sets in, as well as extreme exhaustion and the inability to sleep (now there’s irony). Left untreated, African Trypanosomiasis can be fatal.

Cymothoa exigua is a small crustacean that invades fish via the gills, and then attaches itself to the tongue. From there, it begins to, as advertised, eat the tongue, effectively replacing it in the process. We should all consider ourselves exceedingly lucky that this particular parasite targets fish and not humans, because it is something straight out of a horror film. Then again, we’re not exactly immune to water-based parasitic attacks ourselves. Vandellia Cirrhosa is a small parasitic catfish known to swim up and into the penis of men through the urethra, prompting men of traditional cultures in the Amazon basin to tie the foreskin shut with string when going in the water. Yeesh.

Flies strike again, this time both in Africa and parts of Latin America. In this case, our offending parasite is transmitted by simulium blackflies, known to breed in quick moving bodies of water, such as rivers. As a result, populations dependent upon natural sources of water are most commonly affected. When the host becomes infected with onchocerciasis, they are likely to experience an extremely itchy rash, and, as the condition progresses, deformities of skin and eye conditions. If left untreated, the Onchocerca Volvulus parasite can result in permanent blindness, which is why access to treatment is so crucial.

Mosquitos remain, at least for now, an important part of our global ecosystem, serving as a crucial source of food for many small predators . . .but they sure spread an awful lot of disease between humans. They’re the perfect means of public transportation for lymphatic filariasis, spread by tiny worms (Wuchereria bancrofti being the most common), invisible to the naked eye, but whose effect on the human body is anything but. Lymphatic filariasis can result in both lymphedema, a swelling of the arms and/or legs, and elephantiasis, which results in massive growth of the arms, legs, breasts and male genitals (believe us, not in a good way).

This is another parasite that makes you grateful to be human, and thus, an unsuitable host. Cockroaches… aren’t so lucky. While some parasites simply leech off the host while keeping their impact to a minimum, when the jewel wasp selects its cockroach victim… that roach is a slave for the remainder of its short, miserable existence. The wasp injects the cockroach with venom directly into the ganglia, and then leads the helpless roach around by the antenna, like a dog on a leash. Back at its burrow, the wasp lays eggs in the cockroach to act as a living incubator for the wasp larva, which will eventually eat it from the inside out. The Aristocrats!

Few parasites have gotten more attention or had a more significant (and horrible) impact on humanity than this one. Plasmodium is a family of single-cell parasites, with numerous subtypes; five of them target humans. While four of these have been known to result in malaria, the severity of the disease caused by three strains is relatively low. Then, there’s Plasmodium Falciparum… the killer fourth species, and the most prolific source of malaria. It’s been estimated that between roughly 0.5 and over 1 million people die of malaria each year, with almost every fatality resulting from the P. Falciparum strain.

Parasites wreak havoc on the human body in a wide variety of ways, but few more painfully visible than a leishmaniasis infection, which is spread by sandflies. In its cutaneous form, the infection presents as large ulcers that can affect any part of the body, including the mouth and nose. Though this infection might look painful, the sores, lumps and scabs aren’t known to be particularly sensitive or painful, and will usually heal over time. Good, right? But it’s the internal effects of Visceral Leishmaniasis that you really need to worry about. Left unchecked, v. leishmaniasis causes the liver and spleen to swell, resulting in a significantly lower blood cell count. It can be fatal.


Before we unveil our top pick, here are a few honorable mentions

Leucochloridium Paradoxum


Cochliomyia Hominivorax


Taenia Solium (aka Pork Tapeworm)

You’ve surely heard horror stories about this one. While most parasites discussed today can be treated, there is no known cure or effective treatment for naegleria infection. This is why preventative measures, such as regular water testing, are so incredibly vital to public safety when it comes to natural bodies of water where people swim regularly. When inhaled nasally, it can result in a cerebral infection, known as naegleriasis, which almost always kills the host, typically in as little as two weeks time. To avoid exposure, only swim in bodies of warm freshwater that you know to be tested regularly, and avoid accidentally breathing in through the nose.