15 Parasites That Can Invade The Human Body

Think you’re alone? What if you’re wrong? What if there’s a gang of tiny creatures living inside you right now?

It’s far from a pleasant thought, but parasites that find their way into human bodies are scarily common around the world. It’s particularly creepy when you get to see them up close, with some of the little guys looking like worms, some like something you’d expect to see jumping out of John Hurt’s chest, and some like nothing you’ve ever seen before.

A lot of parasitic infestations can be harmless, or even beneficial to the host as well as the parasite. But others are quite the opposite, leading to some disgustingly nasty symptoms and even when a community has a real outbreak on their hands, high numbers of fatalities.

Read on to find out about 15 weird and disturbing creatures which could be making their residence inside your body, the damage they can do to people, and just why it’s so important to wash your hands...


15 The Worm Inside Your Eye

If you’re squeamish about things happening to your eyes, you’ll want to be careful when visiting certain parts of West Africa, as the roundworm species Loa loa loves making its way into human eyeballs – it’s known as the eye worm for good reason.

After entering the human body via the bite of certain kinds of fly, the eye worm resides in the bloodstream just underneath the skin. Gradually – sometimes over a course of years – it crawls its way towards the face, and the infection only becomes obvious once it can be seen crawling across the white of the eye. More disgustingly, it can be felt there!

It is possible to operate on the eye and remove the worm, as horrifying as that sounds. But it's better than the alternative of leaving the worm in there, especially given that complications can include itching, swelling, and brain damage. And, of course, dealing with the sight of a worm in your eye.

14 That Itch Could Be Scabies Mites


Got an itch you just can’t scratch? It’s probably nothing to worry about. Unless, of course, you have scabies mites. These little fellas, barely visible at under half a millimeter in size, are passed from human to human via human touch. So, transmission can occur through sex, holding hands, or sharing towels.

The female mites then burrow into the skin, while males roam around on top until they find a female to mate with. This not-so-sexy mite sex could cause irritation, but the real problems begin when the female lays her eggs inside the skin. Once these eggs hatch, intense itching can be caused.

Thankfully, scabies mite infestations can usually be cured using topical creams. This isn’t the case, however, for those with weakened immune systems, for example, due to cancer or AIDS, who can end up with crusted scabies. That’s as disgusting as it sounds and includes the build-up of thick crusts of skin containing thousands of mites.

13 Tapeworms Love A Good Gut To Live In


Be careful what you eat. If you eat uncooked meat from infected animals or food that’s been improperly handled by an infected person, you could find yourself with a cestode – or tapeworm – wriggling around inside you.

This long and flatworm would then attach itself to your intestine using hooks on its head, or scolex. After they’ve found themselves a nice bowel to live in, tapeworms mature, and develop reproductive organs – the little baby tapeworms leave your body hidden in feces, heading off into the world on their own adventures.

Tapeworms can live inside a human for up to 25 years, but should ideally be treated quicker than this – the infection can lead to blockage of the intestines or can pass to the liver, heart, eyes, or brain and end up killing you.

12 The Vampire Fish That Swims Up Penises

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It’s difficult to imagine a more horrible injury, and it supposedly happens due to a simple mix-up over dinner. The candiru, or Vandellia cirrhosa, is a tiny fish that lives in the Amazon river; it feeds on other fish by swimming into their gills and nibbling at their blood.

But there have been many stories of the candiru mistakenly seeing people as potential food and swimming up any human orifices exposed to them, including anuses, vaginas, and penises. In one infamous incident, a Brazilian man claimed to have been relieving himself into the river when a hungry fish swam right up the stream of pee.

This story is unlikely to be true, of course, not least due to the questionable fluid dynamics involved. It’s not even been scientifically proven that they attack humans at all. But nor has it been disproven – so for your own sake, if you really do have to go swimming in the Amazon, keep your pants on.

11 The Dragon Worm – Which Grows A Meter Long!

Also known as the Dracunculus, which is Latin for ‘little dragon’, the Dragon Worm is caught when humans swim in or drink infected water. The larvae of the worm are found inside tiny fleas; once inside the human host, the fleas die... and the worm grows.

The horrible thing is that the worm can grow up to a meter long inside you. The nice thing is that it finds its own way out. Actually, thinking about it, that’s horrible too, as it causes an intense fiery pain (hence the name) when it pokes itself through the skin, usually around the legs or feet.

And there’s no easy way to get it out quicker; despite the pain, you’ve just got to go with it. Over several days, the worm will emerge from the skin, and all anyone can do is pull gently to ease it out, clean the area of skin, and wrap the worm around a stick to maintain tension.

10 The Sex-Change Bacteria


If you’re a man and this bacteria infects you, you could find yourself changing into a woman! Well, OK, that’s only if you’re a male insect.

It’s still a pretty freaky ability, though. Wolbachia are passed on via egg cells, so don’t have much use for males. If they end up inside a male insect, they’ll either kill it or force it to change sex. They’ve even been known to enable virgin births in female hosts, eliminating the need for men altogether.

Though Wolbachia mainly infects insects, it has been found in humans. You don’t need to worry about catching it and waking up as the opposite sex, though. On the other hand, there has been speculation about its potential to be used as a biological weapon, which is an even more concerning thought.

9 Roundworm - The Longest Of All The Intestinal Worms


Out of all the types of worm which can grow in your intestine, the roundworm is the longest, able to grow anywhere from 15 to 35 centimeters in length. They mainly cause trouble in developing, tropical countries, particularly where human feces is used to fertilize crops.

After food infected with the roundworm larvae is swallowed, they hatch in the intestines. Horrifyingly, they then burrow their way up through the bloodstream, towards the heart and lungs. When in the lungs, the coughing this causes can make the person swallow the worms and send them back into the gut where they started.

Symptoms can include coughing up blood and breathing difficulties, and sometimes sufferers can even find the worms in their vomit or poo. In other cases, roundworms can remain in the body undetected for years. Thankfully, roundworm can be treated with an easy enough course of medicine.


8 The Mind-Control Bug – Which Half The World Has!


Like something out of a classic sci-fi movie, the microorganism is known as Toxoplasma gondii can have a strange effect on the thoughts of its host – it modifies the neurons of the brain, causing changes in behavior.

It primarily infects rodents, and has a pretty significant brain-washing effect on them – it eliminates their fear of cats, even making them attracted to the smell of cat urine. The cat then eats the mouse or rat; when the bug is passed out of the cat, it finds its way into another rodent.

But Toxoplasma gondii can make its way into humans too, via undercooked meat or handling of cat litter – and in fact, is believed to live in 30 to 50% of the world’s population. Most of these people suffer no symptoms from it, but it can have mind-control effects on some of us – schizophrenia, self-harm and slow reaction times have all been linked to this creepy parasite.

7 The Worm That Causes Elephantiasis

You’ve no doubt seen pictures of people unlucky enough to suffer elephantiasis, the horrible condition that features extreme swelling, but you may not know that this can be caused by a tiny parasite.

The type of roundworm known as Wuchereria bancrofti is prominent in Africa, Asia, and Central and South America. Its larvae enter the human bloodstream via mosquito bites. It then makes its home in the lymph nodes, predominantly those around the leg area, and even in some cases the genitals.

If left untreated, the Wucheria bancrofti will then grow into an adult worm and can go on to cause several problems including severe pain and elephantiasis. Though the symptoms can generally be cured with surgery and drugs, prevention is always a better option – so remember your mosquito net next time you visit Africa!

6 The Blood-Flukes (With Their Weird Sex Habits)


A kind of flatworm, the Schistosoma or blood-fluke is responsible for a disease known as schistosomiasis, which occurs in developing countries in Africa and Asia. They live in water, and you don’t even have to drink it to get infected – come into contact with this contaminated water and the blood-fluke will penetrate your skin.

The parasite will then find its way to one of your organs – possibly the liver, possibly the bladder, depending on the particular species – and make itself a home. Though they can stay here without causing any major damage for decades, they can also cause swelling and even failure of the organ.

As well as the human host, the blood-fluke also spends part of its lifecycle in a snail host, so infections can be prevented by reducing the number of snails in an environment. Another weird thing about the blood-fluke is the way they mate – the male is considerably bigger than the female and encloses her within himself for their entire adult lives, passing food from the host onto her.

5 Itchy Bum? Probably Worm Eggs.

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The most common worm infection in the United States and Europe is one that thankfully doesn’t have the most serious symptoms and isn’t going to kill you, but it can be very irritating – particularly around the anus.

The pinworm, so named because of its long, pin-shaped posterior, is a parasite of about a centimeter long that lives in the intestines of its hosts. Its eggs, however, are laid outside the body, around the anus and perineum, and can cause a lot of itching. This is how they spread – people scratch the itch, and then pass the eggs on when they touch things.

Interestingly, the pinworm is the exception to the rule that parasites are less likely to thrive in affluent areas – it can be found among all sorts of communities in Western cultures, and doesn’t discriminate by social class, race, or culture. It is, however, much more likely to spread when people neglect basic hygiene. If you have to scratch yourself down there, please wash your hands after.

4 The Little Amoeba That Could


It may only be a single cell, but this plucky little ameba can cause a lot of trouble – it kills between 40,000 and 110,000 people each year!

Found in water, damp environments, and soil, as well as contaminated fruit and veg, the Entamoeba histolytica can infect humans, as well as other primates. It can cause a disease called amoebiasis, also known as amoebic dysentery, which is about as fun as it sounds. Symptoms range from mild pain to tissue death via good old bloody diarrhea, with complications such as liver abscesses potentially becoming fatal.

There could be up to 50 million people worldwide infected by Entamoeba histolytica, with infection more common in warmer areas. One infamous outbreak occurred at the Chicago World’s Fair in 1933, where defective plumbing caused sewage to leak into everyone’s drinking water, leading to over a thousand infections and 98 deaths – an ironic fate for an event meant to celebrate human technological progress.

3 From Egg To Flea To Eel To You

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If you thought eels were disgusting, wait until you find out about the creatures that live inside them. The Gnathostoma spinigerem is a kind of nematode (another word for roundworm) which can be picked up from eating undercooked fish, particularly eels.

It actually has quite a complicated ‘old lady who swallowed a fly’-style life cycle, beginning life as an egg hatched in fresh water, which is then eaten by water fleas. The fleas are eaten by fish, which are in turn eaten by carnivores – including us. The larvae hatch in the carnivore’s stomach and get to work.

Because it’s not meant to end up in a human host, our bodies aren’t ideal for Gnathostoma spinigerem and, unlike other parasites, it’s unable to reproduce inside us. Possibly because it’s ticked off about this, it can cause some damage, with symptoms including fever, vomiting, and lesions on the skin.

2 The Parasite In Your Drinking Water

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The glass of water you’re drinking right now could have this disease-causing parasite in it. Alright, it’s extremely unlikely that it does. But it could.

The Giardia lamblia spreads itself through contaminated water, making its way inside a human host’s gut. It then causes inflammation and reduces the digestive system’s ability to absorb nutrition. The symptoms that result are numerous and unpleasant – diarrhea, flatulence, lack of appetite, and, most fun of all, burps that taste so nasty they make you throw up.

This one’s not just restricted to developing countries – in 2007, Giardia lamblia was found in parts of Oslo’s water supply, and people had to be advised to boil water before drinking it. On the plus side, it’s far from the worst of parasitic infections to get, as it goes away on its own after no more than six weeks.

1 The Hookworm Lives Inside Half A Billion People


Named for their slightly bent head, hookworms literally hook themselves onto the walls of your intestine. They then start drinking your blood, which can lead to anemia, a dangerous condition in which lack of red blood cells can cause weakness and even loss of consciousness.

Shockingly, it’s believed that over half a billion people worldwide are affected by hookworm infection, mostly in less developed countries with poor sanitation. They can live in damp soil, spreading to – and penetrating – the skin of anyone who walks on it barefoot.

They can also be picked up from contaminated water, or through fruits and vegetables, which, frankly, makes us want to stick to chips and chocolate for our snacks. Though hookworm infection is generally not fatal in developed countries, it’s still enough to make you think twice about your hygiene standards.

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