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Crypto -

Cryptosporidium is the parasite behind the diarrheal disease cryptosporidiosis, also known as crypto. It's most commonly spread by drinking contaminated water. In fact, the parasite is the top cause of waterborne disease in people in the US. 

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Crabs (pubic lice) -

Many believe crabs are a sexually transmitted infection, because it's commonly passed from person to person during sex. But pubic lice don't cause infections, they're parasitic insects that feed on human blood and are typically found in the genital region. 

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Blastocystis -

Experts aren't sure exactly how people get it, however, poor sanitation and eating or drinking contaminated food or water have been flagged as risk factors. Symptoms include diarrhea, stomach pain, weight loss, and constipation, which can be treated with medication. 

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Head lice -

Pediculosis, commonly known as head lice, is an infestation that spreads most often when people come in contact with an affected person's hair. The culprit is Pediculus humanus capitis, a parasitic insect, which pets can't transmit. Spreading via clothing or hairbrushes is uncommon.

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Dientamoeba fragilis -

This parasitic disease infects the large intestine in humans. Found around the world, scientists aren't sure how people get D. fragilis, but suspect people typically accidentally swallow it. 

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American trypanosomiasis -

Also known as Chagas disease, this parasitic disease is caused by the Trypanosoma cruzi. Found throughout North and South America, insects known as kissing bugs get the parasite from an infected animal or person and then pass the parasites in their feces. Initial symptoms include fever, headache, or rash, but it can become a lifelong illness, resulting in cardiac and gastrointestinal problems.

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Leishmaniasis -

The Leishmania parasite is found in the tropics and subtropics, as well as southern parts of Europe. It causes leishmaniasis, which happens when you're bitten by a sand fly that carries the parasite. There are many different types of leishmaniasis and some cause skin sores, while others affect organs like the liver and spleen. It can be fatal.

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Lymphatic filariasis -

Most common in subtropical and tropical regions, this parasitic disease is caused by worms that live in the human lymphatic system. It's spread via the bites of several mosquito species. It can cause lymphedema and, notably, swelling of the scrotum, called elephantiasis. 

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Giardiasis -

Found worldwide, giardia is a tiny parasite that causes the diarrheal disease giardiasis. You can get it from surfaces, soil, food, or water that's contaminated with the feces of infected people or animals. Some people have no symptoms while others have diarrhea, stomach cramps, vomiting, and dehydration.

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Keratitis -

Found globally in water and soil, this parasitic infection is caused by the single-celled organism Acanthamoeba, a type of amoeba. It can cause infections of the eyes, skin, and central nervous system. It can enter the body through wounds or through the nostrils, and infections have also been tied to swimming with contact lenses. 

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Intestinal roundworms -

Roundworms are a leading cause of parasitic diseases across the world. The worms' eggs pass through feces, and are picked up from contaminated soil, food, or water. There are often no symptoms, though they can include upset stomach or pain. Severe infections can lead to intestinal blockages, or, in children, slow a kid's growth due to malnutrition. Medication is available to treat it.

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Anisakiasis -

Anisakiasis is caused by a species of roundworms known as herringworm, codworm, or sealworm. The larvae get into the water when infected marine mammals defecate, and crustaceans then eat the larvae, which are then eaten by fish. Humans can then get the parasite by eating raw or undercooked seafood. 

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Bedbugs -

Known for damaging furniture and for leaving people itchy, bedbugs can't spread disease like other parasites. They also don't pose a serious medical threat, they're just a nightmare to deal with. 

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Trichomoniasis -

Trichomonas vaginalis is the parasite that causes trichomoniasis, a common STD. Only about 30% of people develop symptoms, which include burning and itching, pain when urinating, and genital discharge. Condoms can reduce the spreading of it.

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Hookworm -

Found around the world, hookworm eggs pass through human feces. It most commonly infects people when they walk on contaminated soil, and poor hygiene plays a role in transmission. Some people have gastrointestinal symptoms, but many have none. Getting diagnosed is key as you can develop anemia due to blood loss. Medication is available to treat it. 

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Naegleria fowleri -

Naegleria fowleri lives in soil and warm fresh water like lakes, rivers, and hot springs. If water containing the parasite goes up your nose, it can get into your brain and cause an infection. Although it's a rare disease, it's almost always fatal. 

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Scabies -

A mite known as Sarcoptes scabiei causes scabies. The condition occurs when the mite digs itself into the skin where it lives and lays eggs. Rashes and itching are the main symptoms of the infestation, which is spread by close contact with a person who has scabies. 

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Pinworm -

Enterobius vermicularis is a roundworm that causes what's known as pinworm infection. The infection can affect anyone, but it's most common in children. It's spread when pinworm eggs are transmitted when contaminated feces comes in contact with someone's mouth. Symptoms include itching around the bottom.

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Malaria -

Malaria is a disease that's caused by a parasite. Anopheles mosquitoes spread malaria from one person to another, as a mosquito can pick up the parasite if it bites a person infected with it. Symptoms are flu-like, such as fever and chills. If it's not treated, the disease can cause complications.

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Toxocariasis -

This roundworm infection is caused by the larvae from two species of Toxocara roundworms, called Toxocara canis, which people get from dogs, and Toxocara cati, which is from cats. Pets that have the parasite shed it in their feces, which can be passed to people if they don't adequately wash their hands or if they eat contaminated food. It can affect the eyes, liver, and lungs. 

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Diphyllobothriasis -

One of the world's largest tapeworms, this parasite can grow up to 30 feet (nine meters) long, and can lead to intestinal obstruction and gallbladder disease. You can get the tapeworm by eating undercooked or raw fish. 

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Cyclosporiasis -

Cyclosporiasis is an illness that affects the intestines, and it's caused by the parasite Cyclospora cayetanensis. People can get it if they eat contaminated food or drink contaminated water. It's often in tropical and subtropical areas of the world. Symptoms can include loss of appetite, stomach cramps, bloating, nausea, and explosive bowel movements. 

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Schistosomiasis -

Also known as bilharzia, schistosomiasis is a disease caused by parasitic worms. The parasitic worms live in some types of freshwater snails, and people can get it if they're exposed to contaminated water. Symptoms include itching, as well as fever, cough, or muscle aches. 

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Cysticercosis -

The larval cysts of the tapeworm Taenia solium can cause a parasitic tissue infection known as cysticercosis. People get it when they accidentally swallow eggs in the feces of a person who has the tapeworm, which can happen if your hands aren't properly cleaned before eating.

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Babesiosis -

Babesia microti parasites cause a disease called babesiosis and get into people when they're bitten by black-legged ticks or deer ticks. They can be found in grassy and wooded areas around the world. Flu-like symptoms can accompany infection, but you may not have symptoms at all.

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Toxoplasmosis -

Toxoplasmosis is a foodborne illness that's considered a leading cause of death from foodborne illnesses in the US. While symptoms are rare, some people who fall ill from the infection will feel like they have the flu or experience swollen lymph glands or muscle aches. Infection can be especially serious in people who get it before or during pregnancy and in those who are immunocompromised.

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Clonorchis -

People who eat raw or undercooked fish in areas where this parasite is found can get infected with the Clonorchis parasite. It mainly infects the liver, as well as the gallbladder and bile ducts. Most people with the parasite don't have symptoms, however, they can include indigestion, stomach pain, diarrhea, and constipation. The infection can last for 25 to 30 years, which is how long the parasites can live in the body. 

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Echinococcosis -

This parasitic disease is caused when a tapeworm in the genus Echinococcosis infects a human. Most people don't have symptoms when infected, but the infestation can lead to enlarged cysts in the liver, lungs, and other organs. 

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Whipworm -

This parasitic worm causes trichuriasis, a disease that's especially common in warm climates with inadequate sanitation. Its eggs pass through the feces of an infected person, and it spreads to others who come into contact with contaminated soil, food, or water. Some people have no symptoms, and some might experience painful bowel movements and rectal prolapse.

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Paragonimus -

The Paragonimus lung fluke, or flatworm, can infect people's lungs if they eat raw or undercooked crab or crayfish. It's uncommon for the flatworm to travel to the central nervous system, but sometimes it can.

Sources: (Live Science) (Business Insider) 

See also: Bizarre tropical diseases you've probably never heard of

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