If you swim in fresh water during the summer, drink unfiltered water or travel to Africa or Asia for any length of time, you may have picked up a few worms or amoebas. While some parasites show no symptoms, others can prove deadly within weeks. In some cases, surgery is an option to help eliminate some organisms. In other cases, vaccines or medicines may help. In all cases, prevention — such as washing hands, maintaining sanitary cooking conditions, wearing shoes when outside and cooking meat or fish thoroughly — can keep you somewhat safe from the invasion of these human parasites.
Also known as nematodes, worms are the most diverse of all animals. Over 28,000 have been described and over 16,000 of those are parasitic. They are adaptable and have been found everywhere. Parasitic varieties include hookworms, pinworms, whipworms and roundworms, among others.
- African Eye Worm: This menatode worm (loa loa) causes a skin and eye disease as the worm migrates throughout the subcutaneous tissue. It does not affect vision, but can be painful as the worm migrates. Microfilaria of Loa loa are transmitted by several species of tabanid flies, located mainly in Africa.
- Anisakis: Anisakiasis is a parasitic infection of the human gastrointestinal tract caused by the consumption of raw or undercooked seafood containing larvae of the nematode Anisakis simplex. It is frequently reported in areas of the world where fish is consumed raw, lightly pickled or salted. Fewer than ten cases occur annually in the United States. To rest your mind (or not), even when thoroughly cooked, A. simplex poses a health risk to humans, but U.S. cases are rare.
- Blood Flukes: The World Health Organization (WHO) considers infection by this trematode (also called a flatworm or Schistosoma) second only to malaria in terms of infestation. It enters the body through the skin of people who come into contact with infested waters and can live in human veins. Several species of Schistosoma affect humans, mainly in Asia and Africa. Freshwater snails represent the main intermediate hosts. The damage to the human body depends upon the location of the schistosomiasis in the body (lungs, liver, etc.).
- Hookworm: The hookworm is a parasitic nematode worm that lives in the small intestine of many mammals, including humans. There are no specific symptoms or signs of hookworm infection. Coughing, chest pain, wheezing, and fever will sometimes be experienced by people who have been exposed to very large numbers of larvae. Indigestion, nausea vomiting, constipation, and diarrhea can occur early or in later stages as well, although gastrointestinal symptoms tend to improve with time.
- Pinworm: This pinworm is a common human intestinal parasite, especially in children. Infection usually occurs through the ingestion of pinworm eggs, either through contaminated hands, food, or less commonly, water. The main symptom includes itching in and around the anus and around the perineum.
- Roundworms: Roundworms (Ascaris lumbricoides) cause Ascariasis in humans, although infected humans can remain asymptomatic for long periods of time. A heavy worm infestation may cause nutritional deficiency; other complications, sometimes fatal, include obstruction of the bowel by a bolus of worms and obstruction of the bile or pancreatic duct. Humans also can contract trichinosis by eating raw or undercooked pork or wild game infected with a species of roundworm.
- Tapeworm: Once anchored to the host’s intestinal wall, the tapeworm absorbs nutrients through its skin as the food being digested by the host flows past it. Tapeworm infection is caused by ingesting food or water contaminated with tapeworm eggs or larvae or by eating undercooked beef or pork. Many people with intestinal tapeworm infection have no symptoms.
- Toxocariasis: Toxocariasis is a zoonotic, helminthic infection of humans caused by the dog or cat roundworm. Transmission of Toxocara to humans is usually through accidental ingestion of infective eggs. Flies that feed on feces can spread Toxocara eggs to surfaces or foods. Eating undercooked rabbit, chicken, or sheep can lead to infection.
- Whipworm: This is s type of roundworm, which causes trichuriasis when it infects a human large intestine. Infection occurs through accidental ingestion of eggs, which often are found in dry goods such as beans, rice, and various grains. They are found more often in warmer regions.
Other Invasive Parasites
- Babesia: This is a protozoan parasite that usually is found in animals, but is increasingly diagnosed in humans because of awareness. The disease caused by Babesia, Babesiosis, is spread through the saliva of a tick when it bites, and the symptoms resemble malaria. Babesia can be diagnosed at the trophozoite stage and can be transmitted from human to human either through the tick vector or through blood transfusions.
- Brain-Eating Amoeba: Naegleria fowleri can invade and attack the human nervous system. N. fowleri propagates in warm, stagnant bodies of freshwater such as contaminated swimming pools and shallow lakes, usually during warm weather. Ingestion into the human body begins when water enters deep into the nose. Infection can spread rapidly, causing primary amoebic meningoencephalitis, with encephalitic symptoms and death within two weeks. Diagnosis is poor — by the time the symptoms have evolved, treatment cannot prohibit the progress.
- Entamoeba histolytica: Cysts survive outside the host in water, soils and on foods, especially under moist conditions. E. histolytica was found to be transmitted through anal-oral sex as well. Symptoms can include fulminating dysentery, bloody diarrhea, weight loss, fatigue, abdominal pain, and amoeboma — the latter may be mistaken for a carcinoma in the right lower quadrant of the abdomen.
- Giardia: Go ahead and drink unfiltered unsanitary water or eat contaminated food to help introduce this little fellow into your small intestine. Symptoms include diarrhea, excess gas, stomach or abdominal cramps, upset stomach and/or nausea. Weight loss and dehydration can occur, which can be harmful if not treated immediately.
- Lice: Officially known as Pediculosis, this is an infestation of lice — blood-feeding ectoparasitic insects. Humans host three different kinds of lice: head lice, body lice and pubic lice (known as “crabs”). The most common symptom of lice infestation is itching. Excessive scratching of the infested areas can cause sores, which may become infected.
- Scabies: Scabies, also known as “the itch,” is a contagious ectoparasite skin infection characterized by superficial burrows and intense itching and caused by a mite. Scabies is highly contagious and can be spread by scratching and then touching another person’s skin. They can be spread onto other objects like keyboards, toilets, clothing, towels, bedding, furniture, and anything else onto which the mite may be rubbed off, especially if a person is heavily infested.
- Swimmer’s Itch: This is a short-term, immune reaction occurring in the skin of humans that have been infected by water-borne trematode parasites. Symptoms include itchy, raised papules, and commonly occur within hours of infection and last for about a week. Humans usually become infected with avian schistosomes after swimming in lakes or other bodies of slow-moving fresh water.
- Ticks: Ticks are external parasites that live on the blood of mammals, birds, and occasionally reptiles and amphibians. Ticks communicate a number of diseases, including Lyme disease, Q fever, Colorado tick fever and other tick-borne diseases. Ticks often are found in tall grass and shrubs where they will wait to attach to a passing host.