Thursday Thirteen

Roundworms and Tapeworms and Flukes, Oh My

Ascaris lumbricoides, giant roundworm, is the most common parasitic worm in humans. According to some estimates 25 % of humans are infected with the disease, ascariasis. Ascariasis occurs worldwide, mostly in tropical and subtropical countries. It has highest prevalence in areas of poor sanitation and where human feces are used as fertilizer 

Human pinworm, Enterobius vermicularis, is the most common parasitic worm infection in the United States and Western Europe. According to one study 11.4 % of people in the US might be infected. Pinworms are easily transmitted from human to human and are particularly common in children. Luckily the disease, enterobiasis, causes only anal itching.

Anisakis worms are parasitic roundworms living in the stomach. Anisakiasis (the disease) is acquired by eating uncooked fish or squid infected with Anisakis simplex (the most common Anisakis species). The parasite has a protective layer against gastric acid and survives burrowed into the gastric wall. Larval Anisakis simplex develops into a reproducing adult only in marine mammals. In humans it cannot survive and dies within a few weeks. But the short time that it lives, it causes stomach pain and nausea. Larval Anisakis simplex is about 2 cm long.

Loa loa is a thread-like worm that lives under the skin in the subcutaneous fat causing loiasis. Because it is often spotted migrating in the eye, it is known as the eye worm. Loiasis is endemic to 11 countries and 12 million Africans are infected mostly in Cameroon, Equatorial Guinea, Gabon, Nigeria, the Central African Republic, the Democratic Republic of Congo and the Republic of the Congo. The disease is also known as subcutaneous filariasis, Calabar swellings, African eye worm infection, Loa loa filariasis and Fugitive swelling.

Whipworm is a parasitic worm infecting 500 million humans in tropical countries. It lives  its adult life in the large intestine. The human whipworm is called Trichuris trichiura and causes trichuriasis. Whipworm more likely infects people who already have other parasites. It gets its name from its appearance. The anterior is thin and long whereas the posterior end is thicker. The thin front part is burrowed in your intestinal wall eating nutrients in the mucosa. Adult female is 35–50 mm whereas male is about 30–45 mm long. Both sexes are white-pink in colour.

Strongyloides stercoralis is a 2 mm long intestinal worm causing a disease called strongyloidiasis. It is common in tropical and subtropical areas but also occurs in temperate zones. Unlike most parasitic worms, Strongyloides stercoralis has a heterogonic life cycle. So in addition to the parasitic life cycle it has a separate free-living cycle where it lives and reproduces without a host in the soil. Strongyloides stercoralis can autoinfect the same host over and over without any intermediate host. This makes strongyloidiasis a very persistent disease.

Diphyllobothrium latum, the fish tapeworm, is the biggest tapeworm in humans. It causes a parasitic infection called diphyllobothriasis which is acquired by eating raw fish infected with the parasite. Diphyllobothriasis is found in Chile, Peru, Uganda and in the Northern Hemisphere (northern Asia, Europe and America) in areas of rivers and lakes. Diphyllobothrium species include: D. cordatum, D. dalliae, D. dendriticum, D. lanceolatum, D. latum, D. pacificum, D. ursi and D. yonagoensis. Diphyllobothrium latum is the most common and mostly found in Scandinavia, the Baltics and western Russia.

Taenia saginata is a large tapeworm that causes an infection called taeniasis. It is commonly known as the beef tapeworm or cattle tapeworm because it uses cows as intermediate hosts. Humans are the only definitive hosts. Taeniasis occurs worldwide and is relatively common in Africa, Eastern Europe, Latin America and the Philippines.

Lymphatic filariasis is a parasitic disease caused by thread-like worms called Wuchereria bancrofti. The parasite is carried from person to person by mosquitoes. 120 million people are infected in subtropical and tropical Asia (mostly in India), Africa, the Pacific and the Americas (mostly in Brazil, Haiti, Guyana and the Dominican Republic). Lymphatic filariasis is the leading cause of permanent disability worldwide. Out of the 120 million more than 30 % are severely incapacitated by the disease. Over one billion people in over 80 countries are at risk of getting infected.

Fasciola hepatica is a parasitic fluke that lives in the liver. In addition to humans it infects cows and sheep. It is known as the sheep or common liver fluke and causes a disease called fascioliasis. Fasciola hepatica is found in areas where cattle and sheep are raised. Adults reach a length of 3 cm and 1 cm width.

Human lung fluke, Paragonimus westermani, infects 22 million people in Africa, Asia and South and Central America. Southeast Asia in particular is affected because raw seafood is very popular there. Humans get infected with the disease, paragonimiasis, by eating raw crabs or fish that are carrying the parasite. Even properly cooked sushi can cause infection, if the cook or waiter is careless when preparing the food. In Asia about 80 % of freshwater crabs are infected with the lung fluke.

Fasciolopsis buski is the largest intestinal fluke in humans. It causes a parasitic disease called fasciolopsiasis and is commonly known as the giant intestinal fluke. Fasciolopsiasis is endemic in China, India, Malaysia, South-East Asia and Taiwan especially in areas where pigs are raised and fed with freshwater plants. According to some estimates there are over 10 million infected people in East Asia.

Toxoplasma gondii is a microscopic protozoa that causes a disease called toxoplasmosis. The disease is found all over the world. Some estimates suggest that over 30 % of human population is infected. For example, in Germany and France most people carry the parasite, whereas in South Korea it is quite rare. More than 60 million people in the United States are said to be infected. Toxoplasmosis is usually asymptomatic, because our immune system keeps the parasite from causing illness. The disease is more problematic for pregnant women and people who have weakened immune systems. Cats are the primary host and humans and other warm blooded animals are just intermediate hosts. In this sense Toxoplasma gondii is not a pure human parasite.

(My source for this delicious topic is: Parasites In Humans)


We’re all waiting for your list over at: Thursday Thirteen!


12 thoughts on “Thursday Thirteen

  1. Huh. Well,an interesting, but creepy topic. I learned enough to be grateful I don’t have any of these little pets/ infections currently. Thanks.

  2. Wowsers. What an interesting post! You’re really brave… I don’t think I could…explore these types of…bugs.

    BTW : I posted my top 13 MALE superheros. ^_^

    Happy Thursday!

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