Blood flukes, which make up the genus Schistosoma, are a type of parasitic flatworm that cause schistosomiasis, an infection that afflicts tens of millions of people a year. Schistosomiasis is in fact the second most socioeconomically harmful parasitic disease in the world, according to the World Health Organization. (Only malaria is more harmful.) Below we provide a brief guide and overview of blood flukes that includes the most essential information about this parasitic disease. We will also provide links to some of the best sources for information about blood flukes online.
Blood flukes came to our attention most recently when answering a reader’s question about thin red worms in the shower. She was likely dealing with bloodworms (or blood worms), which is a name that is occasionally (and unfortunately) applied to blood flukes, so the first point we want to make is simply about usage. Bloodworms, which are the larval form of nonbiting midges, are definitely not blood flukes, which are a type of trematode (i.e., a parasitic Platyhelminthe). Ironically, bloodworms are actually not worms, whereas blood flukes are, but it is best to keep the two names separate. Bloodworms are essentially harmless larvae (but for any pathogens they may carry), whereas blood flukes are a grave threat to a large percentage of the human race.
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Schistosomiasis is transmitted through contaminated water. A person suffering from schistosomiasis can contaminate water with their feces or urine, which contains the eggs of the parasite. The eggs will hatch into larvae in the water and infect snails, which serve as an intermediate host. Once released from the snails, the larvae will seek a new mammalian host. The larvae are able to infect mammals by penetrating their skin when it comes in contact with contaminated water. Once inside a mammalian host, the larvae mature into adult schistosomes. The adult flukes live in the blood vessels of the host, releasing eggs that will be pass from the body in urine or feces. However, some of the eggs become trapped in body tissue, causing immune reactions and organ damage.
Although instances of schistosomiasis have been reported in 78 countries, ranging from China to the Caribbean, from the Middle East to Brazil, it is estimated that at least 90 percent of those suffering from schistosomiasis are in Africa. Schistosomiasis generally only afflicts poor, rural communities that lack potable water and access to adequate sanitation. In frequent contact with water and often insufficiently hygienic, children are especially vulnerable to infection. Schistosomiasis can afflict anyone who comes in contact with contaminated water, however, and migration from rural communities to cities has spread the disease to more densely populated areas.
If you are interested in reading more about blood flukes and want to consult the sources we used, we first call your attention to the World Health Organization’s article on schistosomiasis, which provides a clear and thorough overview of the infection. The Stanford University page dedicated to blood flukes, which has a helpful diagram explaining schistosomiasis transmission, is also worth consulting, as is the Center of Disease Control’s schistosomiasis page.
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