A buddy of mine is studying this Neglected Tropical Disease in China as part of a Fulbright Scholarship. I thought I would give him a shoutout.
bigbigbelly.blogspot.com
From his blog:
"Schistosomiasis, also called snail fever, is known in China as the “blood-sucking disease” (血吸虫病). It is also commonly referred to as bilharzia, or in scientific circles, as Schistosoma japonicum. No matter the name, it has plagued the people of China for at least over a hundred years.
*NOTE: Schistosomiasis, as it is understood in modern terms, was only identified in the mid-19th century. However, symptoms of the disease have apparently been recognized in China for quite some time. Writings that date back well over a thousand years describe a water-borne disease that attacks people in much the same manner that we today understand schistosomiasis to do.
In China, during the 1950s, 10 million people were discovered to be infected with the disease, and the areas affected, or at risk, covered a population numbering near 100 million. However, beginning in the 1950s, in line with Mao’s new ideology (the power of mass movement and cooperative effort), entire populations in schistosomiasis-endemic areas were mobilized against Oncomelania (the vector) snails and recruited to drain rivers and ditches. The number of people infected with schistosomiasis was reduced from 10 million in 1955 to 1.52 million in 1989. Moreover, the area of snail-ridden regions in China was reduced by 76.6% (originally 148 billion m2). Schistosomiasis, which was once an endemic disease in 699 communes in 347 counties, was basically eradicated in more than 200 counties and cities by the end of 1979. Oncomelania snails were eliminated in two-thirds of infested areas and two-thirds of schistosomiasis patients were cured. For more on Mao-era initiatives and achievements, check here. However, several sources document a re-emergence, or rise in schistosomiasis with the beginning of the post-Mao era, particularly in rural areas. And in major schistosomiasis-endemic zones (marsh and lake regions of southern China and the Yangtze River Basin), estimates have been made that 60 to 100 million people are still at risk of schistosomiasis infection/re-infection. For more, check here.
Schistosomiasis is an intestinal parasitic infection caused by Schistosoma japonicum, which involves humans, intermediate snail hosts, and the environment to complete its complicated life cycle. As eggs are discharged into the water via the urine or feces of infected humans or animals, they hatch into larva called miracidia, which must infect the Oncomelania snail in order to continue their life cycle. These adult snails are 6-8 millimeters in length and have a preferred habitat on the surface of the water’s edge, or buried in the mud up to depths of 30 centimeters. Once inside the snail body, the miracidia reproduce and transform into free-swimming larva called cercariae. It is the cercariae that, once fully developed, are distributed into the environment and eventually enter the body of a human or animal target. People may be infected by simple contact with the water (for example, when bathing, farming, fishing or swimming) where infected snails live. Once within the human body, adult female schistosomes release eggs, some of which are passed out in the urine or feces (starting the cycle anew), while others are trapped inside body tissue. The immune reactions to the tissue-imbedded eggs are the cause of disease. In one specific manifestation of schistosomiasis, there is progressive enlargement of the liver and spleen, among other damage. Although treatment is effective and relatively uncomplicated, it does not confer immunity to the disease, meaning that individuals living in endemic areas run a high risk of re-infection. Without treatment, schistosomiasis may lead to chronic urinary tract infection, cirrhosis of the liver, or even death. For more information on morphology, life cycle, or human epidemiology, check here and here and here.
Schistosomiasis is a disease that is transmitted via one of the most common and familiar vectors, especially among Chinese farmers and rural residents; water. The disease can be prevented by interrupting the life cycle of S. japonicum at one of several points – each point posing distinctive problems and requiring a unique approach: While anti-schistosome drugs prove great efficacy, they are expensive and do not prevent re-infection. Eliminating the vector snails is highly time- and labor-intensive and often damaging to the environment through interference with streams, rivers, and lakes, which may harm marine ecosystems and produce other unknown consequences. Lastly, water sanitation/human-waste education is both time- and money-intensive, but could help prevent urine and feces containing live eggs from contaminating the water."
Lesson learned: stay away from snails.
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