Oncomelania hupensis Gredler (1881) belongs to the class Gastropoda, the family Pomatiopsidae, and the genus Oncomelania Gredler. It is the only intermediate host of Schistosoma japonicum. Inhabits fresh water but is amphibious. The body is small, with a shell height of about 10 mm and a width of 3-4 mm. The shape is pointed conical shape. The shell surface is smooth or has thick or thin longitudinal ribs. The shell mouth is oval, with a raised labial ridge on the dorsal side of the outer lip or without it. The meat is edible. Oncomelania are distributed in eastern Asia and Southeast Asia. There is only one type of Hubei snail in mainland my country, and there are 5 subspecies - Hubei snail named subspecies (O.h.h. Gredler). It is widely distributed in the middle and lower reaches of the Yangtze River Basin and Guangdong and Zhejiang provinces; it mostly inhabits low-lying and plain areas. Oncomelania subspecies (O.h.fausti Bartsch) is distributed in low-altitude hilly areas in the middle and lower reaches of the Yangtze River, but is also distributed along the coasts of Dongtai and Dafeng in Jiangsu Province; Oncomelania subspecies (O.h.Tangi Bartsch) is distributed in low-mountain areas along the southeastern coast of Fujian; Oncomelania snails (O.h. quangxiensis Liu et al.) are distributed in northern Guangxi, in thin sand with poor water retention and ravine rocks at an altitude of 200-400 meters. Oncomelania snail Yunnan and Sichuan subspecies (O.h.robertson Bartsch) is distributed in Sichuan and Yunnan provinces of my country at an altitude of 400-1000m, and is also distributed at 2400m. It inhabits irrigation ditches or hillside grasslands. Their distribution is consistent with schistosomiasis endemic areas. Therefore, schistosomiasis is basically prevalent in areas where snails breed. Therefore, it is impossible for patients infected from other places to be infected in snail-free areas. The breeding environment of snails can be divided into three categories: Lake swamp type: mainly distributed along the Yangtze River and around lakes in Hubei, Hunan, Anhui, Jiangxi, Jiangsu and other provinces. There are large shoals with winter land and summer water, as well as small areas in the lower reaches of the Pearl River. Oncomelania snails have a large distribution area and are distributed in sheets. Water network type: mainly distributed in the Yangtze River Delta. The water system consists of rivers and irrigation ditches, crisscrossing each other and as dense as a spider web. Oncomelania are distributed along river banks and mostly inhabit lake embankments and water within 1 meter above and below the waterline. Hill type: Mainly distributed in mountainous areas in Sichuan, Yunnan, Guangxi, Fujian, Taiwan and the middle and lower reaches of the Yangtze River in my country. Oncomelania are distributed according to water systems, with a wide distribution and complex environment. Oncomelania snails are 5-6 mm long and only 1/3 of the size of pipe snails. Schistosoma eggs are discharged into the water along with the feces of patients or sick animals. The miracidia in the eggs mature and hatch, break out of the shell, and then penetrate into the body of the snail. After passing through the stages of mother larvae and daughter larvae, a large number of cercariae mature and swim. Move in the water. When humans and animals come into contact with infected water, the cercariae quickly penetrate into the skin (or mucous membrane) through the action of histolytic enzymes secreted by their head glands and the mechanical movement of their muscle contractions, and shed their tails to become larvae. The worms enter the blood circulation through small veins or lymphatic vessels, and then pass through the right heart and reach the lungs. Later, it enters the general circulation from the capillaries of the lungs through the pulmonary veins and spreads throughout the body. Only the child worms that enter the mesenteric vein can continue to develop into adult worms, and the rest mostly die on the way. Usually, cercariae develop into adults about 3 weeks after infection, and male and female adults can lay eggs after mating. The eggs follow the portal blood flow to the liver, or flow back into the intestinal wall and settle in the tissue. It takes about 11 days to gradually develop into mature eggs containing miracidia. The eggs in the intestinal wall can damage the intestinal mucosa and enter the intestinal cavity, and are excreted with the feces, and the life cycle will repeat again. The lifespan of eggs in tissues is about 21 days. The lifespan of male and female adult worms in the human body is generally 3 to 4 years. When a person comes into contact with water containing schistosomiasis cercariae, the cercariae are quickly adsorbed on the person's skin. After about 10 to 20 seconds, the cercariae penetrate the skin and enter the human body, and the person is infected with schistosomiasis.

After the schistosomiasis eggs fall into the water with human feces, under suitable temperature and water quality conditions, after a certain period of time, the eggs hatch into miracidia. The miracidia have many fine hairs around their bodies and can move. When they encounter a type of snail in the water called "snails" "After the snail is removed, the miracidia penetrate through the soft body part that extends outward, and develop and reproduce into a large number of cercariae inside the snail. Mature cercariae do not remain in the body of the snail for a long time, but they can escape from the snail only when there is water. When the snail crawls in the water or on plant stems and leaves with water droplets, the cercariae leave the snail and enter the water. At that time, if people go into the water (such as fishing in lake areas, harvesting lake weeds, fighting floods, disaster relief, etc.) or walking barefoot on the field ridges in the countryside, they may be infected with schistosomiasis. Schistosoma cercariae mainly invade the human body through the skin. However, according to surveys, drinking raw water containing cercariae can also lead to infection with schistosomiasis, which may indicate that cercariae may enter the human body through the oral mucosa. Once we understand the interrelationship between snails, cercariae, water bodies and people, it is not difficult to understand how schistosomiasis is transmitted and why people will not be infected with schistosomiasis in contact with people. /view/91568.htm Come here to have a look