Oncomelania hupensis, the host of schistosomiasis, generally lives in wild watery areas such as grass beaches, ponds and ditches. If people come into contact with water in unknown waters in the wild, schistosome larvae and cercariae will easily enter the human body, causing infection. At the same time, infected people will carry cercariae in their stools. If they are excreted in the wild at will, the cercariae will enter the body of Oncomelania hupensis through water, which will lead to a vicious circle of large-scale spread.
The scientific name of Schistosoma japonicum is Schistosoma japonicum, Schistosoma mansoni, Schistosoma ehrmani and Schistosoma mae.
There is only Schistosoma japonicum in China, which is bisexual. The male worm is short and thick, with an average body length of 16mm, which is milky white. The female worm is slender, with a slender front end and an average body length of 20mm. The rear part of the worm is dark brown because the intestine is full of digested hemoglobin. Female worms are often in the female-holding groove of male worms, and they are in a state of embracing. They embrace and parasitize in the hepatic portal vein and mesenteric vein system of mammals such as human beings and storage hosts such as cattle, sheep, pigs, rats and rabbits. Some or all of the surface of bisexual adults have small nodules or spines. The oral and abdominal suckers are located at the front end of the worm. The worm is adsorbed on the inner wall of the vein by the suckers. They crawl to the venous end of intestinal submucosa through the suction and separation of the oral and abdominal suckers. Round, light yellow, eggs contain metacercariae. The cellulolytic substances secreted by metacercariae penetrate through the egg shell, destroying the blood vessel wall, leading to inflammation and necrosis of surrounding tissues, and stimulating the increase of intestinal peristalsis, causing changes in intra-abdominal pressure and intra-vascular pressure. Some eggs burst into the intestinal cavity with necrotic tissues, mixed with feces, and discharged from the host. After contacting with water, metacercariae hatched at 25℃-30℃. The metacercariae floated in the water and were nailed by intermediate hosts. Finally, many cercariae with bifurcated tails are formed one after another, and snails often float on the water surface in stages. Cercariae is the infection stage of Schistosoma japonicum. When people and animals come into contact with infected water, cercariae attach to the skin with oral and abdominal suckers, and puncture glands secrete proteolytic substances to dissolve the skin tissue, and then quickly break off their tails and invade the skin and turn into juvenile worms. The juvenile worms enter the vein through microvessels or lymphatic vessels, and enter the systemic circulation with blood flow through the right heart, lung and left heart. Some of them. It migrates to the branch of portal vein system in the liver, and then retrogrades into mesenteric vein to settle down. After cercaria invades the host for 24 days, females begin to lay eggs. One female lays eggs every day 1000. After 5 weeks, eggs can appear in the feces of the host. Schistosoma japonicum can survive in the human body for as long as 30 or 40 years.