How is schistosomiasis transmitted?

Schistosomiasis can actually be transmitted through various channels, so we should also pay attention to understanding the correct prevention methods in our lives. Contact with some water-borne diseases or feces entering the water may become a source of infection.

① Excrement entering water : The way in which excrement pollutes water sources varies depending on the production methods, living habits, and livestock management and breeding methods of local residents. Cleaning toilets near rivers, defecating anywhere, using fresh feces, and grazing cattle are particularly likely to pollute water sources.

② Schistosomiasis is likely to be prevalent only in areas where snails are present . In China, schistosomiasis is prevalent on both sides of the Yangtze River, as well as in the twelve provinces, autonomous regions and Shanghai to its south, and is most serious in the middle and lower reaches of the Yangtze River. After years of prevention and treatment, the prevalence of this disease has been basically brought under control. The infection rate of Oncomelania snails is closely related to the degree of water source pollution, and the sentinel snail method can be used to measure water source pollution. The snail distributed in China is called Hubei snail, which has seven subspecies. Oncomelania snails are amphibious molluscs that breed mostly in irrigation ditches or river shallows that are well-watered, rich in organic matter, overgrown with weeds, and moist and shaded. They usually live above and below the waterline, and in winter they hibernate several centimeters underground as the temperature drops. Oncomelania snails can live on the ground, but their range of movement is limited and their speed is slow. However, snails can attach to various floating objects on the water surface, such as lake grass, reeds, and boats, and spread to distant places, expanding the original breeding range or forming new breeding grounds.

③ Contact with infected water: In epidemic areas, residents are infected due to contact with infected water due to various life and production activities, such as fishing, cutting grass for fertilizer, swimming, washing clothes, washing feet, etc. They may also be infected by walking barefoot on the ground containing cercariae, and the cercariae invade through the skin. The number of cercariae invading is proportional to the degree of water source pollution, the exposed skin area, and the time and number of times of contact with infected water. In addition to the skin, cercariae can also invade the body through the oral mucosa when drinking raw water.

(4) Susceptible population : Generally susceptible. The infection rate of residents is proportional to the local snail infection rate. Most of the patients are fishermen and farmers, especially young and middle-aged people aged 15 to 30 who have a higher infection rate due to repeated contact with infected water. Males are more likely to be infected than females, and the infection is most common in summer and autumn. Children and people in non-epidemic areas may develop a certain resistance once they have suffered a large number of infections, but their tolerance to reinfection is not complete, so repeated infections often occur.