Under what circumstances does the cause of crab occur in life?

Crab is a kind of louse that lays eggs at the root of pubic hair. Adult lice are about the size of sesame seeds. When it sucks blood by piercing human skin with its beak, it not only bites human skin, but also injects its toxic saliva into human body, excreting feces while sucking blood, thus causing pruritus and inflammatory reaction of pudendal skin. The etiology of crabs mostly occurs in people with poor sanitation and crowded living environment. Crabs are usually transmitted through sexual contact, and couples often suffer from crabs. So crabs are also sexually transmitted diseases. In addition, the cause of crabs can also be indirectly transmitted through underwear, mattresses or toilets used by patients. In recent years, it has also been found that some people wear shorts to ride horses and get infected with crabs. But generally speaking, the host of crabs is people, not animals. Because crabs can live for a day or two without human body, they are highly contagious. People will be infected with crabs because they stay in hotels, use public baths, swim in swimming pools and use public toilets on business.