HI, why Trichuris vulpis, a soil-transmitted helminth, is a most common parasite in european wolves? Trichuris vulpis, a soil-transmitted helminth live in the intestine and their eggs are passed in the feces of infected persons. When an infected animal defecates eggs are deposited on soil. Larvae inside the eggs become infective only after they mature in soil. So in what manner does Trichuris vulpis infect wolves in the wild?