There is a worldwide distribution of<unk> , with an estimated 1 billion human infections. However, it is chiefly tropical, especially in Asia and, to a lesser degree, in Africa and South America. Within the United States, infection is rare overall but may be common in the rural Southeast, where 2.2 million people are thought to be infected. Poor hygiene is associated with<unk> sis as well as the consumption of shaded moist soil, or food that may have been fecally contaminated. Children are especially vulnerable to infection due to their high exposure risk. Eggs are infective about 2–3 weeks after they are deposited in the soil under proper conditions of warmth and moisture, hence its tropical distribution. A closely related species,<unk>  suis, which typically infects pigs, is capable of infecting humans. This shows that the two species have very close evolutionary histories. However, morphology and developmental stages remain different, making them two separate species.
Trichuris trichiura
Taenia saginata
Taenia asiatica
Ascaris lumbricoides
Trichinella britovi
Taenia solium
Schistosoma mansoni
Onchocerca volvulus