Where do human schistosomes come from? An evolutionary approach.

Schistosomiases affect between 200 and 400 million people, mainly in the tropical and poorly developed zones of the globe. They are often considered as the 'second' disease of mankind, just after malaria. One important question regarding human parasites is: are they the descendants of parasites that used to infect our primate ancestors and have had an evolution parallel to that of the human lineage, or are they the result of lateral transfers of parasites that evolved in different hosts? Recently, knowledge of the biology of schistosomes has dramatically increased, and answers to this and other questions are beginning to emerge.