The human parasite fauna: towards an analysis and interpretation.

A breakdown of the human parasite fauna shows approximately 270 species, with almost equal numbers of nematodes, flukes and protozoa and smaller numbers of arthropods and tapeworms. More than 70% are 'adventitious' species for which man is an incidental host. Only 16% are 'core' species, dependent on man for their survival. For 26% man is the usual source of human infection, and for 51% the source is other mammals. A sequence is illustrated showing how parasites may arrive by the host-transfer or co-evolutionary pathways. Adventitious parasites have a narrower geographical range than core species. The richest representation of the major species is in the Aethiopian Zoogeographical Region and the poorest is in the Australasian. Some 14 pairs of closely related forms occur in the main fauna. Some implications of this analysis with respect to man's early history are discussed speculatively.