Posted: 22 August 2000

Organism that acts as an essential intermediate host or definite host for a human pathogen and that plays an active role in its transmission; for example, Anpheles species are vectors of malaria. This definition excludes mechanical carriers or infective materials (such as houseflies and cockroaches), strictly passive intermediate hosts (such as the snail hosts of schistosomiasis) and reservoir species (such as foxes in the case of rabies).