MIXED-SPECIES PLASMODIUM INFECTIONS OF ANOPHELES (DIPTERA, CULICIDAE)

Mixed-pathogen infections of vectors rarely are considered in the epid emiological literature, although they may occur in nature. A review of published reports shows that many Anopheles species are capable of ca rrying sporozoites of > 1 Plasmodium species, of doing so simultaneous ly in field conditions, and of acquiring and transmitting these in exp erimental situations. Mixed-species infections in mosquito populations occur at frequencies greater than or equal to the product of the cons tituent species prevalences, whereas human populations have apparent m ixed-species infections at frequencies less than or equal to their cor responding expected values. We present a model for the accumulation of parasite infections over the lifespan of a mosquito that explains thi s surplus of mixed-species infections. However, the expected frequenci es of mixed infections on the basis of our model are greater than thos e found in nature, indicating that the sampling by mosquitoes of Plasm odium species from human malaria infections may not be random.