MIXED-GENOTYPE INFECTIONS OF THE RODENT MALARIA PLASMODIUM-CHABAUDI ARE MORE INFECTIOUS TO MOSQUITOS THAN SINGLE-GENOTYPE INFECTIONS

Interactions between parasite genotypes sharing a host are poorly unde rstood, but have important consequences for the epidemiology and evolu tion of the parasite. In mixed-genotype malaria infections, patterns o f asexual replication and transmission favoured by natural selection m ay be different from those in single-genotype infections. The infectiv ity to mosquitoes of mixed-genotype and single-genotype infections wer e compared using 2 clones of Plasmodium chabaudi inoculated into mice either together or alone. Mice given mixed-clone infections received t he sum of the inocula given to the single-clone controls. Mosquitoes w ere fed on the mice and the numbers of oocysts which developed were co unted to assess transmission intensity. For 3 combinations of starting inocula and feed days, mixed-clone infections produced more oocysts p er mosquito than the sum of the 2 single-clone infections. This effect was correlated with an increase in gametocyte density, but was less c learly related to asexual infection parameters. The results show that interactions between clones in mixed-clone infections can profoundly a ffect transmission.