Research Article

Mixed-genotype infections of the rodent malaria Plasmodium chabaudi are more infectious to mosquitoes than single-genotype infections

L. H. TAYLOR a1 , D. WALLIKER a1 and A. F. READ a1
a1 University of Edinburgh, Institute of Cell, Animal and Population Biology, King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK


Interactions between parasite genotypes sharing a host are poorly understood, but have important consequences for the epidemiology and evolution of the parasite. In mixed-genotype malaria infections, patterns of asexual replication and transmission favoured by natural selection may be different from those in single-genotype infections. The infectivity to mosquitoes of mixed-genotype and single-genotype infections were compared using 2 clones of Plasmodium chabaudi inoculated into mice either together or alone. Mice given mixed-clone infections received the sum of the inocula given to the single-clone controls. Mosquitoes were fed on the mice and the numbers of oocysts which developed were counted to assess transmission intensity. For 3 combinations of starting inocula and feed days, mixed-clone infections produced more oocysts per mosquito than the sum of the 2 single-clone infections. This effect was correlated with an increase in gametocyte density, but was less clearly related to asexual infection parameters. The results show that interactions between clones in mixed-clone infections can profoundly affect transmission.

(Received December 28 1996)
(Revised January 16 1997)
(Accepted January 16 1997)

Key Words: transmission; competition; malaria; Plasmodium chabaudi; gametocytes; oocysts.


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