DETERMINANTS OF TRANSMISSION SUCCESS OF INDIVIDUAL CLONES FROM MIXED-CLONE INFECTIONS OF THE RODENT MALARIA PARASITE, PLASMODIUM-CHABAUDI

Interactions between malaria parasite clones within mixed infections c an have a profound effect on transmission and therefore the epidemiolo gy of the disease. However, factors which determine the relative trans mission success of individual clones from mixed infections are unknown , We have used two clones of the rodent malaria Plasmodium chabaudi to investigate changes in the clonal composition of asexual parasites ov er the course of mixed-clone infections in mice and how these relate t o the clonal composition of transmission (oocyst) populations in mosqu itoes. Clonal composition was determined using monoclonal antibody ana lyses for the asexual blood stage populations and PCR analysis of sing le oocysts for the transmission populations in mosquitoes. The relativ e frequency of the two clones changed dramatically during the course o f the infection in mice, depending on their ratio in the inoculum, The clonal composition of parasites within mosquitoes most closely resemb led that in the asexual infection at the time of transmission rather t han that at any point earlier in the infection. These results provide no evidence that clones increase rates of gametocytogenesis in respons e to competitive suppression. Most likely, transmission success follow s from asexual success in the later parts of the infection. The clone which dominated the earlier part of the infection, when most parasites are produced, did not necessarily dominate the transmission from the infection. The two clones differed in competitive ability and the data suggest that interactions with the host immune system may be a major factor in determining transmission success from mixed-clone infections . (C) 1998 Australian Society for Parasitology. Published by Elsevier Science Ltd.