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Title: Epidemiological and evolutionary consequences of mixed-genotype infections of malaria parasites
Author: Taylor, Louise H.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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In this thesis, three aspects of parasite life history were investigated: the trade-off between asexual growth and reproduction, the virulence of infections and the sex ratio of transmission stages. All three, and the frequency of mixed infections in a population itself, are fundamentally linked to the transmission and pathology of malaria, the reduction of which is the aim of all current control programmes. An experimental system of the rodent malaria Plasmodium chabaudi in mice allows controlled mixed-infections of distinct clones to be initiated and was used to test theoretical predictions. Genetic and immunological techniques were used to monitor the parasite population throughout the life cycle. One of the main findings from the experimental system was also tested in field populations of the human malaria P. falciparum. Compared to single-clone infections, mixed-clone infections of P. chabaudi showed increased transmission rates, higher virulence and in some experiments less female-biased gametocyte sex ratios. These results are in line with theoretical expectations, but in several cases the underlying mechanism responsible was not entirely consistent with that assumed by theory. The relative transmission rates of two clones in a mixed infection were not predicted by their relative starting inocula or their relative asexual parasite abundances four days before transmission was measured. The minority clone in a mixed-clone infection inoculum transmitted at least as well, and often far better, than it did as a single-clone control. Asexual parasite population sizes were often poor predictors of transmission and virulence. However, the data show common patterns across experiments which help to elucidate patterns of interactions between parasite genotypes and the host. The results are consistent with a strong strain-specific component to host immunity, with a suggestion that immune responses to mixed-genotype infections may be more costly for the host than those directed against single-genotype infections. The relevance of all experimental results to the control of human malaria parasites is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available