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Title: The ecology and evolutionary implications of malaria parasite virulence in mosquito vectors
Author: Ferguson, Heather M.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2002
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A laboratory study with the rodent malaria parasite P. chabaudi and A. stephensi vector indicated that mosquito morality varied with parasite genotype, infection diversity and nutrient availability. In standard conditions, mixed clone infections were the most lethal, but when glucose water was limited, mortality was highest in mosquitoes infected with CR. A second experiment showed that under standard conditions, mixed infections also had the greatest impact on vector fecundity. The virulence of mixed infections could not be explained by parasite load, nor their rate of resource uptake by parasites within the mosquitoes. During the parasite development period, infected mosquitoes had the same amount of three key physiological resources (lipids, glycogen, proteins), as those that were uninfected. Furthermore, mosquitoes infected with the most virulent parasite genotypes had an increased abundance of glucose relative to the controls. This is consistent with Plasmodium manipulating mosquito sugar-feeding behaviour in order to increase its own transmission. Several laboratory studies of malaria parasites and some field observations suggest that Plasmodium virulence in vertebrates is positively correlated with transmission to mosquitoes. A final experiment was undertaken to test whether the transmission advantage of infections that are virulent to vertebrates could be offset by an increased probability of causing death to their vectors. Mice were infected with one of seven distinct genetic clones of P. chabaudi that are known to vary in virulence. Infection virulence in mice (weight loss and anaemia) was positively correlated with mosquito infection rate but not with mosquito survival. Vector survival was influenced only by parasite clone and oocyst burden (negative association). These results suggest that vector fitness should not place an upper limit on malaria virulence. Overall, this research demonstrates that Plasmodium can be virulent to its vector, and that the magnitude of virulence is dependent on parasite genotype, infection diversity and environmental conditions. Although P. chabaudi virulence in vectors was not correlated with virulence in vertebrates, parasite genetic differences do impact vector fitness. Thus differential vector mortality could play an important role in determining the genetic composition of Plasmodium populations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available