Anaemia is a common health problem affecting women and children in the developing world. This condition is characterized by a reduction in erythrocyte density, primarily resulting from malnutrition and/or infectious diseases such as malaria. As red blood cells are the most important source of protein for haematophagous mosquitoes, any reduction could impede the ability of mosquito vectors to transmit malaria by influencing their fitness and/or that of the parasites they transmit. The aim of this study was to determine the impact of differences in the density of red blood cells in human blood on human malaria transmission (P. falciparum) by influencing: (i) mosquito vector (An. gambiae s.s.) fitness, (ii) the infectiousness of parasites to mosquitoes, (iii) parasite sporogonic success in mosquitoes, and/or (iv) the virulence of malaria parasites to mosquito vectors. The hypotheses tested are based on the premise that mosquito vector survival, fecundity and malaria parasite sporogony may be influenced by the nutritional value of infectious blood meals. Mosquitoes (An. gambiae) were offered blood meals at different Packed Cell Volume (PCV) of human blood consistent with those arising from severe anaemia (low PCV= 15%) and normal PCV (50%), and containing malaria parasite (P. falciparum) gametocytes infectious to mosquitoes. Mosquito fitness, the success of parasite development within them, and/or the virulence mosquitoes experience from infection were evaluated. The amount of protein that malaria vectors acquired from blood-feeding, and their resultant long term survival, was found to be positively associated with the PCV of human blood. Mosquitoes feeding on blood with low PCV had the same oviposition rates as those feeding on blood of normal PCV, but also showed an increase in fecundity of around 15%. Moreover, it was found that An. gambiae s.s. mosquitoes were substantially more likely to become infected after feeding on gametocyte-infected blood of low PCV rather than normal PCV. However, there was no evidence that blood PCV influenced either the oocyst intensity in infected mosquitoes, or the total number of transmission stage sporozoites they developed by 10 days after the infectious blood meal. Finally, there was no evidence that either consumption of P. falciparum infected blood or the subsequent development of oocysts reduced any measure of mosquito fitness (oviposition, fecundity, survival), in either mosquitoes infected from blood of low or normal PCV. The impact of blood PCV on the energetic reserves of both infected and uninfected mosquitoes was found to be relatively minor. These results demonstrate that variation in human erythrocyte of a magnitude likely to arise in malaria-endemic settings may have a significant impact of the outcome of vector–parasite interactions. Conditions such as severe anaemia, which reduce red blood density, could enhance malaria parasite transmission by increasing parasite infectivity to mosquitoes, while having no deleterious effects on mosquito survival.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:573826 |
| Date | January 2012 |
| Creators | Emami, Seyedeh Noushin |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/3724/ |
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