The human infectious reservoir of Falciparum malaria

• Main Author: Goncalves, B.
• Other Authors: Drakeley, C. ; Bousema, T.
• Published: London School of Hygiene and Tropical Medicine (University of London) 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.740128

Malaria control strategies are often targeted at individuals who suffer most morbidity, not at those driving transmission. This is in part due to our limited understanding, described in Chapter 1, of the human infectious reservoir of falciparum malaria – i.e. individuals responsible for human-to-mosquito transmission of Plasmodium falciparum parasites in endemic areas. This work, whose objectives are listed in Chapter 2, assessed the prevalence of infectiousness in naturally exposed human populations during dry and wet seasons. Exposure to Anopheles mosquitoes, a measure of transmission opportunities, was also quantified; and to determine the value of infectiousness-reducing interventions, the use of primaquine to block transmission from infectious individuals was investigated. Experimental infections of mosquitoes were performed to determine malaria infectivity of randomly selected individuals in two villages in Burkina Faso. Molecular assays were used to quantify parasite, including gametocyte, densities. Less than 10% of the population was infectious to mosquitoes. These results are presented in a manuscript that included data from other study sites (Chapter 3). To assess exposure to malaria vectors, bloodfed mosquitoes were collected indoors in one of the study villages in Burkina Faso. A multiplex PCR assay targeting nine human microsatellites and a gender-specific marker was used to identify the human sources of mosquito blood meals. Although there was substantial variation in the number of mosquito bites each individual received (Chapter 4), on average adults received more mosquito bites than children. This suggests that, despite their lower infectiousness, adults are major contributors to malaria transmission in endemic areas. An efficacy trial of single low dose primaquine was performed in Burkina Faso and pre- and post-treatment infectiousness were quantified by mosquito feeding experiments to assess primaquine’s infectiousness-reducing activity (Chapter 5). Individuals receiving primaquine cleared gametocytes faster than individuals who received artemether-lumefantrine alone. Feeding assays, however, suggest that artemether-lumefantrine blocks most parasite transmission after treatment administration. In Chapter 6, these findings, and how they can inform future control strategies, are discussed.