Abstract
BackgroundArthropod vectors of disease may encounter more than one infected host during the course of their lifetime. The consequences of super-infection to parasite development are rarely investigated, but may have substantial epidemiological and evolutionary consequences.MethodsUsing a rodent malaria model system, behavioural avoidance of super-infection was tested by examining whether already-infected Anopheles stephensi mosquitoes were less responsive to new vertebrate hosts if they were infected. Additionally, a second dose of parasites was given to malaria-infected mosquitoes on a biologically realistic time scale to test whether it impeded the development of a first infection.ResultsNo effect of a second infected blood meal on either the prevalence or parasite burden arising from a first was found. Furthermore, it was found that not only were infected mosquitoes more likely to take a second blood meal than their uninfected counterparts, they were disproportionately drawn to infected hosts.ConclusionsThe alterations in mosquito feeding propensity reported here would occur if parasites have been selected to make infected vertebrate hosts more attractive to mosquitoes, and infected mosquitoes are more likely to seek out new blood meals. Although such a strategy might increase the risk of super-infection, this study suggests the cost to parasite development is not high and as such would be unlikely to outweigh the potential benefits of increasing the contact rate between the parasite's two obligate hosts.
Highlights
Arthropod vectors of disease may encounter more than one infected host during the course of their lifetime
This study has demonstrated that the presence of malaria parasites in either of their two obligate hosts increases the probability of contact with the other
The parasites that depend upon their survival for transmission, have or induce a feeding strategy that increases the risk of multiple infection? Perhaps the most parsimonious explanation is that natural selection on malaria parasites has acted to make infected vertebrate hosts more attractive to mosquitoes, and infected mosquitoes more willing to blood feed
Summary
Arthropod vectors of disease may encounter more than one infected host during the course of their lifetime. Many arthropod disease vectors have multiple opportunities to become infected with the same pathogen species during their lifetime (super-infection). The aim of this study was to investigate the potential epidemiological consequences of super-infection of mosquitoes by malaria parasites. Malaria parasites are a relevant model for studies of vector super-infection because their biology dictates a substantial risk of super-infection in the wild. A substantial proportion of some Anopheles spp. return to the same house on different feeding cycles [e. G. [11]], so that mosquitoes that encounter infected blood are likely to do so again, especially if infected hosts are more attractive to mosquitoes as indicated in some animal models [12,13] A substantial proportion of some Anopheles spp. return to the same house on different feeding cycles [e. g. [11]], so that mosquitoes that encounter infected blood are likely to do so again, especially if infected hosts are more attractive to mosquitoes as indicated in some animal models [12,13]
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