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Ambient temperature and dietary supplementation interact to shape mosquito vector competence for malaria.

ABSTRACT: The extent to which environmental factors influence the ability of Anopheles mosquitoes to transmit malaria parasites remains poorly explored. Environmental variation, such as change in ambient temperature, will not necessarily influence the rates of host and parasite processes equivalently, potentially resulting in complex effects on infection outcomes. As proof of principle, we used Anopheles stephensi and the rodent malaria parasite, Plasmodium yoelii, to examine the effects of a range of constant temperatures on one aspect of host defense (detected as alterations in expression of nitric oxide synthase gene - NOS) to parasite infection. We experimentally boosted mosquito midgut immunity to infection through dietary supplementation with the essential amino acid l-Arginine (l-Arg), which increases midgut nitric oxide (NO) levels by infection-induced NOS catalysis in A. stephensi. At intermediate temperatures, supplementation reduced oocyst prevalence, oocyst intensity, and sporozoite prevalence suggesting that the outcome of parasite infection was potentially dependent upon the rate of NOS-mediated midgut immunity. At low and high temperature extremes, however, infection was severely constrained irrespective of supplementation. The effects of l-Arg appeared to be mediated by NO-dependent negative feedback on NOS expression, as evidenced by depressed NOS expression in l-Arg treated groups at temperatures where supplementation decreased parasite infection. These results suggest the need to consider the direct (e.g. effects of mosquito body temperature on parasite physiology) and indirect effects (e.g. mediated through changes in mosquito physiology/immunity) of environmental factors on mosquito-malaria interactions in order to understand natural variation in vector competence.

SUBMITTER: Murdock CC

PROVIDER: S-EPMC4107084 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Ambient temperature and dietary supplementation interact to shape mosquito vector competence for malaria.

Murdock Courtney C CC Blanford Simon S Luckhart Shirley S Thomas Matthew B MB

Journal of insect physiology 20140606

The extent to which environmental factors influence the ability of Anopheles mosquitoes to transmit malaria parasites remains poorly explored. Environmental variation, such as change in ambient temperature, will not necessarily influence the rates of host and parasite processes equivalently, potentially resulting in complex effects on infection outcomes. As proof of principle, we used Anopheles stephensi and the rodent malaria parasite, Plasmodium yoelii, to examine the effects of a range of con ...[more]

PMID: 24911425

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Project description:BackgroundUntil recently, relatively little research has been done on how mosquitoes behave around the occupied bed net in the indoor environment. This has been partly remedied in the last few years through laboratory and field studies, most of these using video methods and mosquito flight tracking. Despite these recent advances, understanding of the mosquito-bed net environment system, and the principles that underlie mosquito behaviour within it, is limited. This project aimed to further understand this system by studying the effects of gently moving air (such as might be introduced through room design to make the indoor environment more comfortable and conducive to ITN use) and warmer vs. cooler ambient conditions on mosquito activity around ITNs and other bed nets.MethodsThe activity of colonized female Anopheles gambiae around an occupied untreated bed net set up in a mosquito-proof tent in a large laboratory space was recorded under different ambient conditions using a laser detection-video recording system. Conditions tested were 'cool' (23-25 °C) and 'warm' (27-30 °C) air temperatures and the presence or absence of a cross-flow produced by a small central processing unit (CPU) fan pointed at the side of the net so that it produced a 'low-' or 'high-' speed cross-draught (approx. 0.1 and 0.4 m/s, respectively). Near-net activity in recordings was measured using video image analysis.ResultsIn cool, still air conditions, more than 80% of near-net activity by An. gambiae occurred on the net roof. Introduction of the low-speed or high-speed cross-draught resulted in an almost total drop off in roof activity within 1 to 2 min and, in the case of the high-speed cross-draught, a complementary increase in activity on the net side. In warm, still conditions, near-net activity appeared to be lower overall than in cool, still air conditions and to be relatively less focussed on the roof. Introduction of the high-speed cross-draught in warm conditions resulted in a decrease in roof activity and increase in side activity though neither effect was statistically significant.ConclusionsResults are interpreted in terms of the flow of the stimulatory odour plume produced by the net occupant which, consistent with established principles of fluid dynamics, appears to rise quickly and remain more intact above the net occupant in cool, still air than in warm, still air. Cross-draught effects are ascribed to the changes they cause in the flow of the host odour plume as opposed to mosquito flight directly. The implications of these results for house designs that promote indoor air movement, on bed net design, and on other vector control measures are discussed. How mosquitoes approach a net is influenced both by indoor temperature and ventilation and their interaction. This system is in need of further study.

Dataset Information

Ambient temperature and dietary supplementation interact to shape mosquito vector competence for malaria.

Publications

Ambient temperature and dietary supplementation interact to shape mosquito vector competence for malaria.

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