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Most outdoor malaria transmission by behaviourally-resistant Anopheles arabiensis is mediated by mosquitoes that have previously been inside houses.

Killeen GF, Govella NJ, Lwetoijera DW, Okumu FO - Malar. J. (2016)

Bottom Line: Life histories of a well-characterized An. arabiensis population were simulated with a simple but process-explicit deterministic model and relevance to other vectors examined through sensitivity analysis.The estimated proportion of vector blood meals ultimately obtained from humans indoors is dramatically attenuated by availability of alternative hosts, or partial ability to attack humans outdoors.While the exact numerical results predicted by such a simple deterministic model should be considered only approximate and illustrative, the derived conclusions are remarkably insensitive to substantive deviations from the input parameter values measured for this particular An. arabiensis population.

View Article: PubMed Central - PubMed

Affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifakara, Kilombero, Morogoro, United Republic of Tanzania. gkilleen@ihi.or.tz.

ABSTRACT

Background: Anopheles arabiensis is stereotypical of diverse vectors that mediate residual malaria transmission globally, because it can feed outdoors upon humans or cattle, or enter but then rapidly exit houses without fatal exposure to insecticidal nets or sprays.

Methods: Life histories of a well-characterized An. arabiensis population were simulated with a simple but process-explicit deterministic model and relevance to other vectors examined through sensitivity analysis.

Results: Where most humans use bed nets, two thirds of An. arabiensis blood feeds and half of malaria transmission events were estimated to occur outdoors. However, it was also estimated that most successful feeds and almost all (>98 %) transmission events are preceded by unsuccessful attempts to attack humans indoors. The estimated proportion of vector blood meals ultimately obtained from humans indoors is dramatically attenuated by availability of alternative hosts, or partial ability to attack humans outdoors. However, the estimated proportion of mosquitoes old enough to transmit malaria, and which have previously entered a house at least once, is far less sensitive to both variables. For vectors with similarly modest preference for cattle over humans and similar ability to evade fatal indoor insecticide exposure once indoors, >80 % of predicted feeding events by mosquitoes old enough to transmit malaria are preceded by at least one house entry event, so long as ≥40 % of attempts to attack humans occur indoors and humans outnumber cattle ≥4-fold.

Conclusions: While the exact numerical results predicted by such a simple deterministic model should be considered only approximate and illustrative, the derived conclusions are remarkably insensitive to substantive deviations from the input parameter values measured for this particular An. arabiensis population. This life-history analysis, therefore, identifies a clear, broadly-important opportunity for more effective suppression of residual malaria transmission by An. arabiensis in Africa and other important vectors of residual transmission across the tropics. Improved control of predominantly outdoor residual transmission by An. arabiensis, and other modestly zoophagic vectors like Anopheles darlingi, which frequently enter but then rapidly exit from houses, may be readily achieved by improving existing technology for killing mosquitoes indoors.

No MeSH data available.


Related in: MedlinePlus

The influence of varying levels of cattle availability and baseline distribution of human biting exposure indoors and outdoors upon the predicted proportions of all human blood meals that are obtained indoors (a), all blood meals obtained from humans (b), and all blood meals obtained from humans indoors (c). The predictions presented are based on simulations assuming a setting with high bed net usage (Ω = N) and vector mosquitoes have the same ability as Anopheles arabiensis to avoid fatal contact with LLINs or IRS after entering houses [16–19], so that the insecticide treatment status of the net is irrelevant
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Fig3: The influence of varying levels of cattle availability and baseline distribution of human biting exposure indoors and outdoors upon the predicted proportions of all human blood meals that are obtained indoors (a), all blood meals obtained from humans (b), and all blood meals obtained from humans indoors (c). The predictions presented are based on simulations assuming a setting with high bed net usage (Ω = N) and vector mosquitoes have the same ability as Anopheles arabiensis to avoid fatal contact with LLINs or IRS after entering houses [16–19], so that the insecticide treatment status of the net is irrelevant

Mentions: Proportional distribution of human exposure to residual transmission across indoor and outdoor locations in the presence of LLINs is predicted to vary with the corresponding distribution in their absence, regardless of how many alternative hosts are present (Fig. 3a). However, the proportion of blood meals obtained from humans and, therefore, the proportion of transmission events that can be directly interrupted by preventing human exposure, is almost as sensitive to increasing availability of alternative blood sources, such as cattle, as it is to the propensity of the vector to feed outdoors rather than indoors (Fig. 3b). Considering both of these factors, less than half of all blood meals are obtained from humans indoors at high bed net coverage (Qh,i,N < 0.5) unless the cattle populations are sparse (Nc/Nh < 0.1) and the vector almost exclusively attempts to attack humans indoors in the absence of bed nets (πh,i,0 ≥ 90 %) (Fig. 3c).Fig. 3


Most outdoor malaria transmission by behaviourally-resistant Anopheles arabiensis is mediated by mosquitoes that have previously been inside houses.

Killeen GF, Govella NJ, Lwetoijera DW, Okumu FO - Malar. J. (2016)

The influence of varying levels of cattle availability and baseline distribution of human biting exposure indoors and outdoors upon the predicted proportions of all human blood meals that are obtained indoors (a), all blood meals obtained from humans (b), and all blood meals obtained from humans indoors (c). The predictions presented are based on simulations assuming a setting with high bed net usage (Ω = N) and vector mosquitoes have the same ability as Anopheles arabiensis to avoid fatal contact with LLINs or IRS after entering houses [16–19], so that the insecticide treatment status of the net is irrelevant
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4837512&req=5

Fig3: The influence of varying levels of cattle availability and baseline distribution of human biting exposure indoors and outdoors upon the predicted proportions of all human blood meals that are obtained indoors (a), all blood meals obtained from humans (b), and all blood meals obtained from humans indoors (c). The predictions presented are based on simulations assuming a setting with high bed net usage (Ω = N) and vector mosquitoes have the same ability as Anopheles arabiensis to avoid fatal contact with LLINs or IRS after entering houses [16–19], so that the insecticide treatment status of the net is irrelevant
Mentions: Proportional distribution of human exposure to residual transmission across indoor and outdoor locations in the presence of LLINs is predicted to vary with the corresponding distribution in their absence, regardless of how many alternative hosts are present (Fig. 3a). However, the proportion of blood meals obtained from humans and, therefore, the proportion of transmission events that can be directly interrupted by preventing human exposure, is almost as sensitive to increasing availability of alternative blood sources, such as cattle, as it is to the propensity of the vector to feed outdoors rather than indoors (Fig. 3b). Considering both of these factors, less than half of all blood meals are obtained from humans indoors at high bed net coverage (Qh,i,N < 0.5) unless the cattle populations are sparse (Nc/Nh < 0.1) and the vector almost exclusively attempts to attack humans indoors in the absence of bed nets (πh,i,0 ≥ 90 %) (Fig. 3c).Fig. 3

Bottom Line: Life histories of a well-characterized An. arabiensis population were simulated with a simple but process-explicit deterministic model and relevance to other vectors examined through sensitivity analysis.The estimated proportion of vector blood meals ultimately obtained from humans indoors is dramatically attenuated by availability of alternative hosts, or partial ability to attack humans outdoors.While the exact numerical results predicted by such a simple deterministic model should be considered only approximate and illustrative, the derived conclusions are remarkably insensitive to substantive deviations from the input parameter values measured for this particular An. arabiensis population.

View Article: PubMed Central - PubMed

Affiliation: Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, Ifakara, Kilombero, Morogoro, United Republic of Tanzania. gkilleen@ihi.or.tz.

ABSTRACT

Background: Anopheles arabiensis is stereotypical of diverse vectors that mediate residual malaria transmission globally, because it can feed outdoors upon humans or cattle, or enter but then rapidly exit houses without fatal exposure to insecticidal nets or sprays.

Methods: Life histories of a well-characterized An. arabiensis population were simulated with a simple but process-explicit deterministic model and relevance to other vectors examined through sensitivity analysis.

Results: Where most humans use bed nets, two thirds of An. arabiensis blood feeds and half of malaria transmission events were estimated to occur outdoors. However, it was also estimated that most successful feeds and almost all (>98 %) transmission events are preceded by unsuccessful attempts to attack humans indoors. The estimated proportion of vector blood meals ultimately obtained from humans indoors is dramatically attenuated by availability of alternative hosts, or partial ability to attack humans outdoors. However, the estimated proportion of mosquitoes old enough to transmit malaria, and which have previously entered a house at least once, is far less sensitive to both variables. For vectors with similarly modest preference for cattle over humans and similar ability to evade fatal indoor insecticide exposure once indoors, >80 % of predicted feeding events by mosquitoes old enough to transmit malaria are preceded by at least one house entry event, so long as ≥40 % of attempts to attack humans occur indoors and humans outnumber cattle ≥4-fold.

Conclusions: While the exact numerical results predicted by such a simple deterministic model should be considered only approximate and illustrative, the derived conclusions are remarkably insensitive to substantive deviations from the input parameter values measured for this particular An. arabiensis population. This life-history analysis, therefore, identifies a clear, broadly-important opportunity for more effective suppression of residual malaria transmission by An. arabiensis in Africa and other important vectors of residual transmission across the tropics. Improved control of predominantly outdoor residual transmission by An. arabiensis, and other modestly zoophagic vectors like Anopheles darlingi, which frequently enter but then rapidly exit from houses, may be readily achieved by improving existing technology for killing mosquitoes indoors.

No MeSH data available.


Related in: MedlinePlus