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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

A schematic summary of how specific behaviours enable mosquito populations generally, or Anopheles arabiensis in southern Tanzania specifically [16–19], to survive and mediate residual malaria transmission, despite high usage rates of long-lasting insecticidal nets
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Fig1: A schematic summary of how specific behaviours enable mosquito populations generally, or Anopheles arabiensis in southern Tanzania specifically [16–19], to survive and mediate residual malaria transmission, despite high usage rates of long-lasting insecticidal nets

Mentions: The World Health Organization (WHO) has recently acknowledged that residual malaria transmission can persist despite comprehensive, population-wide coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) with active ingredients to which local vector populations are fully susceptible [1, 2]. Residual transmission occurs because vector mosquitoes exhibit one or more behaviours that allow them to evade fatal contact with these front line interventions (Fig. 1) [1–4]. Feeding upon humans when they are unprotected outdoors is the most obvious of these behaviours [3–8], but vectors may also survive and mediate residual malaria transmission despite high coverage with LLINs and/or IRS by feeding upon animals instead [4, 9–12]. While most of these behaviours have always existed naturally in vector populations that can therefore be described as resilient [13], it also appears that heritably modified behaviours have been selected for by widespread use of LLINs and IRS, resulting in vector populations that can be described as behaviourally resistant in the strict sense [14]. Regardless of whether these behaviours represent resilience or resistance, elimination of malaria transmission from many endemic settings will require new or improved anti-vector measures that target mosquitoes when they feed outdoors upon humans or livestock, or at source in the aquatic habitats their immature stages develop in [1, 4].Fig. 1


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)

A schematic summary of how specific behaviours enable mosquito populations generally, or Anopheles arabiensis in southern Tanzania specifically [16–19], to survive and mediate residual malaria transmission, despite high usage rates of long-lasting insecticidal nets
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig1: A schematic summary of how specific behaviours enable mosquito populations generally, or Anopheles arabiensis in southern Tanzania specifically [16–19], to survive and mediate residual malaria transmission, despite high usage rates of long-lasting insecticidal nets
Mentions: The World Health Organization (WHO) has recently acknowledged that residual malaria transmission can persist despite comprehensive, population-wide coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) with active ingredients to which local vector populations are fully susceptible [1, 2]. Residual transmission occurs because vector mosquitoes exhibit one or more behaviours that allow them to evade fatal contact with these front line interventions (Fig. 1) [1–4]. Feeding upon humans when they are unprotected outdoors is the most obvious of these behaviours [3–8], but vectors may also survive and mediate residual malaria transmission despite high coverage with LLINs and/or IRS by feeding upon animals instead [4, 9–12]. While most of these behaviours have always existed naturally in vector populations that can therefore be described as resilient [13], it also appears that heritably modified behaviours have been selected for by widespread use of LLINs and IRS, resulting in vector populations that can be described as behaviourally resistant in the strict sense [14]. Regardless of whether these behaviours represent resilience or resistance, elimination of malaria transmission from many endemic settings will require new or improved anti-vector measures that target mosquitoes when they feed outdoors upon humans or livestock, or at source in the aquatic habitats their immature stages develop in [1, 4].Fig. 1

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