Abstract
BackgroundMosquitoes that feed on animals can survive and mediate residual transmission of malaria even after most humans have been protected with insecticidal bednets or indoor residual sprays. Ivermectin is a widely-used drug for treating parasites of humans and animals that is also insecticidal, killing mosquitoes that feed on treated subjects. Mass administration of ivermectin to livestock could be particularly useful for tackling residual malaria transmission by zoophagic vectors that evade human-centred approaches. Ivermectin comes from a different chemical class to active ingredients currently used to treat bednets or spray houses, so it also has potential for mitigating against emergence of insecticide resistance. However, the duration of insecticidal activity obtained with ivermectin is critical to its effectiveness and affordability.ResultsA slow-release formulation for ivermectin was implanted into cattle, causing 40 weeks of increased mortality among Anopheles arabiensis that fed on them. For this zoophagic vector of residual malaria transmission across much of Africa, the proportion surviving three days after feeding (typical mean duration of a gonotrophic cycle in field populations) was approximately halved for 25 weeks.ConclusionsThis implantable ivermectin formulation delivers stable and sustained insecticidal activity for approximately 6 months. Residual malaria transmission by zoophagic vectors could be suppressed by targeting livestock with this long-lasting formulation, which would be impractical or unacceptable for mass treatment of human populations.
Highlights
Mosquitoes that feed on animals can survive and mediate residual transmission of malaria even after most humans have been protected with insecticidal bednets or indoor residual sprays
An even more important behavioural category of vectors is those which feed readily, opportunistically and flexibly upon either animals or humans [11]. Vectors with such dual feeding preferences are ubiquitously associated with residual malaria transmission because they feed often enough on humans to mediate intense transmission, and often enough on animals to survive and reproduce despite high coverage of long-lasting insecticidal nets (LLINs) and/or indoor residual spraying (IRS) [11]
As humans are increasingly protected with LLINs and IRS, the phenotypically plastic behaviours of most mosquito species allows them to survive by making greater use of animal blood source [2, 17, 19]
Summary
Mosquitoes that feed on animals can survive and mediate residual transmission of malaria even after most humans have been protected with insecticidal bednets or indoor residual sprays. An even more important behavioural category of vectors is those which feed readily, opportunistically and flexibly upon either animals or humans [11] Vectors with such dual feeding preferences are ubiquitously associated with residual malaria transmission because they feed often enough on humans to mediate intense transmission, and often enough on animals to survive and reproduce despite high coverage of LLINs and/or IRS [11]. As humans are increasingly protected with LLINs and IRS, the phenotypically plastic behaviours of most mosquito species allows them to survive by making greater use of animal blood source [2, 17, 19]. New tools targeting partly zoophagic vectors may be needed to eliminate malaria in many settings where they contribute towards sustaining residual transmission [11, 15]
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