Abstract
BackgroundIn the Solomon Islands, the Malaria Eradication Programmes of the 1970s virtually eliminated the malaria vectors: Anopheles punctulatus and Anopheles koliensis, both late night biting, endophagic species. However, the vector, Anopheles farauti, changed its behaviour to bite early in the evening outdoors. Thus, An. farauti mosquitoes were able to avoid insecticide exposure and still maintain transmission. Thirty years on and the Solomon Islands are planning for intensified malaria control and localized elimination; but little is currently known about the behaviour of the vectors and how they will respond to intensified control.MethodsIn the elimination area, Temotu Province, standard entomological collection methods were conducted in typical coastal villages to determine the vector, its ecology, biting density, behaviour, longevity, and vector efficacy. These vector surveys were conducted pre-intervention and post-intervention following indoor residual spraying and distribution of long-lasting insecticidal nets.ResultsAnopheles farauti was the only anopheline in Temotu Province. In 2008 (pre-intervention), this species occurred in moderate to high densities (19.5-78.5 bites/person/night) and expressed a tendency to bite outdoors, early in the night (peak biting time 6-8 pm). Surveys post intervention showed that there was little, if any, reduction in biting densities and no reduction in the longevity of the vector population. After adjusting for human behaviour, indoor biting was reduced from 57% pre-intervention to 40% post-intervention.ConclusionIn an effort to learn from historical mistakes and develop successful elimination programmes, there is a need for implementing complimentary vector control tools that can target exophagic and early biting vectors. Intensified indoor residual spraying and long-lasting insecticide net use has further promoted the early, outdoor feeding behaviour of An. farauti in the Solomon Islands. Consequently, the effectiveness of IRS and the personal protection provided by bed nets is compromised. To achieve elimination, any residual transmission should be targeted using integrated vector control incorporating complementary tools such as larviciding and/or zooprophylaxis.
Highlights
In the Solomon Islands, the Malaria Eradication Programmes of the 1970s virtually eliminated the malaria vectors: Anopheles punctulatus and Anopheles koliensis, both late night biting, endophagic species
In the Solomon Islands, it was found that the proportion of An. farauti biting from 6-8 pm increased from 30% before indoor residual spraying (IRS) to 66% after IRS; the proportion biting indoors changed from 53% before IRS to 33% after IRS [8]
Larval ecology Anopheles farauti larvae were collected from 27 larval sites throughout the Province
Summary
In the Solomon Islands, the Malaria Eradication Programmes of the 1970s virtually eliminated the malaria vectors: Anopheles punctulatus and Anopheles koliensis, both late night biting, endophagic species. In Papua New Guinea, the Solomon Islands and Vanuatu it was found that there was a shift in the behaviour of this vector from feeding indoors late in the night to outdoors early in the night [8,13,14,15,16] This change in behaviour was most likely due to vector irritability caused by the DDT leading to the vector avoiding insecticide exposure [5,14]. Relevant to the efficacy of IRS, was that the excito-repellent effect of the DDT reduced or precluded the time An. farauti spent indoors resting so that at least 45% of An. farauti exited houses without picking up a lethal dose of insecticide [16] This change in resting and biting behaviour reduced the level of personal and communal protection afforded by IRS and led to the failure of the eradication programme despite the addition of mass drug administration to the programme [17,18]
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