Using ecological observations to improve malaria control in areas where Anopheles funestus is the dominant vector

Abstract

The most important malaria vectors in sub-Saharan Africa are Anopheles gambiae, Anopheles arabiensis, Anopheles funestus, and Anopheles coluzzii. Of these, An. funestus presently dominates in many settings in east and southern Africa. While research on this vector species has been impeded by difficulties in creating laboratory colonies, available evidence suggests it has certain ecological vulnerabilities that could be strategically exploited to greatly reduce malaria transmission in areas where it dominates. This paper examines the major life-history traits of An. funestus, its aquatic and adult ecologies, and its responsiveness to key interventions. It then outlines a plausible strategy for reducing malaria transmission by the vector and sustaining the gains over the medium to long term. To illustrate the propositions, the article uses data from south-eastern Tanzania where An. funestus mediates over 85% of malaria transmission events and is highly resistant to key public health insecticides, notably pyrethroids. Both male and female An. funestus rest indoors and the females frequently feed on humans indoors, although moderate to high degrees of zoophagy can occur in areas with large livestock populations. There are also a few reports of outdoor-biting by the species, highlighting a broader range of behavioural phenotypes that can be considered when designing new interventions to improve vector control. In comparison to other African malaria vectors, An. funestus distinctively prefers permanent and semi-permanent aquatic habitats, including river streams, ponds, swamps, and spring-fed pools. The species is therefore well-adapted to sustain its populations even during dry months and can support year-round malaria transmission. These ecological features suggest that highly effective control of An. funestus could be achieved primarily through strategic combinations of species-targeted larval source management and high quality insecticide-based methods targeting adult mosquitoes in shelters. If done consistently, such an integrated strategy has the potential to drastically reduce local populations of An. funestus and significantly reduce malaria transmission in areas where this vector species dominates. To sustain the gains, the programmes should be complemented with gradual environmental improvements such as house modification to maintain biting exposure at a bare minimum, as well as continuous engagements of the resident communities and other stakeholders.

Small-scale field evaluation of PermaNet® Dual (a long-lasting net coated with a mixture of chlorfenapyr and deltamethrin) against pyrethroid-resistant Anopheles gambiae mosquitoes from Tiassalé, Côte d’Ivoire

“…Interceptor G2) in Tanzania [49], soon in Benin [48,50], and the pilot deployments that are part of the New Nets Project led by PATH [51]. Furthermore, PermaNet ® Dual should be tested against wild populations of Anopheles funestus [32], or other main or secondary vectors of malaria in Africa [52][53][54][55][56]. Ultimately, in the present study, the series of hut and laboratory tests demonstrated that the chlorfenapyr component of PermaNet ® Dual could make a major contribution to controlling the pyrethroidresistant An.…”

Entomological Survey of Sibling Species in the Anopheles funestus Group in Tanzania Confirms the Role of Anopheles parensis as a Secondary Malaria Vector

“…However, in recent years, there has been an increasing awareness that populations of An. funestus s.s., known for their high degree of anthropophily and now marked by signi cant pesticide resistance 35,46 , are becoming predominant in many malaria transmission areas, particularly in East and Southern Africa 58, 59 . In areas such as south-eastern Tanzania, this species now mediates 85-98% of new malaria infections, even in villages where it is outnumbered by other species such as An.…”

Distribution and insecticide resistance profile of the major malaria vectorAnopheles funestusgroup across theAfricancontinent

“…funestus may be explained by the fact that An. funestus malaria transmission is highly variable, from short intervals to prolonged periods across the year, depending on the country (Djènontin et al, 2010; Fontenille & Simard, 2004; Kahamba et al, 2022). Additionally, the species is very difficult to raise in the laboratory (Jones et al, 2018), and its ecology is far less understood than for An.…”