Going beyond personal protection against mosquito bites to eliminate malaria transmission: population suppression of malaria vectors that exploit both human and animal blood

Abstract

Protecting individuals and households against mosquito bites with long-lasting insecticidal nets (LLINs) or indoor residual spraying (IRS) can suppress entire populations of unusually efficient malaria vector species that predominantly feed indoors on humans. Mosquitoes which usually feed on animals are less reliant on human blood, so they are far less vulnerable to population suppression effects of such human-targeted insecticidal measures. Fortunately, the dozens of mosquito species which primarily feed on animals are also relatively inefficient vectors of malaria, so personal protection against mosquito bites may be sufficient to eliminate transmission. However, a handful of mosquito species are particularly problematic vectors of residual malaria transmission, because they feed readily on both humans and animals. These unusual vectors feed often enough on humans to be potent malaria vectors, but also often enough on animals to evade population control with LLINs, IRS or any other insecticidal personal protection measure targeted only to humans. Anopheles arabiensis and A. coluzzii in Africa, A. darlingi in South America and A. farauti in Oceania, as well as A. culicifacies species E, A. fluviatilis species S, A. lesteri and A. minimus in Asia, all feed readily on either humans or animals and collectively mediate residual malaria transmission across most of the tropics. Eliminating malaria transmission by vectors exhibiting such dual host preferences will require aggressive mosquito population abatement, rather than just personal protection of humans. Population suppression of even these particularly troublesome vectors is achievable with a variety of existing vector control technologies that remain underdeveloped or underexploited.

Developing an expanded vector control toolbox for malaria elimination

“…6 Also, many of their routine operational practices will not be directly transferable to more financially constrained LMIC contexts, the needs of which are epidemiologically and ecologically diverse. Nevertheless, these interventions have been so successful that their malaria elimination function is often taken for granted, and many of the technologies or experiences may be relevant to malaria control and elimination in LMICs.…”

“…Indeed, such mass population abatement will most likely be essential to eliminate and prevent the reintroduction of malaria anywhere that vectors feed often enough on humans to mediate intense residual malaria transmission but also often enough on animals to evade population control with human-targeted interventions alone. 6 Beyond the well-understood blood-feeding behaviours that are most obvious as targets for mosquito control, other behaviours that are critical to mosquito survival can be targets for malaria vector control (figure 1 and box 3). While female mosquitoes need blood from animals to develop their eggs to maturity, they also feed on plant sugar sources to maintain their energetic requirements.…”

Informing new or improved vector control tools for reducing the malaria burden in Tanzania: a qualitative exploration of perceptions of mosquitoes and methods for their control among the residents of Dar es Salaam

“…For example, many people undertake activities that prevent them from being under a LLIN at the times they are at risk from malaria (e.g., getting up before dawn to get to market or collect wood), or sleep in locations where they are not protected by LLINs due to socio-economic circumstances, climatic obstacles, cultural practices, or personal preferences (e.g., visiting relatives or seasonal migration to farm) [9, 10]. The most obvious of the behaviour known to mediate such residual malaria transmission is outdoor biting in the early evening and/or early morning; behaviour that clearly limits the effectiveness of interventions focused on the prevention of indoor biting [11–13]. These long-standing challenges will clearly require complementary additional vector control tools in order to eliminate transmission in many settings [11–13].…”

Priorities for Broadening the Malaria Vector Control Tool Kit

“…Second, the current core tools are most effective against Anopheles vectors that feed and rest indoors and exhibit a preference for feeding on human hosts during nighttime [2]. Yet in many locations vectors exhibit more diverse behaviors, feeding on other hosts, feeding and resting outdoors, and/or feeding in the early evening [6–8]. A consequence of both these challenges is that there are limits to how much LLINs and IRS alone can reduce transmission, even with further intensification and optimization [9].…”

“…While feeds on non-human hosts represent ‘wasted bites’ in terms of acquiring or passing on the malaria parasite, they allow the mosquito to escape the effects of interventions like IRS and LLINs that center on the human host. Targeting these mosquitoes with livestock-based interventions could play an important role in reducing residual transmission [7,8,69]. …”