A systematic, realist review of zooprophylaxis for malaria control

Abstract

BackgroundIntegrated vector management (IVM) is recommended as a sustainable approach to malaria control. IVM consists of combining vector control methods based on scientific evidence to maximize efficacy and cost-effectiveness while minimizing negative impacts, such as insecticide resistance and environmental damage. Zooprophylaxis has been identified as a possible component of IVM as livestock may draw mosquitoes away from humans, decreasing human-vector contact and malaria transmission. It is possible, however, that livestock may actually draw mosquitoes to humans, increasing malaria transmission (zoopotentiation). The goal of this paper is to take a realist approach to a systematic review of peer-reviewed literature to understand the contexts under which zooprophylaxis or zoopotentiation occur.MethodsThree electronic databases were searched using the keywords ‘zooprophylaxis’ and ‘zoopotentiation’, and forward and backward citation tracking employed, to identify relevant articles. Only empirical, peer-reviewed articles were included. Critical appraisal was applied to articles retained for full review.ResultsTwenty empirical studies met inclusion criteria after critical appraisal. A range of experimental and observational study designs were reported. Outcome measures included human malaria infection and mosquito feeding behaviour. Two key factors were consistently associated with zooprophylaxis and zoopotentiation: the characteristics of the local mosquito vector, and the location of livestock relative to human sleeping quarters. These associations were modified by the use of bed nets and socio-economic factors.DiscussionThis review suggests that malaria risk is reduced (zooprophylaxis) in areas where predominant mosquito species do not prefer human hosts, where livestock are kept at a distance from human sleeping quarters at night, and where mosquito nets or other protective measures are used. Zoopotentiation occurs where livestock are housed within or near human sleeping quarters at night and where mosquito species prefer human hosts.ConclusionThe evidence suggests that zooprophylaxis could be part of an effective strategy to reduce malaria transmission under specific ecological and geographical conditions. The current scientific evidence base is inconclusive on understanding the role of socio-economic factors, optimal distance between livestock and human sleeping quarters, and the effect of animal species and number on zooprophylaxis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0822-0) contains supplementary material, which is available to authorized users.

Livestock ownership is associated with higher odds of anaemia among preschool‐aged children, but not women of reproductive age in Ghana

“…Furthermore, if infection risk is predominantly driven by contact with neighbouring animals, local corralling may not address the problem (Oberhelman et al, ). Research is needed that jointly assesses the diverse direct and indirect pathways linking livestock and anaemia (e.g., diet; exposure to animal faeces, animal slaughter waste [Osbjer et al, ], and zoonotic pathogens linked to livestock disease [Mosites et al, ]); altering human vector interactions [Donnelly et al, ]). Understanding the relative importance of these factors across contexts and their relationships will help to elucidate the complex aetiology of anaemia among agricultural households and inform solutions that maximize the potential dietary benefits of animal production while minimizing disease risks.…”

Exploring the potential of using cattle for malaria vector surveillance and control: a pilot study in western Kenya

“…Zooprophylaxis aims to reduce the number of infective bites for humans. However, the evidence collected thus far, has been contradictory and not conclusive on the extent, if any, of the prophylactic effect of animals [12–16]. …”

Increasing the potential for malaria elimination by targeting zoophilic vectors

“…sinensis (Asia-Pacific region) are all key malaria vectors, yet exhibit strong zoophilic and exophilic behaviors456. That zoophilic vectors can be so important for malaria transmission might seem counterintuitive since Plasmodium parasites responsible for human malaria cannot infect cattle, so bites taken on cattle instead of humans represent reduced opportunities for vectors to acquire or transmit Plasmodium 789. However, livestock kept in close proximity to humans can support higher transmission by attracting mosquitoes into areas where they will encounter and feed on human hosts opportunistically (zoopotentiation)710.…”