Abstract
SummaryDomestic and personal protection measures against malaria exposure either divert host-seeking vectors to other hosts or kill those attempting to feed. Here, we explicitly model mosquito host-seeking processes in the context of local host availability and elucidate the impacts and mechanisms of pyrethroid-treated bed nets in Africa. It has been suggested that excitorepellent insecticides could increase exposure of unprotected humans by concentrating mosquito biting activity on this vulnerable group. This worst-case scenario is confirmed as a possibility where vector populations lack alternative hosts, but an approximate ‘break-even’ scenario, with users experiencing little overall change in exposure, is more likely because of increased mosquito mortality while foraging for resources. Insecticidal nets are predicted to have epidemiologically significant impacts on transmission experienced by users and non-users at levels of coverage that can be achieved by sustainable net distribution systems, regardless of excitorepellency or the ecological setting. The results are consistent with the outcome of several randomised controlled trials, predicting enormous reductions in transmission at individual and community levels. As financial support, technology and distribution systems for insecticide-treated nets improve, massive reductions in malaria transmission could be realised.
Highlights
Insecticidal measures for protection against adult mosquitoes, including treated nets and indoor residual spraying, are amongst the best established and most effec-ITNs protect individuals either by diverting host-seeking vectors to search for a blood meal elsewhere or by killing those that attempt to feed on that person (Fanello et al, 2003; Lindsay et al, 1989, 1991, 1992; Miller et al, 1991; Pleass et al, 1993)
It is theoretically possible that interventions that divert rather than kill mosquitoes could even increase the stability of malaria transmission by increasing vectorial capacity in the most intense foci of transmission (Dye and Hasibeder, 1986; Hasibeder and Dye, 1988; Woolhouse et al, 1997)
We investigate the likely impacts of pyrethroid-treated bed nets under conditions where holoendemic malaria is maintained by either Anopheles gambiae Giles or A. arabiensis Patton in the presence and absence of cattle as alternative hosts
Summary
ITNs protect individuals either by diverting host-seeking vectors to search for a blood meal elsewhere or by killing those that attempt to feed on that person (Fanello et al, 2003; Lindsay et al, 1989, 1991, 1992; Miller et al, 1991; Pleass et al, 1993) This means that treated nets prevent malaria in a protected individual but can reduce malaria risk in unprotected individuals by suppressing the density (Carnevale et al, 1988; Magesa et al, 1991; Robert and Carnevale, 1991), survival (Carnevale et al, 1988; Magesa et al, 1991; Robert and Carnevale, 1991), human blood indices (Bøgh et al, 1998; Charlwood et al, 2001) and feeding frequency (Charlwood et al, 2001) of vector populations. We investigate the likely impacts of pyrethroid-treated bed nets under conditions where holoendemic malaria is maintained by either Anopheles gambiae Giles or A. arabiensis Patton in the presence and absence of cattle as alternative hosts
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