Partial Indoor Residual Spraying with Pirimiphos Methyl as an Effective and Cost Saving Measure for the Control of Anopheles Gambiae S.L. in Northern Ghana
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Date
2021
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Publisher
Springer Nature
Abstract
The scale-up of indoor residual spraying (IRS) and insecticide-treated nets have contributed
significantly to global reductions in malaria prevalence over the last two decades. However,
widespread pyrethroid resistance has necessitated the use of new and more expensive insecticides
for IRS. Partial IRS with pirimiphos-methyl in experimental huts and houses in a village-wide trial
was evaluated against Anopheles gambiae s.l. in northern Ghana. Four different scenarios in which
either only the top or bottom half of the walls of experimental huts were sprayed, with or without
also spraying the ceiling were compared. Mortality of An. gambiae s.l. on partially sprayed walls
was compared with the standard procedures in which all walls and ceiling surfaces are sprayed.A
small-scale trial was then conducted to assess the effectiveness, feasibility, and cost of spraying
only the upper walls and ceiling as compared to full IRS and no spraying in northern Ghana. Human
landing catches were conducted to estimate entomological indices and determine the effectiveness
of partial IRS. An established transmission dynamics model was parameterized by an analysis of the
experimental hut data and used to predict the epidemiological impact and cost effectiveness of partial
IRS for malaria control in northern Ghana. In the experimental huts, partial IRS of the top (IRR 0.89,
p = 0.13) or bottom (IRR 0.90, p = 0.15) half of walls and the ceiling was not significantly less effective
than full IRS in terms of mosquito mortality. In the village trial, the annual entomological inoculation
rate was higher for the unsprayed control (217 infective bites/person/year (ib/p/yr)) compared with the
fully and partially sprayed sites, with 28 and 38 ib/p/yr, respectively. The transmission model predicts
that the efficacy of partial IRS against all-age prevalence of malaria after six months would be broadly
equivalent to a full IRS campaign in which 40% reduction is expected relative to no spray campaign.
At scale, partial IRS in northern Ghana would have resulted in a 33% cost savings ($496,426) that
would enable spraying of 36,000 additional rooms. These findings suggest that partial IRS is an effective, feasible, and cost-saving approach to IRS that could be adopted to sustain and expand
implementation of this key malaria control intervention.
Description
Research Article
Keywords
pirimiphos‑methyl, Anopheles gambiae s.l., Ghana