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

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.

Baseline susceptibility of Anopheles gambiae to clothianidin in northern Ghana

“…arabiensis relatively scarce (<10%). This is consistent with ndings from other studies in the region [24,25,26]. Studies in Ghana and other parts of Africa [26, 27, 28], which ensures the larvae get adequate sunlight exposure.…”

Escalating pyrethroid resistance in two major malaria vectors Anopheles funestus and Anopheles gambiae (s.l.) in Atatam, Southern Ghana

“…PBO-based bed nets have been shown to reduce malaria incidence [41] and increase personal protection [42] in areas with pyrethroid resistance. The full susceptibility to organophosphates indicates that IRS with pirimiphos methyl (Actellic 300CS) could also be an option in curbing pyrethroid resistance in this area as previously shown in northern Ghana [43] and western Kenya [44]. Even though a reduced performance of conventional bed nets was observed with cone assays, more studies using either experimental hut or looking at the delayed mortality are needed to assess the impact of such multiple resistance on the effectiveness of insecticide-based interventions.…”

Prevalence of malaria infection and the impact of mosquito bed net distribution among children aged 6–59 months in Ghana: Evidence from the Ghana demographic health and malarial indicator surveys

“…Even though malaria infection prevalence among children aged 6–59 months is decreasing, the reduction rate seems not to be directly linked with the distribution of mosquito bed nets in Ghana. For a continued distribution of mosquito bed nets, and for Ghana to achieve her Malaria Strategic Plan (NMSP) 2021–2025, program managers should ensure effective use of the distributed nets in addition to other preventive measures and nuanced consideration of community behaviours among bed net users in Ghana ( Abuaku et al, 2018 ; Coleman et al, 2021 ; Gogue et al, 2020 ; Hoke, 2015 ; Suuron et al, 2020 ) and Africa at large ( Hamusse et al, 2012 ; Zhou et al, 2010 ; Zinszer et al, 2020 ). The effective use and care of bed nets should be emphasized as part of the distribution.…”