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Impact of indoor residual spraying with pirimiphos-methyl (Actellic 300CS) on entomological indicators of transmission and malaria case burden in Migori County, western Kenya

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Abongo, Bernard, Gimnig, John E, Torr, Steve ORCID: https://orcid.org/0000-0001-9550-4030, Longman, Bradley, Omoke, Diana, Muchoki, Margaret, terKuile, Feiko ORCID: https://orcid.org/0000-0003-3663-5617, Ochomo, Eric, Munga, Stephen, Samuels, Aaron M, Njiagi, Kiambo, Maas, James, Perry, Robert T, Fornadel, Christen, Donnelly, Martin ORCID: https://orcid.org/0000-0001-5218-1497 and Oxborough, Richard M (2020) 'Impact of indoor residual spraying with pirimiphos-methyl (Actellic 300CS) on entomological indicators of transmission and malaria case burden in Migori County, western Kenya'. Scientific Reports, Vol 10, E4518.

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Abstract

Indoor residual spraying (IRS) of insecticides is a major vector control strategy for malaria prevention. We evaluated the impact of a single round of IRS with the organophosphate, pirimiphos-methyl (Actellic 300CS), on entomological and parasitological parameters of malaria in Migori County, western Kenya in 2017, in an area where primary vectors are resistant to pyrethroids but susceptible to the IRS compound. Entomological monitoring was conducted by indoor CDC light trap, pyrethrum spray catches (PSC) and human landing collection (HLC) before and after IRS. The residual effect of the insecticide was assessed monthly by exposing susceptible An. gambiae s.s. Kisumu strain to sprayed surfaces in cone assays and measuring mortality at 24 hours. Malaria case burden data were extracted from laboratory records of four health facilities within the sprayed area and two adjacent unsprayed areas. IRS was associated with reductions in An. funestus numbers in the intervention areas compared to non-intervention areas by 88% with light traps (risk ratio [RR] 0.12, 95% CI 0.07–0.21, p < 0.001) and 93% with PSC collections (RR = 0.07, 0.03–0.17, p < 0.001). The corresponding reductions in the numbers of An. arabiensis collected by PSC were 69% in the intervention compared to the non-intervention areas (RR = 0.31, 0.14–0.68, p = 0.006), but there was no significant difference with light traps (RR = 0.45, 0.21–0.96, p = 0.05). Before IRS, An. funestus accounted for over 80% of Anopheles mosquitoes collected by light trap and PSC in all sites. After IRS, An. arabiensis accounted for 86% of Anopheles collected by PSC and 66% by CDC light trap in the sprayed sites while the proportion in non-intervention sites remained unchanged. No sporozoite infections were detected in intervention areas after IRS and biting rates by An. funestus were reduced to near zero. Anopheles funestus and An. arabiensis were fully susceptible to pirimiphos-methyl and resistant to pyrethroids. The residual effect of Actellic 300CS lasted ten months on mud and concrete walls. Malaria case counts among febrile patients within IRS areas was lower post- compared to pre-IRS by 44%, 65% and 47% in Rongo, Uriri and Nyatike health facilities respectively. A single application of IRS with Actellic 300CS in Migori County provided ten months protection and resulted in the near elimination of the primary malaria vector An. funestus and a corresponding reduction of malaria case count among out-patients. The impact was less on An. arabiensis, most likely due to their exophilic nature.

Item Type: Article
Subjects: WA Public Health > Preventive Medicine > WA 240 Disinfection. Disinfestation. Pesticides (including diseases caused by)
WA Public Health > Health Problems of Special Population Groups > WA 395 Health in developing countries
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 750 Malaria
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 755 Epidemiology
Faculty: Department: Biological Sciences > Vector Biology Department
Clinical Sciences & International Health > Clinical Sciences Department
IVCC
Digital Object Identifer (DOI): https://doi.org/10.1038/s41598-020-61350-2
Depositing User: Mel Finley
Date Deposited: 12 Mar 2020 12:02
Last Modified: 13 Mar 2020 13:01
URI: https://archive.lstmed.ac.uk/id/eprint/13940

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