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Abong'o B, Gimnig JE, Torr SJ, Longman B, Omoke D, Muchoki M, Ter Kuile F, Ochomo E, Munga S, Samuels AM, Njagi K, Maas J, Perry RT, Fornadel C, Donnelly MJ, Oxborough RM. Impact of indoor residual spraying with pirimiphos-methyl (Actellic 300CS) on entomological indicators of transmission and malaria case burden in Migori County, western Kenya. Sci Rep 2020; 10:4518. [PMID: 32161302 PMCID: PMC7066154 DOI: 10.1038/s41598-020-61350-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2019] [Accepted: 02/25/2020] [Indexed: 11/16/2022] Open
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.
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Affiliation(s)
- Bernard Abong'o
- Abt Associates, PMI VectorLink Project, White House, Milimani, Ojijo Oteko Road, P.O. Box 895-40123, Kisumu, Kenya.
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578, Kisumu, Kenya.
| | - John E Gimnig
- Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, 30333, USA
| | - Stephen J Torr
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
| | - Bradley Longman
- Abt Associates, PMI VectorLink Project, White House, Milimani, Ojijo Oteko Road, P.O. Box 895-40123, Kisumu, Kenya
| | - Diana Omoke
- Abt Associates, PMI VectorLink Project, White House, Milimani, Ojijo Oteko Road, P.O. Box 895-40123, Kisumu, Kenya
| | - Margaret Muchoki
- Abt Associates, PMI VectorLink Project, White House, Milimani, Ojijo Oteko Road, P.O. Box 895-40123, Kisumu, Kenya
| | - Feiko Ter Kuile
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
| | - Eric Ochomo
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578, Kisumu, Kenya
| | - Stephen Munga
- Centre for Global Health Research, Kenya Medical Research Institute, P.O. Box 1578, Kisumu, Kenya
| | - Aaron M Samuels
- Division of Parasitic Diseases and Malaria, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA, 30333, USA
| | - Kiambo Njagi
- Kenya National Malaria Control Programme (NMCP), Ministry of Health, PO Box 19982, Kenyatta National Hospital, Nairobi, 00202, Kenya
| | - James Maas
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
| | - Robert T Perry
- The United States Presidents Malaria Initiative (PMI), US Embassy Nairobi, United Nations Avenue, Nairobi, Kenya
| | - Christen Fornadel
- The United States Presidents Malaria Initiative (PMI), US Agency for International Development, Washington, DC, USA
| | - Martin J Donnelly
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
| | - Richard M Oxborough
- PMI VectorLink Project, Abt Associates 6130 Executive Blv, Rockville, MD, 20852, USA
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