ASSESSMENT OF IMPACTS OF INDOOR RESIDUAL HOUSE SPRAYING ON THE DIVERSITY, ABUNDANCE AND DISTRIBUTION OF HUMAN MALARIA VECTORS IN CHONGWE DISTRICT, ZAMBIA

Abstract

Dominant human malaria vectors in Chongwe District, Zambia, were identified and impacts of Indoor Residual House Spraying (IRHS) on their diversity, abundance and distribution assessed. A case-control type of study design was used in which Chishiko village in the district was the case in point, where houses had been sprayed with DDT insecticide during the 2008- 2009 malaria transmission period through a government of Zambia sponsored IRHS programme and Chiota village was the control, where houses had not been sprayed with any insecticide during the same period. Human malaria vector identification was both morphological using mosquito identification taxonomic keys and molecular, for morphologically inseparable mosquito sibling species complexes through use of Polymerase Chain Reaction (PCR) assays. Vector abundance was determined through computations of mosquito mean densities and comparison of these using ANOVA, while the variance: Mean ratio (S-squared/x-bar ) was used to determine vector distribution patterns in the study areas. Three endophilic mosquito species were identified from the study areas as Culex quinquefasciatus Say 1823, Anopheles squamosus Theobald 1901 and a species from the A. gambiae complex comprising seven morphologically indistinguishable sibling species. Molecular discrimination of the A. gambiae complex species collected from the study areas through PCR revealed that it was A. arabiensis Patton 1905 and further, this species was found to be the major vector of malaria in Chongwe District. The Expected Species Total computed for the study areas indicated the mosquito vector abundance to be three in the study areas, while the variance/Mean ratio showed that malaria mosquito vectors were contagiously distributed in Chiota village (S-squared >x-bar ) and that there were no malaria vectors in Chishiko village. The difference in density of A. arabiensis between DDT-insecticide-sprayed houses in Chishiko village and the non-sprayed Chiota village houses was significant ( p < 0.05) indicating that the IRHS programme exerted a positive impact on the diversity, abundance and distribution of human malaria vectors in Chongwe District. But it is also possible that the vectors might have resorted to feeding and resting outside of the sprayed houses. A longitudinal study would be necessary to complement these findings.