Evaluation of a 'push-pill' strategy for the control of mosquito vectors using long lasting treated bed nets (OlysetTM) and zoo-prophylaxis in Mwea Division, Central Province, Kenya
Kaburi, Josyline Cirindi
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Strategies to eradicate vector-borne diseases are often directed at controlling vectors with insecticides. However, over-use of insecticides leads to the development of insecticide resistance in the vectors hence, control strategies that do not heavily rely on insecticides are required. The World Health Organization has recommended the use of cattle for zooprophylaxis as a protective measure against malaria since 1982. Zoo-prophylaxis is a strategy that can control malaria by attracting mosquitoes to domestic animals that act as dead-end hosts. However, concern has been raised about this practice since some studies have shown that the presence of cattle may instead increase malaria prevalence. Thus, the study was designed to establish the effects of zoo-prophylaxis and Long Lasting Insecticides Treated bed nets (LLITNs) on malaria transmission in an agro-based ecosystem with seasonal transmission. It was carried out in three villages selected randomly within the irrigation scheme. Cattle densities in each homestead within the study villages were determined. Homesteads with no cattle were not issued with LLITNs and acted as controls. Indoor mosquito collections were done using pyrethrum spray catch (PSC) method to determine vector densities in these households. This activity was carried out before and after intervention. The results on sporozoite ELISA showed that out of the 4,148 mosquito samples collected, twelve (12) tested positive (0.3%) for sporozoites. Eleven were A. gambiae species and one was of A. funestus species. Results on blood meal ELISA showed that in the household categories that used bed nets and kept one cattle, there was a decrease in relative change ratio (post/pre intervention) of 87.5% and 19.6% in human and cattle blood intake respectively. On the other hand, in the households that kept 2-4 cattle and used bed nets, there was a decrease in cattle blood intake by 61.9% and an increase in human blood intake by 2%, which was not significant. In households with >4 cattle and bed net, there was significant reduction in the cattle blood intake of 37.5% as compared to the reduction of 10.3% in human blood intake. Therefore, presence of animals within the compound decreased the risk ratios in the presence of LLITNs showing additive effects of the two. The experiment shows that huma biting rates (HBR) ratios decreased significantly, as you move up from households with one cattle and ITNs, and without LLITNs to households with >4cattle and LLITNs and without, with a regression coefficient of -0.96; SE=0.834; P=0.017 (P<0.05). The same happened to HBI but the decrease was not significant and the regression coefficient was 0.239; SE=0.039; P=0.015 (P<0.05) especially in households with >4 cattle. Therefore domestic animals, kept within the households in large numbers increases rather than reducing malaria transmission when the vectors are zoophilic. In conclusion, as you increase the number of domestic animals, there is gradual increase in human biting index and hence increased risk in household with >5 cattle as compared to those with 4 cattle and below. This suggests that if zoo-prophylaxis is to be incorporated in Intergrated Vector Management (IVM) for the control of mosquitoes, then the numbers of animals per household should not exceed four.
- MST-Zoological Sciences