The impact of mosquito proof lids of underground tanks "tanka" on the breeding of Anopheles stephensi in a village in western Rajasthan, India.

backgroundWestern Rajasthan in India has a typical desert climate. Until the introduction of the canal water irrigation system, malaria was an unstable and seasonal occurrence. Due to the scarcity of water, the community practised having one large underground tank (locally known as the tanka) in their house to collect rainwater for long-term household use. Anopheles stephensi, one of the major malaria vectors, breeds in improperly covered "tankas" if not properly covered and harbours a vector population throughout the year.

methodsTwo villages, Ajasar (intervention) and Tota (control), with similar ecological features, were selected for the study. A pre-intervention survey was carried out in both villages to assess the presence and quality of lids of tankas, and mosquito breeding and adult mosquito density. Awareness of the community about malaria and mosquitoes was also assessed during the pre-intervention period. In the intervention village, damaged or improper lids were replaced with improved mosquito proof polyvinyl chloride plastic (PVC) lids and lasted longer than the conventional lids. The fitness of the lids was assessed one year after the pre-intervention survey. The entomological assessment was carried out in both intervention and non-intervention villages. The level of community awareness about malaria, mosquitoes, their breeding places, and the role of tankas in malaria transmission was assessed both during pre- and post-intervention.

resultsDuring the pre-intervention survey, Anopheles breeding was found in 22.1% (58/262) of tankas in the intervention village and 27.1% (19/70) in tankas in the control village. Mosquito breeding was observed in the tankas with iron lids in the intervention village (48.3%) and the control village (42.1%). In the intervention village, out of 262 tankas in the village, 200 lids were replaced, resulting in the complete absence of mosquito breeding. In the pre-intervention survey conducted in May 2018, Anopheles stephensi consisted of 46% of adult mosquitoes in the intervention village and 55% in the control village. Its density was significantly reduced to 0.55 per man-hour (94.95%) and 0.22 per man-hour (97.8%) in the post-intervention survey in June 2018 and a follow-up survey in May 2019, respectively, in the intervention village. DISCUSSION: The density of Anopheles stephensi adults was reduced significantly (97.8%) in the intervention village due to complete prevention of breeding in the underground tankas in the intervention village as compared to the control with no density reduction. The awareness level of the community was also improved due to their involvement in the study.

conclusionProvision of proper metal lids or replacement of damaged lids on underground water storage tanks as an environmental management approach prevented the breeding of  the malaria vector, Anopheles stephensi, in a desert village in western Rajasthan.