Assessment of the Effectiveness of Various Adult Mosquito Sampling Methods in a Thickly Populated Urban Slum Settlement - A study from Besant Nagar, Chennai, India

BackgroundIn an urban scenario, it is an arduous task to collect adult Anopheles stephensi, unlike the immature forms due to various reasons such as the complex spatial heterogeneity, intricacies in feeding, and resting preferences. Thus it is necessary to have more specific and accurate assessments of adult vector density by performing various collection methods and timeframes to achieve appropriate and sustainable vector control strategies.Methods The study was undertaken in two phases, (i) resting dawn collections in cattle sheds from Jan 2015 to Dec 2016 to assess the possibility of maximum collection of An. stephensi compared to dusk collections done previously and to find out the best appropriate collection strategy for vector control and (ii) light trap collections from Jan 2016 to Apr 2017 to determine the efficiency and reliability of CDC light trap in sampling the anophelines including the urban malaria vector, Anopheles stephensi in human dwellings besides, other mosquito species. The man-hour density of An. stephensi in cattle sheds were calculated and its infection rate was analyzed by circum-sporozoite ELISA (CS-ELISA). Binary logistic regression analysis was done to ascertain the variables associated with the collection of Anopheles stephensi using a light trap.Results The resting collections in cattle sheds indicated that dawn collections yielded more Anopheles stephensi than at dusk. The resting stage female (fully fed, semi-gravid, and gravid) mosquitoes were more in dawn collections than in dusk collections. The CDC-light trap collections revealed that An. stephensi collected indoors were more than outdoor in human dwellings. Further, vector incrimination results observed that 0.56% of the female An. stephensi from cattle sheds were infected in 2014 (dusk), 0.15%, and 0.09% in 2015 and 2016 respectively in dawn collections. Nevertheless, 2.3% of An. stephensi collected by CDC light trap in human dwellings were positive for Plasmodium vivax (Pv210) infection. Binary logistic regression analysis proved that the presence of An. stephensi in human dwellings was significantly influenced by seasons, the number of rooms in the house, number of household members, and also the use of repellents.ConclusionsThe different collection (resting and light trap) approaches were assessed to find out the appropriate collection method and time which could yield the maximum number of An. stephensi with the existing resources. The study revealed that dawn collections during the early hours as the most suitable time to collect wild An. stephensi in an urban setting. The present study thus would help in chalking out an operationally feasible vector control strategy with the most appropriate methodology, timeframe useful for effective control of vectors.