Evaluation of the effectiveness of adult mosquito sampling methods in three ecological habitats in Kwale County in South Coast, Kenya
Malaria and lymphatic filariasis transmission along the coastal strip of Kenya is endemic. The predominant mosquito vectors of human malaria include Anopheles gambiae s.l. and Anopheles funestus. The same mosquitoes transmit lymphatic filariasis with an added role for Culex quinquefasciatus. Current control strategies for anthropophagic mosquitoes largely involve methods that sample for adult mosquitoes inside human dwellings before they are implemented. Despite the intensive interventions, these vectors continue to elude the common forms of the adult mosquito control. At the coastal strip of Kenya, where interventions, LLINs and IRS are in place, the use of a single mosquito collection method will not be sufficient to achieve a representative sample of the vector populations in low mosquito densities. Hence, the need for effective mosquito sampling tools for vector surveillance. This research set out to identify the most effective mosquito sampling method for routine surveillance of malaria and lymphatic filariasis in coastal Kenya. The effectiveness of five collection methods: Light traps associated with a person sleeping under a net (LT/N), pyrethrum spray catches (PSC), prokopack aspirator (PP), clay pots (CP) and cow-urine baited traps (UBT) were evaluated in four villages representing three ecological settings during three surveys in south coast, Kenya. Female malaria vectors (An. gambiae s.l. and An. funestus) collected were tested for Plasmodium falciparum circumsporozoite protein and blood fed mosquitoes dissected for the identification of the blood meal sources by ELISA. A longitudinal regression analysis using the generalized estimating equations procedure in SPSS was used to compare mosquito counts of different categories. Kruskal–Wallis test was used to separately compare the performance of the sets of indoor and outdoor methods for each species. Of the five mosquito sampling methods evaluated, light traps were the most efficient for collecting female An. gambiae s.l and An. funestus mosquitoes, while the prokopack aspirator was most efficient in collecting Cx. quinquefasciatus and other culicines not known to transmit lymphatic filariasis. For the paired sets of indoor and outdoor methods, the indoor methods sampled significantly higher numbers of Cx. quinquefasciatus (Kruskal–Wallis χ 2 = 58.30, p<0.0001) and Culex spp. (Kruskal–Wallis χ 2 = 228.89, p<0.0001) than the outdoor methods. Overall, the infection rate was 1.78% with humans as the preferred blood meal source for all the tested species. The findings of this study have demonstrated that light traps remain a relevant tool for host-seeking mosquitoes. Prokopack aspirator has the potential for routine monitoring of indoor resting mosquitoes, and may be substituted for the more labour intensive and intrusive PSC. There remains lack of an efficient mosquito collection method for sampling the outdoor mosquitoes. Prokopack aspirator, pyrethrum spray catch, light traps, urine baited traps and clay pots should be evaluated further to contribute towards improving routine vector surveillance sensitivity in various habitats.
- MST-Zoological Sciences