Utilization of vector bionomics, remote sensing and larval habitat characterization data to inform larval source management decision in the high malaria burden state of Kebbi, Nigeria.

backgroundMalaria remains a public health challenge with Nigeria having the highest burden in cases and deaths worldwide. Increased outdoor and indoor biting of Anopheles gambiae sensu lato (s.l.) and large gaps in protection have become emerging challenges threatening malaria control efforts in Kebbi State, Nigeria. This study provided data on vector behaviour, the distribution, diversity, and other characteristics of larval habitats to inform the feasibility of larval source management in the state.

methodsRoutine entomological data were comparatively analyzed across six entomological monitoring sites located in Akwa Ibom, Ebonyi, Kebbi, Oyo, Plateau and Sokoto states in Nigeria. With a focus on Kebbi State, using Geographical Information System (GIS) data integrated with satellite imagery, potential larval habitats were remotely identified, characterized and mapped in Argungu, Bunza and Kalgo local government areas (LGAs). Field data on larval habitat abundance, larval density, and proximity of larval habitats to human habitation, and breeding index were determined and analyzed.

resultsAnopheles gambiae s.l. was the predominant 13,201(100%) malaria vector species in Kebbi State, in contrast to other states where Anopheles coustani, Anopheles funestus s.l., Anopheles maculipalpis, Anopheles marshallii group, Anopheles moucheti, Anopheles pharoensis and Anopheles rufipes were also collected. The average human biting rate of An. gambiae s.l. in Kebbi was the highest at both indoors and outdoors in the dry (15.2, 8.7 b/p/n) and rainy (42.2, 14.3 b/p/n) seasons across the six routine surveillance sites. The human behavioural observation data in Kebbi showed a protection gap of 0.83 (83%) from mosquito bite exposures both indoors and outdoors. A total of 3218 and 635 potential mosquito larval habitats were sampled by the field enumerators and sample collectors respectively across Argungu, Bunza and Kalgo LGAs. Of the 635 potential larval habitats identified by sample collectors, 460 (97.9%) were positive for Anopheles larvae. Eleven different larval habitat types were identified including temporary and permanent habitats. The proportion of temporary larval habitats within 100 m proximity of inhabited houses was highest in Argungu LGA 464 (43%) Bunza 230 (18%), and Kalgo 276 (61%). The highest proportions of those habitats were rice fields in Argungu 231 (80%), Bunza 446 (96%) and Kalgo 90 (94%).

conclusionThe consistently high entomology indices, measured protection gaps, productive and abundant larval habitats situated near human habitations throughout the year indicate the need for complementary vector control interventions, such as larval source management (LSM) in Kebbi State.