Patterns of occurrence of dengue and chikungunya, and spatial distribution of mosquito vector Aedes albopictus in Swabi district, Pakistan.

OBJECTIVE: Two principal vector species, Aedes aegypti and Aedes albopictus, are known for transmission of dengue (DEN) and chikungunya (CHK) in Pakistan. We aimed to investigate their spatial and temporal distribution.

METHODS AND RESULTS: The Maximum Entropy algorithm revealed current climatic suitability of A. albopictus by highlighting variables contributing to its spatial distribution: Land use cover was the most important environmental factor (63.1%) followed by elevation-normalised difference vegetation index (10.9%), NDVI (8.5%) and annual precipitation (7.9%). As per Normalized Difference Vegetation Index values, the vector's presence was highly likely in areas with little vegetation such as built-up spaces or uncultivated fields, and in areas with sparse vegetation such as grasslands and cultivated fields. Temperature variables showed differing effects on vector ecology with annual temperature being the most important. Logistic regression models showed that presence of the vector, build-up and distance to roads contributed significantly to the distribution of both DEN and CHIK.

CONCLUSION: In Swabi, the mean temperatures of warmest and driest quarters are more important in the spatial distribution of A. albopictus than mean temperatures of the wettest and coldest quarters. Finally, disease modelling reflects a high probability for both DEN and CHIK in the same regions over a huge area.