Use of ovitrap surveillance to assess dengue outbreak risks in selected dengue endemic areas in Sri Lanka

Dengue fever has been endemic to Sri Lanka for several decades. Due to the unavailability of an established prophylactic medicine, dengue prevention depends largely on vector control, where vector surveillance plays a key role. The present study aimed to assess the Aedes mosquito abundance and the risk of disease outbreak using ovitrap surveillance in 14 areas in Sri Lanka, covering four districts with high dengue incidence during 2014 – 2016. A total of 1537 ovitraps were placed in Colombo (Kirulapone, Dematagoda, Grandpass and Thummulla), Gampaha (Kurana and Imbulgoda), Kalutara (Horana, Keselwaththa and Kalamulla) and Kandy (Nawalapitiya, Peradeniya, Edanduwawa, Hanthana Road and Thalwaththa) districts in both indoor and outdoor sites and were collected after five days. The larval counts were used to calculate the Container Index (CI) and Ovitrap Index (OI). Our results revealed significantly higher CI for Aedes species for outdoor compared to indoor sites, indicating a tendency of Ae. aegypti and Ae. albopictus to breed more in outdoor habitats (p 10 % for either or both Aedes species reflecting a possible risk of dengue outbreaks as per the guidelines. Nevertheless, only the abundance of Ae. aegypti (in terms of OI) showed a positive correlation with the number of dengue cases (r = 0.96, p < 0.05) indicating its substantial contribution towards dengue incidences in the studied areas.