Abstract
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 < 0.05). In most co-bred ovitraps, the number of Ae. aegypti larvae were higher than those of Ae. albopictus. The abundance of Ae. aegypti was higher in urban areas compared to rural areas (p < 0.05) whereas no such difference was observed for Ae. albopictus. This suggests that Ae. albopictus has been successful in invading habitats with different levels of urbanization. Further, all studied areas showed an OI > 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.
Highlights
Dengue is ranked as the most rapidly spreading mosquito borne disease in the world– with a 30-fold increase of the global incident rate over the last 50 years according to the World Health Organization
Container Index for Aedes species ranged from 6.3 % (Peradeniya) to 61.5 % (Kirulapone) for indoors and from 11.1 % (Thalwaththa) to 73.8 % (Kirulapone) for outdoors indicating a significantly higher prevalence of Aedes mosquitoes in outdoor premises (p < 0.05) (Table 2)
The present study has shown that the majority of positive ovitraps were infested with Aedes mosquitoes, while all other species occupied less than 3% reconfirming the effectiveness of the ovitrap surveillance method in estimating the prevalence of dengue vectors
Summary
Dengue is ranked as the most rapidly spreading mosquito borne disease in the world– with a 30-fold increase of the global incident rate over the last 50 years according to the World Health Organization. 50 to 100 million dengue virus infections along with 20,000 deaths are reported from all over the world (WHO, 2013). The dengue virus is transmitted to humans mainly by two mosquito species; Aedes aegypti, known as the yellow fever mosquito which is the primary vector or the epidemic vector and is abundant in urban residential areas, and Aedes albopictus the Asian tiger mosquito, which is the secondary vector or the maintenance vector mostly found in rural and sub urban areas with high vegetation (Lounibos & Kramer, 2016). The world’s first dengue vaccine was licensed for use in humans in 2015 (WHO, 2016). According to the revised recommendations by the WHO, the use of the vaccine is restricted to those who have been infected with the dengue virus previously. Vector control still acts as the main method of dengue prevention
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