Aedes larval bionomics and implications for dengue control in the paradigmatic Jaffna peninsula, northern Sri Lanka

Abstract

Background The larval bionomics of Aedes across the Jaffna peninsula in northern Sri Lanka was investigated to obtain information needed for developing more effective larval source reduction measures to control endemic arboviral diseases. Methods The habitats of preimaginal stages of Aedes mosquitoes were surveyed, and ovitrap collections were carried out in densely populated areas of the Jaffna peninsula. Aedes larval productivities were analysed against habitat characteristics, rainfall and dengue incidence. Adults emerging from collected larvae were tested for dengue virus (DENV). Results Only Aedes aegypti, Ae. albopictus and Ae. vittatus were identified in the field habitat collections and ovitraps. Aedes aegypti was the predominant species in both the field habitat and ovitrap collections, followed by Ae. albopictus and small numbers of Ae. vittatus. Tires and open drains were the preferred field habitats for Ae. aegypti, although larval productivity was higher in discarded plastic containers. The three Aedes species differed in field habitat preferences. Concomitant presence of the three Aedes species was observed in the field habitats and ovitraps. Larval productivities were inversely correlated with the salinity of the field habitat. Rainfall in the preceding month significantly correlated with larval productivity in the field habitats. DENV serotype 2 was detected in Ae. aegypti collected from ovitraps in the city of Jaffna. High Breteau, House and Container indices of 5.1, 5.1 and 7.9%, respectively, were observed in the field habitat surveys and ovitrap indices of up to 92% were found in Jaffna city. Conclusions Aedes larval indices in populated areas of the peninsula showed a high potential for dengue epidemics. Unacceptable littering practices, failure to implement existing dengue control guidelines, vertical transmission of DENV in vector mosquitoes and preimaginal development in brackish water and open surface drains, as well as in domestic wells that provide potable water, are serious constraints to the current Aedes larval source reduction methods used to control dengue in the Jaffna peninsula. Similar shortcomings in arboviral disease control are likely present in other resource-constrained tropical coastal zones worldwide.

Reduced Dengue Incidence During COVID-19 Restrictions in Sri Lanka From March 2020 to April 2021

“…Monthly dengue cases during the COVID-19 lockdown period were compared with the predicted number of monthly dengue incidence cases based on data from the prepandemic period from January 2015 to February 2020 using a Seasonal Autoregressive Integrated Moving Average (SARIMA) model described previously [13]. The SARIMA model is appropriate to do the seasonal time series analysis for the monthly dengue incidence data as the dengue incidence is seasonal and closely associated with monsoonal rainfall in Sri Lanka [5][6][7].…”

“…Monthly rainfall data from January 2015 to February 2020 and the reported monthly numbers of dengue cases from January 2015 to April 2021 and the SARIMA model-predicted numbers of monthly dengue cases from March 2020 to April 2021 in the Jaffna district were used to identify variations from the pattern observed in the pre-pandemic years of 2015 to 2019 that we had reported previously [7].…”

“…aegypti than Ae. albopictus were collected from the ovitraps in 2019 at the same location [7] Discussion Numerous non-pharmaceutical public health measures were introduced early in the pandemic in almost all countries to suppress the spread of COVID-19 [14]. These have been supplemented with speci c vaccination that became possible at the end of 2020.…”

“…There is epidemiological evidence to suggest that movement of people outside of their homes is one of the factors that drive the transmission of dengue virus [22], and this is also supported by mathematical modeling studies [23]. In Sri Lanka dengue vectors are highly prevalent in premises of schools, hospital, government o ces, transport hubs and factories [5,7]. The anthropophagic Ae.…”

“…Rainfall is the prominent factor in uencing dengue transmission in Sri Lanka and the Jaffna district [6,7]. The pattern of rainfall in the immediate pre-pandemic period in the whole of Sri Lanka as well as the Jaffna district was not strikingly different from that in 2020 and the rst quarter of 2021.…”