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.
Background Dengue is the major mosquito-borne disease in Sri Lanka. After its first detection in January 2020, COVID-19 has become the major health issue in Sri Lanka. The impact of public health measures, notably restrictions on movement of people to curb COVID-19 transmission, on the incidence of dengue during the period March 2020 to April 2021 was investigated. Methods The incidence of dengue and COVID-19, rainfall and the public movement restrictions implemented to contain COVID-19 transmission were obtained from Sri Lanka government sources. A Seasonal Autoregressive Integrated Moving Average (SARIMA) model was used to predict the monthly dengue incidence from March 2020 to April 2021 for each of the country’s 25 districts based on five years of pre-pandemic data, and compared with the actual recorded incidence of dengue during this period. Ovitrap collections of Aedes larvae were performed in Jaffna city in the Jaffna district from August 2020 to April 2021 and the findings compared with similar collections made in the pre-pandemic period from March 2019 to December 2019. Results The recorded numbers of dengue cases for every month from March 2020 to April 2021 in the whole country and for all 25 districts over the same period were lower than the numbers of dengue cases predicted from data for the five years (2015–2019) immediately preceding the COVID-19 pandemic. The number of dengue cases recorded nationwide represented a 74% reduction from the predicted number of dengue cases for the March 2020 to April 2021 period. The numbers of Aedes larvae collected from ovitraps per month were reduced by 88.6% with a lower proportion of Ae. aegypti than Ae. albopictus in Jaffna city from August 2020 until April 2021 compared with March 2019 to December 2019. Conclusion Public health measures that restricted movement of people, closed schools, universities and offices to contain COVID-19 transmission unexpectedly led to a significant reduction in the reported numbers of dengue cases in Sri Lanka. This contrasts with findings reported from Singapore. The differences between the two tropical islands have significant implications for the epidemiology of dengue. Reduced access to blood meals and lower vector densities, particularly of Ae. aegypti, resulting from the restrictions on movement of people, are suggested to have contributed to the lower dengue incidence in Sri Lanka.
Background: Malaria was eliminated from Sri Lanka in 2013. However, the influx of infected travelers and the presence of potent anopheline vectors can re-initiate transmission in Jaffna city, which is separated by a narrow strait from the malaria-endemic Indian state of Tamil Nadu. Methods: Anopheline larvae were collected from different habitats in Jaffna city and the susceptibility of emergent adults to DDT, malathion and deltamethrin investigated. Results: Anopheline larvae were found in wells, surface-exposed drains, ponds, water puddles and water storage tanks, with many containing polluted, alkaline and brackish water. Anopheles culicifacies, An. subpictus, An. stephensi and An. varuna were identified in the collections. Adults of the four anopheline species were resistant to DDT. Anopheles subpictus and An. stephensi were resistant while An. culicifacies and An. varuna were possibly resistant to deltamethrin. Anopheles stephensi was resistant, An. subpictus possibly resistant while An. varuna and An. culicifacies were susceptible to malathion. DNA sequencing showed a L1014F (TTA to TTC) mutation in the IIS6 transmembrane segment of the voltage-gated sodium channel protein in deltamethrin-resistant An. subpictus-a mutation previously observed in India but not Sri Lanka. Conclusion: Anopheles subpictus in Jaffna, like An. stephensi, may have recently originated in coastal Tamil Nadu. Besides infected overseas travelers, wind-and boat-borne carriage of Plasmodium-infected anophelines across the Palk Strait can potentially reintroduce malaria transmission to Jaffna city. Adaptation to diverse larval habitats and resistance to common insecticides in anophelines are identified as potential problems for vector control should this happen.
Contrary to expectation, dengue incidence decreased in many countries during the period when stringent population movement restrictions were imposed to combat COVID-19. Using a seasonal autoregressive integrated moving average model, we previously reported a 74% reduction in the predicted number of dengue cases from March 2020 to April 2021 in the whole of Sri Lanka, with reductions occurring in all 25 districts in the country. The reduction in dengue incidence was accompanied by an 87% reduction in larval collections of Aedes vectors in the northern city of Jaffna. It was proposed that movement restrictions led to reduced human contact and blood feeding by Aedes vectors, accompanied by decreased oviposition and vector densities, which were responsible for diminished dengue transmission. These findings are extended in the present study by investigating the relationship between dengue incidence, population movement restrictions, and vector larval collections between May 2021 and July 2022, when movement restrictions began to be lifted, with their complete removal in November 2021. The new findings further support our previous proposal that population movement restrictions imposed during the COVID-19 pandemic reduced dengue transmission primarily by influencing human–Aedes vector interaction dynamics.
An amendment to this paper has been published and can be accessed via the original article.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.