Epidemiological and virological factors determining dengue transmission in Sri Lanka during the COVID-19 pandemic

Abstract

Background: With the onset of the COVID-19 pandemic in early 2020 there was a drastic reduction in the number of dengue cases in Sri Lanka, with an increase towards the end of 2021. We sought to study the contribution of virological factors, human mobility, school closure and mosquito factors in affecting these changes in dengue transmission in Sri Lanka during this time. Methods and findings: To understand the reasons for the differences in the dengue case numbers in 2020 to 2021 compared to previous years, we determined the association between the case numbers in Colombo (which has continuously reported the highest number of cases) with school closures, stringency index, changes in dengue virus (DENV) serotypes and vector densities. There was a 79.4% drop in dengue cases from 2019 to 2020 in Colombo. A significant negative correlation was seen with the number of cases and school closures (Spearman’s r=-0.4732, p=<0.0001) and a negative correlation, which was not significant, between the stringency index and case numbers (Spearman’s r= -0.3755 p=0.0587). There was no change in the circulating DENV serotypes with DENV2 remaining the most prevalent serotype by early 2022 (65%), similar to the frequencies observed by end of 2019. The Aedes aegypti premise and container indices showed positive but insignificant correlations with dengue case numbers (Spearman r= 0.8827, p=0.93). Conclusions: Lockdown measures, especially school closures seemed to have had a significant impact on the number of dengue cases, while the vector indices had a limited effect.

Simultaneous co-circulation of two genotypes of dengue virus serotype 3 causing a large outbreak in Sri Lanka in year 2023

“…Viral RNA was extracted from serum samples using MagMAX™ viral nucleic acid isolation kit (Applied Biosystems, USA, Cat: A48310) and an automated KingFisher™ Flex purification system (Applied Biosystems, USA). Quantitative real time PCR was performed using oligonucleotide primers published by the CDC with slight modifications as described previously (4,11). A dual labelled probe for detection of DENV serotypes 1 to 4 was used (Life technologies, USA) based on published sequences (Life Technologies, India) (4).…”

“…The WHO named dengue as one of the top ten threats to global health in 2019 (3). However, during the COVID-19 pandemic, many countries observed a decrease in dengue incidence, reporting low to moderate levels of transmission (4). With the cessation of the global health emergency for COVID-19, the incidence of dengue has markedly increased, attributed to climate change, fragile health systems, political, economic and humanitarian crises, unplanned urbanization and population movement (5,6).…”

“…Sri Lanka has experienced regular outbreaks of dengue since 1989, with the number of cases gradually increasing over the years and spreading into different geographical locations within the country (7). The largest outbreak due to dengue was reported in 2017 with 186,101 cases, associated with the cosmopolitan strain of the dengue virus (DENV) serotype 2 (4,8). DENV-2 continued to be the predominant circulating serotype until October 2019.…”

“…DENV-2 continued to be the predominant circulating serotype until October 2019. DENV-3 began to emerge towards the end of October, with an increase in the number of dengue cases, with a total of 105,049 cases being reported (4). 20,718 cases (one fifth) were reported from Colombo, which is usually the district with the highest incidence.…”