Dengue Incidence and Aedes Vector Collections in Relation to COVID-19 Population Mobility Restrictions

Abstract

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.

Societal Factors Constraining the Control of COVID-19 and Mosquito and Tick-Borne Diseases

“…R0 is directly related to the rate of dengue transmission and therefore the number of dengue cases in the population. Reduced oviposition as a result of decreased blood feeding is consistent with diminished larval collections from ovitraps in Jaffna city [34,35], which was also independently observed in the western Colombo district [36], during the lockdown in Sri Lanka.…”

“…However, the incidence of dengue incidence markedly decreased in all districts of Sri Lanka during the COVID-19 lockdown [34][35][36][37]. An 89% reduction in the number of predicted dengue cases during the most drastic lockdown period from March 2020 to April 2021 in the northern Jaffna district (Figure 4) was also accompanied by an 89% drop in Aedes larvae collected from ovitraps in Jaffna city [34,35]. period B), but removed altogether with the full opening of all schools from 22 November 2021 onward (period C).…”

“…In particular, diminished access of Aedes vectors to blood meals in public places like schools, transport hubs, shops, and temples during the COVID-19 lockdown were postulated to reduce vector densities and vector survival and therefore dengue transmission [34,35]. Additionally, infection of uninfected Aedes vectors through feeding on infected persons, and infection of uninfected persons by infected Aedes vectors in new locations are both promoted by population mobility, and could have contributed to reduced dengue incidence during the COVID-19 lockdown.…”

“…The early expectation of epidemiologists, held also by the WHO, that the incidence of dengue and malaria will increase due to a collapse of vector control programmes during the COVID-19 pandemic [31], was therefore not borne out in India and Sri Lanka. From the perspective of more effective dengue control in Sri Lanka, India and other countries with similar dengue epidemiology, it would appear that this early prevalent view [31] detracts from experimental findings [34,35] which strongly suggest that dengue control measures involving Aedes vector larval source reduction need to be more stringently applied in public places where people congregate.…”

Resistance to the larvicide temephos and altered egg and larval surfaces characterize salinity-tolerant Aedes aegypti

“…Dengue-endemic Sri Lanka and its northern peninsular Jaffna district (Supplementary Fig. 1 ), recorded 105,049 and 8261 dengue cases respectively in 2019 5 – 7 , but the numbers decreased sharply and temporarily in 2020 and 2021 during COVID-19-related movement restrictions 7 , 8 . Aedes aegypti and the secondary arboviral vector Aedes albopictus were recently shown to lay eggs and undergo preimaginal development in brackish water (BW) habitats of up to 15 g/L salt in the 1100 km 2 Jaffna peninsula 6 , 9 – 12 , with FW, BW and saline water respectively defined as containing < 0.5, 0.5–30 and > 30 g/L salt 9 .…”