Implications of the COVID-19 lockdown on dengue transmission and the occurrence of Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) in Malaysia

The impact of movement restrictions (MRs) during the COVID-19 lockdown on the existing endemic infectious disease dengue fever has generated considerable research interest. We compared the curve of weekly epidemiological records of dengue incidences during the period of lockdown to the trend of previous years (2015 to 2019) and a simulation at the corresponding period that expected no MRs and found that the dengue incidence declined significantly with a greater magnitude at phase 1 of lockdown, with a negative gradient of 3.2-fold steeper than the trend observed in previous years, indicating that the control of population movement did reduce dengue transmission. However, starting from phase 2 of lockdown, the dengue incidences demonstrated an elevation and earlier rebound by 4 weeks and grew with an exponential pattern. Together with our data on Aedes mosquitoes, we proposed a stronger diffusive effect of vector dispersal that led to a higher rate of transmission. From the result of the Aedes survey using human landing caught (HLC), we revealed that Aedes albopictus is the predominant species for both indoor and outdoor environments, with the abundance increasing steadily during the period of lockdown. We only recovered Aedes aegypti from the indoor environment, which is relatively fewer than Ae. albopictus, by contrasting their population growth, which suggested that Ae. albopictus invaded and colonized the habitat of Ae. aegypti during the period of lockdown. These findings would help authorities review the direction and efforts of the vector control strategy. Author summaryCOVID-19 pandemic is taking hold globally and dengue fever transmission is not on the top of the list of concerns. With a partial lockdown implemented by Malaysia on 18 March, we postulate the movement restrictions (MRs) of people in large-scale would hamper the regular dengue transmission and aim to reveal the impact of MRs on both dengue incidences and Aedes mosquitoes. We showed a significant decline of dengue incidences at the beginning of lockdown but later rebounded at an earlier time and higher rate compared to the corresponding period of previous years. Our result also reviews how adaptive the Ae. albopictus with the movement of the host, as the human contained in the house, the abundance of the mosquitoes increased significantly during the period of lockdown. We also suggest that Ae. albopictus could be the key substitution vector that contributes significantly to dengue virus circulation, and therefore, the vector control direction and strategies should be redesigned.