Association of Human Mobility and Weather Conditions with Dengue Mosquito Abundance during the COVID-19 Pandemic in Hong Kong

BackgroundWhile Aedes mosquitoes, the Dengue vectors, were expected to expand their spread due to international travel and climate change, the effects of human mobility and low rainfall conditions on them are largely unknown. We aimed to assess these influences during the COVID-19 pandemic in Hong Kong, characterized by varying levels of human mobility. MethodsGoogles human mobility indices (including residential, parks and workplaces) and weather conditions (total rainfall and mean temperature) together with Aedes albopictus abundance and extensiveness monitored using Gravidtrap were obtained between April 2020 and August 2022. Distributed lag non-linear models with mixed-effects models were used to explore their influence in three areas in Hong Kong. FindingsThe relative risk (RR) of mosquito abundance was associated with low rainfall (<50 mm) after 4.5 months, with a maximum of 1.73, compared with 300 mm. Heavy rainfall (>500 mm) within 3 months was also associated with a peak of RR at 1.41. Warm conditions (21-30{degrees}C; compared with 20{degrees}C) were associated with a higher RR of 1.47 after half a month. Residential mobility was negatively associated with mosquito abundance. The model projected that if residential mobility in the year 2022 was reduced to the level before the COVID-19 pandemic, the mosquito abundance would increase by an average of 80.49% compared to the actual observation. SignificanceBoth the human mobility and the lag effect of meteorological factors can be critical for the prediction of vector dynamics, and stay-at-home policy may be useful for its control in certain regions. AUTHOR SUMMARYPrevious studies have demonstrated that both meteorological factors and human mobility were linked to the risk of Dengue transmission, with rainfall potentially exerting delayed effects. Moreover, dry conditions have been found to increase Dengue risk in recent years. However, the impact of these factors on vector (mosquito) activity remains unclear. This study assessed the effect of human mobility and rainfall on the Dengue mosquito. The Gravitrap indices were used to characterize local mosquito (Aedes Albopictus) abundance and extensiveness conditions. We used established Gravitrap indices to characterize mosquito abundance and extensiveness in Hong Kong. We found that i) the decrease in residential mobility might increase mosquito abundance and extensiveness; and ii) low rainfall (<50 mm) was associated with a higher risk of mosquito abundance after 4.5 months. Additionally, heavy rainfall was associated with increased mosquito activity risk.The future mosquito activity risk is expected to increase because of the relaxation of social distancing measures after the COVID-19 pandemic along with climate change. The results suggest that non-linear delayed effects of meteorological factors together with human mobility change can be used for the Dengue mosquito forecast. Social distancing may be a way to reduce the risk of Aedes albopictus.