The Singing Cicadas at 10 P.m.: Urban Night, Wild Habitants, and COVID-19

Where did SARS-CoV-2 come from? Did it spread to 'Patient Zero' through proactive human-animal contact such as wildlife trades, hunting, or bushmeat consumption? Why did humans endure an increasing number of zoonotic diseases in the past few decades? In this article, we propose a new hypothesis that differs from the current ‘market hypothesis’ in the literature. In the last twenty years, zoonotic pathogens such as the severe acute respiratory syndrome (SARS) coronavirus, the Middle East respiratory syndrome (MERS) coronavirus and most recently, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused regional to global outbreaks of infectious diseases. As natural animal reservoirs, bats harbor the largest number of zoonotic viruses among all mammalian orders, while they have a unique and delicate immune system to maintain functioning. Some bat species roost in proximity with human settlements, including urban communities and surrounding areas that are most impacted by anthropogenic activities. Here we review the current knowledge and observational changes in the behaviors of wild habitants, including bats and other wild species, caused by environmental stress factors such as artificial lighting and noise pollution, with a focus on their implications in the spillover of zoonotic pathogens to humans. Artificial lighting attracts insectivorous bats to congregate around streetlights and lit areas, resulting in changes in their diets and more likelihood of contact with humans and animals. Meanwhile, many bat species avoid lit areas by expending more energies on commuting and foraging. Noise pollution has similar negative effects on the behaviors of bats. Bats exposed to chronic noise pollution have weakened immune functions, increased virus shedding, as well as declined immunity during pregnancy, lactation, and other vulnerable periods due to noised-induced stress. In addition to bats, other wild species exposed to artificial lighting and noise pollution show stress-induced behaviors and deteriorated health and survival. Their increased shedding of viral pathogens and likelihood of contacts with humans and domestic animals may exacerbate the spillover of zoonotic pathogens to humans. Overall, the existing evidence leads to the hypothesis that artificial lighting and noise pollution, among a plethora of persisting environmental stress factors, may have been overlooked long-term contributors to the spillover of zoonotic pathogens from wild habitants to humans in urban environments.