Review of animal transmission experiments of respiratory viruses: Implications for transmission risk of SARS-COV-2 in humans via different routes

Exploring transmission risk of different routes has major implications for epidemic control. However, disciplinary boundaries have impeded the dissemination of epidemic information, have caused public panic about air transmission, air-conditioning transmission, and environment-to-human transmission, and have triggered hygiene theater. Animal experiments provide experimental evidence for virus transmission, but more attention is paid to whether transmission is driven by droplets or aerosols and using the dichotomy to describe most transmission events. Here, according to characteristics of experiment setups, combined with patterns of human social interactions, we reviewed and grouped animal transmission experiments into four categories-close contact, short-range, fomite, and aerosol exposure experiments-and provided enlightenment, with experimental evidence, on the transmission risk of severe acute respiratory syndrome coronavirus (SARS-COV-2) in humans via different routes. When referring to air transmission, context should be showed in elaboration results, rather than whether close contact, short or long range is uniformly described as air transmission. Close contact and short range are the major routes. When face-to-face, unprotected, horizontally directional airflow does promote transmission, due to virus decay and dilution in air, the probability of air conditioning transmission is low; the risk of environment-to-human transmission highly relies on surface contamination and human behavior based on indirect path of fomite-hand-mucosa or conjunctiva and virus decay on surfaces. Thus, when discussing the transmission risk of SARS-CoV-2, we should comprehensively consider the biological basis of virus transmission, environmental conditions, and virus decay. Otherwise, risk of certain transmission routes, such as long-range and fomite transmission, will be overrated, causing public excessive panic, triggering ineffective actions, and wasting epidemic prevention resources.

Automated summary

Exploring transmission risk of different routes is crucial for epidemic control, but disciplinary boundaries hinder the dissemination of epidemic information and have led to public panic about various modes of transmission. Animal experiments provide evidence for virus transmission, but there is a focus on the dichotomy of droplet and aerosol transmission. This study reviews and categorizes animal transmission experiments and provides insight into the transmission risk of SARS-COV-2 in humans via different routes.