Capsid and genome damage are the leading inactivation mechanisms of aerosolized porcine respiratory coronavirus at different relative humidities.

Relative humidity (RH) varies widely in indoor environments based on temperature, outdoor humidity, heating systems, and other environmental conditions. This study explored how RH affects aerosolized porcine respiratory coronavirus (PRCV), a model for coronaviruses, over a time range from 0 min to a maximum of 1 h, and the molecular mechanism behind viral infectivity reduction. These questions were answered by quantifying: (i) viral-host receptor interactions, (ii) capsid integrity, (iii) viral genome integrity, and (iv) virus infectivity. We found RH did not alter PRCV-receptor interactions. RHs 45-55% and 65-75% damaged viral genomes (2 log₁₀ reduction and 1 log₁₀ reduction, respectively, in terms of median sample value), whereas RHs 55-65% decreased capsid integrity (2 log₁₀ reduction). No apparent virion damage was observed in RH 75-85%. Two assays were used to quantify virus presence: qPCR for detecting the viral genomes and plaque-forming unit assay for detecting the virus replication. Our results indicated that the qPCR assay overestimated the concentrations of infectious viruses, and RNase treatment with long-range RT-qPCR performed better than one-step RT-qPCR. We propose that understanding the influence of RH on the stability of aerosolized viruses provides critical information for detecting and preventing the indoor transmission of coronaviruses.

Importance: Indoor environments can impact the stability of respiratory viruses, which can then affect the transmission rates. The mechanisms of how relative humidity (RH) affects virus infectivity still remain unclear. This study found RH inactivates porcine respiratory coronavirus by damaging its capsid and genome. The finding highlights the potential role of controlling indoor RH levels as a strategy to reduce the risk of coronavirus transmission.