Distribution and viral load of canine respiratory coronavirus in naturally infected dogs: evidence from clinical sampling sites and tissue detection

Abstract

Canine respiratory coronavirus (CRCoV) is a respiratory pathogen associated with the canine infectious respiratory disease complex (CIRDC). Although CRCoV is primarily considered a respiratory virus, its distribution beyond the respiratory tract remains poorly understood. This study investigated the prevalence, anatomical distribution, viral loads, and tissue localization of CRCoV in naturally infected dogs using both antemortem and postmortem samples. A total of 267 dogs were sampled using nasal (NS), oropharyngeal (OS), and rectal swabs (RS). CRCoV RNA was detected in 10.49% of dogs tested by reverse transcription quantitative PCR (RT-qPCR), and viral loads were quantified using reverse transcription digital PCR (RT-dPCR). CRCoV RNA was detected across all sampling routes, with significantly higher viral loads in NS than in OS ( p < 0.001) and RS ( p < 0.001), and higher viral loads in OS than in RS ( p < 0.01). Longitudinal sampling demonstrated that viral RNA became undetectable within one week in most dogs; however, viral shedding persisted in one severely ill dog that subsequently died. In postmortem samples, CRCoV RNA was detected in both respiratory and extra-respiratory tissues, and was successfully localized within the mesenteric lymph node by in situ hybridization, consistent with possible extra-respiratory detection. These findings provide new insight into the tissue distribution of CRCoV in naturally infected dogs, demonstrating a predominance in the respiratory tract while suggesting possible extra-respiratory detection. Further studies are needed to determine the biological significance of these findings and to confirm whether CRCoV undergoes systemic dissemination or active replication beyond the respiratory tract.