OBJECTIVE To examine the susceptibility of cultured primary equine bronchial epithelial cells (EBECs) to a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pseudovirus relative to human bronchial epithelial cells (HBECs). SAMPLE Primary EBEC cultures established from healthy adult horses and commercially sourced human bronchial epithelial cells (HBECs) were used as a positive control. METHODS Angiotensin-converting enzyme 2 (ACE2) expression by EBECs was demonstrated using immunofluorescence, western immunoblot, and flow cytometry. EBECs were transduced with a lentivirus pseudotyped with the SARS-CoV-2 spike protein that binds to ACE2 and expresses the enhanced green fluorescent protein (eGFP) as a reporter. Cells were transduced with the pseudovirus at a multiplicity of infection of 0.1 for 6 hours, washed, and maintained in media for 96 hours. After 96 hours, eGFP expression in EBECs was assessed by fluorescence microscopy of cell cultures and quantitative PCR. RESULTS ACE2 expression in EBECs detected by immunofluorescence, western immunoblotting, and flow cytometry was lower in EBECs than in HBECs. After 96 hours, eGFP expression in EBECs was demonstrated by fluorescence microscopy, and mean ΔCt values from quantitative PCR were significantly (P < .0001) higher in EBECs (8.78) than HBECs (3.24) indicating lower infectivity in EBECs. CLINICAL RELEVANCE Equine respiratory tract cells were susceptible to cell entry with a SARS-CoV-2 pseudovirus. Lower replication efficiency in EBECs suggests that horses are unlikely to be an important zoonotic host of SARS-CoV-2, but viral mutations could render some strains more infective to horses. Serological and virological monitoring of horses in contact with persons shedding SARS-CoV-2 is warranted.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causal agent of COVID-19, can infect animals by binding to the angiotensin-converting enzyme 2 (ACE2). Equine infection appears possible due to high homology (≈97%) between human and equine ACE2, evidence ofin vitroinfection in cell lines expressing equine ACE2, and evidence of seroconversion in horses after exposure to persons infected with SARS-CoV-2. Our objective was to examine susceptibility of cultured primary equine bronchial epithelial cells (EBECs) to a SARS-CoV-2 pseudovirus relative to human bronchial epithelial cells (HBECs; positive control). ACE2 expression in EBECs detected by immunofluorescence, western immunoblotting, and flow cytometry was lower in EBECs than in HBECs. EBECs were transduced with a lentivirus pseudotyped with the SARS-CoV-2 spike protein that binds to ACE2 and expresses the enhanced green fluorescent protein (eGFP) as a reporter. Cells were co-cultivated with the pseudovirus at a multiplicity of infection of 0.1 for 6 hours, washed, and maintained in media. After 96 hours, eGFP expression in EBECs was demonstrated by fluorescence microscopy, and mean Δ Ct values from quantitative PCR were significantly (P < 0.0001) higher in HBECs (8.78) than HBECs (3.24) indicating lower infectivity in EBECs. Equine respiratory tract cells were susceptible to infection with a SARS-CoV-2 pseudovirus. Lower replication efficiency in EBECs suggests that horses are unlikely to be an important zoonotic host of SARS-CoV-2, but viral mutations could render some strains more infectious to horses. Serological and virological monitoring of horses in contact with persons shedding SARS-CoV-2 is warranted.