Experimental innoculation of young calves with SARS-CoV-2

Authors: Falkenberg, Shollie; Buckley, Alexandra; LAVERACK, MELISSA - Cornell University; MARTINS, MATHIA - Cornell University; Palmer, Mitchell; Lager, Kelly; DIEL, DIEGO - Cornell University

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2021
Publication Date: 3/9/2021
Citation: Falkenberg, S.M., Buckley, A.C., Laverack, M., Martins, M., Palmer, M.V., Lager, K.M., Diel, D. 2021. Experimental innoculation of young calves with SARS-CoV-2. Viruses. 13(3). Article 441. https://doi.org/10.3390/v13030441.
DOI: https://doi.org/10.3390/v13030441

Interpretive Summary: Numerous questions have been raised about the source and potential reservoirs of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), due to the potential link to the seafood market in China where many live wild animal species are sold. Therefore, the susceptibility of animals to the virus has received significant interest. Importantly, host prediction studies based on receptor binding of the virus, have shown that cattle may be susceptible to SARS-CoV-2. The goal of the current study was to inoculate naïve calves via two different inoculation routes (intratracheal and intravenous) to evaluate susceptibility as determined by evaluation of blood, urine, fecal, nasal swab samples as well as tissues samples as the conclusion of the study for detection of the virus. Serum was also evaluated for neutralizing antibody titers as a method to determine recognition by the immune system. Results of the current study suggest that cattle are not susceptible to SARS-CoV-2 as virus was not detected in most of the samples collected. A nasal swab and a lymph node was positive in one calf in the intratracheal group and one nasal swab was positive for a calf in the intravenous group. Furthermore, neutralizing titers were not detected at conclusion of the study suggesting lack of recognition of the virus by the immune system. Collectively these results indicate that there was no productive replication of SARS-CoV-2 in inoculated calves.

Technical Abstract: The host range of SARS-CoV-2 and the susceptibility of animal species to the virus are topics of great interest to the international scientific community. The angiotensin I converting enzyme 2 (ACE2) protein is the major receptor for the virus, and sequence and structural analysis of the protein has been performed to determine its cross-species conservation. Based on these analyses, cattle have been implicated as a potential susceptible species to SARS-CoV-2 and have been reported to have increased ACE2 receptor distribution in the liver, kidney, and lungs. The goal of the current study was to determine the susceptibility of cattle to SARS-CoV-2 utilizing inoculation routes that facilitated exposure to tissues with increased ACE2 receptor distribution. For this, colostrum deprived calves approximately 6 weeks of age were inoculated via the intratracheal or intravenous routes. Nasal and rectal swab samples, as well as blood and urine samples were collected over the course of the study to evaluate viral shedding, viremia and seroconversion. Pyrexia was used as the primary criteria for euthanasia and tissue samples were collected during necropsy. Importantly, SARS-CoV-2 RNA was detected in only two nasal swab samples collected on days 3 and 10 post-inoculation (pi) in two calves, one calf in the intratracheal group and the other calf in the intravenous group, respectively. Additionally, the calf in intratracheal group that was positive on day 3 pi, also had a positive tracheobronchial lymph node on day 9 pi. Viral nucleic acid load on these samples, based on PCR cycle threshold values were low and no infectious virus was recovered from the samples. These results suggest that there was no productive replication of SARS-CoV-2 in calves following intratracheal and intravenous inoculation.