Intravenous, intratracheal, and intranasal inoculation of swine with SARS-CoV-2

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

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2021
Publication Date: 7/30/2021
Citation: Buckley, A.C., Falkenberg, S.M., Martins, M., Laverack, M., Palmer, M.V., Lager, K.M., Diego, D. 2021. Intravenous, intratracheal, and intranasal inoculation of swine with SARS-CoV-2. Viruses. 13(8). https://doi.org/10.3390/v13081506.
DOI: https://doi.org/10.3390/v13081506

Interpretive Summary: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus that causes coronavirus disease 19 (COVD-19) in humans. SARS-CoV-2 was first reported in Wuhan, Hubei province, China, in December 2019 and some of the first reported cases had an epidemiological link to a wet market where several live animal species were sold. Due to the presumed zoonotic origin of SARS-CoV-2, the susceptibility of animals and their potential to act as reservoirs and/or intermediate hosts has received significant interest worldwide. Due to interactions with people, the susceptibility of companion animals and livestock to SARS-CoV-2 infection was a priority. Pigs are susceptible to multiple coronaviruses, have a history of transmission of viruses to humans, and have been used as an animal model for other human infectious diseases; therefore, we performed a SARS-CoV-2 challenge experiment in swine to determine susceptibility. Pigs were challenged via intravenous, intratracheal, or intranasal routes of inoculation (n=4/route). No pigs developed clinical signs, but at least one pig in each group had one or more PCR positive nasal/oral swabs or rectal swabs after inoculation. All pigs in the intravenous group developed a transient neutralizing antibody titer, but only three other challenged pigs developed titers. No gross or histologic changes were observed in tissue samples collected at necropsy. In addition, no PCR positive samples were positive by virus isolation. Challenged animals were unable to transmit virus to naïve contact animals. These results as well as results from other pig challenge studies indicate that it is unlikely swine are a reservoir or contributing to the epidemiology and spread of SARS-CoV-2 in the human population. Continued research to determine animal species that could serve as reservoirs for the virus or play a role in transmission will remain important.

Technical Abstract: Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the susceptibility of animals and their potential to act as reservoirs or intermediate hosts for the virus was of significant interest. Due to amount of human contact, the susceptibility of companion animals and livestock species was a research priority. Pigs are susceptible to multiple coronaviruses and have been used as an animal model for other human infectious diseases. Research groups have experimentally challenged swine with SARS-CoV-2 with results suggesting limited to no viral replication. For this study, a SARS-CoV-2 isolate shown to replicate in another animal species, white-tailed deer, was utilized for inoculation. Pigs were challenged via intravenous, intratracheal, or intranasal routes of inoculation (n=4/route). No pigs developed clinical signs, but at least one pig in each group had one or more PCR positive nasal/oral swabs or rectal swabs after inoculation. All pigs in the intravenous group developed a transient neutralizing antibody titer, but only three other challenged pigs developed titers greater than 1:8. No gross or histologic changes were observed in tissue samples collected at necropsy. In addition, no PCR positive samples were positive by virus isolation. Challenged animals were unable to transmit virus to naïve contact animals. The data from this experiment as well as from other laboratories supports that swine are not likely to play a role in the epidemiology and spread of SARS-CoV-2.