Clinical evidence suggesting varying levels of susceptibility to SARS-CoV-2 (COVID-19) virus infection in animals
Understanding of COVID-19 transmission, particularly as it relates to pets, is rapidly evolving. COVID-19 is primarily a human disease that is transmitted directly from person to person in respiratory droplets.1–4 Leading experts (including the AVMA, CDC and OIE) continue to report that there is no evidence of pets playing a significant role in spreading COVID-19 disease to humans. However, there is growing evidence that pets, especially cats and ferrets, can be at risk of being infected with the SARS-CoV-2 virus following exposure to infected humans in rare cases.
In light of this new information, IDEXX Reference Laboratories is making the IDEXX SARS-CoV-2 (COVID-19) RealPCR Test available to veterinarians, enabling a rapid, reliable and specific testing option for rare cases when certain criteria are met.
On 11 March 2020, the World Health Organization officially declared COVID-19 a pandemic. At that point, it was believed that pets were not at risk of contracting COVID-19 from their owners. In the weeks that followed, however, several isolated reports of reverse zoonotic transmission to animals emerged, including two dogs and a cat in Hong Kong, a cat in Belgium and a tiger (and possibly other large felids) in the Bronx Zoo.5–7 There is evidence, including seroconversion in one dog, consistent clinical signs in the tiger and the Belgian cat, and positive virus isolation in the other dog, that at least some of these cases are true infection, not just environmental contamination. In addition, recent experimental infection studies have demonstrated that cats and ferrets can be infected with the SARS-CoV-2 virus and can transmit the infection to other cats or ferrets.8,9 Infected cats and ferrets may be asymptomatic or may have fever, mild respiratory signs or gastrointestinal signs. Neither of the two infected dogs showed clinical signs. A serologic survey suggests that asymptomatic infection in cats may be more common than previously suspected.10 Dogs appear to be more resistant to infection and especially to clinical disease compared to cats or ferrets, likely due to differences in their ACE receptors, which the virus uses to enter the cells.8,11
Based on what has been seen so far, natural human-to-pet infection appears to be very rare, is often asymptomatic and generally of shorter duration than human infections. IDEXX Reference Laboratories’ surveillance data,12 which demonstrates no SARS-CoV-2 positive results in over 5,000 patient specimens submitted for respiratory PCR panels across North America, Europe and South Korea between 14 February and 1 April, supports the expert opinion that reverse zoonotic transmission from humans to pets is uncommon.
IDEXX’s guidance, aligned with that of medical experts, is that veterinarians should order the IDEXX SARS-CoV-2 (COVID-19) RealPCR Test after consultation with a public health authority (for example, a state public health veterinarian in the United States) and three specific criteria are met: the pet is living in a household with a human who has COVID-19 or has tested positive for the virus; the pet has already been tested for more common infections that have been ruled out by a veterinarian; and the pet (especially cats and ferrets) is showing clinical signs consistent with COVID-19. Testing of symptomatic pets in COVID-19 infected households may not always be indicated as clinical signs, when present, may be mild and transient. The IDEXX SARS-CoV-2 (COVID-19) RealPCR Test may be considered when investigating respiratory disease in ferrets or cats after more common respiratory infections have been ruled out. Testing should be limited to those animals with known or strongly suspected COVID-19 exposure.
- Centers for Disease Control and Prevention. Coronavirus Disease 2019 (COVID-19). www.cdc.gov/COVID19. Accessed 19 April 2020.
- World Health Organization. Coronavirus disease (COVID-19) outbreak. www.who.int/emergencies/diseases/novel-coronavirus-2019. Accessed 19 April 2020.
- American Veterinary Medical Association. COVID-19: What veterinarians need to know. www.avma.org/coronavirus. Accessed 19 April 2020.
- World Small Animal Veterinary Association (WSAVA). The new coronavirus and companion animals – advice for WSAVA members. www.wsava.org/news/highlighted-news/the-new-coronavirus-and-companion-animals-advice-for-wsava-members. Accessed 19 April 2020.
- Questions and answers on the 2019 coronavirus disease (COVID-19): Surveillance and events in animals. World Organisation for Animal Health (OIE) website. www.oie.int/en/scientific-expertise/specific-information-and-recommendations/questions-and-answers-on-2019novel-coronavirus. Updated 9 April 2020. Accessed 19 April 2020.
- Low-level of infection with COVID-19 in pet dog [news release]. Hong Kong: Government of the Hong Kong Special Administrative Region; 4 March 2020. www.info.gov.hk/gia/general/202003/04/P2020030400658.htm. Accessed 19 April 2020.
- USDA statement on the confirmation of COVID-19 in a tiger in New York. USDA Animal and Plant Health Inspection Service website. www.aphis.usda.gov/aphis/newsroom/news/sa_by_date/sa-2020/ny-zoo-covid-19. Updated 6 April 2020. Accessed 19 April 2020.
- Shi J, Wen Z, Zhong G, et al. Susceptibility of ferrets, cats, dogs and other domesticated animals to SARS-coronavirus 2. Science. 2020;eabb7015. doi:10.1126/science.abb7015
- Kim Y, Kim SG, Kim SM, et al. Infection and rapid transmission of SARS-CoV-2 in ferrets [published online ahead of print 5 April 2020]. Cell Host Microbe. 2020;S1931-3128(20)30187-6. doi:10.1016/j.chom.2020.03.023
- Zhang Q, Zhang H, Huang K, et al. SARS-CoV-2 neutralizing serum antibodies in cats: a serological investigation [preprint]. doi:10.1101/2020.04.01.021196
- Wan Y, Shang J, Graham R, Baric RS, Li F. Receptor recognition by the novel coronavirus from Wuhan: An analysis based on decade-long structural studies of SARS coronavirus. J Virol. 2020;94(7):e00127-20. doi:10.1128/JVI.00127-20
- COVID-19 RealPCR Validation Studies: sequence blast analyses and cross-reactivity studies. March 2020. Data on file at IDEXX Laboratories, Inc. Westbrook, Maine USA.