Q&A: Research about COVID-19 transmission in animals is ‘urgently needed’
The U.S. Department of Agriculture’s National Veterinary Services Laboratories has confirmed a case of COVID-19 in a tiger at a zoo in New York, according to a statement on their website. The case represents the first instance of a tiger being infected with COVID-19.
According to the CDC, zoonotic diseases can spread from animals to humans via direct and indirect contact, vector-borne sources like ticks and foodborne and waterborne sources. CDC data also show that children aged less than 5 years, adults aged 65 years and older, people with weakened immune systems and pregnant women are also at particularly high risk for zoonotic disease.
Infectious Disease News Editorial Board Member Arnon Shimshony, DVM, professor of veterinary medicine at Hebrew University’s Koret School of Veterinary Medicine, spoke with Healio about current and future research into the transmission of COVID-19 in animals, as well as the potential for transmission to humans. – by Eamon Dreisbach
Q: From a clinical standpoint, is it worthwhile to conduct further research into the possible transmission of COVID-19 in animals?
A: Although the virus has acquired strikingly effective human-to-human infection capacity since its initial introduction from animals (from a species yet to be identified), its continued circulation in animals is yet to be clarified. This is particularly important when pets are considered.
Research into this question is operational. Two laboratories, in China and Germany, have already published preliminary results of their experimental infection trials. Combined, the results have indicated that cats, as well as ferrets and bats, are susceptible to SARS-CoV-2 inoculation; dogs, pigs, chickens and ducks are not. Furthermore, the Chinese trials suggested that sentinel cats got contact-infected.
In view of the potentially serious consequences of even the slightest exposure of the (unvaccinated) elderly to SARS-CoV-2, “ifs” and “probably” in the guidelines, in relation to pets, deserve to be minimized. This may become essential when the current movement restrictions for other segments of the population are relieved or discontinued. Priority should be given to the study of viral and clinical course of infection in cats: minimal infection dose, potential virus propagation and dissemination capacity, virus particles exhaled or excreted through other routes (eg, feces) and more.
The World Organisation for Animal Health’s (OIE’s) ad-hoc group for COVID-19 stipulated the following for research and investigations:
- Identify the animal reservoir and intermediate host through surveillance/investigation strategies;
- Transmission pathways;
- Host range;
- Dynamics of wildlife trade;
- Possible role of livestock and;
- Possible role of companion animals in epidemiology of human disease.
Some of these subjects have already been addressed.
Q: Have we seen transmission from humans to animals (or vice versa) with other coronaviruses?
A: During the initial SARS event in 2003 to 2004, caused by SARS-CoV-1, domestic cats living in the Amoy Gardens apartment block in Hong Kong, where more than 100 residents contracted SARS, were found to be infected without visible clinical signs. Later, cat experimental animal models, in addition to macaque and ferret models, were developed, allowing for comparative pathogenesis studies for SARS–CoV-1 infections and testing of different interventions. No cases of human infections from cats were reported.
Six coronaviruses have been known to infect humans before the COVID-19 event, namely 229E, NL63, HKU1, OC43, SARS-CoV and MERS-CoV, of which the latter two have been identified as zoonotic and exhibiting a high mortality rate (the source animals being civet cats and camels, respectively). OC43, the more prevalent human coronavirus causing the “common cold,” has been shown to be closely related to canine respiratory coronavirus (CRCoV) and, in particular, to bovine coronavirus (BCoV), but they have not shown interspecies cross-infection.
Q: Do you believe transmission of the virus could be possible from an animal to a human?
A: All four companion animals confirmed, so far, globally as COVID-19 cases (two dogs and a cat in Hong Kong and a cat in Belgium) were found to get infected by SARS-CoV-2 from their owners. There is, at present, not a single case reported as an animal-to-human case (zoonotic). The OIE stated that there is no evidence that dogs or cats are playing a role in the spread of this human disease; however, in line with the old aphorism, "Absence of evidence is not evidence of absence.” To close the knowledge gap, further studies are required urgently.
Q: Does this development mean anything for clinicians?
A: Clinicians should advise their patients to keep their pets indoors. Preferably, the relevant veterinary practitioner should be informed about the owner’s COVID-19 case, to decide about the need to test the pet and/or report to the authorities. At present, Hong Kong is the only territory requiring isolation of such pets.
Q: What message do you have for the general public regarding the infection of animals with COVID-19?
A: When handling and caring for animals, basic hygiene measures should always be implemented. This includes hand-washing before and after being around or handling animals, their food or supplies, as well as avoiding kissing, licking or sharing food.
It is advisable to keep animals, just like humans, at a social distance from other animals and humans. An animal can carry the virus just as objects could. Also avoid freely walking the dog as well as allowing the dog to be patted by other people. Feces should be hygienically removed from the environment.
Keep pets of infected patients indoors as much as possible while avoiding close contact between the patient and others with these animals, minimizing contact with them and complying with all hygiene measures.
In the case of a hospital admission by the owner, the pet should be taken care of locally in the familiar environment by a family member or acquaintance.
Dogs or cats with COVID-19 have become infected by close contact with an infected person. They should be quarantined or euthanized.
Last but not least: Stray cats should not have access to the premises of nursing homes for the elderly. Cats of the residents should be kept permanently indoors.
CDC. Zoonotic diseases. https://www.cdc.gov/onehealth/basics/zoonotic-diseases.html. Accessed April 8, 2020.
United States Department of Agriculture. USDA statement on the confirmation of COVID-19 in a tiger in New York. https://www.aphis.usda.gov/aphis/newsroom/news/sa_by_date/sa-2020/ny-zoo-covid-19. Accessed April 8, 2020.
Disclosure: Shimshony reports no relevant financial disclosures.