Essential COVID-19 Research Topics

When, in addition to reports of infected dogs, initial reports emerged of two cats testing positive for SARS-CoV-2,^1,2 so too did questions regarding what species could actually be infected. Subsequent research in China suggested that cats could both be infected and were also able to experimentally transmit the virus.³ A pre-peer review study evaluated samples from a cross-section of cats in Wuhan, China (n = 102), and 14.7% were seropositive for the SARS-CoV-2 receptor binding domain by indirect ELISA; there was no FIPV cross-reactivity observed.⁴ Lions and tigers also appear to be capable of infection, as several lions and tigers in the Bronx Zoo were reportedly exhibiting respiratory clinical signs, with at least one tiger confirmed positive for SARS-CoV-2 by the USDA; an asymptomatic zookeeper was believed to be the source of infection.⁵  Additional research examining infection and transmission potential in dogs, cats, and other companion animal species, particularly ferrets,³ is essential to understanding multi-species infection risk.

The Bronx Zoo infections in large cats appeared to corroborate the multi-species study that suggested cats could transmit SARS-CoV-2 to one another via respiratory droplets,³ as it is unlikely that a single zookeeper could directly transmit to multiple cats at once. It is unclear whether sustained transmission is possible in domestic or wild cats and whether they could ultimately serve as reservoir hosts. Elucidating animal-to-animal transmission dynamics is critical in implementing effective disease control programs. 

Similarly, it is undetermined whether companion animals will be able to sustain adequate viral load and generate enough viable, aerosolized, or transmissible virus to infect human beings. If future research suggests that companion animals are effective sources for human infection, or (worse yet) become a reservoir species, the paradigm for handling these animals could change dramatically.

Although COVID-19 disease is predominantly respiratory in nature, gastrointestinal signs have been documented in both human clinical cases⁶ as well as a probable feline clinical case.⁷ Reports of fecal PCR-positive samples in humans have suggested that SARS-CoV-2 may replicate in the GI tract.^8,9

Potential fecal-oral transmission will affect risk management in the veterinary clinical setting. 

The Wuhan study indicated that 14% of surveyed cats were seropositive⁴;  however, it is unclear which of these cats were clinically affected, as lockdown measures in China likely prevented veterinary visits. The role of potential subclinical companion animal carriers needs to be further characterized.

The Wuhan serological study identified no cross-reactivity between antibodies to SARS-CoV-2 and FIP coronavirus,⁴ but it is unclear whether this is applicable on a broader scale. Other coronavirus antibodies may play a role in preventing or enhancing disease, particularly in species that may be used as animal models to test vaccines and therapeutics. Cross-reactivity will also need to be distinguished from cross-protection; although antibodies may be present, whether they actually prevent or enhance disease requires careful study.

The level of environmental contamination observed in cruise ships and hospital environments strongly suggests that animals may function as fomites. With viral RNA detected on cabin surfaces 17 days after an infected passenger left a cruise ship,¹⁰ and environmental samples from hospitals being positive from many locations (including air ducts),¹¹ it would be unlikely for an animal from a home with a confirmed SARS-CoV-2 case not to harbor virus particles, particularly on parts in contact with the ground and/or the owner (eg, pads, muzzle, areas without a hair-coat barrier).

It is now clear companion animals can become infected, likely from their owners and possibly secondary to close contact, environmental contamination, aerosols, or a combination thereof. Determining length of virus survival time on an animal’s hair coat is a key step in determining transmission risk.  

Initial guidance from the AVMA¹² suggested that there was no evidence that SARS-CoV-2 could be transmitted from exposure to the animal’s fur, but there was also no evidence showing that it could not be transmitted in that manner. There has been evidence of contamination on similarly porous PPE materials.¹¹   

One may speculate that an oily hair coat may actually prolong virus survival and allow for efficient transfer to hands and other contact points. Whereas the virus may survive for a shorter period on a porous hair coat than it would on a hard surface, leash, or collar, survival times may be similar to that of cardboard (≤24 hours).¹³ Some nurses in Wuhan shaved their heads to prevent transfer of virus via long hair.¹⁴ 

Given the worldwide PPE shortage, an understanding of additional precautions when handling subclinical veterinary patients or any species potentially able to spread SARS-CoV-2 to other animals and/or humans is necessary. At minimum, clinically-affected pets and pets from owners symptomatic for COVID-19, should be handled as potentially infectious to other pets or human beings at least until there is a clear understanding of potential routes of infection and infectious dose required for each route. Ensure that client service representatives query pet owners about their own health status along with the pet’s status. At minimum, a lab coat or surgical gown, gloves, and surgical mask are recommended PPE for clinically affected pets and thorough hand washing should be standard practice.