SARS-CoV-2: Why, when, and how to test veterinary patients
Source: dvm360 Karen Todd-Jenkins, VMD
As testing for SARS-CoV-2 becomes more widespread among the American population, it’s only natural to wonder whether veterinarians should be testing more of our patients. If the answer to that question is yes, then how should we decide which patients should be tested? And what are the recommended testing procedures?
What’s the real disease risk for pets? Do pets pose a risk to humans?
Disease risk should be a consideration when deciding whether to test. But despite active research, questions about the true risk of SARS-CoV-2 in pets, and whether pets can spread the illness to other pets or humans, remain unanswered.
Worldwide, millions of people have been diagnosed with SARS-CoV-2, but so far there have been only a few reports of positive test results in companion animals. Case reports and experimental studies have suggested that cats, dogs and ferrets can test positive for SARS-CoV-2, but field study data are still limited. Dr. Weese warned that surveillance studies are critically important when trying to answer these questions. “Experimental studies are interesting, but we can’t rely on that,” he said. “We need field data.”
As part of a surveillance study, Idexx Laboratories tested over 5,000 samples from sick dogs, cats and horses in South Korea, the United States, Canada and Europe. So far, all those samples have been negative for SARS CoV-2. Antech Diagnostics reported in late April that two feline samples from New York State tested positive in its surveillance program. These are the only known pet cases in the United States.
Of the samples tested by Idexx, Dr. Weese noted that “we don’t know how many, if any, of these animals had possible exposure to infected humans.” He added that surveillance testing itself poses a challenge, because samples from pets should be obtained soon after (ideally within 1 to 2 weeks) a human positive case is confirmed. Because a COVID-19–positive person is advised to remain at home, surveillance testing for pets requires either that investigators enter the homes of potentially infected humans to collect pet samples or potentially exposed pets must be brought into a practice or other facility for testing. Both procedures present important logistical challenges. “That’s why these studies are developing slowly, and results are trickling in,” he said. So far, SARS-CoV-2 in animals appears to be uncommon, but the extent to which clinical disease occurs in dogs and cats is still unknown.
Spreading on a Pet's Fur?
The question of pet fur acting as a fomite was also addressed. Evidence for this type of transmission risk is limited. Dr. Sykes noted that the virus likely only lives on a pet’s coat for a few hours. However, Dr. Weese added that pets acting as fomites could be a potential concern for veterinarians. “If someone is infected and coughing on their cat, we (veterinarians) might be handing that cat a few minutes later. I think that’s where the main theoretical risk comes in. We just don’t know what the risk is. That’s one of the reasons to take extra precautions.”
Dr. Sykes echoed that advice, emphasizing that human-to-human interactions drive disease transmission. “We still have no evidence of animal-to-human transmission, but we also haven’t proven that it can’t happen. So, we still need to take precautions,” she said.
What should pet owners do if their pet develops signs?
Potential signs of COVID-19 in pets include respiratory disease, fever, vomiting, diarrhea and inappetence, especially if these signs are observed within seven to 14 days following exposure to a COVID-19–positive person. However, Dr. Sykes noted that pets presenting with these signs are more likely to be sick from something else, such as regular upper respiratory tract disease, so it’s important to consider other illnesses as part of a diagnostic evaluation.
Owners who suspect their pet may be ill should call their veterinarian. If the pet needs to be seen, someone else should bring the pet to the practice. Optimally, clinics should offer car-side or telemedicine consultations to initiate evaluation of these pets. In-contact physical exams may not always be required. “The need for examination should be based solely on the clinical status of the pet, not because of fears about COVID-19,” Dr. Weese said.
Regarding risk assessment and the need for an examination, Dr. Weese contrasted two patient scenarios. “If a dog that lives in a household with a COVID-19–positive human and routinely visits a dog park (being walked by someone else in the home) presents with a low-grade fever and mild cough, I’m not terribly worried about that dog having COVID-19. If the dog is otherwise healthy, it may not need to be seen," he said. "But if I see an indoor cat that has been very close with owners who are COVID-19 positive, and that cat develops acute-onset, severe respiratory disease, I’m more concerned about COVID-19 because that cat’s illness is less likely to have another infectious cause. That cat should probably be seen.”
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