Now that various veterinary diagnostic labs have geared up SARS-CoV-2 tests, there’s increasing discussion around if, when, how and why to test domestic animals (and actually, “where” is part of the discussion as well, so we’ll get all of those covered).
At first glance, it might seem like a strange question. Human testing is key for control so you might assume that animal testing is similarly critical. However, the epidemiology, risks and control measures are very different.
Two general messages I always emphasize are “never do a test without a (good) reason” and “never do a test without a plan to use the result.” Essentially, there should be a question that needs to be answered, and a realistic expectation that a test will help answer it.
- For example, a question could be “Does that dog have a broken leg?” The test, reason and plan would be to take a radiograph to help figure out if the bone is fractured, and how best to treat the injury.
- For COVID-19, some of the questions and reasoning might be:
- “We need to figure out how commonly SARS-CoV-2 is transmitted from infected people to their pets” so we can better understand the dynamics and risks of this virus and make appropriate recommendations for control practices in animals.
- “We need to figure out if SARS-CoV-2 is a cause of disease in cats (or other species)” so we can better understand the potential animal health aspects, and guide future clinical and infection control practices.
- “We need to look at if/how often animals admitted to shelters are infected in high-risk areas” to give us an idea of risk in these animal populations since we don’t know the exposure history for strays, to see whether there may have been movement of the virus into feral populations, and to guide shelter infection control practices.
All of these are hypothesis-driven surveillance studies that are achieved by testing specific populations, that is to say groups of animals that meet certain criteria (e.g. live with person who has or had active COVID-19 in the past week), and sampled using standard procedures (e.g. a set of oropharyngeal, nasal and rectal swabs).
Testing should NOT be done because “I’m freaked out about this virus and want my cat tested.” Sporadic clinical testing might sometimes be useful but it can also be a waste of time and effort, and can actually cause more problems if things haven’t been thought through properly.
Routine testing for SARS-CoV-2 in animals is typically discouraged by various agencies for a few reasons:
- Testing is most often considered because there’s an infected owner in the house. If that’s the case, then we don’t want anyone leaving the house and we’d rather not have them get someone to come over to get the animal (creating another human contact point).
- If the owner is infected, we still have unanswered questions about hair coat contamination of the pet. So, we need to consider that risk during transit and handling. It’s best not to have to take that risk at all if we can avoid it.
- Clinics need to be able and prepared to safely sample such an animal, based on the assumption that the animal could be positive.
- There’s no health benefit for the individual animal. A positive vs negative result won’t change how a sick animal is treated since it wouldn’t be clear that SARS-CoV-2 was the cause of illness and there’s no specific treatment.
- A single result from an individual animal without much context (e.g. clear information about potential exposure) doesn’t tell us anything about the bigger picture.
- A clear communication plan needs to be established in advance. Positive results need to be properly communicated through various channels. Owners need to be properly counseled about what a positive means, so there’s no excessive fear or a knee-jerk panic reaction like asking to euthanize the animal or abandoning it.
Testing can be very useful, when it’s done right. That’s why we’re doing surveillance. However, testing is best done as part of a surveillance study where the goals, methods and communication of results are all well thought out in advance.