A new pandemic

What I would like to see/do in terms of H5N1 influenza testing in pets

Surveillance testing

1. Testing of cats/dogs with clinical signs suggestive of H5N1 influenza infection.
   • Right now, the focus is on pets with severe neurological and/or respiratory disease. Testing these animals lets us know how common the infection is in these cases, lets us investigate risk factors and transmission risks, and lets us do viral sequencing.
   • Currently the most widespread testing for H5N1 flu in pets is probably secondary testing of rabies suspects, whereby cats that are being tested for rabies (which often have neurological disease) get tested for flu if the rabies test is negative. This is a convenient and useful surveillance method that can contribute useful infomation, especially if other organized surveillance is lacking, but the sample is limited.
2. Testing of dogs/cats with more common respiratory or flu-like illness signs.
   • We need this to understand the scope of disease caused by H5N1 influenza in pets. Are severe cases all that occur or are they all that we’re currently diagnosing? We need to know if there’s a fraction of cases that only have milder disease, particularly to help us assess and mitigate transmission risks.
   • We can’t test every sneezing cat, but we can do targeted surveillance by focusing on animals with a realistic risk of exposure to the virus. So, I’d like to test sick cats and dogs in areas where H5N1 flu is active (i.e. in wild birds) and where there’s a reasonable risk of exposure (e.g. outdoor access). This balances throwing a wide net to get a better broad understanding, and being efficient with our time and money.

Clinical testing

This is a tougher call. Most often, H5N1 flu testing would not impact patient care. It could help inform us about risk to the clinic or household, so it’s good information to have, but we can’t dismiss risk based on a negative test, so it doesn’t have a huge impact on what we do regardless.

The less surveillance testing there is, the more valuable opportunistic clinical test is for quasi-surveillance purposes, but that’s usually going to be at the owner’s cost. Spending a couple of hundred dollars to test a severely ill animal with little expectation that the test will change the response or the outcome is hard to justify. If money is tight, I’d rather have owners spend that on treatment.  Some people will pay for the testing because they want to know, or because they are worried about exposure of family members, but relying on owners to cover testing isn’t a great approach. It’s still worth discussing in any case since there can be some limited benefits.

What about rapid in-clinic tests for H5N1 influenza in pets?

It’s been suggested that veterinarians should start stocking rapid in-clinic H5N1 tests and use them liberally when presented with sick dogs and cats. I’m a bit wary of this because we don’t know how good those tests are. If we test a lot of low-risk animals and the test isn’t 100% specific, most of our positives are likely to be false positives. That’s alright if we’re just using it as a screening test and we follow-up with a proper test ASAP, but sometimes people rely too much on the screening test, and that can lead to over-reactions and other problems. On the other hand, if the test isn’t very sensitive, we run a good chance of missing the small number of true positives. If the test is no better than a coin toss, it won’t help.

Collecting good samples can be a challenge (especially trying to swab cats) so that drops the functional sensitivity of any test (i.e. we get more false negatives because of poor samples.

To be useful, we would need:

•  a rapid test with high sensitivity (reliably detects all the infected animals) AND high specificity (gives us very few false positives)
• AND good samples
• AND the capacity to follow up positive tests with PCR testing
• AND a communication plan for animals that are confirmed positive

But we’re not necessarily there yet. I’d consider rapid testing appealing, but probably not ready for prime time.