H5N1 antivirals in animals…should we use them?

The long answer to this is in a WormsAndGermsPod podcast I just put up but I’ll give a summary here.

If you asked people on the street “should we use the limited antivirals we have to treat people with flu on dogs and cats?” the common answer would probably be “no“…with a few “hell no!!“‘s added in.

On the surface, that makes sense. We have limited antiviral and they are important in some situations. However, we shouldn’t dismiss antiviral use in animals, in selected circumstances with good controls.

Early antiviral (oseltamivir (Tamiflu)) treatment could be effective against H5N1 flu in some animals and there may be a role of prophylaxis in high risk situations (e.g. housemate of a cat with H5N1 flu). Both of these scenarios would involve companion animals, and non-reservoir species, so no livestock (including backyard chickens).

What about antiviral resistance?

We can’t ignore it. Antiviral resistance is a concern and it’s a random event that can occur as flu spreads, regardless of whether antivirals are used or not. It’s been found in poultry (that were not treated with antivirals) and the more flu transmission and the more antiviral use, the greater the risk of resistance spreading.

But….it’s different than antibacterial resistance. Antivirals are much more specific in their effects, and viruses don’t transmit resistant genes like bacteria do. If we treat an animal or person with an antibiotic, there will be myriad bacteria in that individual that are resistant, can become resistant or can spread resistance genes. If we treat an animal with an antiviral, it’s different.

If the animal gets oseltamivir prophylactically and doesn’t have flu, it can’t get resistant flu.

If we use it and the animal has flu, there’s a chance of resistance developing, and that’s not good. However, it’s only a broader problem if that flu virus is passed to another individual. We don’t know if dogs and cats can transmit H5N1 flu but we have to be prudent and assume that they can. So, if we’re using an antiviral, we need to do all that we can to reduce transmission, something we can probably do much more effectively than in a person that’s being treated with an antiviral.

Use as little as possible but use enough.

That’s my mantra when it comes to anti-infectives. We need to be prudent and be good stewards of these drugs, but we also shouldn’t miss opportunities to intervene when we can do so effectively and with minimal risk.

When would I use Tamiflu in a dog or cat?

Early treatment of known or high risk cases where there’s a concern for development of serious disease (any cat, and probably most dogs) AND when the animal can be properly treated AND when the animal cat be kept isolated during and shortly after the treatment period.

A cat in a household or vet clinic?

• Yes. We can properly treat, isolate, monitor and test them.

A cat that gets outside?

• No, not unless it’s kept inside during the treatment and monitoring period, since I don’t want to risk an antiviral resistant strain developing and then the cat spreading it to other cats or, worse, birds.

Basically, do they need it and can I confidently ensure that the animal won’t be able to infect another individual are my two main questions. If I can comfortably say yes to both of those, I think it’s reasonable to use them.

A backyard chicken?

• No. These are livestock, so they are approached differently (and usually culling is required). They are highly susceptible and infectious, and clearly can infect people. Also, an antiviral is probably too little, too late for a species that is so susceptible.