As the unprecedented global H5N1 avian flu outbreak continues (with no real end in sight), and as we get the spring mix of migrating birds, mingling bird populations, more active wildlife and a pending crop of baby wild critters, concerns about spillover infections from birds to mammals are on the rise.

The current H5N1 influenza A virus has infected an impressive array of mammals. That doesn’t necessarily mean it’s worse (for mammals at least) than previous H5N1 influenza strains, as the higher number of spillover infections in mammals may just be because there are so many infected birds involved in this ongoing outbreak. However, it’s still concerning.

• The good news is that the currently circulating strains are quite poorly adapted to infect and transmit between mammals.

• The bad news is that could change.

There are various animal populations and situations to considered. One is animal shelters, because they handle lots of animals, many with outdoor access (and therefore access to wild birds) and with unknown histories. Diseases are common in shelter animals, and teasing out high-consequence infections from “routine” diseases is a daily challenge. Many shelters also take in birds, including wild birds and domestic birds like backyard poultry (a particularly high risk group when it comes to exposure and susceptibility to avian flu).

What do we need to think about when in comes to avian flu and animal shelters?

As with any emerging disease situation, answers to some common questions may change over time as we learn more and as the disease evolves, but here are some initial thoughts:

How common are H5N1 infections in mammals?

Spillover infections to mammals are rare. The exact incidence is impossible to say. Even if the spillover risk is really low, with millions of infected birds, we’re bound to see at least some transmission to other species – that part is just a numbers game. Some mammalian species seem at higher risk (e.g. foxes), maybe because of combinations of more frequent / higher exposure (e.g. scavenging infected birds) and greater inherent susceptibility. However, we probably need to consider all mammals to be at some degree of risk. At that same time, we have to remember that the vast majority of mammals with respiratory or neurological disease don’t have flu.

What are some flags in shelter animals that flu might be a concern?

There are two major things to think about here. One is risk factors for disease exposure, which are primarily related to the animal species (e.g. waterfowl or contact with waterfowl) and the local situation (e.g. lots of dead birds in the area).

The other factor to consider is the clinical status of the animal. We’re still learning about what this virus does to different species, and clinical signs can be highly variable. I’m going to be most concerned about animals with severe respiratory and/or neurological disease. There are other things that can cause these signs, and not all H5N1 infected animals will have these kinds of signs (especially early in disease), but a dog that’s in an area with dead birds that has respiratory disease and is starting to develop neurological disease would set off a lot of alarm bells in my head.

What’s the risk of spread of H5N1 from mammals in shelters to humans?

Human risks are low but not zero. The same applies to other mammal-to-mammal transmission. The currently circulating strains are still very poorly adapted to people and other mammals, so spillover infections are rare and transmission risks from a spillover infection (e.g. an infected cat infecting another animal or a person) are very low.

What’s the risk of spread of H5N1 between mammals in a shelter?

As for humans (another mammal), the risk is probably very low. This virus isn’t currently adapted for mammal-to-mammal transmission, so most mammalian spillover infections are probably “dead ends,” meaning the mammal can’t infect anyone else and the virus dies out when the animal recovers, or succumbs. However, “probably” dead ends is far from definitive. We have no real idea of the risk, because the infections are so rare and are difficult to study. Viral loads in some infected mammals (inferred by PCR results) seemed pretty high – high enough that I think transmission risk is plausible during some stages of infection in some animals.

So, we should assume that there is some degree of risk from any infected animal, albeit relatively low and probably fairly easy to mitigate.

Are there any issues with disinfection in a shelter if H5N1 may be present?

No. Surfaces pose limited risk (especially compared to handling an infected animal) and influenza virus doesn’t survive long outside the host. Any routine disinfectant will deactivate the virus – it’s just a matter of actually doing a good job of cleaning and disinfection so that the disinfectant can work.

How should H5N1 suspects be housed in a shelter?

Ideally, they aren’t. High risk cases (e.g. wild bird with neurological disease in an area with flu activity) are best triaged outside, and, if they are to be housed, for that to be done outside the main shelter. Setting up a secure outdoor triage area and housing area (even just for short term housing while testing is being done and more information is being gathered) can be invaluable, whenever possible. It helps protect individuals in the shelter, and also avoids any risk of other animals at the shelter potentially needing to be quarantined or euthanized by preventing exposure to infected animals.

If suspect animals have to be housed in the shelter, they should be isolated, ideally individually (though isolation of a group from the same area with the same flu risk is also reasonable). That would seem to be intuitive but it’s not always the case in shelters, since sometimes isolation units house a variety of different potentially infectious cases (e.g. all sneezing cats go into the same ward). However, we don’t want that here since we don’t want our flu suspect to be in the same room with another animal that has little chance of having flu. So, housing them in individual isolation is best, ideally a room with separate ventilation. Adding a HEPA filter to the room is never a bad idea (flu or otherwise).

How should H5N1 suspects be handled?

Handle suspects using contact precautions, including gown, gloves, mask (ideally N95/KN95/FFP2) and eye protection or a face shield.

And handle them as little as possible.

What about testing of animals for H5N1 (or other influenza A strains)?

Testing is great. Negatives are not a guarantee that an animal is truly not infected, but testing helps us identify infected cases so we know what’s going on, helps with getting compliance with infection control measures, and helps us to better understand the broader risks.

For domestic animals, testing is most often going to be at the shelter’s expense (despite the value of supporting testing in high risk situations). Shelters can burn through a lot of money testing every dog and cat with respiratory disease, so realistically testing would focus on animals with severe or atypical disease, especially respiratory and neurological disease combined, and where there’s a plausible chance of exposure to wild birds.

What to test is still a grey area because we don’t have much data. At this point, I’d recommend oropharyngeal, nasal and rectal swabs (in that order of priority). Also remember that the lab test must be able to detect H5N1. Not all tests do that, so it’s important to ask about the test itself before sending off a sample.

Remember: Sample collection is probably one of the highest risk human-animal interactions. Everyone involved in sample collection should wear proper personal protective equipment (PPE), including face/eye protection.

What is the risk to staff that have to recover animals from the field?

This work creates a few high risk situations, such as close contact with a struggling animal (e.g. if the animal needs to be caught and restrained) and being the same vehicle (enclosed space) for transport back to the shelter.

• PPE should be worn for any contact with high-risk flu suspects.

• For transportation of any suspect animals, maximizing ventilation (e.g. opening vehicle windows or maximizing flow-through air) is a good idea, and it’s reasonable to have anyone in the vehicle wear a mask (ideally N95/KN95/FFP2) and ideally also eye protection. The size of vehicle, position of the animal, type of animal, animal behaviour (e.g. barking) and travel time would influence risk.

Should flu vaccination of shelter staff be recommended or required?

Vaccination of staff is a great recommendation for a few reasons. One is just because human flu is an important cause of disease. Current human flu vaccines likely provide little to no protection against H5N1, but they are still useful in the context of this outbreak because we don’t want to create situations where multiple flu viruses can get together and make a new flu virus. The more people with human flu that are exposed to animals with avian flu, the greater the risk of multiple flu viruses recombining. Odds of that are very low in a shelter but they’re not zero, so it’s great to have high flu vaccine coverage of staff.

Related to that, people with potential human flu shouldn’t be at a shelter, for the sake of both routine protection of other personnel and to avoid making the shelter a human/avian flu mixing vessel.

What about vaccination of animals against H5N1?

For dogs, we have H3N2 and H3N8 vaccines, but those would offer little to no protection against H5N1. As with people, we want to avoid different flu viruses getting together in the same animal, so having the dog population protected against canine flu is never a bad idea. However, given vaccine availability issues, limited impact on virus shedding, the time required to have protective immunity from the two dose series, and cost considerations, it’s pretty low yield in this scenario.

That’s it for this morning’s flu thoughts. There will probably be a “Part 2” since I’m sure I’ll realize I missed a lot of questions as soon as I post this.