
The recent situation has raised more discussion about the role of mass culling in response to H5N1 influenza infection in domestic / captive birds. After H5N1 flu was identified on an ostrich farm in British Columbia, the CFIA ordered all 400 birds to be culled, but the owner is trying to find options to preserve her herd.
It’s a tough decision, and views on the matter vary drastically depending on perspective and mandate (e.g. animal owner versus public health versus protecting trade and treaty obligations and and broader animal health across the country). So it gets messy.
I have not been involved in any discussions about this particular situation, so this post is more of a generic discussion of when, where, how and why culling can be used for disease control.
- On one hand, culling can be necessary to eliminate a pressing and poorly controllable threat in order to protect other people and animals.
- On the other hand, culling can (at times) be an overly heavy hammer that’s used to simply remove concerns altogether. Killing affected animals is a very definitive (and irreversible) response to a disease concern, but question is whether it actually achieves much in terms of reducing risk, depending on the specific situation.
There are a lot of issues to consider when determining the best response to an infectious disease in animals. There’s no magic rule that says “if X happens, then the best thing to do is always Y.” There are lots of grey areas, nuances and case-by-case variations, which makes it a big challenge from a regulatory standpoint, because regulations and policies are usually designed to be as black and white as possible (“do this, or do that” full stop). That’s good for clarity, but it runs the risk of inappropriate or unnecessary responses in cases that fall in the grey.
While lots of factors come into play, in general, culling makes more sense when there’s an imminent and substantial risk to human or animal populations from the affected animals that’s too hard to contain by any other means. In the case of H5N1 influenza, culling is easier to justify in poultry where those infected birds would not likely ever end up going into the food chain anyway (due to illness and mortality from the disease), so keeping them alive would just put the people handling them at risk (as well as potentially birds on nearby or linked properties) for little net benefit to the birds.
As H5N1 influenza is now well-established in wild birds in Canada and internationally, there’s less argument for culling from the standpoint of controlling disease. Previously, if we had rare incursions of highly pathogenic flu, culling would make more sense as it would quickly eliminate a large infected group of birds when there’s limited or no known infection in birds outside of that group. Here, we can’t say that. Now if we have H5N1 in a group of domestic birds, we still likely have lots of H5N1 circulating in wild birds in the area. If an individual group of birds is a drop in the bucket now that H5N1 is widely distributed, culling probably has little benefit to the larger population. There’s still some impact, but it’s probably low, and if it’s a small group, transmission isn’t sustained and there are some basic infection control measures in place, the risk that they will infect other birds or mammals is low.
Human health risk is a major consideration, but the risk is only for a short period of time with a group of domestic birds, because H5N1 influenza would be expected to burn through the population quickly and then be gone. If they can limit contact with the birds and use good infection control practices for necessary contacts, the risk is lowered further. However, it’s “lowered” not “eliminated.”
The value (economic, conservation, emotional) of the birds or animals is also part an important factor. The conservation aspect is particular important when it comes to rehabilitation facilities or zoos have infected animals, where culling could have important impacts on some uncommon species. The same doesn’t apply to ostriches or many other poultry and non-poultry species, but economic and emotional values might.
Ultimately, whether or not to cull birds on an infected premises is a cost-benefit decision where we can’t really quantify the costs or benefits well. The easiest thing from a risk aversion standpoint is to cull, but that’s not necessarily always the best thing from a broader standpoint.
I sketched this out for a synopsis of considerations for culling. The more answers end up in the red, the greater the value of culling:

Here are my answers for commercial chickens:

Here are my answers for ostriches:

How about for dairy cattle?
Cattle infected with H5N1 influenza probably pose at least as much (or likely more) risk to domestic animals and people as poultry. I’d score them similarly or sometimes a bit more to the right compared to chickens and ostriches, apart from the value row. The economic value of a dairy cow is much higher than a chicken, and I doubt culling would be on the table just because of that. Economics are likely going to be a major driver of any decision of this kind.
Does that mean we should or shouldn’t cull the ostriches? That’s beyond my pay grade, but I think these are some of the things we need to seriously consider when making those decisions.