H5N1 in a cow: The Netherlands
A few months ago, a cluster of cats that died from H5N1 influenza was identified in the Netherlands. This itself wasn’t too surprising since H5N1 is circulating internationally and we know that cats are highly susceptible to the virus, often developing severe disease.
The cats were on what was reported as a dairy goat farm, which always raises some concern that they could have gotten infected from milk. That’s a concern because of the situation with H5N1 influenza in cattle in the US. There, the virus spilled over into cattle, then spread widely amongst dairy farms, often infecting (and killing) cats that got infected. We’d assumed investigation of other animals on the farm was done, and more information was recently released.
It turns out the farm was a dairy cattle farm (or at least had cattle as well as goats) and when they tested healthy cattle, they found that one cow had antibodies against the virus. If the test isn’t a false positive (always a potential concern with rare outcomes and antibody tests), that would mean at least one cow was infected with the H5N1. It wasn’t noticed to have been sick and eliminated the infection, but antibodies remained in its blood as an indicator that it was infected. There’s no evidence that other cattle were sick.
So, that’s a good new/bad news situation.
The H5N1 dairy issue has been a mess in the US (both in terms of the impact and the approach to control) and we’ve been watching to see if it would develop somewhere else. Sporadic bird-mammal infections that go nowhere are not uncommon and hopefully that’s what happened on this farm. However, every time H5N1 jumps into a mammal, it creates more potential that it will adapt to spread more easily in mammals or that the strain that jumps is one that’s already adapted to spread more easily. The more it’s in domestic animals, the greater risk of human exposure, more adaptation to infect humans and recombination with human flu viruses to make another strain that could be worse for us.
The good news is that this seems to have been a one-off situation on this farm. It spread to at least one cow but didn’t cause overt disease, didn’t seem to spread further in cattle and the situation seems to have resolved itself with no damage because the initial cluster of infected cats.
That’s good.
It should also be a reminder of why we need to pay attention to H5N1 and try to control it as much as we can. This situation didn’t cause a problem but a nationwide outbreak in dairy cattle will likely start with a single spillover on a single farm, so we need to remain diligent.