
When it comes to food safety risks with H5N1 influenza, we know it’s a problem with raw (unpasteurized) milk from cattle, so I often get asked if it’s a concern with milk from other animals, such as goat’s milk. It’s a good question. My typical response has been that we really don’t know. There haven’t been any reports of H5N1 flu in other dairy species (except for one report at this time last year of infection in neonatal goats on a farm in Minnesota that had infected poultry), but we have a lot more dairy cattle living on much bigger farms in North America. So it’s hard to say if cattle are actually at greater risk, or if we’re just more likely to recognize problems on a big dairy where the animals are monitored closely.
There is now a report from the UK about H5N1 infection in a single ewe (a female sheep) in Yorkshire, which was on a farm that also had infected captive birds. While this doesn’t tell us about the risk in goats or the overall difference in risk between dairy cattle and other dairy animals, it shows that cattle are not the only dairy species of concern.
The ewe tested positive on a milk sample, which was collected as part of the response to the infected birds on the farm (a smart surveillance approach that helps with early detection of spillovers and helps us understand transmission risks and patterns). Only one sheep from the flock was positive, but we have to assume the risk is likely broader – if one sheep can be infected, then other sheep could be too, if exposed to enough of the right virus.
The infected sheep was culled, which is understandable, as it removes the risk from that sheep. Unfortunately but it also removes any ability for us to learn more about what H5N1 flu does in a naturally infected sheep. It would have been ideal to isolate the sheep and monitor it for signs of illness and test it for virus shedding, but that’s not always possible.
There are a few good take-aways from this report:
- It shows the value of surveillance. If they hadn’t tested the other animals on the farm, we’d have no idea the sheep was infected, as the sheep did not appear sick.
- Presumably, this was a direct spillover from the infected birds on the property. Hopefully that means the virus in not established in sheep anywhere else (like it is in dairy cattle in the US), and that this was an interesting one-off infection but not of broader concern.
- If there really was only one infected sheep, removal of that ewe may have prevented it from infecting other sheep, and the other sheep all tested negative. I hope there will be a bit more testing on this farm to make sure there are no secondary cases.
I guess we can’t rule out the possibility that the sheep infected the birds. However, since they tested all the other livestock and only this one sheep was infected, it’s pretty safe to assume this was a direct bird-to-sheep spillover. Sequencing of the virus will help confirm this. Serological testing of other sheep on the farm would be interesting to see if there’s evidence of earlier infections.
Does finding H5N1 flu in a single sheep change anything?
No, not really. We know that H5N1 has spilled into a wide range of different mammals, and this just expands that list. We’ve assumed there’s some risk from other dairy livestock species, and this shows that’s a reasonable concern. We’ve also talked about risks from raw milk even before H5N1 was concern, there are lots of infectious disease risks with drinking any type of raw milk.
However, this report does raise the stakes a bit. We don’t want continued spillovers into mammals, because that increases the risk of this virus adapting to become better able to infect more mammals (including people). We don’t want endemic transmission in domestic mammals, as that increases human exposure risk. We also don’t want H5N1 flu in the food supply (but remember that pasteurization will kill the virus).
UK Chief Veterinary Officer Christine Middlemiss’ statement sums things up well:
“We have confirmed the detection of influenza of avian origin (H5N1) in a single sheep on a farm in Yorkshire. Strict biosecurity measures have been implemented to prevent the further spread of disease.
“While the risk to livestock remains low, I urge all animal owners to ensure scrupulous cleanliness is in place and to report any signs of infection to the Animal Plant Health Agency immediately.”
The UK Health Security Agency (UKHSA) has said that avian influenza is primarily a disease of birds and the risk to the general public’s health is very low, but people should not touch any dead or sick wild birds they find.
The Food Standards Agency advises that properly cooked poultry and poultry products, including eggs, remain safe to eat and avian influenza poses a very low food safety risk to UK consumers since the H5N1 virus is not normally transmitted through food.”
Awareness.
Diligence.
Good use of routine infection control and biosecurity practices.
Continued surveillance.
Those are the key factors for limiting the risk from this virus.