Yes, I’m prone to making typos. No, this title isn’t one of them.
While we’re in the midst of an unprecedented international outbreak of H5N1 avian flu (with ongoing spillover into mammals), there’s a new kid on the block: H5N5 influenza. I think recent reports of H5N5 were glossed over by some who didn’t realize we’re talking about a different strain from the H5N1 we’ve been dealing with the last couple of years. While it’s not necessarily a game-changer, we need to pay attention to new strains like this.
The story starts with the finding of H5N5 flu in birds in Atlantic Canada, which started in January 2023. The genetic makeup of the virus indicates it’s a Eurasian lineage that’s circulating in birds in Europe. It’s suspected that it made it to Canada via migratory birds last fall.
More recently, and more concerningly, this H5N5 strain was identified in two raccoons in Charlottetown, Prince Edward Island. As far as I know, this is the first report of H5N5 in mammals. Presumably the raccoons were infected from eating infected birds, which is how we suspect most mammalian wildlife with H5N1 get infected too.
With reports of “new” diseases, we always have to consider surveillance bias. We’re looking and testing a lot more now because of H5N1, so we’re more likely to find other things (such as other strains, like this) as well. That raises the question of whether this is truly something new or just something we’ve found now because we’re looking harder. Based on the genomics of the virus (being a Eurasian lineage), it’s probably something new for this region.
Regardless, the presence of yet another avian flu strain and more spillover into mammals is a bit disconcerting, to say the least. Recent genetic study of this H5N5 virus has indicated that it’s likely also capable of long-term circulation in birds and recombination with other flu viruses, so this is a virus to watch.
That’s not to say that we’re heading into a massive H5N5 outbreak. It’s one more flu virus in the mix, one more flu virus with the potential to recombine with other (human, avian, swine, equine, canine, etc.) flu viruses, and one more flu virus that can (even in its current state) spillover into mammals. So we need to stay on alert. There are lots of influenza viruses out there: some are nasty, they are prone to changing, and sometimes that can be bad for humans or other species.