#18,008
This week WOAH reported (see below) more detections of HPAI H5N5 (clade 2.3.4.4b) virus in raccoons from Nova Scotia and Prince Edward Island. The virus had previously been detected in wild birds, but turned up in dead raccoons on Prince Edward Island a year ago (see CIDRAP Report Canada reports first H5N5 avian flu in a mammal).
While our biggest concern is currently HPAI H5N1, we've seen closely related H5N3, H5N4, H5N5, H5N6, and H5N8 viruses - the product of H5N1 reassorting with other LPAI viruses - infecting both birds and mammals around the globe.We report additional cases of highly pathogenic avian influenza Fully Eurasian H5N5 (2.3.4.4b) virus in raccoons from Nova Scotia and Prince Edward Island. Outbreaks are reported by province/territory. The geographical marker is on the capital. For detailed and current information on high pathogenicity avian influenza cases in wildlife, please consult : http://www.cwhc-rcsf.ca/avian_influenza.php.
Several of the same authors wrote about additional isolates of the H5N5 virus in the journal Veterinary Microbiology (see Characterization of three H5N5 and one H5N8 highly pathogenic avian influenza viruses in China), that were isolated in China in 2009-10, suggesting that the first detection wasn’t a fluke.
Although we have looked at the the threat and evolution of HPAI H5N5 a number of times in the past (see here, here, and here), recent changes to clade 2.3.4.4b viruses probably make findings before 2021 less relevant.
Published 21.06.2022 Modified 22.06.2022
In recent weeks, an abnormally high number of sick and dead birds has been observed in several places along the Norwegian coast. In May and June, the Veterinary Institute detected highly pathogenic avian influenza (HPAI) of subtype H5N5 in sea eagles, ravens, crows and several gull species in Troms and Finnmark. In the North Sea and along the coast in Rogaland, a high number of dead ospreys have been observed, and HPAI of the subtype H5N1 has been detected in several of these. In addition, HPAI has been detected in wild birds in Oslo, Bergen and several places in Trøndelag and Møre og Romsdal.
In the most recent ECDC/EFSA Quarterly Avian Influenza Overview Dec 2023 - Mar 2024, there were several mentions of HPAI H5N5, including:
- Subtype A(H5N5), genotype EA-2021-I, which has persistently been detected in Norway since the 2021–2022 epidemiological year, has since September 2023 spread to Iceland, the United Kingdom, Greenland and Germany, and – besides infecting wild birds – infected red foxes in Norway. A(H5N5) was also detected in Faroe Islands and Japan during the current epidemiological year.
- Unlike the mammalian infections reported in Europe during the summer months in 2023, mainly caused by the EA-2022-BB genotype, the recent A(H5) viruses identified in wild mammals belonged to different A(H5N1) and A(H5N5) genotypes. The detection of A(H5N5) virus in two red foxes from Norway represents the first detection of this subtype in mammals in Europe.
It is for this reason there is so much concern about HPAI H5 spilling over into pigs, which would give it access to a wide array of swine and human viruses.
But other species, including humans, marine mammals, mink, and even dogs and cats could serve as an effective `mixing vessel'.
Six years ago, HPAI H5N8 was the dominant H5 subtype, but was supplanted by H5N1 in 2020. It is entirely possible that we could seen another shift - from H5N1 to H5N5, or H5N6, or to some other n-type, in the months or years ahead.
And while clade 2.3.4.4b is currently in the driver's seat, we've seen a resurgence in clade 2.3.2.1c in Cambodia over the past year, and last week the FAO warned of a Reassortment Between H5N1 Clade 2.3.4.4b & Clade 2.3.2.1c Viruses In Mekong Delta Region.
While we expect all influenza A viruses to change over time, HPAI H5 seems to be working overtime.
