#17,968
While one can be comforted by the relatively low number of confirmed human avian flu infections since 2015 (see ECDC/EFSA chart above), by almost every other metric the avian flu threat appears to be increasing around the globe.
HPAI H5Nx clade 2.3.4.4b in particular has made great strides, expanding both its geographic and host range, but it is far from alone. We are also closely monitoring several other zoonotic influenza viruses including H3N8, H5N6, LPAI H9N2, and H5N1 clade 2.3.2.1c.
The HPAI H5 threat has changed substantially over the past 8 years, starting out with a recently reassorted H5N8 in 2016, then transitioning (via reassortment) to H5N6 in 2018, and then finally back to H5N1 in 2020. With these changes in subtype came significant changes in its behavior.
While H5N1 is the dominant subtype, there dozens of genotypes circulating in Europe, with even more globally. Some of these genotypes are likely more dangerous, or better adapted to mammals, than others.
Perhaps most concerning, we've seen a record number of mammalian spillovers around the world - most recently involving farmed cattle and goats in the United States - something which has never been reported previously. This is in addition to tens of thousands of marine and terrestrial mammals killed by the virus over the past 3 years.
Four times a year the ECDC publishes a highly detailed avian influenza surveillance report and while they tend to be EU centric, in its 69 pages you'll find substantial coverage of outbreaks and infections from around the world.Surveillance and reporting from many regions of the world being limited, it is likely that many spillover events - and some human infections - go unreported.
These reports make excellent (and frequently updated) reference material, and I keep the latest version on my desktop for that very reason.
Due to its length, I've just reproduced the executive summary and link below. Highly recommended.
Avian influenza overview December 2023–March 2024
Surveillance and monitoring
26 Mar 2024
Time period covered: December 2023–March 2024
Between 2 December 2023 and 15 March 2024, highly pathogenic avian influenza (HPAI) A(H5) outbreaks were reported in domestic (227) and wild (414) birds across 26 countries in Europe.
Executive summary
Compared to previous years, although still widespread, the overall number of HPAI virus detections in birds was significantly lower, among other reasons, possibly due to some level of flock immunity in previously affected wild bird species, resulting in reduced contamination of the environment, and a different composition of circulating A(H5N1) genotypes.
Most HPAI outbreaks reported in poultry were primary outbreaks following the introduction of the virus by wild birds. Outside Europe, the majority of outbreaks in poultry were still clustered in North America, while the spread of A(H5) to more naïve wild bird populations on mainland Antarctica is of particular cpossibly due to some level of flock immunity in previously affected wild bird speciesoncern.
For mammals, A(H5N5) was reported for the first time in Europe, while goat kids in the United States of America represented the first natural A(H5N1) infection in ruminants.
Since the last report and as of 12 March 2024, five human avian influenza A(H5N1) infections, including one death, three of which were clade 2.3.2.1c viruses, have been reported by Cambodia. China has reported two human infections, including one fatal case, with avian influenza A(H5N6), four human infections with avian influenza A(H9N2) and one fatal case with co-infection of seasonal influenza A(H3N2) and avian influenza A(H10N5). The latter case was the first documented human infection with avian influenza A(H10N5).
Human infections with avian influenza remain rare and no sustained human-to-human infection has been observed. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA. The risk of infection remains low to moderate for those occupationally or otherwise exposed to infected animals.
Avian influenza overview December 2023–March 2024 - EN - [PDF-2.71 MB]
