#17,826
As we've discussed often the HPAI H5 threat is both multi-faceted and continually changing. Influenza viruses evolve through a combination of antigenic drift and reassortment (antigenic shift), and over the past 25+ years we've seen H5 go through dozens of major (and hundreds of minor) changes.
While H5N1 was the most common HPAI H5 until a decade ago, between 2014 and 2017 HPAI H5N8 clade 2.3.4.4 became the dominant subtype (green in the chart below). Briefly, in 2018-2019, we saw a relatively small spate of HPAI H5N6 outbreaks (not related to China's deadlier HPAI H5N6 virus) reported across Europe and Asia.
In late 2020 H5N1 clade 2.3.4.4b (red in the chart below) returned as the clearly dominant HPAI H5 subtype (see ECDC/EFSA chart below), although we occasional hear of the odd H5N5 or H5N6 detection.
This week, however, South Korea is reporting at least 8 outbreaks (in both poultry & wild birds) over the past 2 weeks from an HPAI H5N6 virus (see WOAH report) This is the first time this HPAI subtype has been reported in South Korea since 2018.
The only other country to report H5N6 in 2023 was the Philippines last January. Right now we don't have much information about this H5N6 virus, but it is likely the result of a recent reassortment between HPAI H5N1 virus and an avian HxN6 virus.
For now we have the following (translated) report from South Korea's MAFRA.
Highly pathogenic avian influenza type H5N6 confirmed in poultry farm2023.12.11 00:00:00 Quarantine Policy Bureau Avian Influenza Quarantine Division
The Highly Pathogenic Avian Influenza Central Accident Control Headquarters ( Head: Jeong Hwang-geun , Minister of Agriculture, Food and Rural Affairs , hereinafter referred to as Central Investigation Headquarters ) reported H5 -type highly pathogenic avian influenza (3 cases) that occurred at poultry farms in Muan, Jeollanam-do and Iksan, Jeollabuk-do from February 5 to December 6 . ) was finally confirmed as the H5N6 type on December 11th .
In addition, in the case of H5N1 type highly pathogenic avian influenza that occurred at a poultry farm in Goheung, Jeollanam-do on December 3 , additional tests confirmed that it was a mixed infection of H5N6 type .
* H5 highly pathogenic avian influenza serotype test results ( as of December 11 )
‧ H5N1/H5N6 mixed (1 case )
: 1st (12.3.) Goheung, Jeollanam- do ( broiled duck )
‧ H5N6 (3 cases )
: 2nd (12.5.) Muan, Jeollanam-do ( broiler duck ), 3rd to 4th ( 12.6 .) Iksan, Jeollabuk -do ( broiler breeders )‧ Inspection in progress (2 cases )
: 5th ( 12.8 .) Gimje, Jeonbuk ( laying hens ), 6th ( 12.8 .) Asan, Chungnam ( laying hens )
As a result, H5N6 type highly pathogenic avian influenza , which had not occurred in Korea since March 17 , 2018 , was confirmed in wild birds ( 12.4. mandarin ducks , 12.6. mallard ducks ) and poultry farms .
Meanwhile , Joongsubon announced that avian influenza H5 type antigen was detected in a laying hen farm in Gimje-si, Jeollabuk- do ( rearing about 70,000 birds ) and a duck farm in Wanju-gun, Jeollabuk-do ( rearing about 8,400 birds ) .
* Poultry farm outbreak ('23.12.3.~): 6 cases ( 2 cases in broiler ducks , 2 cases in broiler breeders , 2 cases in laying hens )
** ( Inspecting ) 7th laying hen farm in Gimje-si , Jeollabuk -do ( tentative ) , 8th round duck farm in Wanju-gun, Jeollabuk- do ( tentative )
As soon as the avian influenza antigen is confirmed, Jungsubon deploys an initial response team to the site and is implementing preemptive quarantine measures such as controlling access to the farm , preventive culling , and epidemiological investigation .
In a situation where two types of highly pathogenic avian influenza viruses (H5N1 type and H5N6 type ) have been introduced into the country , highly pathogenic avian influenza is occurring one after another in wild bird and poultry farms , and farm owners and workers must use vehicles entering and exiting the farm .
Disinfection of people , changing boots and disinfecting hands before entering the barn , daily disinfection inside and outside of the barn . It was emphasized that quarantine rules, including cleaning, should be strictly observed .
In addition , as early reporting is important to prevent the spread of avian influenza and minimize damage, we requested that you immediately report to the quarantine authorities even if minor symptoms * as well as major symptoms suspected of highly pathogenic avian influenza, such as increased mortality and decreased egg laying rate, are confirmed in the poultry being raised .
* Decreased feed intake , depression , drowsiness , respiratory symptoms , green stool , etc.
Whether this is just a temporary blip - like we saw in 2018/2019 - or the emergence of a competitive subtype for H5N1 (like happened with H5N8 in 2014), remains to be seen.
We also don't know if there is any functional difference (transmissibility, replication, or pathogenicity) between this H5N6 virus and the current H5N1 clade 2.3.4.4b virus.
