Avian Flu Diary: DEFRA: Updated Outbreak Assessment #16

#15,829

After three years of subdued activity, over the past 6 months the world has seen the biggest resurgence of Highly Pathogenic Avian Influenza (HPAI) since Europe's record setting H5Nx epizootic, and China's H7N9 5th wave of human infections, over the winter/spring of 2016-2017.

China's 5th Wave H7N9 Credit FAO

Fearing that H7N9 was on the verge of sparking a pandemic, in 2017 China unveiled a massive, nationwide, H5+H7 poultry vaccination campaign which produced a remarkable drop in human infections, poultry outbreaks and virus detection from routine surveillance (see OFID: Avian H5, H7 & H9 Contamination Before & After China's M assive Poultry Vaccination Campaign).

Human H5N6 infections in China also slowed appreciably, and globally H5Nx (H5N8, H5N6, H5N1) outbreaks in wild birds and poultry declined as well, but never quite went away. Russia, in particular, continue to report outbreaks in poultry in 2018 and 2019.

Although we saw some early signs of life in the winter/spring of 2020, HPAI H5N8 began making a big move - both in Asia and in Europe - last fall. H7N9 remains mostly subdued, although it continues to circulate and evolve in China (see EID Journal EID Journal: Evolution and Antigenic Drift of Influenza A (H7N9) Viruses, China, 2017–2019).

South Korea has reported in excess of 100 poultry outbreaks of (mostly) H5N8, and Japan has reported 50 H5N8 poultry outbreaks across 17 Prefectures. Both nations have lost millions of farmed birds to the virus, and to culling, since last fall.

China has also reported 5 H5N6 human infections since December of 2020 (see China's Recent Resurgence Of Human HPAI H5N6 Infections), after a lull of more than a year.

Over the winter India, the Middle East, and Africa have all reported increased HPAI H5Nx outbreaks in wild birds and in poultry, but by far the biggest outbreaks have been reported across Europe.

Fortunately for humans, the bulk of these outbreaks have been due to HPAI H5N8 Clade 2.3.4.4 and its reassorted offshoots (H5N5, H5N3, H5N2, etc.) which - while quite deadly to poultry and some wild birds - have never been shown to infect humans.

At least, not until the announcement last Saturday (see Russian Media Reports 7 Human Infections With Avian H5N8), from which we are awaiting an official statement and further details from the OIE or WHO.

The potential for seeing H5Nx Clade 2.3.4.4 evolve into a human infection threat has always been there (see J. Virulence Editorial: HPAI H5N8 - Should We Be Worried?), and as recently as a month ago researchers warned (once again) of the possibility (see The Innovation - Dealing with Highly Pathogenic Avian Influenza: An Impending Crisis).

While the events reported by Russia this past week are something less than alarming, they do suggest that HPAI H5N8 may be on an evolutionary path leading towards greater mammalian adaptation.

Yesterday the UK's DEFRA published their 16th updated Outbreak Assessment on HPAI H5 in the UK and Europe - which has a cut off date of February 15th - and alas, does not address the new information on human infections in Russia.

It does, however, update avian flu activity in the UK and Europe in the week of Feb 8th-15th, and discusses the unprecedented detection of 4 related HPAI H5 subtypes (H5N1 H5N5 H5N8 H5N3) in the UK in the same epizootic event.

Some excerpts from the 12-page report follow, but click the link to download and read the PDF report in its entirety. Hopefully we'll have more details on the Russian event by the time the next update is published.

I'll have a postscript when you return.

15 February 2021: Highly pathogenic avian influenza (HPAI) in the UK, and Europe
PDF, 1.65MB, 12 pages

15 February 2021 Ref: VITT/1200

HPAI in the UK and Europe Disease Report Since our last report (on 08 February), in the United Kingdom; there has been one new outbreak of highly pathogenic avian influenza (HPAI) H5N1 in Scotland. There have been no new cases of HPAI H5N8 in wild birds in the UK. According to OIE, elsewhere in Europe since 08 February, HPAI H5N8 has been reported in poultry in the Czech Republic (2), Finland (1), Germany (4), Hungary (3), Luxembourg (4), Poland (3) and Ukraine (1). HPAI H5N8 in wild birds has been reported in Austria (1), Denmark (36), Finland (1), France (1), Latvia (1) and Poland (1). HPAI H5Nx (N untyped) has been reported in poultry in Bulgaria. HPAI H5N3 has been reported in wild birds in Denmark (1). HPAI H5N5 has been reported in wild birds in Austria (1) and Poland (1).

(SNIP)

Implications for the UK

The detection of four HPAI H5 subtypes in the same epidemic event is unparalleled in the UK. All these viruses are genetically closely related through their H5 haemagglutinin gene, which is the key viral gene influencing pathogenesis, host range, transmission, and host immunity.

Continued virus change by genetic reassortment in wild birds is not unexpected, and further genetic variation at genome level may be expected as the epidemic progresses. Surveillance within the disease control zones continues, and results of investigations will be published in a comprehensive epidemiological report.

The migration season for wild waterfowl to overwinter in the UK has ended. A large population of migratory waterfowl are still present however, and will not be leaving the UK until March/April. Moreover, the higher survival rate of the virus in the environment during winter means the risk of environmental transmission remains, and hence the continued risk of secondary spread into indigenous UK wild bird species.

Higher environmental temperatures, together with increasing sunlight intensities, will reduce environmental levels of HPAI virus and its associated risks, in the spring.

(SNIP)

Conclusion

The risk of HPAI incursion in wild birds in GB remains VERY HIGH. The overall risk of exposure of poultry in GB remains MEDIUM (with stringent biosecurity) TO HIGH (where biosecurity is not adequate). An Avian Influenza Prevention Zone is in place in England, Scotland and Wales and the UK Chief Veterinary Officer, alongside the CVOs from Scotland, Wales and Northern Ireland are urging bird keepers across the UK to take additional biosecurity measures; in order to prevent further outbreaks of avian influenza in the UK.

(Continue . . . )

While HPAI H5 outbreaks may continue in Europe for several more months, with spring we generally see a reduction of the threat; migratory birds depart for their northern summer roosting areas, and local environmental HPAI contamination begins to decay.

The larger concern is what happens, largely out of sight, this summer in the high latitude nesting areas.

A study, published in 2016 (see Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1), posited that waterfowl pick up new HPAI viruses in the spring (likely from poultry or terrestrial birds) on their way north to their summer breeding spots - where they spread, amplify, and potentially evolve - only to redistribute them on their southbound journey the following fall.

This pattern is repeated year after year. Roosting areas promote the mixing and matching of avian flu viruses, which can help drive avian influenza's evolution through both reassortment (antigenic shift) and antigenic drift.