DEFRA Risk Assessment Of HPAI H5N1 Occurring in Cattle In the UK

 

#18,034

Other than a story in Sky News last week which reported the UK was not planning on testing cows for HPAI, we've seen very little comment outside of North America on the detection of HPAI H5N1 in dairy cattle in the United States.  

Yesterday, however, the UK's DEFRA (Department for Environment, Food & Rural Affairs) published a risk assessment (below), which finds the risks of something similar affecting UK cattle very low. 

They base their assessment on the fact that the B3.13 genotype found in US cattle was created from the European H5 virus reassorting with North American birds.  

As a segmented virus with 8 largely interchangeable parts, the flu virus is like a viral LEGO (TM) set which allows for the creation of hundreds of unique variants (via reassortment) called genotypes.

As as result, there are scores of different genotypes of H5N1 in circulation around the world, and they can have significant differences in their pathogenicity, transmissibility, and host range.  

The ability of genotype B3.13 to infect cows - thus far - appears to be a rare skill set for H5N1. 

Whether it is truly unique, has yet to be established.  

They also reassure that the B3.13 genotype - which may spread north and south via the North American Flyways (see graphic below), are far less likely to spread east across the Atlantic to the UK. 

That said, HPAI H5 crossing the Atlantic to North America in late 2021 was once considered a long-shot, as was H5N1's arrival in the Antarctic last fall. 

When discussing the spread of HPAI via migratory birds, one never likes to say `never'. 

First, some excerpts from the DEFRA risk assessment, then I'll return with a brief postscript.

Preliminary Outbreak Assessment 

Influenza A (H5N1) of Avian origin in domestic livestock in the United States of America

 25 April 2024 

Disease report 

On 26 March 2024, the United States of America (USA) made an immediate notification to the World Organisation for Animal Health (WOAH) of an outbreak of Influenza A (H5N1) of avian origin (Influenza A (H5N1)) affecting dairy cattle in Texas. Milk samples and oropharyngeal swabs tested positive for viral RNA after cows showed clinical signs including decreased lactation, thickened discoloured milk, fever, and low appetite.

 The material detected has been sequenced and shown to belong to clade 2.3.4.4b strain B3.13, a viral reassortant between Eurasian High Pathogenicity Avian Influenza (HPAI) H5N1 and North American Low Pathogenicity Avian Influenza (LPAI) strains.

This strain has not been detected in the UK, and none of the viruses detected in the UK over the 2020 to 2024 HPAI outbreak period have contained genetic material originating from North or South American viruses. 

Additional testing of cattle was carried out on farms where clinical signs have been observed, with deceased wild birds noted on the Texas farm, and since then, and as of 24 April 2024, there have been 32 further reports of Influenza A(H5N1) in dairy cattle in 8 states (USDA). There have also been further reports of the same strain in domestic and wild mammals, including 6 cats showing signs of neurological illness in dairy farm settings where the cattle were also positive (at least 3 of which were reported to have died) and a skunk in North America. There has been one infection in a person exposed to infected dairy cattle, who showed symptoms of conjunctivitis prior to recovery following isolation and anti-viral treatment.

 The risk to GB of H5N1 in livestock is assessed at very low. 

(SNIP)

The emergence of a strain of H5N1 capable of infecting cattle, or any other domestic mammal, is thought to be a rare event, which is made even less likely by implementing biosecurity practices and disease control measures. The full genome of the virus affecting cattle has been made publicly available, and the virus is different to, and distinguishable from, H5N1 that has been circulating in Great Britain and Europe.

This is also the case for other H5N1 viruses circulating in poultry and wild birds in North America since they have been evolving independently from European viruses since 2022. Therefore, the likelihood of the same sequence of events occurring in Great Britain resulting in an identical virus emerging in cattle is highly improbable.

While a similar event could be possible with a UK virus adapting to more mammalian livestock species, this would still be very rare, and would likely require a high initial introductory dose as well as close proximity between mammalian livestock and poultry.

Whole Genome Sequencing (WGS) of H5N1 viruses detected on poultry farms in Great Britain has taken place throughout the HPAI H5 epizootic and pigs present on the same premises as poultry outbreaks have been sampled for avian influenza (with negative results). The avian influenza surveillance carried out to date in Great Britain gives a very high level of confidence that this strain has not been detected in Great Britain. 

Conclusion 

Available trade data shows that only a small proportion of consignments of dairy products could contain H5N1 virus, and given the low prevalence of disease in dairy cattle in the USA so far, it is very unlikely that these would come from infected farms. Additionally, the mitigation measures that are currently in place in the USA, along with the mandatory testing and reporting that are soon to be implemented will reduce this likelihood further. Migratory birds could be a plausible route of introduction of H5N1 virus affecting dairy cattle to Great Britain, although not directly and would be considered rare events. Therefore, the risk of entry of H5N1 virus capable of infecting domestic livestock is very low. We will continue to monitor the situation as it evolves.

There are always concerns around infected products entering the UK in passenger luggage and the subsequent waste being discarded in areas where livestock or wildlife could access them. We would like to highlight to all cattle keepers, dairy producers, smallholders and general public that it is illegal to feed cattle catering waste, kitchen scraps or dairy products, and to adhere to the swill feeding ban.

All dairy keepers should remain vigilant and ensure that any visitors to their premises have not had any recent contact with dairy cattle or cattle premises in the affected regions. People who have been working on farms or with animals returning from any affected areas should avoid any contact with domestic cattle or domestic poultry in commercial holdings and smallholdings. All clothing, footwear or equipment should be disinfected before entering dairy cattle or other livestock areas. Any suspect cases must be reported promptly. 

If you suspect a notifiable disease in your animals, you must report it immediately by calling the Defra Rural Services Helpline on 03000 200 301. In Wales, call 0300 303 8268. In Scotland, contact your local Field Services Office. Failure to do so is an offence. We will continue to monitor the situation. 

         (Continue . . . )

While it seems reasonable that the B3.13 genotype is unlikely to infect UK cattle anytime soon, the assumption that another cattle-affecting genotype won't evolve elsewhere in the world (including in the UK or Europe) is a tad optimistic. 

Nature continues to conduct countless GOF (Gain of Function) experiments with HPAI around the globe, and B3.13 should be viewed as a proof-of-concept.  If it happened once, it can presumably happen again. 

While we might not like what we find, our best strategy is to greatly increase testing and surveillance around the world; to start looking for the virus in previously presumed unlikely places, like in cows, pigs, goats, cats, and anyone who works with them. 

Otherwise, we're just basically waiting and praying the virus goes away.