Avian Flu Diary: UK HAIRS Risk Statement On Avian Influenza (H5N1) In Livestock

#18,088

While nations outside of the United States (and to a lesser extent, Canada) have been largely silent on the outbreak of HPAI H5N1 in American livestock, today the UK's HAIRS (Human Animal Infections and Risk Surveillance) group has released a detailed statement on the risks posed by H5N1 genotype B3.13 to people in contact with infected animals in the UK.

These HAIRS risk assessments are generally quite detailed (see here, here, and here), but this one suffers somewhat from an apparent data cut off date of nearly of 3 weeks ago.

They make no mention of the 2nd human infection (reported May 22nd) from Michigan, or reports of infected cats not linked to dairy barns, and they state : `As of 9 May 2024, 42 dairy farms across 9 states have reported confirmed cases in cattle.'

Since their risk assessment only concerns itself with possible human exposure from UK livestock, I assume this 3 week gap in the data would have little impact on their findings.

Although they currently state that H5N1 genotype B3.13 presents ` at most, a very low risk' in the UK, they also recognize that there are sizable evidence gaps, and a full assessment is not possible at this stage.

This is a lengthy report, and while I've reproduced some excerpts below, many will want to follow the link below and read it in its entirety. I'll have a postscript after the break.

Research and analysis
HAIRS risk statement: Avian influenza A(H5N1) in livestock
Published 29 May 2024
Date of this assessment: May 2024
Version: 1.0

Risk Statement

This risk statement provides a qualitative description of the zoonotic risk avian influenza (AI) A(H5N1) clade 2.3.4.4b genotype B3.13 presents to people in contact with infected animals in the UK, and highlights evidence gaps and recommendations for mitigating the risk of zoonotic transmission.

Based on the current available information, the HAIRS group determined that this currently presents, at most, a very low risk.

This is a rapidly emerging situation and there remain several evidence gaps, therefore a full assessment is not possible at this stage. This statement will be reviewed as the evidence becomes available.

(SNIP)

UK Context

It should be emphasised that the AI A(H5N1) clade 2.3.4.4b genotype B3.13 reassortant virus implicated in USA dairy cattle has never been detected in the UK or Europe. Similarly, no other Eurasian-North American reassortants have been recorded in the UK or Europe, despite detections of these viruses in Canada and the USA since 2014.

In Great Britain (GB), outbreaks of AI on poultry premises are followed-up with sequencing. Additionally, a proportion of wild bird cases will also be sequenced annually. Of all the GB sequences submitted to GenBank, none have been indicative of reassortants with North American strains.

This can be visualised in the Global Initiative on Sharing All Influenza Data regional genome analysis from 2019 to 2024, where only a link for European viruses entering North America has been observed in this period (14) (Figure 1). The synchronisation of the migratory seasons and circulating avian influenza viruses have not been conducive to spread from west to east via these flyways.

Figure 1. Regional genome analysis and introductory routes of highly pathogenic avian influenza virus subtypes from 2019 to 2024. Source: Global Initiative on Sharing All Influenza Data. Accessed: 27 April 2024.

The likelihood of the presence in the UK of AI A(H5N1) clade 2.3.4.4b genotype B3.13 and undetected disease in cattle is considered to be very low. The risk level associated with AI in wild birds and poultry in the UK has recently been reduced from medium to low. On 29 March 2024, the UK self-declared zonal freedom from highly pathogenic AI (15) and is in the process of applying for disease free status, given the length of time since the last commercial poultry outbreak.

Mastitis frequently occurs in British cattle, although rarely to the high prevalence levels as reported in these cases in the USA. It is most commonly caused by bacterial infections of the mammary glands, and only in rare cases the aetiological agent is not found. Nevertheless, mastitis cases are not routinely tested for AI viruses as there has never been any evidence to suggest a testing requirement.

The Animal and Plant Health Agency’s (APHA) cattle dashboard (16) reports the number of cases of mastitis tested and the causative agents identified under a voluntary scheme (as such, underreporting is likely). In 2024, there have been 44 cases of mastitis; 13 due to Escherichia coli infection, 16 due to Streptococcus species, 6 due to Staphylococcus infection and only 1 was undiagnosed. Between 2021 and 2024, there were 48 cases of mastitis in dairy herds in which no diagnosis was confirmed. From 2017 to 2020, there were 40 cases in which no diagnosis was confirmed.

(SNIP)

Possibility of human exposure in the UK

AI A(H5N1) Clade 2.3.4.4b, genotype B3.13 has not been detected in the UK. If infection was detected in UK dairy cattle, the likely pathways of human exposure are occupational and include farm and dairy workers, veterinary professionals and laboratory exposures. Historically, AI infections in humans have predominantly been acquired via direct contact with an infected animal or their contaminated environments. Current evidence suggests that the likelihood of human infection and onward spread is very low, and no sustained human-to-human transmission of AI viruses has ever been reported.

Consumption of unpasteurised, contaminated animal products is a possible but less likely source of exposure for humans (22), due to animal health and welfare and food safety guidelines in the UK around producing and consuming raw dairy products (23), particularly for vulnerable people.

There is currently no surveillance in dairy workers for AI A(H5N1). The only clinical sign in the USA human case was conjunctivitis, and while this is known to be a possible symptom of human infection with A(H5N1), it is unlikely that cases of conjunctivitis would be tested for AI A(H5N1).

(SNIP)
Interim outcomes and recommendations

Although there are evidence gaps affecting the interpretation of the risk AI A(H5N1) clade 2.3.4.4b genotype B3.13 presents to people in contact with infected animals in the UK, the HAIRS group determined that, based on the currently available information:

it is very unlikely this new Eurasian/North American reassortant is already circulating in dairy cattle in the UK, due to the lack of incursion pathways and the low level of AI cases in the UK since November 2023, when this virus strain emerged in the USA. Furthermore, there is ongoing genomic surveillance in place that aids early detection of new AI strains in wild bird and poultry in the UK. To date, this genotype has not been detected in the UK
the current risk to people in contact with animals infected with his strain in the UK is therefore, at most, very low (medium uncertainty). This is based on likelihood of exposure and impact of infection
there are some limited imports of raw dairy products including colostrum and these are being considered by not only Defra Imports team but also the Food Standards Agency. It is not certain whether current pasteurisation methods would be effective in completely eliminating the viral load of a large volume of thick, discoloured milk from infected cattle; however, milk from cattle showing such clinical manifestation would be identified as unfit for human consumption and disposed-of on the farm; it would not be added to the bulk tank, which is only for milk destined for human consumption. Nevertheless, exposure to such products (prior to pasteurisation) or equipment is a potential risk pathway which needs further assessment
unknowns which make a full assessment too uncertain at this stage, include the source of infection into and between herds in the USA – whether this is a rare spill-over event or an evolutionary change in the ability of the virus to infect cattle and in particular mammary gland cells; the duration of virus persistence in infected cattle or on equipment in the milk production process ; the transmission to calves from infected dams

Based on the above, the HAIRS Group makes the following recommendations:

For animal health and veterinary professionals to:

continue close monitoring of the situation in the USA, including further understanding of likely pathways of introduction into the UK
report any clinical signs associated with an unexplained reduction in milk yield, thickened milk (that is uncharacteristic for the stage of lactation) combined with reduced feed intake, low rumination and/or fever in dairy cattle to the APHA
report any unexplained mortality, neurological and/or respiratory symptoms in other animals (for example birds or other mammals) on dairy premises to the APHA
continue monitoring for new evidence as to the presence of AI A(H5N1) Clade 2.3.4.4b genotype B3.13 in wild birds, poultry and livestock in the UK
raise awareness and encourage farm and dairy workers to maintain sensible biosecurity on dairy farms (for example, the use of aprons, gloves and eye protection in parlours and sterilization of milking equipment)
undertake prompt investigation into possible transmissible zoonotic diseases on farms
include testing milk from UK dairy farms in surveillance plans for animal that meet the case definition (as published on GOV.UK (34))
ensure sharing of data between animal and human health agencies to ensure a one health approach is adopted to issues on dairy farms

For public health professionals to:

continue close monitoring of the situation in the USA, including likely transmission pathways to humans
raise awareness regarding consumption of raw dairy products including colostrum
consider the rapid investigation and testing of farm or dairy workers with respiratory or compatible symptoms, particularly on affected premises
ensure sharing of data between animal and human health agencies to ensure a one health approach is adopted to issues on dairy farms

(Continue . . . )

For what its worth, I highly doubt that H5N1 genotype B3.13 is currently circulating in UK cattle, and I agree the risk to people living in the UK is probably quite low.

This HAIRS report does a good job describing the various barriers the virus would need to cross to reach the UK, and while formidable, they are not insurmountable.

Their perceived lack of risk, however, is being used to rationalize not aggressively testing for the virus. A bit surprising, since this opinion is based on very limited testing (of both cattle and humans), which they admit is proffered with medium uncertainty.

As stated in this report:

" . . . mastitis cases are not routinely tested for AI viruses as there has never been any evidence to suggest a testing requirement. "

"There is currently no surveillance in dairy workers for AI A(H5N1)."

"The only clinical sign in the USA human case was conjunctivitis, and while this is known to be a possible symptom of human infection with A(H5N1), it is unlikely that cases of conjunctivitis would be tested for AI A(H5N1)."

While genotype B3.13 appears to be a regional threat (at least for now) for North America, there is nothing to say another genotype couldn't emerge somewhere else in the world with a similar ability to infect livestock.