#18,782
Yesterday the EFSA (European Food Safety Authority) published a lengthy (55-page) risk assessment on the potential for the Bovine B3.13 genotype H5N1 virus to arrive in Europe and spread to local dairy cattle.
While remarkably detailed, this report all but ignores the D.1. genotype which in recent months has spilled over into cattle in at least two U.S. states, has caused severe (even fatal) illness in humans, and which has spread with remarkable speed via migratory birds.The UK also reported an H5N1 infected Sheep earlier this year (genotype D1.2), and last summer the FLI successfully infected cattle with a contemporary European H5N1 virus, finding it replicated efficiently in bovine mammary tissue and could produce adaptive mutations (PB2 E627K) during replication.
While not mentioned, it is possible a separate risk assessment is in the works on other HPAI H5 genotypes.
First, the EFSA press release - followed by a few excerpts from the risk assessment - after which I'll have some comments.
Bird flu: EFSA analyses situation in US and tracks possible routes of spread3 July 2025
2 minutes read
The seasonal migration of wild birds and the importation of certain US products, such as those containing raw milk, could be potential routes for the introduction of the highly pathogenic avian influenza (HPAI) genotype currently affecting US dairy cows into Europe, a new report released by EFSA says. This virus type has not been reported so far in any country other than the USA.
EFSA’s scientists highlight that key European stop-overs with high-density bird congregations, such as Iceland, Britain, Ireland, western Scandinavia, and large wetlands like the Wadden Sea on the Dutch, Danish and German coasts would be useful places for early detection of the virus during the seasonal migration of wild birds.
The report also addresses the potential for the virus to be introduced into Europe through trade, concluding that the importation of products with raw milk from affected areas in the USA cannot be completely excluded and therefore could be a possible pathway. The importation of dairy cows and bovine meat could also be a potential route for virus introduction. However, the virus has rarely been found in meat, animal imports are very limited, and very strict trade regulations are in place for meat and live animals entering the EU.
EFSA’s report also provides an overview of the situation in the USA, where 981 dairy herds across 16 states were affected between March 2024 and May 2025. The report, which was reviewed by the US authorities, highlights that cattle movement, low biosecurity, and shared farm equipment contributed to the spread of the virus.
By the end of the year, EFSA will assess the potential impact of this HPAI genotype entering Europe, recommending measures to prevent its spread.
SCIENTIFIC REPORT
Open Access
European Food Safety Authority (EFSA), Julio Alvarez, Alessio Bortolami, Mariette Ducatez, Claire Guinat, Jan Arend Stegeman … See all authorsFirst published: 03 July 2025
Approved: 28 May 2025
Abstract
The emergence of highly pathogenic avian influenza (HPAI) A(H5N1), clade 2.3.4.4b, genotype B3.13 in U.S. dairy cattle marks a significant shift in the virus' host range and epidemiological profile. Infected cattle typically exhibit mild clinical signs, such as reduced milk production, mastitis and fever, with morbidity generally below 20% and mortality averaging 2%.
Transmission within farms is primarily driven by contaminated milk and milking procedures, while farm-to-farm spread is mainly linked to cattle movement and shared equipment. The virus demonstrates high replication in mammary glands, with infected cows shedding large quantities of virus in milk for up to 3 weeks, even in the absence of clinical signs. Shedding through other routes appears limited. Infected cattle develop virus-specific antibodies within 7–10 days, offering short-term protection, though the duration and robustness of immunity remain unclear.
Between March 2024 and May 2025, the virus was confirmed in 981 dairy herds across 16 U.S. states, with California particularly affected. Risk factors identified for between-farm spread include cattle movement, shared equipment and contact with external personnel, while biosecurity measures, including waste management and wildlife deterrence, may reduce the risk of virus introduction. In response to the outbreaks, U.S. authorities implemented strict movement controls, mandatory testing and enhanced biosecurity protocols.
Potential pathways of introduction of HPAI B3.13 virus into EU via trade from US could be the import of lactating cows and bovine meat, although strict trade regulations, absence of animal import and limited virus detection in meat, especially in muscle tissue, do not support this occurrence. Import of products containing raw milk could also be potential pathways for virus introduction.
Migratory birds – particularly waterfowl – pose potential pathways for introduction during seasonal migrations. The detection of mammalian-adaptive mutations and zoonotic cases underscores the virus' public health relevance and the need for research, surveillance and cross-sectoral preparedness.
The caveat in all of this is that much of this risk analysis is based on findings by our own USDA (see example below), whose understanding of the virus continues to evolve.
According to the USDA, the spread of HPAI A(H5N1) virus between farms within and between States is likely linked to movement of lactating dairy cattle and shared equipment or workers between farms, while within farm spread is considered to be driven by mechanical cow-to-cow transmission, for example through contaminated milking equipment (USDA, online-b; Le Sage et al., 2024a).
While this theory is widely embraced by the USDA and many dairy farmers, there remain a great many unknowns surrounding the spread of the virus.
Two weeks ago in Preprint: Dairy Cows Infected with Influenza A(H5N1) Reveals Low Infectious Dose and Transmission Barriers, we looked at a study that was unable to duplicate the spread of the virus via contaminated milking equipment under controlled experimental conditions.
Similarly, limited surveillance and testing of humans, non-dairy cattle, and peridomestic animals in and around cattle farms has left us with huge gaps in the data (see EID Journal: Avian Influenza A(H5N1) Virus among Dairy Cattle, Texas, USA).
This EFSA report acknowledges a number of uncertainties in their analysis (see below).
While the fall southbound bird migration from their high latitude roosting areas doesn't begin in earnest for another 45-60 days, we are already seeing sporadic cautionary reports of avian flu activity coming from Europe (see below).
Notice to the public regarding Avian Flu
From: Department of Housing, Local Government and Heritage
Published on: 3 July 2025
Last updated on: 3 July 2025
Highly Pathogenic Avian Influenza HPAI (H5N1) is currently circulating in wild birds, especially in breeding seabirds around Ireland. Over the last three weeks in particular, including following intensive surveillance by NPWS, and reports from others, there have been a number of cases of groups of dead wild sea birds washing up on shorelines in counties Kerry, Clare and Galway. A number have been tested by the Department of Agriculture, Food and Marine, and gulls and Guillemot have so far been confirmed with HPAI; and many multiples of that are likely to have HPAI. In total, 25 wild birds have tested positive for highly pathogenic avian influenza (HPAI) in 2025 (January-June).
Meaning that any lull in HPAI activity we may be enjoying during these summer months, could easily evaporate this fall.
Stay tuned.
