The Biden administration has released nearly $2bn to tackle the outbreak, the majority of which ($1.5m) allocated to the USDA to stop the spread among animals. Of the total, $360m has been spent to protect the public, as the risk to humans remain low according to the CDC.
But with the H5N1 outbreak in US dairy cattle being the largest to affect domestic mammals close to humans, experts warn that allowing transmission to continue risks the highly adaptable virus to mutate enough for human-to-human transmission.
The sector has found some relief in that pasteurized milk - the only type allowed to be commercially sold interstate – is safe to consume as the thermal treatment eliminates the virus.
H5N1 infections in numbers, US
- 74 human infections
- 917 dairy herds
- 10,922 wild birds
- 130,674,361 poultry
(information correct as of January 7, 2025)
H5N1 bird flu has also not been associated with mortality rates in dairy in the same way it has been in poultry – but veterinarians have reported the disease can amplify existing health and management issues, such as mastitis.
However, the outbreak is now threatening to become an economic issue for the sector.
In California, the nation’s largest dairy-producing state, where around 650 herds (nearly 70% of the state’s dairies) have caught the virus since August 2024, production has dropped in nearly double-digit terms.
The impact of the outbreak – which causes lactating dairy cows to dry up or produce thick, colostrum-like milk – has been linked to the 9.2% decrease in California milk production YoY in November 2024.
This is the largest decrease in 20 years; with 2004 being the last year when production fell under 3 billion pounds (November 2024: 2.957bn lb).
California governor Gavin Newsom announced a state of emergency to fast-track measures to tackle the outbreak – which has now spread to 16 US states since March 2024 – but experts including the WHO warn a holistic approach is needed to stamp out the disease effectively.
In a research paper published in mBio, a team of US and British researchers conclude that if transmission in cattle continue to occur, a H5-subtype vaccination program for cattle ‘could be necessary to limit the impact on the sector and new transmission routes to other mammalian species, including humans’.
However, there are no approved vaccines against HPAIV H5N1 for cattle or humans, and the seasonal flu vaccines do not provide protection or provide limited protection against avian influenza viruses, the researchers said.
“We are facing a critical time to understand and address this new threat before the virus continues evolving and adapting.
“Although it is always possible that the outbreak in cows dwindles by itself, especially if infected cows are non-susceptible to reinfection, ignoring or minimizing the threat of the continuous adaptation of this virus to new hosts exposed to infected cattle and infected milk could lead to severe consequences for animal and human health.”
Meanwhile, non-profit policy research organization the Center for Strategic and International Studies criticized the US response so far, highlighting gaps in public health capabilities and ‘dangerous shortcomings’ in pandemic preparedness, including slow coordination and planning and lagging data and gaps in surveillance.
“It is not too late to change course,” the position paper’s authors Michaela Simoneau, Sophia Hirshfield, and Maclane Speer wrote.
“Strong interagency, interstate, and global coordination; better protections for farm workers; accelerated planning and investment in surveillance; and the development and promotion of better vaccines and therapies remain the essential elements to prevent the sustained spread of H5N1.”
US records first H5N1 bird flu fatality
On January 6, 2025, the Louisiana Department of Health reported the death of the first US patient with a severe infection caused by H5N1.
The patient was over the age of 65 and had underlying medical conditions, according to the authorities. The patient contracted H5N1 after exposure to a combination of a non-commercial backyard flock and wild birds.
The virus that infected them belonged to the D1.1 genotype, according to CDC – and differs from the B3.13 genotype detected in dairy cows.
What’s the latest advice for producers?
The National Milk Producers Federation advises dairy farmers to practice a raft of biosecurity measures, including limiting livestock movement; isolating newly-introduced cattle from the herd for at least 30 days; delaying or stopping non-essential visits to the farm; limiting the movement of vehicle or equipment on and off premises; avoiding the mix of species, particularly where dairy cows and poultry are co-located; and avoiding feeding raw milk to calves and other animals, as there’s evidence that the virus is transmissible through raw milk intake.
Experts have now established that the most likely route of cow-to-cow transmission is via infected milking devices, which then spread the virus to the cow’s mammary tissue during milking.
Sources:
Avian influenza A (H5N1) virus in dairy cattle: origin, evolution, and cross-species transmission
Authors: Martinez-Sobrido, L., et al
Published: mBio, Volume 15, issue 12, 13 November 2024
DOI: 10.1128/mbio.02542-24
