Avian Influenza: What we know as jump to dairy herds raises concerns

The Avian Influenza first detected on U.S. cattle farms on March 25 has spread to at least 33 dairy herds in eight states. Fragments of the virus have been detected in pasteurized milk in the U.S. A farmer in Texas has been infected.

On the heels of the COVID pandemic, the pace of these reports has sparked widespread concerns that another virus will upend our lives.

So far, there have been no reports of the virus circulating in Canadian cattle or livestock. The Canadian Food Inspection Agency says it is keeping a close eye on the situation and has asked Canadian farmers to monitor their cows for signs of the virus.

So, what is the Avian flu?

Highly Pathogenic Avian Influenza – a brief history

HPAI, a contagious and often deadly disease in poultry, is caused by highly pathogenic Avian Influenza A (H5) and A (H7) viruses. The current highly infectious strain that is spreading is the H5N1. It is not new. It was first detected in chickens in Scotland in 1959; however, that strain underwent significant evolution around 1997 and was very different from the current version of H5N1. Sporadic cases and outbreaks have resulted in hundreds of human cases of the H5 Avian Influenza virus, particularly the H5N1 subtype, predominantly from direct contact with infected birds in commercial poultry farming.

The H7 subtypes have been recorded even earlier. It used to be called the “fowl plague” and was only sequenced as various H7 subtypes in the mid-1950s. Between 2013-2018, the H7N9 strain caused several outbreaks, with the majority of human cases in China.

What about the current Avian flu outbreak?

This degree of spread outside of birds and poultry is unprecedented for Avian flu – and therefore highly concerning. The Texan dairy farm worker was infected with an H5N1 subtype. There is some data to show that this strain requires a lot more direct contact for spread to humans than H7 subtypes.

In addition to the dairy herds, Avian flu has been reported in several wild animals globally (including Canada) such as racoons, skunks, red foxes, minks, cats, and even polar bears. It has not yet been reported in pigs, which is a good thing since they are susceptible to both avian and human flu.

Officials estimate that the current outbreak of the Avian flu, which is carried by wild birds, has been spreading among dairy cattle since late 2023.

How is Avian flu transmitted?

Avian flu can be transmitted by directly touching sick animals, their saliva, mucous, blood or feces and then touching your eyes/nose/mouth. The virus is also airborne and spread through droplets.

The good news for now is that Avian flu is not adapted to spread well between humans.

The good news for now is that Avian flu is not adapted to spread well between humans, so human-to-human transmission risk is still low. This, of course, can change should the virus mutate sufficiently.

What does that mean for us now?

The fact that the Avian flu, which has been mostly limited to wild birds and poultry, is spreading rapidly in other mammals brings us closer to a scenario in which the virus could more easily be adapted for human spread. But we aren’t there yet and, hopefully, we are able to curb this spread before such a situation occurs.

For the general public:

Be vigilant. If you come across a sick or dead wild bird, please keep your distance. You can call your city’s wildlife phone line and report it. Make sure you keep your pets away from wild birds as well.

If you are a backyard hobbyist, take all necessary protocols to keep your birds/chickens/cows away from wild birds. Use personal protective equipment if you think your bird, poultry or cow may be sick. If you are a poultry or dairy farm worker, please refer to Centres for Disease Control’s guidance for enhanced protection.

On food consumption:

Pasteurized milk is safe for consumption. A report from the U.S. Food and Drug Administration (FDA) found remnants of the Avian flu in pasteurized milk. However, the milk was tested using a quantitative polymerase chain reaction (qPCR) technique that picks up all genetic material, dead or alive. The FDA says these remnants are simply dead viral matter and not infectious. What was concerning was how much of the milk had these viral remnants, which lends credence to the assumption that Avian flu was likely spreading rapidly in dairy cattle since late 2023.

Current recommendations are to ensure you are drinking pasteurized milk and cooking chicken and beef thoroughly. Data seems to show that pasteurization of eggs, even though done at a temperature lower than milk, is effective in killing Avian flu virus; although most eggs sold in Canada are not pasteurized.

Vaccines and treatments:

The CDC completed testing that showed the current H5N1 flu virus is susceptible to medications used in seasonal flu treatments (e.g., oseltamivir, zanamivir, peramivir). Another new drug (baloxavir marboxil, sold under the brand name Xofluza) showed some promise, but more studies are needed.

Our current influenza vaccine does not cover H5 viruses, so they probably do not provide much protection. However, from the genetic sequencing in the Texan dairy farm worker, two existing H5N1 candidate vaccines could be effective, studies suggest. These could be used to quickly produce vaccinations for humans if needed. Another vaccine – Audenz – was approved by the FDA in 2020 and indicated against Influenza A(H5N1). The U.S. has a stockpile available. Annual influenza vaccine production is a well-oiled machine. We would need to ramp up supply, and while it won’t be easy, it is very doable.

Learning from past mistakes

Increasingly, scientists have voiced concerns that the United States Department of Agriculture has not been forthcoming with information. There have been several challenges with lack of transparency, data availability, genetic sequencing and adequate testing. This must be immediately and firmly addressed.

The Avian flu outbreak is a rapidly changing situation. It is essential for us to continue diligently monitoring farm animals with thorough surveillance including robust preparedness efforts. Timely and transparent communication to the public, even when information is not fully available or certain, also is critical. Trust in public health is at an all-time low, we cannot afford to make the same mistakes again.

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Sabina Vohra-Miller


Sabina Vohra-Miller is the co-founder of the Toronto-based Vohra Miller Foundation, which aims to improve the health of the planet and its people.

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