Expert delves into the complexities of HPAI and milk consumption
Heidi Crnkovic, Associate Editor | AGDAILY
June 14, 2024
In February, Texas dairy farmers began to notice sick cattle. Nearly two months later, veterinarians identified the root cause: a highly pathogenic strain of avian influenza: H5N1. Even though H5N1 has circulated for almost three decades, its transmission to dairy cattle in the U.S. was unexpected.
Without early detection, the outbreak rapidly spread to several other states with cattle movement.
Avian influenza virus type A (H5N1) has now been confirmed in dairy cattle in 12 states: 24 herds in Michigan, 22 in Idaho, 18 in Texas, eight in New Mexico, five in South Dakota, four each in Kansas and Colorado, three in Minnesota, and one each in Iowa, North Carolina, Ohio, and Wyoming.
After detection, the news rapidly flooded with information, bombarding the public with concerns about HPAI’s H5N1 variant, especially as virus particles were found in one out of five milk samples tested by the Food and Drug Administration.
The announcements caused people to question, “Is milk safe to drink?” The answer is consistently and overwhelmingly, “Yes if it’s pasteurized” — meaning the milk has been heat treated to sterilize it.
We asked biomedical scientist and founder of Immunologic, Dr. Andrea Love, to clear up some of the concerns and confusion swirling around HPAI, dairies, and beef. Along with a passion for helping the public and healthcare professionals understand scientific topics, Love is a subject-matter expert in infectious disease and immunology, and she was recently featured on the Food Bullying Podcast thanks to her passion for translating complex topics for the public.
Why is it called avian influenza, even in cattle?
This particular virus strain is called H5N1, named after the virus’ historic infection of wild and domestic birds. HPAI is particularly serious and deadly in poultry. Cattle and humans, however, have different stories.
“Since 2003 to the present day, there have been less than a thousand human cases across 21 countries,” said Love.
It’s no lie that avian influenza viruses have large ecological and agricultural implications in poultry operations. H5 bird flu is widespread in wild birds worldwide and is causing outbreaks in poultry. In birds, the mortality rate is nearly 100 percent. It has even proved deadly in half of barn cats at one dairy farm that drank (unpasteurized) milk from dairy cattle.
Meanwhile, cattle impacted by HPAI have exhibited low appetites, flu-like symptoms, and thick and discolored milk accompanied by a sharp reduction in milk production. No cattle have died from infection. Only four humans (all farm workers) have reportedly contracted HPAI from cattle and experienced mild symptoms as well. There are currently no confirmed cases where the virus has spread from person to person.
Understanding how avian flu is characterized and categorized is important for understanding H5N1 and the concerns surrounding it.
“When we talk about flu, it’s a really big bucket of viruses that are all classified as influenza viruses. There are five main types: Type A, B, C, D, and E,” explained Love. “When we talk about a human seasonal flu, we’re usually talking about Flu A and Flu B, which predominantly infect humans.”
Avian flu is often categorized as H5N1. The H and the N refer to two proteins that stick out on the outside of the flu virus: hemagglutinin and neuraminidase.
“There are up to 198 possible types of influenza B, and some of them are not going to infect people that well, which is the case in H5N1,” said Love.
The reason behind this is that the proteins, the H and the N attach to certain receptors or proteins on their host cells, specifically sialic acid receptors. The ones that bind H5N1 the best are not present in humans. In order to be successfully infected, it requires quite a lot of exposure in humans.
“H5N1 likes a specific version of that site, which is found in the respiratory tracts of birds. And, that’s why these H5N1 viruses are typically called avian flu is because they predominantly impact birds,” Love noted.
While Flu A can infect a broad array of other animals, most of the other types of flu have a lesser ecological and public health impact.
Influenza viruses have a segmented genome, so their RNA is in eight pieces and can move around from one virus to another, which means that the influenza viruses can change. They have the general mutation process, called antigenic drift, which was talked about a lot during the COVID pandemic. In those instances, every time a virus replicates, errors happen, and sometimes those errors can lead to an advantage for a virus, and one that’s going to be selected for evolutionarily.
If two somewhat compatible flu viruses get together, they can also exchange pieces of their genome, leading to an entirely new flu.
That’s the big concern here. This can lead to the emergence of an entirely new flu virus that animals and humans haven’t seen yet. And when that happens, that can lead to pandemic flu, which is very different from seasonal flu.
One of the primary concerns with sick cattle currently is that they may serve as a reservoir if they’re in contact with poultry on a farm or even wild birds in the vicinity; they could act as a vehicle to spread the virus.
Agriculture Secretary Tom Vilsack told Reuters that 24 companies are currently working on developing an avian flu vaccine for cattle.
The other consideration is whether avian influenza could become a new flu virus — especially if things move to pigs, far more so than cattle.
“Pigs are considered a very good mixing vessel where an avian flu virus and a human flu virus could cause a whole new flu virus to emerge, which would be the immediate public health concern for people,” Love said.
How do we know milk is safe?
While immediately jumping to testing milk and meat products may have sparked some alarm, finding killed virus particles in pasteurized milk products was not only good news for food safety but an important indicator in monitoring disease spread.
By examining the origins of outbreaks, researchers gathered crucial insights into their initiation and spread. This information can help mitigate the impact of an epidemic and, ideally, prevent future ones. Field observations and genomic analyses have identified Texas as the starting point for this cattle outbreak.
To ensure the safety of the food supply, the FDA and the U.S. Department of Agriculture began testing finished dairy products, including pasteurized milk and pasteurized dairy products earlier this year.
That helps to back-calculate and monitor when and where dairy cattle might be infected — and, whether remnants of the virus are live or killed.
Using a technique called polymerase chain reaction, or PCR, scientists look for fragments or pieces of the virus’ genome (RNA). In follow-up studies, it was confirmed that virus fragments found were just that — small pieces of inactivated virus, thanks to pasteurization processes.
“They’re not able to cause illness, and they’re not able to reproduce,” Love confirmed. “Once upon a time, there might have been active flu virus, but because they’re pasteurized, we’ve destroyed them. …
“Heat does a really good job of rendering things dead or inactive. It denatures proteins that are essential for viruses to survive while it does not compromise the quality of the food product,” she added.
Virus particles in milk are killed and destroyed very effectively by pasteurization, a process that has been used since the 1860s after French microbiologist Louis Pasteur demonstrated that thermal processing would deactivate unwanted microorganisms in wine.
Today, the pasteurization process is used in milk, eggs, canned foods, fruit juices, and more.
“Raw milk, in particular, has been the cause of over 200 foodborne disease outbreaks in the U.S. in the past 20 years,” Love said. “We’re seeing an increase in these rates because of public pressure to relax laws about prohibiting raw milk products.”
At the federal level, the U.S. Food and Drug Administration bans the interstate sale or distribution of raw milk. While drinking or consuming raw milk is legal in all 50 states, raw milk sales are legal at different levels in all but Hawaii, Nevada, Rhode Island, and Washington, D.C.
Yet, even the allowances in sales differ from state to state. For example, on-farm sales are legal in over 20 states. Meanwhile, herd shares, a membership that allows consumers to purchase a share in a dairy herd, are legal in an additional half-dozen states. Other states allow herd share but have no laws regulating it. Meanwhile, a handful of states also allow the sale of raw pet milk.
The reality is that life is filled with bacteria and viruses, most of which are harmless to humans, and that life cannot happen without them. But, while some of them are beneficial, others remain inconsequential, and a few, of course, will make you sick.
“The same is true for cows. They have a microbiome on their hair, skin, udders. Even if you’re milking a cow with the utmost cleanliness and hygiene processes, bacteria are everywhere; they’re in the environment,” Love said.
What are the public health risks associated with HPAI?
Despite mass publications touting the growing concerns surrounding avian influenza, Love said that the risk to human health is currently low.
“That’s the good news,” she said. “But it’s easy for outlets to end up on repeat and feed into health anxiety. I’m an infectious disease immunologist, and disease spread and transmission of zoonotic diseases are always a concern for me. But, I think we’re just kind of scaring people unnecessarily.”
So, what changes do the general public need to make? “Nothing,” Love said, “except don’t touch wild birds. Now, if you’re a dairy farmer, you now have regulations you have to comply with. Dairies have milk testing, border crossing restrictions, and so on.”
Could this be a situation where that changes? “Yes, it could,” she said. “But that’s why we need to be prepared, including those involved in those decisions within the government and all of the scientific organizations. And, they’re doing that.”
To help prepare, stockpiles of H5N1 vaccines wait and continue to be developed to help protect populations from a potential pandemic. U.S. federal officials recently confirmed that CSL Seqirus will deliver approximately 4.8 million doses of pre-pandemic vaccine that is well-matched to the H5 of the currently circulating HPAI strain.
The European Union also recently signed a framework contract to receive 665,000 doses of the influenza vaccine Seqirus.
“While the threat of avian influenza to the general population remains low, we need to protect people at higher risk, such as poultry and farm workers or certain veterinarians,” said Stella Kyriakides, commissioner for health and food safety at the EU. “Today, we announce an agreement on behalf of participating countries to secure access to over 40 million doses of avian influenza vaccine. We are ready to take further action should the situation evolve in the future.”
The vaccine is the only preventive zoonotic avian influenza vaccine currently authorized in the EU.
So, what’s currently the biggest concern?
“The stability (not safety) of our food supply and wild bird species,” Love said. “I know it’s not sensational, but I think when we’re talking about the big picture, this is what’s most immediately concerning: the loss of biodiversity.”
