Why dangerous bird flu is spreading faster and farther than first thought in US cattle – CBC News Achi-News

This story is part of CBC Health’s Second Opinion, a weekly analysis of health and medical science news emailed to subscribers on Saturday mornings. If you haven’t subscribed yet, you can do so by click here.

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Discovery of a dangerous type of bird flu virus in the lungs a US dairy cow that showed no symptoms. Viral particles identified in processed, pasteurized milk Genetic sequences showing noticeable changes in this H5N1 strain that has been spreading rapidly throughout American cattle.

Those were just a handful of the rapid-fire developments this week as the unprecedented H5N1 outbreak among US dairy cattle continues to evolve.

Scientists are now warning that this type of bird flu is likely to be more common in cows, and that it is transmitted for longer than official reports suggest. And while American officials are increasing testing – all in an effort to prevent sick cows from being moved between states – others say we are already several steps behind the spread of a disease that could pose a major threat to human health.

Michael Worobey, a BC researcher who now heads the department of ecology and evolutionary biology at the University of Arizona, said these cattle infections may have been “flying under our radar for months,” providing continued opportunities for the virus this acquired adaptations that could lead to a flu pandemic.

“I think, in many ways, this is the biggest news story in the world right now.”

Tracing the root causes

After the US Department of Agriculture posted more than 230 genetic sequences from the country’s growing outbreak of H5N1 last Sunday, Worobey was among the scientists who raced to analyze the complex data set.

The sequences came from cattle – amid an outbreak that affected more than two dozen herds across nine US states – but also several species of birds, cats, skunks and raccoons.

Local birds may have transmitted the virus to local farms, in different states, and they are all spreading a similar genetic lineage, he said. But Worobey believes that what is far more likely is that the cattle outbreaks have a single point of origin.

In an interview with CBC News, he outlined the evolutionary tree of H5N1, with a particular branch of sequences associated with cattle. Those sequences all share the same mutations, Worobey added.

“This is a single jump token, which is at the heart of this case,” he said.

And that jump probably happened earlier than the the first known cases of cattle infections at the end of March.

A single introduction could have happened as far back as November or December, with a distinct lineage of H5N1 then spreading undetected for months, Worobey said. He added that missing details in the initial US data dump – including the exact locations and dates of cattle – made it difficult to know for sure.

The cattle sequences also contain “at least two different mutations” known to increase the risk of influenza virus infection and transmission in humans, Worobey added.

“We’re producing more and more [opportunities] for evolution to reach something that can transfer in humans, and potentially kill a large proportion of them,” he said.

Milk discoveries

What’s not yet clear is how, exactly, the virus is spreading among cattle, although several scientists have told CBC News that possibilities include close contact between cows being transported between states or equipment contaminated milking.

“If the cattle really have [infection] in the chairs, then transmission could be via milking equipment,” said Michelle Wille, senior research fellow with the University of Melbourne’s Center for Pathogen Genomics and the department of microbiology and immunology.

“A number of infected states have noted that [avian flu] has been found in dairy herds that recently received cattle from Texas – so cattle shipping is likely to play a role in spread.”

At this point, it’s still unclear how the virus “maintains transmission” in cattle populations, added virologist Angela Rasmussen, of the University of Saskatchewan’s Institute of Vaccines and Infectious Diseases.

It is also likely that the virus is transmitted even when cows do not show symptoms – which so far have been mild, including low appetite and reduced milk production – several scientists agreed.

This week, officials announced twin discoveries of H5N1 in the lungs of an asymptomatic cow in North Carolina, along with viral particles in pasteurized milk, suggesting that infected cows may have slipped into the food supply chain.

The Ohio State University researchers also said they recently did their own independent sleuthing, collecting 150 commercial dairy products from dairy processing plants across 10 states. The team found fragments of viral RNA in nearly 60 samples – nearly 40 percent of the products, all available on store shelves.

Rasmussen emphasized that the discovery of viral RNA in milk does not necessarily mean it can make people sick if it is fragments of a virus, not something infectious. Dairy products also go through pasteurizationa heating process that is supposed to eliminate a variety of pathogens.

But in an update on Thursday, the US Food and Drug Administration (FDA) said additional testing was still needed “to determine whether an intact pathogen is still present and whether it remains infectious, which would helps inform a decision as to whether there is any risk of illness associated with eating the product.

The FDA added that retail milk studies have so far not shown any results that would change its assessment that the commercial milk supply in the United States is safe.

What’s more worrying, Rasmussen said, is that these developments suggest that the cattle outbreak is “far greater than originally thought.”

Like buying lottery tickets

To better understand the scope of the spread of H5N1 among cattle, increased testing of dairy cattle is now a key aspect of America’s response.

The United States will require that dairy cattle moving between states for trade be tested for bird flu, Agriculture Secretary Tom Vilsack told reporters this week. All labs and states must also report positive tests for any type of flu.

The concern from officials and scientists alike stems from the potential effects on animal health and the food supply chain, and the possibility that this virus is approaching a pandemic level threat to humans as well. Although the reported cattle infections have not been serious, scientists warn that they could trigger adaptations that could make it easier to infect more mammals.

Since 2022, only two human infections have been reported in the United States, with the latest one linked to these recent cattle outbreaks. Both were mild. But sporadic human cases linked to contact with previously infected animals have been occurring around the world, with many causing severe symptoms, severe pneumonia, or even death.

Based on human case data available to date, the death rate for this type of bird flu is it is believed to be a staggering 52 per centalthough scientists say that much milder cases are likely to be underreported and skew that data.

However, with so many cattle being infected and coming into contact with farm workers every day, the number of human exposures is increasing, Worobey warned. “It’s like buying more and more lottery tickets in the lottery, ‘Can a new pandemic virus really evolve?'”

Infectious disease doctors in Canada keep a close eye on the intersections of livestock, wildlife and humans.

Officials at the Canadian Food Inspection Agency have not yet responded to a series of questions from CBC News, but they said online that it has not detected this type of bird flu in Canadian cattle, so it does not test raw or pasteurized milk. at this time.

“[Highly pathogenic avian influenza] It is not a food safety concern as pasteurization kills harmful bacteria and viruses,” the agency said on X, formerly Twitter.

Dr. Samira Mubareka, a clinician scientist at the Sunnybrook Research Institute and the University of Toronto, is watching for any signs that the virus is becoming more adept at transmitting between mammals, including humans.

“From the perspective of the virus, the more transmission there is, the more opportunities to adapt,” Mubareka said. “That’s worrying.”

Mubareka said any improved change in transmission among mammals would also indicate an improved ability to transmit among humans, which is why it is so important to find out if those in close contact with cattle or wildlife are at greater risk.

He said that even if this H5N1 virus does not infect more people, the virus has already hit animal health significantly and could affect food prices, food security and livelihoods.

Rasmussen agreed, and said the effects could be severe if human-to-human transmission begins.

“It would have a devastating effect on human and animal health, on the economy, on the food supply,” he said. “It would be a worst case scenario.”

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