Scientists concerned about avian influenza H5N1 outbreak in cattle and infection in Canada: Shots

More than 650 dairy farms have been affected by the avian influenza outbreak. Dozens of people have been infected through contact with infected cattle and poultry.

Charlie Neighborgal/Associated Press

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Charlie Neighborgal/Associated Press

Scientists believe it was about a year ago that the influenza virus that kills birds in the Texas Panhandle encountered a new and surprisingly hospitable host: dairy cows.

This encounter was enough to spark today's cattle epidemic, and scientists who study influenza warn that the infection could become a new pandemic.

The virus has already passed between hundreds of herds and repeatedly entered humans. And in a troubling development, several cases have emerged in North America with unknown sources of infection, most recently. child A teenager in the San Francisco Bay Area and a teenager in British Columbia remain hospitalized in serious condition.

Genetic sequencing of the incident in Canada suggests the culprit may have been a wild bird, and changes in the virus that may help it attach to and replicate in human cells more efficiently. Pointed out.

“This is exactly what we don't want to see,” he says Louise Moncla“The British Columbia case shows that influenza never ceases to surprise us,” said a virologist at the University of Pennsylvania.

Fortunately, Canadian health officials have found no evidence that the teen contracted the virus or passed it on to others. And isolated cases of this kind are not unheard of in parts of the world where bird flu has been endemic for many years.

But scientists are clear-eyed about the risks ahead.

Dairy cows, poultry, and wild birds remain carriers of the virus, and there is a good chance that it could spread to humans. Meanwhile, the virus contained in raw milk On store shelves. And during flu season, there is a growing alarming prospect that bird flu could mix with seasonal flu.

“It's not that easy to get rid of this virus.” Dr. Jurgen Richta veterinary microbiologist at Kansas State University. “We will have to live with this situation for the next few years.”

Canada incident raises concerns

Since the first human infections associated with dairy cows were detected in the spring, there have been two reassuring constants.

There is still no strong evidence that people are spreading the virus to each other, and infections have mainly resulted in mild symptoms.

But on that second point, the Canadian case represents a departure.

What started as conjunctivitis in early November progressed to fever and eventually full-blown acute respiratory distress syndrome. According to Canadian health officials.

The young man had no underlying health conditions.

A thorough investigation was unable to determine exactly how the teenager, who was too unwell to be interviewed, contracted the virus. Repeated tests on the dog showed no signs of bird flu.

Based on the genetic evidence, the best guess is that an encounter with a wild bird or intermediate species sowed the seeds of infection. Dr. Bonnie Henry In collaboration with the British Columbia Ministry of Health.

“We may never know exactly where they were exposed,” she told reporters Tuesday during an update on the case.

Viruses collected from teenagers still belong to the same “”, butcladeMoncla said the H5N1 virus circulating in cattle originates from a “rare, genetically distinct group of viruses” that arrived from Asia several years ago. The virus is very similar to the virus that infected poultry workers in nearby Washington state.

But of particular concern are signs that the virus has evolved as it replicates in teenagers' bodies.

Moncla said some mutations that affect proteins on the virus's surface (the proteins it uses to bind to receptors on cells) help the virus infect humans more efficiently. states that it is possible.

Canadian health officials are investigating whether any of these changes made it easier for the virus to infect cells deep in the lungs, which is likely why this boy ultimately developed such a severe illness. This may explain why.

This is a disturbing finding, although more research is needed to understand its impact. Scientists are keeping an eye on these changes in the virus, as they are seen as a key step in starting an avian influenza pandemic.

So far, these worrisome mutations, which affect how the virus enters cells, have not appeared in bird flu that passes through cattle.

The breasts are already rich in receptors used by bird-like viruses. That means, at least in these animals, the virus may feel less “pressure” to adapt in a way that makes it more dangerous to humans, Licht said.

But, he added, “there are a lot of unknowns here.”

unchecked fad

For a while, Licht was optimistic that the country could eradicate the dairy cow outbreak.

His experiments with infected cows suggest that bird flu is spread primarily through virus-laden milk rather than as a respiratory disease, making it much harder to control. Dew.

“I thought this was good news. I thought if we could control the contamination of milk, we might be able to control the epidemic,” he recalls. “Apparently that didn't happen.”

Instead, the virus ended up in many different places. 670 dairy herds The virus spreads across 15 states, with California currently bearing the brunt of the outbreak.

“I don't think it's an exaggeration to say that control efforts have largely failed,” he says. michael osterholmwho runs the Center for Infectious Disease Research and Policy at the University of Minnesota.

Without new strategies and closer collaboration with industry, there is little sign that the situation will change, given all the ways the virus “could enter a susceptible dairy farm and explode”, he said. say. Gregory Grayan epidemiologist at the University of Texas Medical Branch.

Milk containing high concentrations of virus can easily spread within milking parlors. Rodents and other animals can carry infectious substances. Humans can become infected through contact with clothing or agricultural equipment.

“Unless there's a massive vaccination campaign, we just don't know how to control it,” he says.

So far, more than 50 people have been infected in the United States, but the actual number may be much higher.

“It's clear that we're probably missing a lot of cases,” Gray said.

for example, the study The testing, conducted by the Centers for Disease Control and Prevention, targeted farm workers in Michigan and Colorado after outbreaks of bird flu in cattle in those states. About 7% of people had evidence of previous infection, and about half did not remember having symptoms at the time.

Currently, this country is repeating the “mistakes of the new coronavirus''. Dr. Deborah Birxwho helped oversee the pandemic response during the first Trump administration.

“The most important thing is to track where the virus is,” said Birx, now a research fellow at the George W. Bush Institute. “And what we've learned over the last five years is that many viruses spread without symptoms.”

She says the true scale of the outbreak will remain unclear unless testing of cattle and associated human infections is stepped up. Initially, the infection may spread relatively quietly from person to person, but it will be difficult to get ahead of that.

A few isolated human cases in North America with no clear link to infected animals are disturbing, but historically this has not allowed viruses to circulate in wild birds for a long time. Osterholm points out that this is happening in regions of the world that have experienced the same upheaval.

”I'm not surprised,” he said, noting that some contact with migratory birds could “certainly explain” the infection. ”Is it possible that other incidents like this are happening? absolutely. Are there many other seriously ill people? no. “

Reassortment could change the virus

Scientists fear that under the right circumstances, a process known as reassortment – the genetic mixing of two viruses – could create a new version of bird flu that is more adapted to humans. There is.

The prospect of this happening in pigs, which are considered particularly dangerous “mixing containers,” has long worried influenza researchers. So far, there has been only one recorded case of birds being infected with avian influenza during the outbreak in the United States.

However, it is also quite possible that humans could cultivate the virus this way.

And flu season could cause this, says Kansas State University's Licht.

The idea is that some unlucky souls can be infected with seasonal influenza and avian influenza at the same time.

“We believe that all past pandemic viruses that have occurred in human influenza have been reassortment events between viruses circulating in humans and viruses circulating in other species,” Moncla said. says. “I don’t think it’s possible to translate that into the probability that we’re close to a pandemic or that a pandemic will happen now.”