Scientists tracking avian influenza in cows and milk want answers to four questions:

Avian influenza is spreading to dairy cows in the United States. Scientists say the risk to people is minimal, but unanswered questions remain, including how widespread the infection is and how the virus spreads.

Douglas Magno/AFP via Getty Images

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Douglas Magno/AFP via Getty Images

Avian influenza is spreading to dairy cows in the United States. Scientists say the risk to people is minimal, but unanswered questions remain, including how widespread the infection is and how the virus spreads.

Douglas Magno/AFP via Getty Images

One month has passed since the surprising event. Discovery of avian influenza At Dairy Cows, each week seems to bring more surprises.

Please take latest revelation: Virus fragments in retail milk.

Scientists do not consider this an imminent threat to human health.

The genetic material is not the same as the infectious virus, and pasteurization is expected to inactivate the virus in milk, but the findings speak to broader uncertainties about the extent of the outbreak.

“There's still a lot of important things we need to know to get a better picture of how bad, or not so bad, this is,” said Dr. Rick Bright, a virologist and former Director of the Defense Advanced Research Projects Agency. To tell. (DARPA).

Federal health agencies began releasing details this week, but Bright said there's still not enough transparency.

“The feeling of emptiness just makes everyone anxious,” he says.

Other scientists say there are still many unanswered questions given the novelty of this infection.

“There are some big unknowns right now,” said Louise Moncla, a virologist at the University of Pennsylvania School of Veterinary Medicine.

Scientists tracking the virus say: still I want to know:

How prevalent is the virus in dairy cows?

It's not clear yet.

Official counts show it has been detected in eight states and a little more than 30 herds, but the actual number is likely much higher.

First of all, there is no extensive testing of cattle.

The fact that viral material is now being detected in retail milk suggests that “this virus is probably quite widespread,” he said. Richard Webbya virologist at St. Jude Children's Research Hospital in Tennessee.

On Thursday, the FDA announced that preliminary results from a national sample of retail milk show that about 1 in 5 samples are positive for traces of the virus. In a study of retail milk in the Midwest, 58 of 150 samples tested positive, said Andrew Bowman of Ohio State University.

Webby realized this for herself when she went to the store to pick up a carton of milk that she was planning to use as a negative control in a study on H5N1.

Surprisingly, even that eventually turned out to be positive (without taking any steps, he continued to drink milk).

The virus has now been detected in only a small portion of the U.S. dairy herd, but without details on the total number of cows tested, it's hard to know the significance of the discovery, said Dr. Tom Inglesby. says. Director of the Johns Hopkins Center for Health Safety.

”These are kind of fundamental questions that can be very helpful in getting a more accurate truth quickly,” he says.

USDA just took some new steps That might give us a better picture of the trend. If a cow tests positive, it will be required to be reported, and dairy cows will be required to test negative for the virus before traveling across state lines.

Potential complications: An unknown number of cows may be shedding the virus without showing obvious symptoms. Federal health officials said I confirmed this.

“We don't know how many animals have this condition,” said Alexis Thompson, a veterinarian at the Texas A&M Veterinary Medical Diagnostic Laboratory. “Very little sampling has been done. We don't know how much has been done.” [sick] The animals we keep. We don't know how many animals are asymptomatic. That test has not yet been carried out. ”

Milk from sick cows is supposed to be thrown away, so this could help explain how remnants of the virus got into the milk supply.

If it turns out that many animals are shedding the virus but are asymptomatic, the outbreak could be “much larger” than we realize, Inglesby said. “To get to the bottom of it, we'll need to do surveillance testing in places that haven't yet had an obvious outbreak.”

Does the milk on retail shelves that has tested positive contain an infectious virus?

So far, it doesn't look like that, but scientists studying this possibility admit that it's too early to say so with absolute certainty.

PCR tests that have found evidence of virus fragments in milk on grocery store shelves don't actually tell whether it's a “live” virus, meaning it can replicate.

They say this form of test is very sensitive and can detect small amounts of genetic material. lee ann jaycusa food microbiologist at North Carolina State University.

“While there is evidence that the milk may have contained the virus at some point, there is no evidence, at least from the information we currently have, that the virus is infectious,” she says. .

Pasteurizing milk can kill bacteria and viruses. However, it does not erase all traces of those bacteria.

Federal health officials say that avian influenza cannot tolerate high temperatures and that past research on pasteurization has shown that it is “very likely to effectively inactivate heat-sensitive viruses like H5N1 in cow's milk.” The company emphasizes that it has been shown to be “high.”

“We have not seen anything that would change our assessment that the commercial milk supply is safe,” said Don Prater of the Food and Drug Administration.

Studies on pasteurizing eggs, which is done at lower temperatures than milk, have shown that this process inactivates avian influenza viruses.

Jacas and other scientists agree that the discovery of viral material does not necessarily indicate an immediate threat to human health.

“It's really important not to let the fear of drinking milk get out of control,” says Jacas.

However, there are important caveats. No direct studies have been conducted on how pasteurization of milk affects avian influenza viruses. Those studies are currently being conducted.

He said early experiments on a small number of samples suggest there is no viable virus present in these positive samples. Jeanne MarazzoDirector of the National Institute of Allergy and Infectious Diseases.

Mr Webby, who examined the milk samples sent by Mr Bowman, said he had tried growing the virus in cultured cells and embryonated chicken eggs, which influenza likes to grow, but found that the virus did not grow.

“This is pretty good evidence. I'm not saying it's not there at all, but if it's there, it's at a very, very, very low level,” he says.

Even if milk happens to contain small amounts of infectious virus, “there's no evidence that that's how influenza is transmitted,” Jacas says.

Rick Bright, on the other hand, has more concerns about milk.

“It's a little inconvenient for me not to drink milk until we have more data, but it doesn't mean I think everyone should stop drinking milk. This is a personal risk assessment. ” he says.

He said the key questions are how much virus is in the milk and whether the situation would change if more cows got sick and more virus entered the milk supply. says.

“The higher the amount of virus in the milk, the harder it is for pasteurization to work fully,” he says. “If it shows that there is no viable virus in the milk at this point, then that's it. And what's really important is that the FDA continues to monitor this.”

How exactly does the virus spread?

In recent weeks, the prevailing theory has been that the main route of transmission is through milk. High concentrations of the virus have been detected here.

This general idea was reaffirmed this week by Mike Watson of the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, who said the evidence still points to some form of “mechanical transmission.”

The virus can be spread on “milking equipment,” by “individuals moving from facility to facility,” and through rodents moving around in contact with milk, he said.

Federal health officials and scientists believe the virus moved from one herd to another with lactating cows. But how it is transferred from cow to cow on a particular farm is “an important knowledge gap,” Webby said.

Moncla, who analyzes genomic data, said genetic sequencing shows there was likely a single introduction from birds to cattle, which then spread further among cattle. Stated.

“Many of these cow sequences are very similar to each other, suggesting that some degree of cow-to-cow transmission is almost certainly occurring,” she says.

Moncla said it was difficult to say exactly how long the virus had been circulating through dairy cows, although some scientists have suggested it may have been widespread. circulating Earlier than February, for many months.

The USDA also noted another concerning development: There have been several cases of the virus being transferred from domestic poultry to cattle.

“Given the extent of the infection and the fact that it is likely that no cattle cases will be found, there is some concern,” Moncla said.

As the virus continues to spread, what are the risks to humans?

First, some encouraging news. Despite all these cows being infected, only one case of human infection has been recorded during the current dairy cow outbreak.

The man was a dairy worker in Texas who had conjunctivitis.

Federal health officials said this week that the overall risk to the general public remains low, in part because “we have not observed any changes in the genetic structure of the virus that would suggest enhanced transmissibility among humans or between humans.” He repeatedly said that it was low. Dr Nirav ShahPrincipal Deputy Director, CDC.

He said the states have so far tested 23 people for bird flu and are monitoring 44 people who are considered at risk of infection.

In general, avian influenza rarely infects humans; to become infected, a large amount of the virus must be ingested, for example through direct contact during the slaughter of poultry. Since 2022, 26 cases of H5N1 virus infection have been reported worldwide.

Webby said the cows may not be putting as much “pressure on the virus to change,” which may be one reason why scientists haven't seen any surprising mutations in the samples they've collected. Ta.

From a human risk perspective, “I don't think the needle has moved at all,” he says.

Of course, there is a long-standing fear that the virus could mutate in cows or intermediate animals and then invade humans.

Scientists have documented several mutations of avian influenza that have occurred as it spread to other mammals. But previous research has shown that a number of changes are needed to become a pandemic threat, not least of which is an evolution in the way the virus binds to receptors in the human upper respiratory tract. be.

When it comes to cows, the CDC Sanja Olsen It says it is not yet known whether exposure to raw milk on farms is the main risk to humans. “I don't know if that will happen. [surface] contagion; infection. I don't know if there is aerosolization of milk. ”

Instead of waiting for cases to show up in emergency rooms, Dr. Bright said the CDC should conduct antibody tests on dairy workers to see if human cases are escaping detection. Stated.

“I'm going to keep my radar up,” he says. “If this gets out of hand, we have to be ready to respond very quickly, and I'm not sure we're fully prepared to respond if necessary. ”