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Raw milk from cows infected with the H5N1 bird flu has been shown to contain of the virus, making it quite risky for people to consume.

With showing some 4.4% of Americans drank raw milk at least once a year, and 1% drank it once a week or more, millions of Americans may be at risk of contracting the virus.

The question is, would an H5N1 infection from raw milk look like a typical influenza infection to most doctors, or would its symptoms be different? And would doctors be testing for influenza?

On that first question, Andrew Pekosz, PhD, professor of molecular microbiology and immunology at Johns Hopkins University Bloomberg School of Public Health in Baltimore, said it's likely an H5N1 infection from raw milk "would be primarily a respiratory infection based on what happens to other animals that either ingest H5N1-containing milk, or what we see with predatory birds and other carnivores who get infected by eating an H5N1-infected bird."

"In those animals, the infection is in the lungs, but also spreads to a lot of other organs, which is what leads to the death of the animal," Pekosz told 番茄社区app in an email.

Those animals include cats; in April, data published in the CDC's Emerging Infectious Diseases showed that more than half of 24 domestic cats fed raw milk from sick cows on a dairy farm in north Texas in mid-March became sick and died.

The cats had signs of systemic influenza infection, including lots of nasal discharge, depressed mental state, and stiff body movements, the researchers reported at the time.

If the infection looks like a typical, or possibly more severe, influenza infection, would a doctor or hospital even test for influenza, let alone search for the H5N1 strain?

Pekosz said emergency departments and healthcare professionals have received communications from health authorities, such as , to be aware of potential H5N1 infections.

"However, it is not something that is high on most healthcare providers' lists of pressing concerns, so it is possible a case could initially be missed, particularly if it's not a severe infection," he added.

James Lawler, MD, MPH, an infectious diseases expert at the University of Nebraska Medical Center's Global Center for Health Security in Omaha, agreed that it would be easy to miss cases of H5N1 infections from raw milk.

"If we do have sporadic cases popping up every now and then, given the state of surveillance in our public health system, we're probably not going to find it," Lawler told 番茄社区app. "If a 20-year-old shows up to an emergency department with severe pneumonia in July, many places will not test that person for flu."

"I'm really concerned about people who are consuming raw milk," he added. "I think there's a high likelihood that we're having even more human cases and those are going undetected."

While most human cases in the recent cattle outbreak have been tied to large dairy farms, and a key route of transmission among cows appears to be contaminated equipment, any cattle exposed to wild birds could potentially become infected, experts said. Also, companion animals that drink H5N1-contaminated raw milk -- and interact with humans -- may pose a risk.

Lawler said, ideally, animal caretakers who sell raw milk should recognize that milk from an animal with symptoms "shouldn't be put into the supply chain." However, cows early in infection, or with latent infection, or those that are only mildly symptomatic "still have high amounts of virus in their milk" and thus pose a risk to the supply chain.

While Lawler acknowledged that the chances of H5N1 evolving to efficiently spread between humans remains low, the stakes are high if it does gain that advantage -- and the more chances it has to spread in mammals, and in humans, the more likely that adaptation is to happen, he said.

Cow mammary glands are a particularly problematic substrate because they contain that the virus uses to bind to host cells, he said: alpha 2,3, which is common in birds; and alpha 2,6, which is common in human upper airways.

Humans also have alpha 2,3 receptors, but these are deeper down in the lungs, Lawler said, which is a likely reason H5N1 has been particularly lethal (with greater than 50% mortality) in historic human cases, as it causes severe pneumonia.

Letting the virus persist in cows "means you're potentially allowing the virus to select for strains that can bind to both, and that would be a potentially dangerous virus," he said.

"All these things are concerning, and I'm pretty disappointed in the lack of a sense of urgency we've seen from the federal government and some state agencies as well," Lawler said. "We seem to be relying on hope as our strategy."

"We're continuing the messaging that this is low risk, and I would argue that it's not," he added. "Risk is the product of threat, and then vulnerability and consequence. While the threat is low -- the probability that this virus is going to mutate into something that transmits efficiently between humans is probably still low -- the problem is, if that happens, then our vulnerability and the consequences of that event would be incredibly high."

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