- The H5N1 avian flu virus has infected a third person in the United States, this time showing respiratory symptoms.
- The new patient’s cough and sore throat could help the virus better infect humans.
- Experts fear the United States is missing crucial opportunities to check the virus’s DNA for new mutations.
The H5N1 avian flu virus has again infected a human. But this time, the unlucky patient had a cough and sore throat, marking a new step in the spread of the virus in the United States.
The H5N1 virus has become a pandemic among animals, raging among bird populations around the world and now among cattle herds in the United States.
This latest human case, confirmed Thursday by the U.S. Centers for Disease Control and Prevention, is the third known human case in the United States, after Texas and Michigan.
The three people are dairy farm workers who were exposed to infected cows, according to the CDC.
However, the first two cases only involved eye symptoms, including conjunctivitis or conjunctivitis. This means the infection was likely limited to their eyes. Now it’s hit someone’s lungs.
The risk to the general public is still low, the CDC says, but these new symptoms suggest the virus may have entered a new phase of flirting with human infection.
The lungs give the virus more opportunities to adapt to humans
St. Jude virologist Richard Webby is a leading researcher on an H5 group of influenza viruses, which have been circulating in bird populations for about 25 years.
Since 2021, the H5N1 virus has spread to new frontiers of sustained spread, infecting dolphins and porpoises, migrating to the Americas, culling sea lions and seals, and now spreading through American cattle herds.
“This virus continues to throw up surprises,” Webby, who directs the World Health Organization Collaborating Center for Influenza Ecology Studies in Animals and Birds, told Business Insider. “If you had asked me at the beginning of the year what the chances were of H5 appearing in cows, I would have said extremely low.”
Yet, he added, H5N1 is more of an avian virus than a mammalian virus. This is mainly due to the receptors it binds to in order to enter its host’s cells and replicate.
“Avian viruses bind to one form of this receptor on the host cell. Mammalian viruses bind to a different form,” Webby said.
The mucus lining the human eye (where the first farm worker contracted conjunctivitis) is rich in receptors picked up by avian viruses, he said. There, the H5N1 virus can continue to function as an avian virus capturing avian receptors, without needing to adapt to human receptors.
But our respiratory tract is full of both forms of this receptor — the preferred form of avian viruses and the preferred form of mammalian viruses. SO, According to Webby, being in the lungs gives H5N1 greater exposure to the receptors that mammalian viruses use.
This gives H5N1 more opportunities to undergo a mutation that would allow it to bind to these mammals. receptors, adapting better to the human body.
That’s the problem, but it’s not clear if it actually happened in this patient’s lungs. For such a mutation to be significant, it would have to spread to other people as well. So far, based on all known cases, the virus has not been able to spread from person to person.
Sequencing viral tests for mutations
In an opinion piece published Sunday in The New York Times, virologist Rick Bright said the emergence of respiratory symptoms indicates “a dangerous inflection point” for the virus.
After all, he writes, “coughing can spread viruses more easily than eye irritation.”
But for Webby, the Michigan patient’s cough “doesn’t change much.”
Two previous one-off human cases of H5N1 – one in Chile and one in Ecuador – had respiratory symptoms.
The virus didn’t necessarily need to mutate to infect the Michigan farm worker’s respiratory system, according to Webby. The person could simply have encountered a large amount of virus, perhaps a particularly sick cow.
“It’s me looking a little bit at the crystal ball,” he said, adding that it’s “the more likely explanation for what we’re seeing, rather than the other, which is of course much scarier, that this virus has already changed.”
Either way, scientists won’t know if any scary mutations have occurred until they can examine the DNA sequence of the virus from this new case. The patient, however, carried such small amounts of virus that it’s possible the CDC didn’t have enough to obtain the sequence, Webby said.
DNA sequences are essential. By checking the virus’s genes in each new human case, regardless of symptoms, scientists can identify any new mutations that help it adapt to humans. If H5N1 becomes a real mammalian virus, they could observe its transformation in real time.
“The very first signals we’re going to get that this virus is changing are probably going to come from human infections,” Webby said.
However, so far, government surveillance may not be strong enough to detect these mutations at an early stage.
Experts call for more testing to avoid missing mutations
The FDA has detected fragments of the virus in commercial milk and beef. Although food is unlikely to infect you, public health experts told BI, careful people can cook their eggs and meat all the way through. No one should drink unpasteurized milk, that is, raw milk, they say.
The real risk is to people who work directly with sick animals, especially farmworkers like the three who have been infected so far.
Nationwide, the government is monitoring about 350 people who may have been exposed to H5N1, most of them in Michigan, CDC Deputy Director Nirav Shah told reporters at a briefing Thursday. press. However, only about 40 farmworkers have been tested for the virus, the New York Times reported.
“We would like to do more testing,” Shah said, according to STAT News.
Bright argues that the government’s weak testing regime could allow infections among farm workers to go unnoticed.
However, undetected cases are not the same as undetected spread.
Bright’s essay raises the alarm about unknown human-to-human transmission, but Webby finds this unlikely. Even with its current monitoring, the CDC would likely detect sustained human spread, he said.
Rather, the problem with undetected cases is that no one can sequence their samples. These are windows into the virus’s DNA (and its possible mutations) that no one looks at.
Webby and Bright agree that scientists need more sequences of the virus, faster. Despite the herd’s continued spread, for example, the USDA hasn’t shared new footage of an infection sample from a cow in weeks, according to Bright.
“Ultimately, we need more information about what exactly this virus does,” Webby said. “The more we understand, the more I believe we can control it well, or at least control it much better than we can.”