As the H5N1 bird flu virus continues to rage through US dairy herds, it has also infected human farm workers. Another strain has also recently infected poultry farm workers in Washington state. On Wednesday, the US Department of Agriculture announced that the virus had been detected detected in a pig first time on a farm in Oregon. Now, as the seasonal flu season approaches, some health experts wonder if it will give a dangerous boost to bird flu.
They have been at least 39 human H5N1 cases in the US this year. Fifteen were in California, 10 in Colorado, nine in Washington state, two in Michigan, one in Texas and one in Missouri. (A second person in Missouri was also likely infected, but blood test results did not meet the official definition of a “case.” And officials say person-to-person spread there has been ruled out.) These have mostly been known cases. mild, with minor eye infections and respiratory symptoms.
In addition The Missouri caseall these people confirmed contact with infected farm animals. Nine of the cases in Washington State and nine in Colorado involved workers at farms that slaughtered infected chickens. The remaining cases were dairy farm workers. In total 395 herds of cows 14 states have tested positive for H5N1.
About supporting science journalism
If you like this article, please consider supporting our award-winning journalism subscribing. By purchasing a subscription, you’re helping to ensure a future of impactful stories about the discoveries and ideas that shape our world.
The steady rise in cases—in both farm animals and humans—has some experts worried about the risk of a wider outbreak of this potentially pandemic virus. Influenza viruses have several characteristics that are suitable for this: first, they constantly mutate in a process called genetic drift, which is why a new flu shot is needed every year. If there are enough mutations of the right kind, the virus undergoes a quantum leap known as genetic modification, which may be able to unleash a pandemic.
Another tool in the flu virus kit is what is known as reassortment. The genetic material of the influenza virus consists of eight RNA segments. When several viruses infect the same cell and replicate, they can exchange these segments, creating one of 256 possible combinations. This reassortment can produce a virus that has characteristics of both parent viruses, making it more transmissible and virulent. The process is believed to have created the 2009 H1N1 swine flu from a mixture of US and European swine flu viruses, triggering a (hopefully mild) pandemic.
Could such a resurgence occur if a person were infected with the H5N1 bird flu virus and the seasonal flu at the same time, resulting in an H5N1 version that would be more contagious in humans? That’s possible, experts say. But reassortment alone cannot produce a virus capable of triggering a human pandemic, he says Richard Webbyof Memphis, Tenn. St. Jude Children’s Research Hospital infectious disease researcher. The virus should also accumulate some specific mutations.
“To get from where we are now to a pandemic virus, reshuffling alone — at least in my opinion — won’t get us there,” says Webby, who directs the World Health Organization’s Collaborating Center for the Study of Influenza Ecology. In the Animals and Birds section. “It will require regeneration, followed by some critical mutation in a specific gene.” To date, no key mutations necessary for the virus to spread efficiently between humans have been detected in genetically sequenced human cases.
If H5N1 develops these mutations, the rearrangement could help it move from one virus to another infected human eye (the site of the most common farm worker infections) to the respiratory tract, Webby says. If that were to happen, the mix-up would likely occur in a human host, he says. Although cattle can be infected with human influenza virusesthese viruses are likely to replicate in the udders of cows, which is where H5N1 seems to replicate.
Historically, pigs have been seen as an ideal mixing bowl for pandemic pathogens, as they are susceptible to both human and avian influenza. Seasonal human virus spills into pigs occur fairly regularly, says Amy Baker, USDA’s veterinary medical officer. Baker and his colleagues have shown that the H5N1 strain currently circulating in wild birds and dairy cattle is 2.3.4.4b. can be replicated in pigs.
The pig that tested positive for H5N1 in Oregon was on a backyard farm with poultry and other animals. It is not yet clear whether the pig transmitted the virus to another animal, but health authorities are investigating. The farm’s five pigs have been euthanized. Because the farm is a non-commercial operation, there are no concerns about the nation’s pork supply, USDA officials said in a recent statement.
“This appears to be a fairly limited episode on a backyard farm, so I personally think it poses no particular risk, assuming there was no movement of animals to other farms,” says Webby. But if this represents an actual infection in the pigs and not just a positive nasal swab, he says, “it suggests they may be naturally exposed to the virus.”
If H5N1 were to start infecting pigs on commercial pig farms, that would increase the chances of it spreading with seasonal flu. “We know that a lot of reorganization takes place in pigs; There are viruses in pigs that are closely related to these humans. So it would absolutely, absolutely increase the risk.”
There are still many unanswered questions about how the H5N1 virus first got into cattle and started to spread, Baker says. He agrees with Webby that there is little risk of the virus re-emerging with human seasonal influenza viruses in cattle because there is no evidence that the latter pathogens infect animals. But if a pig or person were to become infected with both viruses at the same time, he says there is “always the possibility” of a more dangerous hybrid virus.
That risk is one reason the Centers for Disease Control and Prevention he asked the farm workers to get seasonal flu shots. The US a H5N1 vaccine stockpilebut he has not distributed it yet. There is some concern that low confidence in vaccines may affect uptake. It is not clear what the threshold for various officials to disseminate H5N1 vaccines among agricultural workers and other susceptible individuals might be, although evidence of sustained human-to-human transmission would likely be a strong factor.
“It’s not a bright-line rule,” CDC Deputy Director Nirav Shah said. American scientific last week at the press conference. “There are really a number of factors that we think about as we evaluate the pros and cons of vaccination.” Among others, the occurrence of person-to-person spread and an increase in the virulence or severity of the disease, and none of these factors have yet been seen, he added. In the meantime, people infected with H5N1 and their close contacts are being treated The drug oseltamivir (Tamiflu).
Some scientists have called for livestock vaccinations against H5N1, and the USDA’s Center for Veterinary Biologicals has approved a couple. field safety trials of vaccines. “I think there’s an opportunity to use H5 vaccines in cattle because it’s the only subtype known to infect cattle at this point,” says Baker. “And if we could reduce the amount of virus that is shed through milk, I think that would be beneficial for milk production, as well as protecting farm workers and the public.”
Right now, the chances of a farm worker contracting the H5N1 seasonal flu are slim, Webby says. But as the flu season heats up this winter, that risk may increase. Hundreds of humans have been infected with bird flu in the last quarter of a century, and it has not yet begun to spread among us. In fact, Webby says, “the hurdles this virus has to overcome to become a human virus are high. But anything that gives it more of a chance to do that is obviously a concern, more human infections of farm animals or that ability to repopulate with a human seasonal virus. Those things all would increase the risk.’
