After public health officials confirmed H5N1, the virus also known as bird flu, jumped from poultry to cows and recently infected an American, they’ve warned that if the virus strain made its way to pigs, it could be a time to press the panic button. That's because swine are closer to humans in genetic terms, acting as a prime reservoir for viruses to mutate into something that could turn into a far-reaching pandemic in people.
But now, a new study suggests that dairy cows might have the same potential as pigs, which could improve the bird flu’s capability of being more human-to-human transmission.
As reported by Nature, preliminary data shows that the flu virus can jump back and forth between cows and birds thanks to a specific receptor. This specific trait might allow the virus to spread more widely and develop more mutations along the way. If a single cow can be a host to multiple types of influenza over time, it could evolve to more readily infect humans.
“The biggest question is whether cows are mixing vessels like pigs; pigs are well-known mixing vessels for influenza because they have both avian and human receptors and that allows a virus to mutate pretty easily and to make it more susceptible to humans,” Katelyn Jetelina, an epidemiologist and author of the newsletter Your Local Epidemiologist, told Salon. “And this preprint said that cows have both avian and human receptors in the mammary glands as well as other areas of the cow, which may suggest that they're a mixing vessel.”
Jetelina emphasized that “may” is a key word.
“Because although they have the receptor it doesn't necessarily mean it's active, it doesn't necessarily mean it's exactly how we see the dynamics playing in pigs,” she said. “So it really opens up more questions and answers at this point.”
Dr. Rajendram Rajnarayanan of the New York Institute of Technology campus in Jonesboro, Ark., told Salon this preliminary report “changes things a lot.”
“That means that if you let the virus collect in cows a lot, then soon you’re going to see an adaptation that's going to pick it up in humans and other mammals,” he said. Pigs can get infected with multiple viruses at a time. This could make it easier for the virus to mutate into a new one that could more easily jump from mammal to mammal, like say, from one human to another. If that’s the case with cows, as Rajnarayanan said, “that's going to be a problem.”
According to data from the U.S. Department of Agriculture (USDA), at least 42 dairy cattle farms have been infected in at least nine states. But infectious disease experts highly suspect there are more since testing is voluntary, unless they are being moved between state lines. The USDA also reported this week more confirmed cases of H5N1 in poultry and wild birds, including pigeons at a Michigan dairy where an outbreak has occurred. Meanwhile, the Centers for Disease Control and Prevention (CDC) has also urged state health officials to provide personal protective equipment for livestock workers.
On Thursday, the CDC announced the launch of a dashboard to track wastewater samples of the virus and confirmed the presence of influenza A in wastewater samples. But as Reuters reports, "The wastewater tests are capable of detecting many types of influenza A, including the H5N1 subtype, but the findings do not indicate the source of the virus or whether it came from a bird, cow, milk or from farm runoff or humans."
Notably, bird flu is not a new virus like SARS-CoV-2, which causes COVID-19, was when it first began spreading in late 2019. H5N1 has been spreading in birds since at least 2021, killing hundreds of millions of them around the world. It has also infected other mammals, including seals and bears. However, this outbreak is the first time officials have confirmed that the virus has jumped from a cow to a human, and the line of transmission suggests it’s easily passed between cows.
The last time a human tested positive for H5N1 was in April 2022 in Colorado, when an individual got infected from poultry. Recently, a report published in the New England Journal of Medicine shed more light on the one confirmed human case where someone got infected from an infected cow. A photo in the journal showed the patient with conjunctivitis in both eyes, also known as pink eye, with a subconjunctival hemorrhage, which is like a bruise, making them appear bloody. The patient was treated with an antiviral right away, and close contacts were given post-exposure prophylaxis. Notably, the patient didn’t have any respiratory symptoms, and household contacts remained in good health, according to the report.
“I think they acted quickly on that person, and that was good,” Rajnarayanan said. “But the only thing is, we haven't really heard about anything else.” He added it’s likely that there have been more cases that haven’t been recorded. Jetelina agreed she wouldn’t be surprised to hear of more human cases either. As noted in Nature, there have been anecdotal reports of farm workers being infected. One expert told the publication that they suspect the exposure is widespread.
Jetelina said it’s important to note “the social context” in which this situation is unfolding. Primarily, a majority of farmer workers are undocumented, Spanish-speaking immigrants.
“There's not really an incentive for them to test,” Jetelina said. “If they test positive that means they're out of work for two weeks, which has huge implications to their family and there's a lot of language barriers as well.”
In order to move forward, Jetelina said there needs to be better data transparency and communication.
“And this isn't just disease-based, this is working with humans and all the behaviors and values that those humans possess,” she said. “And I think all we can do is try to explain why we want them to be tested, protect them with incentives for example, paid time-off would be great.”
But as it stands, Jetelina said “we’re flying blind.”
Rajnarayanan said at the moment, he’s at his “highest level of concern.”
“We are running blind, we don't really have a lot of data,” he said. “The data is coming here and there, but it's [difficult] to connect the dots sometimes when you have dots that are so far from each other.”
