by Serious gaps in animal and human testing may be obscuring the true rate of bird flu cases in the US and making it difficult to understand how the H5N1 virus is spreading – and how to stop it, experts say.
Faced with reluctance from farms to test workers and animals, scientists are now turning to experimental studies to understand how H5N1, a highly pathogenic bird flu, spreads through cows and on to other farms .
The number of bird flu among US dairy herds continues to rise, but infections are more widespread than previously realized, testing of commercially available milk shows.
Although the risk to humans remains low, this may change as the virus evolves, so its continued circulation remains a major concern.
“This epizootic is a big surprise,” said Gregory Gray, a professor of infectious diseases at the University of Texas Medical Branch. The scientists knew that cows could be infected with the four different types of flu, “but we haven’t seen this much infection, and we haven’t seen it move this fast.”
Understanding how the virus moves is key to stopping it – but testing, which could reveal such transmission patterns, was slow and inadequate.
A dairy worker in Texas, the only person confirmed to have H5N1 in this outbreak and the first documented case of transmission of the virus from mammals to humans, requested testing at a local health department, a recent study shows. The worker reported a form of conjunctivitis which resulted in hemorrhage and red eyes.
But after the positive test, the officials were not able to test any other workers or animals on the farm where the person was working. That makes it difficult for scientists to understand how the virus spread to the worker and whether it affected others.
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“The people we need to get the most now are the other people on these farms who are being exposed to massive amounts of virus in these environments,” said Richard Webby, a virologist at the infectious diseases department at St Jude’s children’s research hospital. “That’s not easy, and it’s not happening at a rate that we probably need.”
Only about two dozen people were tested for H5N1 in this entire outbreak. The Centers for Disease Control and Prevention does not recommend testing unless symptoms develop after close contact with animals – even if a cow is sick or someone infected lives with an infected person.
The lack of testing could hide the true rate of transmission for people, if workers and their close contacts are not suffering from symptoms, or if they are unable or unwilling to seek medical care.
Barb Petersen, the veterinarian who discovered the first case of H5N1 in a Texas cow, said dairy workers were also sick — some sick enough to miss work, which she said was highly unusual — but not tested. them for the highly pathogenic poultry. flu.
Other types of cattle, including beef cattle and calves, appear not to have been tested, despite evidence that the virus can be asymptomatic in cattle.
“We don’t know when this thing moves in beef cattle, and nobody’s really talking about that,” Gray said.
And pigs, which play a role in fueling human flu epidemics, appear to be under-monitored more than usual, despite evidence that bird flu has spread from cows to nearby chicken farms and it could spread in the same way as pig farms.
Pigs are a concern because they can mix animal and human influenza viruses, which can lead to more transmissible or milder variants in humans.
Cows may have similar abilities, according to early research co-authored by Webby. Like pigs, cows have receptors for avian and human flu, and could make a “hybrid virus” that could affect people more, Webby said.
But, he warned, the animals would have to be infected with both types of flu at the same time, which is relatively rare – especially at this time of year, when human flu rates are low. “It’s theoretically possible, but maybe not likely – but at the same time, if we continue to spread this virus, it increases the chances, even if those chances are very small.”
Another challenge for scientists: the genomic sequences released so far by US agencies have been stripped of key data – such as when and where they were collected – making it very difficult to track what is happening and how the virus is changing, scientists say. This has global implications for understanding and tracking outbreaks in livestock.
The animal agriculture industry has largely resisted any attempts at testing, with one Texas agriculture official telling the Biden administration to “back off,” in part because of the lack of trust in federal agencies among farmers.
Another problem is that cow farmers are not compensated for financial losses from lower milk yields or are unable to export cows to other markets, Gray said.
“They are very concerned that if they raise the ‘we have the virus here’ flag, they will be penalized economically or by having their operating procedures disrupted,” he said. “We have to find a way to overcome that and protect the farms.”
It points to poultry farms, which have a federal compensation scheme for killing infected birds – and monitor poultry much more closely for infectious diseases, allowing them to take quick action to address outbreaks like this.
Scientists like Gray are also collaborating with farm veterinarians to test animals under non-disclosure agreements to avoid identifying farms.
And some of those vets are doing their own studies on the farms to understand transmission, Gray said. “For example, is the virus being moved through the milking procedure from cow to cow, is the virus aerosolized, is the virus moving from cow to cow in other ways?”
There are also questions about the extent to which people may be unknowingly spreading the virus, he said.
Some scientists who are unable to trace the transmission currently occurring on farms, are turning to experimental infection of healthy cows. The results of these experiments should come in the next few weeks, Webby said.
“Is there really anything different about this particular virus itself? Does it have properties that the other H5 circulating in wild birds does not have?” he asked. He expects that outbreaks like this among cows are rare, but understanding how they occur and then how they spread is critical to responding now and in the future.
“Let’s say we eradicate this. What are the chances of it happening again?” Webby asked. “If we can figure out how it’s moving, I think we can think about completely eradicating this virus from cows.”
