Achi news desk-
An unusual outbreak of bird flu in dairy cows has now affected at least 13 herds in six states, according to federal and state officials. These infections represent the first time that a highly pathogenic avian influenza virus, which is often fatal in birds, has been detected in US cattle.
At least one person in Texas has been diagnosed with bird flu after coming into contact with suspected infected dairy cows, state officials said Monday. The patient’s primary symptom was conjunctivitis; the individual is treated with an antiviral drug and recovers, according to the Centers for Disease Control and Prevention.
The virus has been identified as the same version of H5N1, an influenza subtype, that is circulating in North American birds. Scientists have not found evidence that the virus has acquired the mutations it would need to spread easily between humans, officials said.
The risk to the public remains low, experts say. But these developments add a worrying dimension to an outbreak of bird flu which has already affected millions of birds and marine mammals around the world.
Here’s what to know:
What is bird flu?
Avian influenza, or avian flu, is a group of influenza viruses that are mainly adapted for birds. The particular virus in these new cases, called H5N1, was first identified in 1996 in geese in China, and in people in Hong Kong in 1997.
In 2020, a very new pathogenic form of H5N1 emerged in Europe and spread rapidly around the world. In the United States, it has affected more than 82 million farm birds, the worst outbreak of bird flu in US history.
Since the virus was first identified, sporadically cases have been found in humans in other countries. But a large majority resulted from prolonged direct contact with birds.
H5N1 does not yet appear to have adapted to spread efficiently among people, experts say.
How did cows get bird flu?
Cows were not thought to be a highly endangered species.
“The fact that they’re vulnerable – the virus can replicate, make them sick – that’s something I wouldn’t have predicted,” said Richard Webby, an influenza virologist at St Jude’s Children’s Research Hospital .
But this year, reports of sick cows began to emerge in Texas and New Mexico. Dead birds were also found on some of these farms, and laboratory tests confirmed that some cows were infected with bird flu. (In Texas, three symptomatic cats also tested positive for the virus, the Texas Animal Health Commission said in an email. Feline infections are not new; cats are known to be susceptible to the virus, which they can pick up when they hunt or eating infected birds.)
It is not entirely clear how the virus found its way into cattle. But one likely route, several experts say, is that infected wild birds, which shed the virus in their feces, saliva and other secretions, have contaminated the cows’ food or water.
How have cows been affected?
Although the virus is often fatal in birds, it appears to cause relatively mild illness in cows.
“This is not killing animals, and they seem to be getting better,” said Dr. Joe Armstrong, a veterinarian and cattle production specialist at the University of Minnesota Extension. Last week, the USDA said there were no plans to “depopulate,” or cull affected flocks, which is the standard procedure when poultry flocks are infected with the virus.
The disease mainly affects older cows, which have developed symptoms including loss of appetite, low-grade fever and a significant reduction in milk production. The milk the cows produce is often “thick and discolored,” according to Texas officials. The virus has also been found in unpasteurized milk samples collected from sick cows.
It is not yet clear whether the bird flu virus is the sole cause of all the reported symptoms and illnesses, experts warned.
How widespread is the problem?
It is unclear. On Tuesday, the USDA said its National Veterinary Services Laboratories had confirmed bird flu infections in 12 flocks so far: seven in Texas, two in Kansas and one each in Michigan, New Mexico and Idaho. On Wednesday, the Ohio Department of Agriculture announced that it had also received confirmation of an affected herd from the national laboratories.
So far, the virus has only been found in dairy cattle and not in beef cattle.
But because cows are not routinely tested for bird flu, and the illness has been relatively mild, there could be other infected herds that have escaped detection, experts say.
And moving cattle between states could carry the virus to new locations. The affected dairy in Michigan had recently imported cows from an infected herd in Texas. When the cows were transported, the animals showed no symptoms. The Idaho farm also recently imported cattle from an affected state, Idaho officials said.
How does it spread?
That is a key question, which remains unanswered. It is possible that the infected cows contract the virus independently, especially if shared food or water sources are contaminated.
A more worrying possibility, however, is that the virus is spreading from cow to cow. On Friday, the USDA noted that “transmission between cattle cannot be ruled out.”
Several scientists said they would be surprised if there wasn’t some cow-to-cow transmission. “How else could he move so fast?” said Dr. Gregory Gray, an infectious disease epidemiologist at the University of Texas Medical Branch.
If the virus can easily spread between cows, that could lead to larger, more persistent outbreaks. It would also give the virus more opportunities to adapt to its new mammalian hosts, increasing the risk of it acquiring mutations that make it more dangerous to humans.
What do we know about the human cause?
This is only the second outbreak of H5N1 bird flu in humans in the United States; the first was in 2022.
The patient worked directly with sick dairy cows, said Lara M. Anton, spokeswoman for the Texas Department of State Health Services. “We’ve tested about a dozen symptomatic people who work in dairies, and only one person has tested positive” for the virus, he said in an email Monday.
A sample of virus from the patient showed one mutation that allows it to infect people more easily. But in order to be able to spread from one person to another, the virus must acquire several additional mutations – no easy evolutionary feat.
The CDC is working with state health departments to monitor other people who may have been in contact with infected birds and animals, the agency said Monday. It also urged people to avoid coming into contact with sick or dead birds and animals, and to raw milk, faeces or other potentially contaminated materials.
How will officials know if bird flu is adapting to spread between people?
Analysis of the genetic sequence of the virus from infected birds, cows and people can reveal whether H5N1 has acquired mutations that help it spread among people.
Scientists have been keeping a close eye on infections in birds and marine mammals and, now, cows. So far, the virus does not appear to have the ability to spread efficiently between people.
In 2012, scientists showed that H5N1 could spread through the air between ferrets – a popular model for studying the transmission of respiratory viruses in humans – after acquiring five mutations.
A sample of bird flu isolated from a Chilean man last year had two mutations that indicate adaptation to infecting mammals. But those mutations have been seen before without the virus evolving further to spread between people, experts say.
Is it safe to eat dairy products?
Federal officials have stressed that commercially processed milk remains safe to drink. Dairies are required to keep milk from sick animals out of the human food supply, and milk sold across state lines must be pasteurized, a process in which the milk is heated to kill potential pathogens. Pasteurization “has been consistently proven to inactivate bacteria and viruses, such as influenza, in milk,” the Food and Drug Administration says in a new online guide to milk safety.
Dr. agreed. Gail Hansen, a veterinary public health expert and independent consultant, said the risk was probably “very low.” He added, “I wouldn’t want people to stop drinking milk because of that.”
But the possibility could not be completely ruled out, he said, expressing some concern that federal officials had been “overconfident in the face of so many unknowns.” If cows shed virus into their milk before they show signs of illness, that milk could find its way into the commercial supply, he said. And different pathogens may require different pasteurization temperatures and periods; the specific conditions required to inactivate this particular virus remained unclear, Dr. Hansen said.
The risk of becoming infected by the virus by eating unpasteurized, or raw, dairy products is unknown, the FDA said. Raw milk is known to pose a variety of potential disease risks beyond bird flu.
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