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 announcement adds a worrying dimension to an outbreak that has affected millions of birds and marine mammals worldwide and, most recently, cows in the United States.
So far, there is no sign that the virus has evolved in a way that would help it spread more easily among people, federal officials said.
The patient’s main symptom was conjunctivitis; According to the Centers for Disease Control and Prevention, the person is being treated with an antiviral medication and is recovering.
The Department of Agriculture reported the first cases last week in dairy herds in Texas and Kansas and a few days later in another herd in Michigan. Preliminary testing suggests cows in New Mexico and Idaho may also be infected.
The virus was identified as the same version of H5N1, an influenza subtype that circulates in North American birds.
The CDC is working with state health departments to monitor other people who may have come into contact with infected birds and animals, the agency said Monday. People were also urged to avoid contact with sick or dead birds and animals, as well as raw milk, feces or other potentially contaminated materials.
This is only the second case of H5N1 avian influenza in humans in the United States; the first was in 2022. The risk to the general public remains low, experts said. However, testing and analysis is ongoing and there are many unanswered questions.
“This is a rapidly evolving situation,” the USDA said in its announcement last week.
Here’s what you should know:
What is bird flu?
Bird flu or bird flu is a group of flu viruses that are primarily adapted to birds. The particular virus in these new cases, called H5N1, was first identified in geese in China in 1996 and in humans in Hong Kong in 1997.
In 2020, a new, highly pathogenic form of H5N1 emerged in Europe and quickly spread throughout the world. In the United States, more than 82 million farmed birds were affected, the worst avian influenza outbreak in U.S. history.
Sporadic since the virus was first identified Cases have been identified in people in other countries. But the vast majority resulted from prolonged, direct contact with birds.
H5N1 does not appear to have yet adapted to spread efficiently among humans, experts say.
How did cows get bird flu?
It was not assumed that cows were a particularly endangered species.
“The fact that they’re vulnerable – the virus can multiply and make them sick – I wouldn’t have predicted that,” said Richard Webby, an influenza virologist at St. Jude Children’s Research Hospital.
But this year reports surfaced of sick cows 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.
There are several ways the virus could have gotten into cattle. Several experts said the likely route was that infected wild birds, which shed the virus in their feces, saliva and other secretions, contaminated the cows’ feed or water.
But other wild animals known to be susceptible to the virus, such as cats and raccoons, may also have transmitted the virus to dairy farms.
How are cows affected?
Although the virus is often fatal in birds, it appears to cause relatively mild illness in cows.
“It doesn’t kill any animals and they seem to be recovering,” said Dr. Joe Armstrong, a veterinarian and livestock specialist with the University of Minnesota Extension. Last week, the USDA said there were no plans to “depopulate” or cull affected flocks, which is standard procedure when poultry flocks are infected with the virus.
The disease primarily affects older cows, which exhibit, among other things, loss of appetite, mild fever and a significant decrease 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 from sick cows.
It is not yet clear whether the bird flu virus is the sole cause of all reported symptoms and illnesses, experts warned.
How widespread is the problem?
It is unclear. As of last Friday, the USDA’s National Veterinary Services Laboratory had confirmed bird flu infections in two flocks in Texas, two flocks in Kansas and one flock in Michigan.
Initial tests indicate that other herds in Texas, New Mexico and Idaho may also be infected with the virus. However, these results have not yet been confirmed by the national laboratory. So far, the virus has only been detected in dairy cows and not in beef cattle.
But because cows are not routinely tested for bird flu and the illness has been relatively mild, there may be other infected herds that have escaped detection, experts say.
And the movement of cattle between states could carry the virus to new places. 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 cows from an affected state, Idaho officials said.
How does it spread?
This is a central and still unanswered question. It is possible for the infected cows to contract the virus on their own, especially if shared feed or water sources are contaminated.
However, a more worrying possibility is that the virus spreads 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 degree of cow-to-cow transmission. “How else could it happen so quickly?” said Dr. Gregory Gray, an infectious disease epidemiologist at the University of Texas Medical Branch.
If the virus can spread easily between cows, it 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 that it acquires mutations that make it more dangerous to humans.
How do officials know if bird flu adapts to spread between people?
Analyzing the genetic sequence of the virus from infected birds, cows and humans can reveal whether H5N1 has acquired mutations that contribute to its spread among humans.
Scientists have closely tracked infections in birds and marine mammals and now cows. So far, the virus does not appear to be able to spread efficiently between people.
In 2012, scientists showed that H5N1 was able to spread through the air between ferrets after acquiring five mutations – a popular model for studying respiratory virus transmission among humans.
An avian flu sample isolated last year from a Chilean man had two mutations that indicate adaptation to infecting mammals. However, these mutations were previously observed without the virus continuing to evolve and spread between people, experts said.
Is Eating Dairy Products Safe?
Federal officials have emphasized 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 shown to inactivate bacteria and viruses such as influenza in milk,” says a new online milk safety guide from the Food and Drug Administration.
Dr. Gail Hansen, a veterinary public health expert and independent consultant, agreed that the risk of infection from pasteurized milk was probably “very low.” She added: “I don’t want people to stop drinking milk because of this.”
But the possibility cannot be completely ruled out, she said, expressing concern that federal officials have been “overconfident in the face of so many unknowns.” If cows shed viruses in their milk before they show signs of illness, that milk could potentially end up in the commercial milk supply, she said. And different pathogens may require different pasteurization temperatures and durations; The specific conditions required to inactivate this particular virus remain unclear, said Dr. Hansen.
The risk of contracting the virus from consuming unpasteurized or raw dairy products remains unknown, the FDA said. Raw milk is known to pose a variety of potential disease risks beyond bird flu.
Source link
2024-04-01 22:32:27
www.nytimes.com
