At least one person in Texas has been diagnosed with bird flu after coming into contact with a possibly infected dairy cow, state officials announced Monday.
The announcement adds a worrying dimension to an outbreak that has affected millions of birds and sea mammals around the world, and most recently, cattle in the United States.
So far, federal officials say there is no sign that the virus has evolved in a way that spreads more easily between people.
The patient's main symptom was conjunctivitis. The U.S. Centers for Disease Control and Prevention said the person is being treated with antiviral drugs and is recovering.
The USDA announced last week that the first cases occurred in dairy herds in Texas and Kansas, followed a few days later in an additional herd in Michigan. Preliminary testing suggests cattle in New Mexico and Idaho may also be infected.
The virus has been confirmed to be the same version of H5N1, a subtype of influenza circulating in birds in North America.
The CDC announced Monday that it is working with state health departments to monitor people who may have come into contact with infected birds or animals.
This is the second case of H5N1 avian influenza in the United States. Experts say the risk to the general public remains low. However, testing and analysis are ongoing and there are many unanswered questions.
“This is a rapidly evolving situation,” the USDA said in a statement last week.
Here's what you need to know:
What is avian influenza?
Avian influenza, or avian influenza, is a group of influenza viruses that are primarily adapted to birds. The specific virus involved in these new cases is called H5N1, which was first identified in geese in China in 1996 and in people in Hong Kong in 1997.
In 2020, a new highly pathogenic H5N1 strain emerged in Europe and rapidly spread around the world. More than 82 million farmed birds were affected in the United States, making it the worst outbreak of bird flu in U.S. history.
sporadically since the virus was first identified. Cases have also been found in people from other countries. However, most of this was due to long-term direct contact with birds.
Experts say the H5N1 virus does not yet appear to be adapted to spread efficiently among people.
How did cows become infected with avian influenza?
Cattle were not considered a high-risk species.
Richard Webby, an influenza virologist at St. Jude Children's Research Hospital, said: “The fact that the virus is transmissible, that it can replicate and cause disease, is something I could not have predicted.'' It was,” he said.
But this year, reports of sick cattle started appearing in Texas and New Mexico. Dead birds were also found on some of these farms, and laboratory tests confirmed that some of the cattle were infected with avian influenza.
There are various ways the virus could have entered the cows. Experts say the likely route is that infected wild birds could have shed the virus in their feces, saliva or other secretions, contaminating the cattle's feed and water.
However, other free-ranging animals known to be susceptible to the virus, such as cats and raccoons, may also have introduced the virus to dairy farms.
How were the cows affected?
The virus is often fatal in birds, but appears to cause a relatively mild illness in cattle.
“The animal was not killed and appears to be recovering,” said Dr. Joe Armstrong, a veterinarian and animal husbandry expert at 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 become infected with the virus.
This disease primarily occurs in older cows, and symptoms include loss of appetite, low-grade fever, and a significant decrease in milk production. Texas officials say the milk cows produce is often “thick and discolored.” The virus has also been detected in unpasteurized milk samples taken from sick cows.
Experts caution that it is not yet clear whether the avian influenza virus is the sole cause of all the symptoms and illnesses reported.
How widespread is the problem?
It's unclear. As of last Friday, the USDA's National Veterinary Services Laboratory had confirmed cases of avian influenza in two herds in Texas, two herds in Kansas, and one herd in Michigan.
Initial testing suggests other herds in Texas, New Mexico and Idaho may also be infected with the virus, but those findings have not yet been confirmed by national labs. . So far, the virus has only been found in dairy cattle, not beef cattle.
But experts say there may be other infected herds that have escaped detection because cattle are not regularly tested for bird flu and the symptoms are relatively mild.
Additionally, the movement of cattle between states can carry the virus to new locations. The affected Michigan dairy farm had recently imported cattle from an infected herd in Texas. The cows were not showing any symptoms when they were transported. Idaho officials said an Idaho farm had recently imported cattle from the affected state.
How is it spreading?
That's an important question, but one that remains unanswered. Infected cattle may be transmitting the virus on their own, especially if shared feed or water sources are contaminated.
But a more worrying possibility is that the virus is spreading from cow to cow. On Friday, the Department of Agriculture noted that “the possibility of transmission between cattle cannot be ruled out.”
Some scientists said they would be surprised if there was not some degree of cow-to-cow transmission. “How else could it move so fast?” said Dr. Gregory Gray, an infectious disease epidemiologist at the University of Texas Medical Branch.
If the virus can spread easily among cattle, it could lead to larger and more sustained outbreaks. It would also give the virus more opportunity to adapt to new mammalian hosts, increasing the risk of it acquiring mutations that would make it more dangerous to humans.
How do authorities know if bird flu is contagious between humans?
Analyzing the genetic sequences of viruses taken from infected birds, cattle and people will reveal whether H5N1 has acquired mutations that make it more likely to spread between humans.
Scientists are closely tracking infections in birds, marine mammals, and now cattle. So far, the virus does not appear to have the ability to spread efficiently between humans.
In 2012, scientists discovered that H5N1 can spread through the air among ferrets (a common model for studying respiratory virus transmission among humans) after acquiring five mutations. We showed what we can do.
A sample of bird flu isolated from a Chilean man last year had two mutations that indicate adaptation to the mammals it infects. But experts say these mutations, which have been seen before, do not allow the virus to evolve further and spread between people.
