The number of California dairy herds where outbreaks of H5N1 bird flu have occurred has risen to eight.
Authorities have declined to disclose the location of the infected herds but have said they are nearby, somewhere in California's Central Valley, an 18,000-square-mile expanse that is roughly the size of Vermont and New Hampshire combined.
They say they are still investigating the source of the virus, but at a news conference Thursday, federal officials said genetic sequencing of the first three outbreaks suggests the strain is similar to one seen in other states. They say it does not appear to have been caused by birds or wild animals.
“This is the same virus we have been seeing in dairy herds since H5N1 first emerged in dairy cattle,” said Eric Deeble, deputy undersecretary for marketing and regulatory programs at the U.S. Department of Agriculture. “Sequencing of samples from the five additional facilities will likely be completed later this week or over the weekend.”
He said the California Department of Food and Agriculture has been “doing very extensive tracing, and all herds that have been detected in California to date have been subject to their investigation.”
There have been 201 herds infected with the virus in 14 states since the outbreak was first reported in March.
State officials continue to reassure the public that the risk to the general population is low and that pasteurized milk and dairy products are safe for human consumption.
Deeble said his agency is in the process of authorizing field safety studies for a vaccine against the H5N1 virus in cows.
An agency spokesperson said the development of the vaccine does not mean that the biosafety protocols followed by the USDA and state governments have failed. Nor does it mean that the virus is here to stay.
“Vaccine development is part of an overall strategy that includes enhanced and strengthened biosecurity efforts to contain the virus and help mitigate the spread,” said USDA spokesman Will Clement.
“Bovine vaccines can prove to be an important tool to help eliminate the virus from dairy cattle in the country, but developing a vaccine requires many steps and it will take time to test, approve and distribute a successful vaccine,” he said. “That’s why we have opened the way to field trials of the vaccine, even as we continue to deploy all available efforts, including an emphasis on biosecurity and requiring testing of lactating dairy cattle moving across state lines.”
Federal health officials also say they have not been able to fully sequence the H5N1 sample isolated from a human case in Missouri. That person had no known contact with dairy products or poultry, and a preliminary investigation has not been able to determine the source of the infection.
There have been no reports of infected dairy herds in Missouri.
“At this point, the evidence points to this being an isolated case,” said Nirav Shah, principal deputy director of the Centers for Disease Control and Prevention.
Shah said the patient, who was hospitalized with flu-like symptoms and has since recovered, had low levels of the virus circulating in his body. As a result, sequencing has been difficult.
While officials can confidently say the virus is of the H5 subtype, they have not been able to sequence the N part.
But the H5 part appears to resemble the H5 subtype in infected dairy cows.
“We are doing everything we can to achieve this, but ultimately a full sequence may not be technically feasible due to the low concentration of viral RNA,” Shah said.
