California officials have declared a state of emergency over the spread of bird flu, which is tearing through dairy cows in the state and causing sporadic illnesses in people in the US.
Here’s what you need to know.
How did bird flu spread in the US?
The virus, also known as Type A H5N, has spread for years in wild birds, commercial poultry and many mammal species. It was detected for the first time in US dairy cattle in March. Since then, bird flu has been confirmed in at least 866 herds in 16 states.
More than 60 people in eight states have been infected, with mostly mild illnesses, according to the US Centers for Disease Control and Prevention (CDC). Almost all of those have been farmworkers with direct exposure to infected dairy cattle or poultry.
One person in Louisiana has been hospitalized with the nation’s first known severe illness caused by the virus, health officials said this week. That patient was infected through a backyard flock.
In addition to direct contact with farm animals and wild birds, the H5N1 virus can be spread in raw milk. Pasteurized milk is safe to drink, because the heat treatment kills the virus, according to the US Food and Drug Administration (FDA).
There have not been any reports of person-to-person transmission.
How has it spread in California?
California is the US’s top milk producing state, and three-quarters of the infected herds in the country, about 650 of them, are located in the state.
The state has been looking for bird flu in large milk tanks during processing, and the virus was detected in four southern California dairy farms earlier this month after being found in the state’s Central valley since August.
The detection in the southern California farms made clear the state needed “a shift from regional containment to statewide monitoring and response”, the California governor, Gavin Newsom, said in his emergency declaration.
What does the emergency declaration do?
The declaration allows the state to better position state staff and supplies to respond to the outbreak, Newsom said.
“This proclamation is a targeted action to ensure government agencies have the resources and flexibility they need to respond quickly to this outbreak,” he said in a statement.
What’s the risk to the public?
Officials with the CDC stressed again this week that the virus currently poses low risk to the general public.
But the case of severe illness in the US this week shows that while previous cases mostly caused eye redness, the virus could pose a danger to some people.
The patient in Louisiana, who is older than 65 and had underlying medical problems, is in critical condition. Few details have been released, but officials said the person developed severe respiratory symptoms after exposure to a backyard flock of sick birds. That makes it the first confirmed US infection tied to backyard birds, the CDC said. Tests showed that the strain that caused the person’s illness is one found in wild birds, but not in cattle.
Last month, health officials in Canada reported that a teen in British Columbia was hospitalized with a severe case of bird flu, also with the virus strain found in wild birds.
It’s possible that as more people become infected, more severe illnesses will occur, said Angela Rasmussen, a virus expert at the University of Saskatchewan in Canada.
“I assume that every H5N1 virus has the potential to be very severe and deadly,” Rasmussen said.
What are other reasons experts are worried?
While there have not been any reports of person-to-person transmission and no signs that the virus has changed to spread more easily among humans, experts warn that flu viruses are constantly mutating and small genetic changes could change the outlook.
Flu experts say it’s too soon to tell what trajectory the outbreak could take. “The entirely unsatisfactory answer is going to be: I don’t think we know yet,” said Richard Webby, an influenza expert at St Jude Children’s Research Hospital.