Breaking down the escalating bird flu situation in the US

California authorities have declared a state of emergency due to the spread of bird flu, as infections in dairy cows are increasing and are sporadically leading to human illnesses in the United States

That raises new questions about the virus, which has been spreading among wild birds, poultry and many mammal species for years.

The virus, also known as Type A H5N1, was first detected in U.S. dairy cattle in March. Since then, bird flu has been confirmed in at least 866 flocks in 16 states.

According to the US Centers for Disease Control and Prevention (CDC), more than 60 people in eight states have been infected, with mostly mild illnesses. A person in Louisiana has been hospitalized with the first known serious illness caused by the virus, U.S. health officials said this week.

Here’s what you need to know:

Why did California declare a state of emergency?

Gov. Gavin Newsom said he declared a state of emergency to allow state personnel and supplies to better respond to the outbreak.

California has been checking for bird flu in large milk tanks during processing. And they have detected the virus in at least 650 herds, representing about three-quarters of all affected dairy herds in the United States.

VIEW | Why WHO wants stronger animal surveillance of H5N1:

WHO says “much stronger” H5N1 surveillance is needed in animal populations

Dr. Maria Van Kerkhove, director of epidemic and pandemic preparedness at the World Health Organization, is calling for increased global surveillance of animal populations known to be susceptible to H5N1, including wild birds, poultry, pigs and cattle.

The virus was recently discovered on dairy farms in Southern California after being found in the state’s Central Valley since August.

“This proclamation is a targeted measure to ensure government agencies have the resources and flexibility they need to respond quickly to this outbreak,” Newsom said in a statement.

How big is the risk to the general public?

CDC officials reiterated this week that the virus poses a low risk to the general public.

Importantly, there are no reports of person-to-person transmission and no evidence that the virus has changed to spread more easily among people.

In general, flu experts agreed with that assessment and said it was too early to tell what course the outbreak might take.

“The completely unsatisfactory answer will be: I don’t think we know yet,” said Richard Webby, an influenza expert at St. Jude Children’s Research Hospital in Michigan.

But virus experts are cautious because flu viruses are constantly mutating and small genetic changes could alter the outlook.

Are the cases becoming more serious?

This week, health officials confirmed the first known case of serious illness in the United States. All U.S. cases so far — there have been about 60 — have been generally mild.

The Louisiana patient, who is over 65 years old and had underlying health issues, is in critical condition. Few details have been released, but officials said the person developed severe respiratory symptoms after being exposed to a flock of sick birds in the backyard.

That makes it the first confirmed U.S. infection linked to backyard birds, the CDC said.

Tests showed that the strain that caused the person’s illness is found in wild birds but not cattle. Last month, health authorities in Canada reported that a teenager in British Columbia was hospitalized with a severe case of avian flu, also with the strain of the virus also found in wild birds.

Previous infections in the United States have almost exclusively affected farm workers who were directly exposed to infected dairy cattle or poultry. In two cases — an adult in Missouri and a child in California — health authorities have not determined how they became infected.

Dr. Amesh Adaljia, a senior scientist at the Johns Hopkins Center for Health Security and an infectious disease physician in Baltimore, said H5N1 does not currently pose a threat to the general public, but that doesn’t mean it should be ignored entirely given the exposure to farm workers.

“We’ve only had one really severe case in the United States and understanding why most cases are mild is also a big challenge,” Adaljia said in an interview with CBC News.

The B.C. case was a strain more related to what’s circulating in geese, while the Louisiana version is more related to what’s circulating in poultry, Adaljia said.

How can people protect themselves?

People who come into contact with dairy cows, farm poultry or backyard birds are at higher risk and should take precautions such as respiratory protection, eye protection and gloves, the CDC and other experts said.

“When birds start getting sick or dying, they should be very careful about how they handle these animals,” said Michael Osterholm, a public health disease expert at the University of Minnesota.

The CDC has funded flu shots to protect farmworkers from seasonal flu — and the risk that workers could become infected with two types of flu at the same time, potentially causing the bird flu virus to mutate and become more dangerous. The U.S. government also said farm workers who come into close contact with infected animals should be tested and offered antiviral drugs, even if they showed no symptoms.

Dr. Jesse Papenburg, a pediatric infectious disease specialist at Montreal Children’s Hospital, said Canadians should be aware of the increased risk of exposure and transmission to humans through contact with poultry and wild waterfowl, other animals or their environment.

“Be very aware of the situation regarding influenza-like illnesses, especially as Canada enters flu season along with the U.S.,” Adalja said.

How else is bird flu spread?

In addition to direct contact with farm animals and wild birds, the H5N1 virus can also be spread through raw milk. According to the U.S. Food and Drug Administration, pasteurized milk is safe to drink because the heat treatment kills the virus.

However, high levels of the virus have been found in unpasteurized milk. And two brands of raw milk sold in stores in California have been recalled in recent weeks after the virus was detected on farms and in the products.

In Los Angeles, county officials reported that two indoor cats fed the recalled raw milk died from avian influenza infections. Officers investigated additional reports of sick cats.

Health officials are urging people to avoid consuming raw milk as it can spread a variety of germs in addition to bird flu.

The U.S. Department of Agriculture has increased testing of raw milk across the country to detect and contain the outbreak. A federal order issued this month mandates testing, which began this week in 13 states.