Bird flu has started again – California authorities have declared a state of emergency due to the rapid spread of bird flu, which is affecting dairy cattle in the state and causing occasional illnesses in humans across the U.S.

This development brings new concerns about the virus, which has been circulating for years among wild birds, commercial poultry, and various mammal species.

First identified in U.S. dairy cattle in March, the Type A H5N1 virus has since been confirmed in at least 866 herds across 16 states.

Over 60 individuals in eight states have contracted the virus, with most cases resulting in mild symptoms, according to the U.S. Centers for Disease Control and Prevention (CDC). However, health officials reported this week that one individual in Louisiana has been hospitalized with the country’s first severe case linked to the virus.

California declared a state of emergency. Bird flu has started again?

Governor Gavin Newsom stated that the emergency declaration aims to allocate resources and staff more effectively to combat the outbreak.

The state has been testing large milk tanks for bird flu during processing and found the virus in at least 650 herds, which accounts for about 75% of all affected U.S. dairy herds. Initially detected in California’s Central Valley, the virus has now spread to dairy farms in Southern California.

“This declaration ensures government agencies have the flexibility and resources necessary for a swift response,” Newsom explained in a statement.

What is the risk? Bird flu has started again?

CDC officials have reiterated that the overall risk to the public remains low. There have been no reports of human-to-human transmission or any indication that the virus has evolved to spread more easily among humans.

Flu experts agree with this assessment, though they note it is too early to predict the outbreak’s trajectory. Richard Webby, an influenza specialist at St. Jude Children’s Research Hospital, emphasized that uncertainty remains, while other experts caution that flu viruses constantly mutate, and even minor genetic changes could alter the situation.

Are cases becoming more severe?

This week, the U.S. confirmed its first severe case of bird flu. Previously, all approximately 60 reported cases in the country were mild.

The critically ill patient in Louisiana, over 65 years old with underlying health conditions, developed severe respiratory symptoms. These symptoms arose after contact with a backyard flock of infected birds. This marks the first confirmed U.S. case linked to backyard birds, according to the CDC.

The strain responsible for the illness is associated with wild birds and not cattle. In a similar incident last month, Canadian officials reported a severe case in a teenager in British Columbia. That case also appears to be linked to a strain of the virus found in wild birds.

In the U.S., earlier infections were primarily among farmworkers exposed to infected dairy cattle or poultry. However, two cases — one in Missouri and another in California — remain unexplained.

Angela Rasmussen, a virologist from the University of Saskatchewan, noted that as infections increase, more severe cases could emerge. According to the World Health Organization, nearly 1,000 cases of H5N1 infection have been recorded worldwide since 2003. More than half have been fatal.

“I assume every H5N1 strain has the potential to cause severe and fatal infections,” Rasmussen warned.

How can people protect themselves?

People working around dairy cattle, commercial poultry or backyard birds should take precautions. Wearing respiratory and eye protection, as well as gloves, is most important, according to CDC guidelines.

Michael Osterholm, a public health expert at the University of Minnesota, urged people to handle sick or dying birds with extreme care.

The CDC is also funding flu vaccinations for farmworkers to reduce the risk of dual infections from seasonal flu and bird flu, which could lead to more dangerous mutations. The government advises farmworkers in contact with infected animals to undergo testing and take antiviral medications, even if asymptomatic.

How else does bird flu spread?

The H5N1 virus can also be transmitted through raw milk. While pasteurized milk is safe due to heat treatment that eliminates the virus, unpasteurized milk poses a significant risk. In recent weeks, California stores have recalled raw milk after the virus was detected at farms and in products.

In Los Angeles, two indoor cats fed recalled raw milk died from bird flu, prompting investigations into additional cases of sick cats. Health officials advise against consuming raw milk, as it can spread a variety of pathogens, including bird flu.

To contain the outbreak, the U.S. Department of Agriculture has intensified raw milk testing nationwide. A federal mandate issued this month now requires testing in 13 states, which began earlier this week.