Four more cats have tested positive for H5N1 bird flu in connection with a growing outbreak in dairy cows in the United States, according to state and federal officials, raising the number of cases in the current outbreak to seven.

Sonja Olsen, the Associate Director of Preparedness and Response at CDC’s Influenza Division, reported three new cases in cats on Thursday and state officials reported a fourth case on Friday.

“The reports we heard were of cats having neurologic symptoms, rapid decline, and death,” Olsen told BNO News.

Three of the new cases were found at two dairy farms in Curry County, New Mexico and all of them died, according to the state’s Agriculture Department. The fourth case was found at a dairy farm in Wood County, Ohio.

This follows the recent deaths of three other cats at dairy farms in Texas.

The global spread of H5N1 clade 2.3.4.4b – and the recent spread to a growing number of mammals – has raised concern about the possibility of a future variant which could lead to human-to-human transmission. So far, only a few human cases have been found after contact with infected birds or cattle.

The U.S. Department of Agriculture (USDA) announced in late March that bird flu had been found in unpasteurized milk from sick cows in Kansas and Texas, making those the first-ever cases in cattle. The number of outbreaks at dairy farms has since risen to 34 in 9 states and a farm worker in Texas also tested positive.

Earlier this week, officials confirmed that viral fragments of H5N1 bird flu had been found in samples of commercial milk. Experts say milk is still believed to be safe because of pasteurization and tests are currently underway to confirm this.

“The risk of avian influenza is evolving with the virus and needs real-time monitoring,” the World Health Organization said in a statement on Friday. “WHO and partners are asking countries to rapidly share information to enable this.”

Cats are known to be vulnerable to this new strain of H5N1 bird flu. The first case in a cat with this variant was reported near a duck farm in southern France in December 2022, causing it to be euthanized.

Months later, in 2023, nearly 40 cats died at two animal shelters in South Korea after eating contaminated cat food. And in Poland, more than a dozen cats died in an outbreak presumably caused by contaminated raw meat.

In the United States, at least 20 cats have been infected with H5N1 bird flu, including the 7 cases reported this month. The other 13 happened last year in connection with infected poultry or wild birds.