WASHINGTON — The commissioner of the U.S. Food and Drug Administration said at a congressional hearing Wednesday the agency is preparing for the possibility the strain of avian influenza affecting dairy cattle could jump to humans, though he cautioned the probability is low.

Robert Califf told senators on the panel in charge of his agency’s funding that top officials from the FDA, Agriculture Department and Centers for Disease Control and Prevention are speaking daily to keep a handle on the situation. He also stressed that pasteurized milk is safe.

“This virus, like all viruses, is mutating,” Califf said. “We need to continue to prepare for the possibility that it might jump to humans.”

Califf told senators that the “real worry is that it will jump to the human lungs where, when that has happened in other parts of the world for brief outbreaks, the mortality rate has been 25%.”

That would be about 10 times worse than the death rate from COVID-19, he said.

Califf stressed the possibility is low and the CDC continues to maintain its assessment that “the current public health risk is low.”

The H5N1 bird flu strain has had an impact on 36 dairy herds in Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota and Texas, according to the CDC.

Two cases have been reported in people — one who had exposure to dairy cows in Texas that were “presumed to be infected” and one in Colorado “involved in the culling (depopulating) of poultry with presumptive H5N1 bird flu.” Both cases were reported in April, according to the CDC.

The Texas case “reported eye redness (consistent with conjunctivitis), as their only symptom” while the Colorado case reported “fatigue for a few days as their only symptom and has since recovered,” according to the CDC.

Multiple federal agencies involved

Califf told the Senate Agriculture Appropriations Subcommittee during the hearing the Agriculture Department holds jurisdiction over the dairy cows, the FDA is in charge of making sure milk and other foods are safe and the CDC has the responsibility to ensure the safety of farmworkers.

The FDA has repeatedly tested milk on store shelves throughout the country and found no live virus, due to pasteurization, he said.

The agency is interested in testing milk before the pasteurization process begins, though Califf said they’ve had some difficulties getting access to dairy farms.

“Access to the farms, for example, is really something that has to be negotiated through the states,” he said. “The farmers and the owners of dairy farms are more comfortable with people that they know that are in their state. So all this has to be coordinated.”

Califf explained that when cows are milked, that “goes into bulk tanks, which is a mixture of a number of cows.”

“That’s a very sensitive area because it does point, if there are infected cows, as to where the infections are,” Califf testified. “And technically it’s no problem, but we want to make sure we have trust. And so there’s negotiation that needs to go on to make sure there’s a safe way to handle the data and that people are not going to be castigated if they happen to have an infected herd. So we’re working through all that state by state.”

Wisconsin Democratic Sen. Tammy Baldwin urged the FDA to coordinate and communicate frequently with farmers and the public.

Her home state, she noted, has more than 5,000 dairy herds, making up 22% of the nation’s total herd count. “So this is a big deal for us.”