The United States Department of Agriculture (USDA) took steps on Wednesday to curb the spread of the H5N1 bird flu virus among dairy cattle, issuing a federal order that requires animals to test negative for the virus before they can be moved across state lines. Additionally, laboratories and state veterinarians are now obligated to report any animals that have tested positive for H5N1 or any other influenza A virus to the USDA. Farms that move cattle across state lines and have animals that test positive for H5N1 or any influenza A virus will be required to provide investigators with access to their records so they can trace the movement of cattle from infected herds.
The order currently applies to lactating dairy cows but could be expanded if necessary, said Mike Watson, administrator for the Animal and Plant Health Inspection Service. The FDA’s representative, Don Prater, acting director of the Center of Food Safety and Applied Nutrition, reiterated that while traces of H5N1 RNA were found in commercially purchased milk products, the agency believes pasteurization kills the viruses that those findings indicate were once in the milk.
The FDA announced late Tuesday that it had found evidence of the virus in milk products. He evaded questions about where the positive milk samples were purchased and what percentage of samples contained traces of the virus when tested by PCR – polymerase chain reaction testing – saying that the agency has an analysis of its work that will be made public “very shortly.” Some support was offered for the oft-repeated claim that pasteurization would kill the virus in milk from Jeanne Marrazzo, the new NIAID director. She said that some NIAID-funded researchers had also found PCR-positive milk in samples bought from stores, but that when the researchers tried to grow virus from those samples, they could not.
“The results that those investigators got indicated that the PCR-positive material was not alive,” Marrazzo said, though she warned that work was done on a small number of samples and needs to be confirmed by the larger FDA effort. “While this is welcome news, the effort studied a small number of samples that is not necessarily representative of all retail milk,” she said. “So to really understand the scope here, we need to wait for the FDA effort.”
To date, the USDA has reported that 33 herds in eight states have tested positive for H5N1, though a recent analysis suggests more infections have occurred than have been recognized to date. Given the size of the U.S. milk supply, the finding of evidence of virus in milk products on store shelves also suggests there have been more infections than have been detected or at least reported.
Watson confirmed that USDA has encountered some resistance from farmers suspected of having infected cows. Farmers have been told they must discard any milk produced by cows that are infected with H5N1 virus, though it’s not clear if or how that recommendation is being enforced. Evidence that milk containing virus has entered the milk supply suggests either some farmers have ignored the advice or asymptomatic infected cows may be emitting viruses in their milk.
“There has been a little bit of reluctance from some of the producers to allow us to gather information from their farms. That has been improving more recently,” he said, suggesting the federal order should also increase USDA’s access. “With the federal order going into place, this is going to really help us address any gaps that might exist in terms of … knowing what’s happening with the cattle,” Watson said.
Likewise, Nirav Shah, the CDC’s principal deputy director, acknowledged there has been some difficulty in investigating the health of workers on some farms where H5N1 has been detected. “We’ve had a diversity of levels of engagement with farms,” Shah said. “These situations are challenging. There may be owners that are reluctant to work with public health to say nothing of individual workers who may be reluctant to sit down with somebody who identifies themselves as being from the government in some way.” He said CDC is working with trusted local sources where outbreaks have been identified, including veterinarians, who have regular access to farms and can serve as public health’s “eyes and ears.”
Shah was asked whether wastewater surveillance, which proved useful in gauging levels of transmission of Covid-19 in communities, could be helpful in trying to find H5N1 outbreaks in cattle. The CDC is exploring the idea, he said, but noted that farms may not be linked to municipal wastewater systems, and sampling water around farms might lead to false positives if infected wild birds are clustered in an area.
