The U.S. Department of Agriculture (USDA) has issued a nationwide order to test milk for the H5N1 bird flu, targeting entities that handle raw milk, including bulk transporters and dairy processors.

The objective is to swiftly identify infected dairy herds and curb the spread of the virus among livestock, reported NBC News. Currently, 718 dairy herds across 15 states have been affected by the H5N1 strain, which has also caused significant poultry outbreaks. USDA Secretary Tom Vilsack emphasized the importance of this initiative in safeguarding both farm animals and farmworkers while striving to control the virus’s transmission on a national scale.

Testing under this new mandate will begin on December 16, starting with six states: California, Colorado, Michigan, Mississippi, Oregon, and Pennsylvania.

Dairy farm owners whose cattle test positive will be required to share detailed information to support surveillance efforts. This new order builds on an earlier mandate from April, which stipulated that dairy cows needed to be tested before being transported across state lines, with reporting managed by private labs and state veterinarians.

The USDA’s new directive reflects a growing urgency to address the spread of bird flu among livestock, a situation scientists fear could extend into a public health issue. While transmission among animals is the primary concern, there’s a possibility that bird flu could spread to humans, particularly through raw milk consumption. The Centers for Disease Control and Prevention (CDC) warns that untreated milk may pose a risk of infection, although pasteurization effectively neutralizes the virus, ensuring milk remains safe for consumption.

Despite CDC warnings, the sale and consumption of raw milk remain popular in some areas, with about 30 states permitting local sales. In November, California health officials detected bird flu in raw milk from a local farm, prompting a state-wide recall of milk and cream products from retail shelves. Fortunately, no human infections have been connected to these products.

The CDC has confirmed 58 human bird flu cases in the United States, most of which were linked to exposure to infected animals, either poultry or dairy cows. Arizona recently saw two new cases among poultry workers, marking the first such infections in the state. Though symptoms among infected humans remain mostly mild — such as coughs, sneezing, or pinkeye — some cases could be asymptomatic, which raises further concerns.

The bird flu strain’s ability to spread across mammals poses a unique risk. Research indicates the virus can be transmitted between cows and other animals like cats and raccoons, primarily through raw milk, since infected cows excrete high amounts of the virus via their mammary glands. This efficient transmission among mammals highlights a significant risk within dairy farms, where the virus could spread quickly across different species.

Scientists remain vigilant about the possibility of H5N1 mutating to allow human-to-human transmission, which could spark a future pandemic. A recent study published in Science underscores these concerns, revealing that a single genetic mutation in the current bird flu strain could enable the virus to spread more easily among people. Such findings highlight the USDA and CDC’s efforts to prioritize testing and containment measures, ensuring that preventive actions address potential risks before the virus poses a broader public health threat.