Increased Spread of US Bird Flu Could Raise Human Infection Risk, Officials Warn

By Leah Douglas and Julie Steenhuysen

Further spread of bird flu among dairy herds in the U.S. could increase the risk of human infections, federal officials warned on Thursday, emphasizing the need for farms to implement enhanced biosecurity measures to control the virus.

Since late March, the U.S. Department of Agriculture has reported bird flu in 94 dairy herds across 12 states. Although the current risk to public health remains low, the potential for the virus to spread further could elevate that risk, according to Nirav Shah, the principal deputy director for the U.S. Centers for Disease Control and Prevention (CDC), during a media briefing.

“The more infections there are among cows, the more risk there is for infections to occur among humans,” Shah stated.

The CDC has been monitoring over 500 individuals and has conducted tests on at least 45 people during this outbreak. So far, three dairy farm workers have tested positive since the virus began affecting dairy cows. To mitigate exposure, U.S. officials have advised farm workers to wear protective gear. Both the U.S. and Europe are working on vaccines aimed at protecting farm workers this year.

A genetic analysis of the third human case revealed no mutations in the virus that would facilitate easier transmission among humans, Shah noted.

When asked if the CDC should test asymptomatic individuals who have been exposed to the virus, Shah expressed confidence in the agency’s current testing approach, highlighting that testing such individuals could lead to identifying people carrying the virus without actually being infected.

The spread of bird flu among dairy farms is believed to occur through animal movement, shared personnel, and equipment used across multiple farms, according to Kammy Johnson, a veterinary epidemiologist with the USDA. Wild birds, which are initial carriers of the virus, do not appear to be transmitting it between herds or to poultry farms, according to a USDA report released on Thursday.

Johnson emphasized the importance of biosecurity measures, such as cleaning equipment and restricting the movement of sick animals, to help contain the virus’s spread. When questioned about how many additional farms with infected cows might be unreported, Johnson acknowledged, “That’s the $64,000 question. We don’t know what we don’t know.”

The USDA is urging farmers to test their herds if they observe symptoms of the virus and is offering financial support for milk and animal testing. So far, farmers from 11 of the 94 infected dairy herds have enrolled in these programs, according to Mark Lyons, a USDA official.

Agriculture Secretary Tom Vilsack informed that approximately two dozen companies are currently developing an avian flu vaccine for cattle.