Six states have reported new cases of highly pathogenic avian influenza (HPAI), also known as H5N1, in dairy cattle over the past 30 days. Washington has reported 41 cases during the same period, while Indiana and Oregon have confirmed their first infections in dairy cattle.
USDA confirmed HPAI in an Indiana dairy herd Nov. 2, marking the state’s first reported case. On Nov. 10, federal officials confirmed the virus in an Oregon dairy herd, also the state’s first detection.
Dairy cattle in 22 states have been infected since the outbreak began in March 2024. The recent detections in Indiana and Oregon add to the outbreak’s geographic reach.
HPAI Reaches More Dairy States
The latest detections show HPAI continuing to spread into new areas of the country. With Indiana and Oregon now reporting infections, the virus has reached more dairy-producing states as cases continue to accumulate across the U.S.
“While this detection is significant, it is not unexpected given the continued spread of HPAI among dairy cattle nationally,” says Dr. Ryan Scholz, state veterinarian with the Oregon Department of Agriculture.
Both herds were identified through routine milk testing under the National Milk Testing Strategy. The Oregon herd had consistently tested negative in previous rounds of testing before its latest sample detected the virus.
“Oregon’s milk surveillance program worked exactly as intended, identifying this infection quickly and allowing us to respond rapidly with our state and federal partners,” Scholz says.
USDA and state officials are conducting additional testing and investigations in both states. In Oregon, federal officials are also completing genetic sequencing to learn more about the virus detected in the herd.
Washington Cases Climb Quickly
Washington’s first two dairy cattle cases were confirmed Oct. 8 in Yakima County. Within weeks, the Washington State Department of Agriculture reported 34 affected herds, including 33 in Yakima County and one in neighboring Benton County.
The first detections came after more than 7,000 negative surveillance tests over the previous two years. USDA later confirmed the virus in the initial Washington herds was consistent with transmission from Idaho, likely through cattle movement.
“Seeing the virus move to another county is disappointing but our dairy farmers are working hard to implement their biosecurity plans, share lessons learned and help each other get through this,” says Washington State Veterinarian Amber Itle, VMD, MS.
“This isn’t new for the country, but it is new for Washington. I’ve been in awe of how hard our veterinarians and dairy farmers work together every day to keep their cows healthy, keep their workers safe and keep operating despite all the uncertainty this virus brings with it,” she says.
Washington Reports Human Infections
Yakima County has reported three confirmed human HPAI cases linked to exposure to infected dairy cattle. One case involved a dairy employee who tested positive Oct. 15 and experienced eye irritation and upper respiratory symptoms but no severe illness.
On Nov. 1, the Yakima Health District announced one of the three individuals had died from avian influenza complications after exposure at an infected dairy. The individual had underlying health conditions.
“Our hearts go out to the individual’s family and loved ones during this difficult time,” says Dave Atteberry, DVM, health officer with the Yakima Health District. “Avian influenza can cause severe illness, particularly among people who have underlying health conditions. While this is a serious and heartbreaking outcome, the risk to the general public remains low. We continue to work closely with our public health partners to monitor the situation and protect the health of our community.”
The CDC continues to assess the risk to the general public as low.
Researchers Explore Vaccines as HPAI Spreads
As HPAI continues to reach new dairy herds, researchers are evaluating vaccination as another way to protect cattle. A new University of Pennsylvania study tested an mRNA vaccine designed to help cows develop an immune response against H5N1.
Researchers gave four lactating Holstein cows two vaccine doses, three weeks apart. Four additional cows received saline injections as controls. Seven weeks after the first dose, all eight cows were exposed to H5N1 through direct inoculation into the mammary gland.
Vaccinated cows had peak levels of viral RNA in milk about 1,000 times lower than unvaccinated cows. They also maintained milk production more consistently, while unvaccinated cows began experiencing production declines two days after infection. Researchers found less inflammation and tissue damage in the vaccinated cows’ mammary glands.
Scott Hensley, a University of Pennsylvania researcher, says reducing the amount of virus in livestock could also lower the risk of human infections.
“If we can reduce the amount of virus in birds and cattle, we’re ultimately reducing the chance that this virus has of infecting humans,” Hensley says.
Hensley has also called for a different approach to controlling H5N1, saying, “We have to do something different because what we’re doing now is clearly not working.”
Other studies have examined mRNA and adenovirus-vectored vaccines in dairy cattle. More research is needed to determine how well vaccination protects herds under farm conditions, how long immunity lasts and whether it reduces transmission.
