Avian influenza virus type A (H5N1) in U.S. dairy cattle

Last updated: May 1, 2024
On March 25, the U.S. Department of Agriculture (USDA), Food and Drug Administration (FDA), and Centers for Disease Control and Prevention (CDC) announced that highly pathogenic avian influenza (HPAI), specifically avian influenza virus type A (H5N1), had been identified in U.S. dairy cattle for the first time. Here are important details on this rapidly evolving situation:

• Avian influenza virus type A (H5N1) has been confirmed in dairy cattle in nine states: 12 herds in Texas, eight in New Mexico, six in Michigan, four in Kansas, two in Idaho, and one each in Ohio, North Carolina, South Dakota, and Colorado. Get updates on detections here and answers to frequently asked questions here.
• Tests so far indicate that the virus detected in dairy cattle is H5N1, Eurasian lineage goose/Guangdong clade 2.3.4.4b. This is the same clade that has been affecting wild birds and commercial poultry flocks and that has caused sporadic infections in several species of wild mammals and neonatal goats in one herd in the United States.
• Common clinical signs in affected cows include low appetite, reduced milk production, and abnormal appearance of milk (thickened, discolored).
• While avian influenza virus type A (H5N1) is associated with high morbidity and mortality in birds ("highly pathogenic"), this hasn't been the case for dairy cattle. Affected animals reportedly recover with supportive treatment and with little to no mortality.
• The spread of the H5N1 virus within and among herds indicates that bovine-to-bovine spread occurs, likely through mechanical means. Evidence also indicates that the virus can spread from dairy cattle premises to nearby poultry facilities.
• The USDA has urged veterinarians and producers to practice good biosecurity; monitor for, separate, and test sick animals; minimize cattle movements; and isolate and monitor any newly received dairy cattle for 30 days upon arrival. In addition, starting April 29, a federal order is in effect, requiring testing of lactating dairy cattle for HPAI prior to interstate movement, and reporting of positive nucleic acid detection and serology results for livestock to APHIS. While the movement restriction initially applies to lactating dairy cows, this may be adjusted based on an evolving scientific understanding of the disease and risks. Find answers to frequently asked questions about the order here and guidance for producers and veterinarians here.
• At the state level, at least 22 states have issued restrictions on the importation of dairy cattle:
  Alabama, Arizona, Arkansas, California, Delaware, Florida, Hawaii, Idaho, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Nebraska, New York, North Carolina, Oregon, Pennsylvania, South Dakota, Tennessee, Utah, and West Virginia. State-specific restrictions on cattle movement must be followed in addition to federal requirements. If and where a particular state’s requirements are more restrictive than the federal order, that state’s requirements must be followed.
• Federal and state agencies continue to conduct testing of clinical samples, including unpasteurized milk, nasal swabs, and tissue samples, as well as samples of milk along all stages of production. They also are performing viral genome sequencing. The USDA and state health officials encourage producers to work with their veterinarians to support sampling and testing.
• Testing conducted thus far has not found changes in the virus that would make it more transmissible to humans.
• The American Association of Bovine Practitioners (AABP) has created a working group of its members that, together with AVMA, is communicating with federal and state officials and working on additional biosecurity guidance. AABP members can find more information about these activities here. AABP guidance on navigating the federal order can be found here.

Impact on other animals and public health

• Seven sick or dead cats on dairy farms in Texas, New Mexico, and Ohio also have tested positive for avian influenza virus type A (H5N1). In cats—a species previously known to contract the virus, illness reportedly has been severe, manifesting as neurological signs, copious oculonasal discharge, and a high mortality rate. These findings reinforce the importance of keeping pets away from wild birds and raw milk or colostrum. The CDC advises veterinary staff to take precautions when working in close contact with cats with confirmed or suspected exposure to HPAI.
• Infection with avian influenza virus type A (H5N1) was confirmed in a dairy farm worker in an area of Texas where the virus has been found in dairy cattle and wild birds. Eye redness (consistent with conjunctivitis) was their only symptom. The patient was told to isolate and received an antiviral for flu. The case of H5N1 in this person does not change the health risk assessment for the U.S. general public, which the CDC continues to consider low. So far, the CDC's surveillance team has found no uptick in human cases of flu.
• People with close or prolonged, unprotected exposure to infected animals or their environments are at greater risk of infection. For tips on how to protect yourself, see the CDC's updated interim recommendations.

Impact on food safety

• The USDA, FDA, and CDC continue to state they have no concerns about the safety of the commercial milk supply because milk from impacted animals is being diverted or destroyed so it does not enter the human food supply. In addition, products are pasteurized before entering interstate commerce for human consumption.
• Although the FDA has found fragments of the H5N1 virus in some pasteurized milk samples from grocery stores, preliminary results of additional tests show the absence of live, infectious virus in those samples. Overall, the results indicate that pasteurization is effective in inactivating the virus, and reaffirm the FDA's assessment that pasteurized milk is safe for human consumption.
• The FDA strongly encourages that any milk diverted for feeding calves be heat treated to kill harmful bacteria or viruses before feeding.
• The FDA recommends that the dairy industry refrain from selling raw milk or raw/unpasteurized cheese products made from milk from cows showing signs of illness.
• People are advised not to drink raw milk or eat raw milk-based cheese, and to properly handle and cook meat to an internal temperature of at least 165°F. This includes any meat used to feed pets.

For the most current information and resources from the USDA, FDA, and CDC, see the USDA Animal and Plant Health Inspection Service (APHIS) page on HPAI detections in livestock.