Avian influenza virus type A (H5N1) in U.S. dairy cattle. AVMA: June 11, 2024

Mary Wilson · Jun 11, 2024

Last updated: June 11, 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 12 states: 24 herds in Michigan, 19 in Idaho, 18 in Texas, eight in New Mexico, five in South Dakota, four each in Kansas and Colorado, three in Minnesota, and one each in Iowa, North Carolina, Ohio, and Wyoming. 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, since April 29, a federal order has been 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.
Michigan has issued an emergency order to control and prevent the continued spread of HPAI within the state by requiring that poultry and livestock producers develop and implement specific biosecurity practices.
Canada has tightened import requirements on dairy cattle from the United States.
The USDA has announced assistance for producers with H5N1-affected premises to improve on-site biosecurity, as well as financial tools for lost milk production in affected herds.
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.
The CDC recommends monitoring people exposed to HPAI-infected animals of any species—including people wearing recommended personal protective equipment. Those who develop symptoms of HPAI should be tested for H5N1 virus at a state or local public health department.

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.
The National Veterinary Services Laboratories (NVSL) confirmed the detection of avian influenza virus type A (H5N1) in alpacas from a premises where HPAI-affected poultry were depopulated in May 2024. While this HPAI confirmation is not unexpected due to previous HPAI detection on the premises, the high amount of virus in the environment, and co-mingling of multiple livestock species on-farm, it is the first HPAI detection in alpacas.
To date, infection with avian influenza virus type A (H5N1) has been confirmed in three dairy farm workers exposed to infected cows—two in Michigan and one in Texas. Symptoms in two workers were limited to eye redness (consistent with conjunctivitis). The third worker is the first person in the current cattle outbreak known to have developed respiratory symptoms (cough without fever). All three patients were told to isolate, received an antiviral for flu, and have recovered or are recovering. The CDC, who has been closely monitoring the situation, assures these human cases are unrelated to each other, with no indication of person-to-person transmission. Furthermore, there has been no uptick in human cases of flu. Based on the available information, the CDC continues to consider the risk of HPAI to the general public low.
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 and the USDA’s personal protective equipment 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 USDA’s Food Safety and Inspection Service (FSIS) has tested ground beef samples from stores in states with confirmed-positive dairy cattle herds. The samples tested negative for the virus using polymerase chain reaction (PCR) methods, reaffirming that the meat supply is safe, too.
The FSIS also has tested 109 muscle samples from cull dairy cows that had been condemned at slaughter because of systemic disease. Overall, 108 samples tested negative for H5N1 viral particles, and one tested positive. Meat from condemned cows is prohibited from entering the human food supply, so the USDA remains confident that the meat supply is safe.
The FDA has recommended that states that permit the sale of raw milk (for human or animal consumption) within their state use their regulatory authorities to stop that sale if the milk may contain viable H5N1 virus, as may occur when the milk comes from an infected herd and is not pasteurized.
The FDA strongly encourages that any milk diverted for feeding calves be heat treated to kill harmful bacteria or viruses before feeding.
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.

Additional resources

https://www.avma.org/resources-tool...ian-influenza-virus-type-h5n1-us-dairy-cattle

Avian influenza virus type A (H5N1) in U.S. dairy cattle. AVMA: June 11, 2024

Mary Wilson

Well-known member