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Last updated: December 23, 2024

On March 25, [2024] 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 16 states: 660 herds in California, 64 in Colorado, 35 in Idaho, 29 in Michigan, 27 in Texas, 13 each in Iowa and Utah, nine each in Minnesota and New Mexico, seven in South Dakota, four in Kansas, two in Oklahoma, and one each in Nevada, 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 and domestic mammals in the United States.

Common clinical signs in affected cows include low appetite, reduced milk production, and abnormal appearance of milk (thickened, discolored). Lactating cows have been most highly affected, and signs of illness have been reported in less than 10% of cows within a herd.

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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. Most affected animals reportedly recover with supportive treatment, and the mortality/culling rate has been low at 2% or less.

The spread of the H5N1 virus within and among herds indicates that bovine-to-bovine spread occurs. Overall, animal movement is a recognized risk for disease transmission. Evidence also indicates that the virus can spread from dairy cattle premises to nearby poultry facilities. Potential risk factors for local transmission between facilities include shared personnel between premises; shared, uncleaned vehicles and equipment between premises; and frequent visitors on/off premises.

There currently is no genomic or epidemiologic evidence that wild birds are spreading H5N1 to cattle, but this possibility cannot be ruled out.

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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 the USDA’s Animal and Plant Health Inspection Service (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 issued an emergency order on May 1 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.

As of July 22, Colorado is requiring all licensed dairy cow farms in the state that are not under separate order for quara ntine or testing to submit weekly bulk-tank samples for HPAI testing, with the aim of preventing further spread of the virus among dairy and poultry farms.

Canada has tightened import requirements on dairy cattle from the United States.

The USDA has announced financial assistance for producers with H5N1-affected premises to improve on-site biosecurity, as well as compensation for lost milk production. Additional financial help to promote biosecurity and viral testing is available for producers whose herds have not tested positive for H5N1.

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 USDA continues to invest heavily in vaccine research and development to help prevent the spread of H5N1 virus among animals. The agency has approved two vaccine field safety trials for vaccine candidates designed to protect dairy cattle from the virus, and is exploring vaccine options for other species.

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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

So far, at least 52 cats have tested positive for avian influenza virus type A (H5N1) in states where the virus also has been found in dairy cattle. 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 cases reinforce the importance of keeping pets away from raw milk or colostrum, raw meat, and wild birds and other wildlife.

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nThe CDC advises veterinary staff to take precautions when working in close contact with cats with confirmed or suspected exposure to HPAI. Find more details on H5N1 in cats here.

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.

The NVSL also has confirmed detection of avian influenza virus type A (H5N1) in one of five pigs in an Oregon backyard (noncommercial) farming operation where poultry and livestock are comingled, representing the first detection of the virus in U.S. swine. This finding is not surprising given that poultry on the farm also tested positive and shared water sources, housing, and equipment with livestock. The USDA notes that the pig was healthy and states it has no concern about the safety of the nation’s pork supply. Overall, the situation reinforces the importance of strong biosecurity practices.

Since April 2022, infection with avian influenza virus type A (H5) has been confirmed in 65 people in the U.S. Twenty-four of these cases involved poultry farm workers exposed to infected poultry in Washington (11 cases), Colorado (10 cases, including a single case in 2022), and Oregon (1 case). Thirty-nine other cases involved dairy farm workers exposed to sick or infected cows—35 in California, two in Michigan, one in Texas, and one in Colorado. Reported symptoms in farm workers generally have ranged from eye redness or discharge (consistent with conjunctivitis) to more typical flu symptoms, such as fever, chills, coughing, and sore throat/runny nose. Another two cases involved one person in Missouri and a child in Colorado with no known exposure to sick or infected animals. The CDC, which 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.

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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 information for workers exposed to the virus and the USDA’s recommendations on personal protective equipment. For tips on how to protect your workers, see the CDC’s interim guidance for employers.

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.

The FDA, alongside federal and state partners, continues to undertake research activities to help ensure the safety of the milk and milk product supply during the outbreak. A variety of retail dairy samples from multiple states have been tested for the virus, including pasteurized milk; pasteurized milk-based products, such as butter, ice cream, and various cheeses; and aged raw milk cheese. Although fragments of the H5N1 virus have been found in some samples, additional tests have shown 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.

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To better understand the implications of the H5N1 virus on beef destined for human consumption, the FSIS will start testing dairy cows at slaughter as part of its existing national residue monitoring program, beginning September 16. In the event of a positive test result, the USDA will work with industry to ensure the relevant carcass does not enter the food supply.

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. In early December, all raw whole milk and cream from a California dairy was recalled following detection of the virus in multiple samples from retail stores and dairy storage and bottling sites. While no illnesses were reported, the finding serves as a good reminder of the risks of foodborne disease inherent to unpasteurized milk and milk products.

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.

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Originally posted by 6ixStringJack:
If this were Twitter in 2021, you'd have gotten banned for writing that.

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"I don't find this stuff amusing anymore." ~Paul Simon

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