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

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Source: American Veterinary Medical Foundation (AVMF)

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 eight states: 12 herds in Texas, six each in New Mexico and Michigan, four in Kansas, and one each in Idaho, Ohio, North Carolina, and South Dakota. 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.
  • Veterinarians and producers are urged to practice good biosecurity, test cattle before necessary movements, minimize cattle movements, and isolate sick cattle. At this time, the USDA believes taking these precautions should limit disease spread sufficiently to avoid the need for federal regulatory restrictions or quarantines.
  • At the state level, however, at least 20 states have issued restrictions on the importation of dairy cattle: Alabama, Arizona, Arkansas, California, Delaware, Florida, Hawaii, Idaho, Kentucky, Louisiana, Maryland, Mississippi, Nebraska, North Carolina, Oregon, Pennsylvania, South Dakota, Tennessee, Utah, and West Virginia. Other states where avian influenza virus type A (H5N1) has not yet been detected in cattle may follow.
  • Federal and state agencies continue to conduct testing of clinical samples, including unpasteurized milk, nasal swabs, and tissue samples, and are also 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.
  • Three sick cats on a Texas dairy farm also have tested positive for avian influenza virus type A (H5N1). This is not surprising, as cats are among the mammals previously known to contract the virus, but it reinforces the importance of keeping pets away from wild birds. 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.
  • 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 interim recommendations.
  • 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 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.
  • 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.

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