USDA requires HPAI testing for lactating dairy cattle before movement, reporting for all livestock

Genetic material from virus found in milk supply, but FDA says there's little risk to consumers

The federal government will soon require the testing of dairy cattle for highly pathogenic avian influenza (HPAI, more specifically avian influenza type A H5N1) before being transported to another state.

While testing will initially apply to lactating dairy cattle, there may be future adjustments to include other types of dairy cattle based on the evolving scientific understanding of the disease and its risks.

Further, laboratories and state veterinarians must report positive results of tests for influenza A in livestock. Both changes are effective April 29.

The U.S. Food and Drug Administration (FDA) recently confirmed the presence of remnants of HPAI virus in commercially available milk, with a higher number of positive results coming from areas with infected herds. The agency noted that quantitative polymerase chain reaction (qPCR)–positive results for HPAI do not necessarily represent actual virus that may be a risk to consumers.

Several dairy cows lined side by side in a barn
The U.S. Department of Agriculture, the U.S. Food and Drug Administration, and the Centers for Disease Control and Prevention, along with state partners, continue to investigate an outbreak of highly pathogenic avian influenza virus impacting dairy cows in multiple states. Infection with the virus is causing decreased lactation, low appetite, and other clinical signs in affected cattle.

“Additional testing is required to determine whether intact pathogen is still present and if it remains infectious, which would help inform a determination of whether there is any risk of illness associated with consuming the product,” the FDA said in an April 25 statement.

Meanwhile, research continues by federal agencies and partners to understand transmission of the disease and its origins in dairy cattle, cats, and other mammals.

Federal order

The U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) issued its federal order April 24 to prevent the spread of HPAI. That comes after at least 22 states have imposed import restrictions on dairy cattle from states or premises where the virus is known to have infected dairy cows.

Prior to interstate movement, lactating dairy cattle will be required to receive a negative result of testing for influenza type A virus, as performed by an approved National Animal Health Laboratory Network (NAHLN) laboratory.

Owners of herds in which dairy cattle test positive will be required to provide epidemiological information, including animal movement tracing. Lactating dairy cattle from herds that have tested positive for influenza A are not eligible for interstate movement for 30 days from the most recent collection of any sample that tests positive from any individual animal in the herd. After the 30-day period, animals must be tested again for movement.

That’s according to an April 26 guidance document from APHIS that outlines requirements and recommendations for HPAI H5N1 in livestock for state animal health officials, accredited veterinarians, and producers.

The document also says the interstate movement of all lactating dairy cattle must be accompanied by a certificate of veterinary inspection.

In addition, veterinary diagnostic laboratories and state veterinarians must report to APHIS positive influenza Type A nucleic acid detection diagnostic results (e.g. polymerase chain reaction–based assays (PCR) or genetic sequencing) and serology diagnostic results in livestock, the order states.

APHIS says it will reimburse for testing at NAHLN laboratories, including samples submitted for the following:

  • Dairy cattle suspected of disease due to clinical signs
  • Premovement testing
  • Producers interested in the disease status of their asymptomatic animals
  • Samples taken from other animals on dairies associated with this disease event

Samples submitted to an NAHLN laboratory are usually returned within one to three days, according to an FAQ that APHIS published on the federal order. Any sample that is non-negative undergoes confirmatory testing at the USDA’s National Veterinary Services Laboratories (NVSL), which is usually completed within one to two days.

Testing for HPAI in milk

The FDA said in an April 25 announcement that HPAI H5N1 viruses have been detected in initial results from its nationally representative commercial milk sampling study.

“The agency continues to analyze this information; however, the initial results show about 1 in 5 of the retail samples tested are quantitative polymerase chain reaction (qPCR)-positive for HPAI viral fragments, with a greater proportion of positive results coming from milk in areas with infected herds,” the agency stated.

The FDA says more testing is needed to determine whether the intact pathogen is still present after pasteurization and if it remains infectious. That will help officials decide if there is any risk of illness associated with consuming the milk.

The pasteurization process is highly likely to kill the virus but does not remove it. Since the start of the HPAI outbreak in dairy cattle this March, the FDA has been evaluating milk from infected cattle, in the processing system, and on grocery shelves on a national scale.

The FDA says it’s further assessing any positive findings through egg inoculation tests, a gold-standard for determining if infectious virus is present. Early work by National Institutes of Health–funded investigators “indicates an absence of infectious virus in their studies of retail milk. To date, the retail milk studies have shown no results that would change our assessment that the commercial milk supply is safe.”

Results from multiple studies will be made available in coming days to weeks, according to the agency.

In the meantime, the FDA continues to recommend the following:

  • Any milk diverted for feeding calves should be heat treated to kill harmful bacteria or viruses before feeding.
  • The dairy industry should refrain from selling raw milk or raw or unpasteurized cheese products made from milk from cows showing signs of illness.
  • Producers should take precautions when discarding milk from affected cows so that it does not become a source of further spread. This includes heat treatment, pasteurization or its equivalent, of discarded milk prior to dumping in lagoons and ensuring biosecurity around lagoons.

The FDA is collaborating closely with the Centers for Disease Control and Prevention (CDC) food safety group, as well as its surveillance team, which is monitoring human emergency department data and flu testing data for any unusual trends in flu-like illness, flu, or conjunctivitis. So far, surveillance systems have not shown unusual trends or activity. The CDC says risk to the general public remains low.

Ongoing testing and research

As of April 24, the NVSL had confirmed the HPAI H5N1 virus genotype in dairy cattle in eight states: 12 herds in Texas, six each in New Mexico and Michigan, four in Kansas, two in Idaho, and one each in Ohio, North Carolina, and South Dakota.

The NVSL also confirmed that eight poultry farms have been infected with the same HPAI H5N1 virus genotype detected in dairy cattle in five states.

“HPAI has already been recognized as a threat by USDA, and the interstate movement of animals infected with HPAI is already prohibited,” according to the USDA statement. “However, the detection of this new distinct HPAI H5N1 virus genotype in dairy cattle poses a new animal disease risk for dairy cattle—as well as an additional disease risk to domestic poultry farms—since this genotype can infect both cattle and poultry.”

Female veterinarian taking a goat milk sample in a barn
APHIS information says while it is still unclear exactly how virus is spreading, the virus is shed in milk at high concentrations; therefore, anything that comes in contact with unpasteurized raw milk may spread the virus, including other animals, vehicles, and other objects.

Further, APHIS said its microbiologists have identified a shift in an H5N1 sample from a cow in Kansas that could indicate that the virus has an adaptation to mammals. The CDC conducted further analysis of the specimen sequence, APHIS information states, “which did not change their overall risk assessment for the general public, because the substitution has been seen previously in other mammalian infections and does not impact viral transmission.”

Earlier in the week, USDA announced it was publishing 239 genetic sequences of the HPAI H5N1 virus genotype—specifically known as U.S. H5N1 clade influenza virus—to encourage more disease research. The samples were taken from cattle, cats, chickens, a skunk, a raccoon, a grackle, a blackbird, and a goose.

Researchers expressed disappointment that information was not provided on where the samples came from specifically, what part of the body of the infected animal it was taken from, or when the collections occurred.

In an updated fact sheet, APHIS said that while wild migratory birds are believed to be the original source of the virus, it has been passed from cow to cow in some instances.

“Additionally, we have similar evidence that the virus also spread from dairy cattle premises back into nearby poultry facilities through an unknown route,” according to APHIS.

HPAI has been in the U.S. since February 2022, and since then, nearly 80 million domestic birds have died from HPAI or in eradication efforts. This includes mostly egg-laying hens and turkeys raised for human consumption. HPAI strains are deadly to domestic poultry and can wipe out entire flocks within days.

A paper published online April 10 in JAVMA said the current HPAI outbreak is unique in global expansion and in the wildlife species diversity that it is impacting and the range of wild mammals in which it is being detected. However, most spillover has been dead-end events, sporadic, in small numbers, and associated with mild disease.

“Though the risk to humans remains low, this unexpected outbreak well illustrates the continued need for vigilance and further study. As the range of HPAI expands and the frequency of mammalian infections increase, the risk of zoonotic transmission continues to increase,” the authors wrote. “This is why it is critical that robust surveillance occurs and appropriate biosafety caution is exercised, particularly in novel and atypical hosts, so that evidence for mammalian adaptation and mammal-to-mammal spread can be captured as early as possible.”

For the most current information about highly pathogenic avian influenza, visit the AVMA website or the U.S. Department of Agriculture Animal and Plant Health Inspection Service’s website.