April 30, 2024 – As the bird flu outbreak in cattle spreads, federal officials have stepped up safety measures while insisting that the public health risk is low. But questions and fears linger amid the outbreak that has impacted at least 34 dairy herds across nine states.
The newest precaution, announced Monday by the U.S. Department of Agriculture, comes from sampling of ground beef from states with infected herds. (Meat production from “retired” dairy cows makes up about 10% of U.S. commercial beef production.)
The decision to sample beef follows several other precautions:
- Lactating dairy cattle must now be tested for the bird flu virus, H5N1, before interstate travel.
- Dairy workers and others at risk should wear protective personal equipment (PPE) and take other precautions, the CDC advises.
- With the USDA and state partners, the CDC is monitoring exposed workers.
- The CDC is using its flu surveillance systems to monitor for H5N1 activity in people.
Despite all those precautions, federal officials insist our milk and meat supplies are safe and fit for consumption. As the CDC puts it: “While the current public health risk is low, CDC is watching the situation carefully and working with states to monitor people with animal exposures.”
The measures to combat the spread of avian flu are supported by the dairy industry. In a statement, National Milk Producers Federation CEO Gregg Doud called the USDA actions on testing and travel “appropriate.”
But concerns remain. Chief among them: If the H5N1 viruses become able to spread easily among humans, how possible is large-scale transmission or a pandemic? In a report issued April 3, the European Centre for Disease Prevention and Control discussed possible drivers for an avian flu pandemic. It noted that the viruses continue to evolve and said: “If avian A(H5N1) influenza viruses acquire the ability to spread efficiently among humans, large-scale transmission could occur due to the lack of immune [defenses] against H5 viruses in humans.”
Read on for a look at the current outbreak.
What About a Human Vaccine?
Speaking at the World Vaccine Congress in early April, Peter Marks, MD, PhD, director of the FDA’s Center for Biologics Evaluation and Research, said he was confident the avian flu vaccines in the U.S. stockpile would work if vaccination of people becomes necessary. Under the U.S. Department of Health and Human Services, the Biomedical Advanced Research and Development Authority (BARDA) has long-standing partnerships with vaccine makers to strengthen preparedness and response capabilities for the next influenza pandemics. In 2018, researchers reported that a vaccine against H5N1, stored in the national stockpile, did not lose effectiveness after 12 years. However, other experts have questioned whether the older vaccines would work against the current strain and whether supplies would be sufficient. Federal officials on Wednesday said two possible vaccines could be ready within weeks if needed.
About the Virus and Its Spread
The bird flu now affecting dairy herds, known as a highly pathogenic avian influenza (HPAI) or H5N1 virus, is an A type influenza. It can be spread by wild birds to domestic poultry and other bird and animal species, the FDA says. Wild birds are thought to be the source of the virus with the infected cattle, but the USDA investigation includes some cases where the virus spread between herds. While bird flu viruses don’t typically infect people, human infections have occurred.
According to a World Health Organization report, 888 cases of human infection with H5N1 have been reported from 2003 until March 28, 2024, from 23 countries; the fatality rate was 52%.
One human case, involving a worker exposed to dairy cattle in Texas, has been reported with the recent outbreak.
When the first dairy herd infection was reported in late March, it was the first time H5N1 has been reported in cattle, according to the CDC. The nine states with infected dairy herds are Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota, and Texas.
Milk Concerns: The Timeline
Concern about milk supplies arose on April 25 when the FDA received results from its nationally representative commercial milk sampling study finding that about 1 in 5 retail samples tested were positive for viral fragments of the bird flu virus on a test known as polymerase chain reaction (qPCR). Those tests don’t necessarily represent actual viruses, experts explain.
“Finding the fragments does not mean the virus is intact or biologically active and capable of causing infection,” Terry Lehenbauer, DVM, MPVM, PhD, a professor and director of the Veterinary Medicine Teaching and Research Center, University of California Davis, Tulare, said in a telephone interview. “It just means there is evidence of the virus having been in the milk.”
On Friday, the FDA announced results of more rigorous testing known as the egg inoculation test. In this, an embryonated chicken egg is injected with a virus sample to see if the virus replicates. There was no live, infectious virus found. The agency also tested several small samples of powdered infant formula and powdered milk products marketed as toddler formula. All qPCR tests were negative. The agency is further testing samples of 239 retail dairy products from states with infected herds.
Pasteurization, the process of heating liquids at high temperatures for brief periods to kill harmful microbes, protects against avian flu virus, experts agree.
“Based on the evidence we have, it’s reasonable to expect our current pasteurization techniques of milk to be effective for inactivating viruses, including the avian influenza that we’re dealing with right now in dairy cattle,” Lehenbauer said.
He said he told his family that. “Here is the closing line that I sent in an email yesterday afternoon [April 25] to my son’s and daughter’s families, which include five grandchildren (ages between 8 and almost 2): “Keep giving all of the grandkids their milk and dairy products! It is still safe and wholesome nutrition!”
Asked if consumers might do anything to prepare in case the outbreak worsens,Lehenbauer advised nothing beyond normal food safety measures. “All the evidence and current information have indicated that the risk for people drinking milk is very low, and that is based on two primary factors. One is the stringent regulations governing dairy production, and the other is the federal advice to consume only pasteurized dairy products."
Renewed Warnings About Raw Milk
The FDA has long advised against drinking raw (unpasteurized) milk but now emphasizes that advice. Despite that advice, the Raw Milk Institute says that drinking raw milk is not dangerous even in the current avian flu environment.“HPAI [an umbrella term for avian influenza A (H5) and A (H7) viruses] is old news,” Mark McAfee, chairman of the Raw Milk Institute, said in an email when asked if his organization would advise against drinking raw milk for the time being. “It’s been around for 3 years and does not cause human illness. It lacks the gene to make the jump to humans."
But Andrew Pekosz, PhD, a professor and virologist at Johns Hopkins University Bloomberg School of Public Health, said that's wrong.
“It can infect humans. It lacks the ability to transmit from human to human.” That’s true currently, he said, but “it's one of the things we are paying close attention to. Could it mutate?”
Long-Standing Infections
While news of the infected milk samples is recent, experts say the virus has been prevalent in cattle for some time. “It probably has been here for several months,” Lehenbauer said.
Others are trying to track how it got to the cattle. After the USDA released 239 genetic sequences from the H5N1 virus found in samples from poultry, birds, and cattle, scientists rushed to analyze it. One analysis by University of Arizona professor Michael Worobey concluded that “there was a single origin [from birds], at least for these sequences.”