The bird flu virus that is spreading through American dairy cows can probably be traced to a single rebound event. Late last year, scientists believe, the virus jumped from wild birds to livestock in the Texas region. By this spring, the virus, known as H5N1, had already traveled hundreds of miles or more, appearing on farms in Idaho, North Carolina and Michigan.
The virus did not travel these distances alone. Instead, it hitched a ride with its cow hosts, moving to new states as cattle were transported from the epicenter of the outbreak to farms across the country.
The transport of live animals is essential for industrial livestock farming, which has become increasingly specialized. Many facilities focus on just one step of the production process – producing new offspring, for example, or fattening adults for slaughter – and then shipping the animals.
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The exact number of chickens, cows and pigs transported on trucks, ships, planes and trains within the United States is difficult to determine because there is no universal national system for tracking their movement.
But estimates from official sources and animal advocates offer a sense of the scale: In 2022, about 21 million cattle and 62 million pigs were shipped to states for breeding or feeding, according to the Department of Agriculture; these numbers do not include birds, movements within the same state or trips to slaughter. That same year, more than 500,000 young dairy calves, some just a few days old, were transported from just six states, according to the Animal Welfare Institute, a nonprofit group. Some traveled more than 1,500 miles.
“Movement can contribute to long-distance transport of pathogens and make outbreaks and outbreak management challenging,” said Colleen Webb, a livestock epidemiology expert at Colorado State University.
Many livestock pathogens, including bird flu, are zoonotic, meaning they can pass from animals to humans. Larger, longer-lasting livestock outbreaks can increase the chances of people coming into contact with infected animals or contaminated food products and create more opportunities for pathogens to evolve.
Since March, bird flu has been confirmed in 51 dairy herds in nine states and has infected at least one dairy worker. Last month, in an effort to contain the outbreak, the USDA began requiring influenza A testing for lactating cows that cross state lines.
“But this represents only a small fraction of the problem,” said Ann Linder, associate director of the animal law and policy program at Harvard Law School.
The United States places few restrictions on the transportation of farmed animals, posing an often-ignored threat to animal and human health, experts say. Cattle movements present what Linder called “a perfect combination of factors that can facilitate disease transmission.”
Transport fever
Each step of the transportation process provides opportunities for the spread of pathogens.
Trucks and holding facilities can cram animals from multiple farms into small, poorly ventilated spaces. In a randomized study, researchers found that 12% of chickens slaughtered on farms harbored Campylobacter bacteria, a common cause of food poisoning. After transport, the bacteria was found in 56% of the birds.
Transport conditions can also have a physical impact. Animals can be subjected to extreme heat and cold, transported hundreds of miles without rest and deprived of food, water and veterinary care, experts say. There is practically no data on how many people get sick or die while traveling.
Such stressful conditions “compromise the animal’s health and well-being and also weaken its immune system, which obviously increases the risk of disease transmission,” said Ben Williamson of Compassion in World Farming, a nonprofit animal welfare organization. -being animal.
Numerous studies suggest that shipping can suppress cows’ immune systems, leaving them vulnerable to bovine respiratory disease, often known as “shipping fever.”
As they travel, farm animals can also leave pathogens in their wake. In one study, scientists found that disease-causing bacteria, including some that were resistant to antibiotics, flowed from moving poultry trucks and into the cars behind them. The trucks were “just spreading these antibiotic-resistant bacteria,” said Ana Rule, a bioaerosol expert at the Johns Hopkins University Bloomberg School of Public Health and an author on the study.
Contaminated transport vehicles are also known to spread pathogens long after infected animals have disembarked and may be playing a role in the dairy cow outbreak, officials said.
Infected animals can then trigger outbreaks at their destinations, including livestock auctions, which often attract animals that are too old, sick or small for the commercial food supply. These auctions “would be a great place for H5N1 to move from cattle to pigs,” Linder said.
Pigs are of particular concern. They can be infected by several types of flu at the same time, allowing different strains to exchange genetic material and giving rise to new versions of the virus.
The global trade in live pigs fueled the evolution of swine flu, sending pigs carrying one flu virus to parts of the world where different flu viruses circulate. New harmful forms of Streptococcus suis, bacteria that can sicken both pigs and humans, have emerged through a similar process.
The global pig trade is “increasing the diversity of pathogenic strains around the world,” said Gemma Murray, an evolutionary geneticist at University College London who led the strep research.
Gaps and gaps
The Department of Agriculture has the authority to restrict the interstate movement of livestock, but in practice there are few barriers to transportation across the country. “I think USDA, for the most part, wants to make this life cycle journey as simple as possible,” Linder said.
Under a federal law first passed in 1873, cattle transported for more than 28 consecutive hours must be unloaded for at least five hours for food, water and rest. But critics say the 150-year-old law is more flexible than regulations in comparable countries and rarely enforced. The Animal Welfare Institute has found only 12 federal investigations of possible violations in the past 15 years.
The law also exempts shipments by sea or air. Compassion in World Farming has documented the use of “cowtainers” to transport calves from Hawaii to the continental United States, on boat trips that can last five days or more.
Cattle traveling between states must carry a veterinary inspection certificate, issued by the state department of agriculture or an accredited veterinarian, declaring that the animals are healthy. But these visual inspections would not detect infected animals, but rather asymptomatic ones, which likely played a role in the spread of bird flu to new dairy herds.
Some states have their own disease testing requirements. Utah, for example, requires that some cattle test negative or be vaccinated against brucellosis, a bacterial infection, while Maryland requires that chickens test negative for pullorum disease and typhoid fever.
But most routine disease surveillance happens at the end of the supply chain. “There are inspectors at slaughterhouses who inspect carcasses as they arrive for signs of disease,” Webb said.
When inspectors identify sick animals, experts can perform epidemiological investigations to determine the animal’s origin. But these investigations are not always successful.
Many countries in Europe now have mandatory livestock identification and tracking systems, which record the movements of individual animals throughout their lives. “It’s a no-brainer in the modern world where we are so connected,” said Dr. Dirk Pfeiffer, a veterinary public health researcher at City University of Hong Kong.
While some states, including Michigan, have created similar systems, none exist nationally. A USDA spokesperson defended the American system in an email, noting that the U.S. livestock industry is much larger than that of any European nation.
A national tracking system could have allowed authorities to quickly track the paths of dairy cows infected by bird flu, identify affected farms and perhaps contain the outbreak, scientists said.
“The faster you have data on where infectious animals might be, the faster you can implement your controls,” Webb said. “When you’re trying to control an outbreak, it’s really a race against time.”
Animal welfare advocates are calling for the approval of new regulations for livestock transportation. One bill, proposed by Sen. Cory Booker, D-N.J., would shorten the law from 28 hours to eight hours and require stricter recordkeeping. Representative Dina Titus, Democrat of Nevada, plans to introduce another bill that strengthens oversight and requires adherence to international transportation standards.
“Consumers and Americans should be concerned about how farmed animals are transported because they are sentient beings, capable of suffering,” said Dena Jones of the Animal Welfare Institute. “But also because their well-being has an impact on the safety of our food and our health.”
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