The avian influenza virus spreading among American dairy cows can likely be traced to a single spillover event. Scientists believe the virus jumped from wild birds to cattle in Texas late last year. By this spring, the virus known as H5N1 had traveled hundreds of miles or more, appearing on farms in Idaho, North Carolina and Michigan.
The virus could not cross these distances on its own. Instead, as the cattle moved from the epicenter of the outbreak to farms across the country, they hitched a ride with their hosts, the cows, and moved to new states.
Live animal transportation is of great importance in increasingly specialized industrial animal agriculture. Many facilities focus on a single step in the production process (e.g. raising fledglings or fattening adults for slaughter) and then ship the animals away.
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It is difficult to determine the exact number of chickens, cows, and pigs transported by trucks, ships, planes, and trains in the United States because there is no universal national system to track their movements.
But estimates from official sources and animal advocates give some idea of the scale: About 21 million cattle and 62 million pigs were sent to states for breeding or feeding in 2022, according to the Department of Agriculture; These figures do not include poultry, movements within the same state or trips to slaughter. That same year, more than 500,000 young dairy calves, some only a few days old, were shipped from six states alone, according to the Animal Welfare Institute, a nonprofit group. Some traveled more than 1,500 miles.
“Movement can contribute to the transport of pathogens over long distances, causing outbreaks and making outbreaks more difficult to manage,” said Colleen Webb, a livestock epidemiologist at Colorado State University.
Many animal pathogens, including bird flu, are zoonotic, meaning they can jump from animals to humans. Larger, longer-lasting livestock outbreaks may increase the likelihood that humans will come into contact with infected animals or contaminated food products, creating more opportunities for pathogens to thrive.
Since March, bird flu has been confirmed in 51 dairy herds in nine states and infected at least one dairy worker. Last month, in an effort to stem the outbreak, the USDA began requiring influenza A testing for lactating cows crossing state lines.
“But that only touches a very small part of the problem,” said Ann Linder, associate director of Harvard Law School’s animal law and policy program.
The U.S. places too few restrictions on the transportation of livestock, which pose an often overlooked threat to animal and human health, experts said. The movement of livestock offers what Linder calls “the perfect mix of factors that can facilitate disease transmission.”
Transport Fever
Each step in the transport process provides opportunities for pathogens to spread.
Trucks and storage 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. Once transported, the bacteria was found in 56% of the birds.
Transport conditions can also have a negative physical impact. Animals can be exposed to extreme heat and cold, dragged hundreds of kilometers without a break, and deprived of food, water and veterinary care, experts said. There is almost no data on how many people fell ill or died on the journeys.
Ben Williamson of Compassion in World Farming, an animal welfare nonprofit, said such stressful conditions “compromise the health and welfare of the animal and also weaken the immune system, which obviously increases the risk of disease transmission.”
Multiple studies suggest that transportation suppresses cows’ immune systems, leaving them vulnerable to bovine respiratory diseases commonly known as “transport fever.”
Farm animals can also leave pathogens behind as they travel. In one study, scientists found that disease-causing bacteria, including some that are resistant to antibiotics, flow from moving poultry trucks to the cars behind them. The trucks are “just spreading these antibiotic-resistant bacteria,” said Ana Rule, a bioaerosol expert at the Johns Hopkins University Bloomberg School of Public Health and author of the study.
Contaminated transportation vehicles are known to spread pathogens long after infected animals land and may have played a role in the dairy cow outbreak, officials said.
Infected animals can then trigger outbreaks in their destinations, including livestock auctions that often attract very old, sick or small animals for the commercial food supply. Such auctions “would be a great place for H5N1 to jump from cattle to pigs,” Linder said.
Pigs are of particular concern. They can be infected with more than one strain of flu at the same time, allowing different strains to exchange genetic material and new versions of the virus to emerge.
The global trade in live pigs accelerated the evolution of swine flu by sending pigs carrying an influenza virus to parts of the world where different influenza viruses were circulating. As a result of a similar process, harmful new forms of the Streptococcus suis bacteria that can sicken both pigs and humans emerged.
Evolutionary geneticist Gemma Murray of University College London, who led the research on strep disease, said the global pig trade was “increasing the diversity of pathogenic species around the world”.
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 interstate transportation. “I think USDA mostly wants to make this lifecycle journey as seamless as possible,” Linder said.
Under a federal law first passed in 1873, animals transported for more than 28 consecutive hours must be evacuated for at least five hours for food, water and rest. But critics say the 150-year-old law is looser than regulations in similar countries and is rarely enforced. The Animal Welfare Institute found only 12 federal investigations into potential violations in the past 15 years.
The law also exempts shipments by water or air. Compassion in World Farming has documented the use of “guards” to transport calves from Hawaii to the continental United States on boat trips that can last five days or more.
Animals traveling between states must carry a veterinary inspection certificate issued by the state department of agriculture or an approved veterinarian, declaring that the animals are healthy. However, these visual inspections will capture infected but asymptomatic animals; This likely played a role in the spread of bird flu to new dairy herds.
Some states have their own disease testing requirements. For example, Utah requires some cattle to test negative or be vaccinated against brucellosis, a bacterial infection, while Maryland requires chickens to test negative for pullorum disease and typhoid.
However, most routine disease surveillance occurs at the end of the supply chain. “Slaughterhouses have inspectors who inspect incoming carcasses for signs of disease,” Webb said.
When inspectors identify sick animals, experts can conduct epidemiological studies to determine where the animal came from. However, these studies are not always successful.
Many countries in Europe now have mandatory animal identification and tracking systems that record the movements of animals throughout their lives. Dr D., a veterinary public health researcher at the City University of Hong Kong. “This is not a simple thing in the modern world where we are so interconnected,” said Dirk Pfeiffer.
While a handful of states, including Michigan, have created similar systems, no such system exists 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 country.
The national tracking system could allow authorities to quickly track the routes of dairy cows infected with bird flu, identify affected farms and perhaps contain the outbreak, scientists said.
“The quicker you have data on where infectious animals might be, the quicker you can put your controls in place,” Webb said. “When you’re trying to control an epidemic, it’s essentially a race against time.”
Animal welfare advocates are demanding the adoption of new live animal transportation regulations. Sen. Cory Booker, D.N.J. A bill proposed by would reduce the 28-hour work law to eight hours and require stricter record keeping. Rep. Dina Titus, D-Nev., plans to introduce another bill that would strengthen enforcement and require compliance with international transportation standards.
“Consumers and Americans should care about the way farm animals are transported because they are sentient beings who can suffer,” said Dena Jones of the Animal Welfare Institute. “But also because their well-being affects the security of our food and our health.”
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