The avian influenza virus spreading through dairy cows in the United States can likely be traced back to a single spillover event. Scientists believe the virus jumped from wild birds to cattle in the Texas Panhandle late last year. By spring, the virus, known as H5N1, had traveled more than hundreds of miles and appeared on farms in Idaho, North Carolina and Michigan.
The virus did not travel that distance alone. Instead, it traveled to new states along with host cows as they were transported from the source to farms across the country.
Transporting live animals is essential to the increasingly specialized industrial livestock industry. Many facilities focus on one step in the production process, such as producing new pups or fattening adults for slaughter, and then send the animals on their way.
It is difficult to determine the exact number of chickens, cows, and pigs transported by truck, ship, plane, or train in the United States. This is because there is no national system for tracking the movement of chickens, cows and pigs.
But estimates from official sources and animal rights groups give a sense of its scale. In 2022, about 21 million cattle and 62 million hogs were shipped to states for breeding and feed, according to the Department of Agriculture. These numbers do not include poultry, movement within the same state, or movement to slaughter. That year, more than 500,000 young dairy calves, some just days old, were shipped from just six states, according to the nonprofit Animal Welfare Association. Some traveled more than 1,500 miles.
“This movement could contribute to long-distance transport of the pathogen, potentially causing outbreaks and making outbreaks difficult to manage,” said Colleen Webb, an expert in livestock epidemiology at Colorado State University.
Many livestock pathogens, including avian influenza, are zoonotic and can jump from animals to humans. Larger and longer-lasting outbreaks in livestock may increase the likelihood that people will come into contact with infected animals or contaminated food, increasing the opportunity for pathogens to evolve.
Since March, avian influenza has been confirmed on 51 dairy farms in nine states, with at least one dairy worker infected. Last month, in an effort to curb the outbreak, the Department of Agriculture began requiring influenza A testing for lactating cows crossing state lines.
“But that's only part of the problem,” says Ann Linder, associate director of the Animal Law and Policy Program at Harvard Law School.
Experts say the United States has few restrictions on livestock transportation, which poses an often overlooked threat to animal and human health. The movement of livestock is what Linder calls “the perfect combination of factors that can promote disease transmission.”
shipping heat
Every step of the transportation process creates opportunities for pathogens to spread.
Trucks and storage facilities can cram animals from multiple farms into small spaces with poor ventilation. In one randomized study, researchers found that 12 percent of chickens slaughtered on farms carried Campylobacter, a common cause of food poisoning. Bacteria were detected in 56% of the birds after transport.
Depending on traffic conditions, it may be physically taxing. Animals are exposed to extreme heat and cold, transported hundreds of miles without rest, and may be without food, water or veterinary care, experts say. There is virtually no data on how many people got sick or died while traveling.
Such stressful situations “not only compromise the animal's health and welfare, but also weaken the immune system, clearly increasing the risk of disease transmission,” says animal welfare nonprofit Compassion in World Farming. Ben Williamson said.
Many studies suggest that transportation can suppress cows' immune systems, making them more susceptible to a disease known as “bovine respiratory disease.” “Delivery fever.”
Livestock can also leave pathogens on the road as they move. In one study, scientists found that pathogens, including those resistant to antibiotics, escaped from a moving poultry truck and entered the cars following it. Trucks are “just spreading antibiotic-resistant bacteria,” said study author Anna Ruhl, a bioaerosol expert at the Johns Hopkins Bloomberg School of Public Health and author of the study.
Contaminated transport vehicles are known to spread pathogens long after infected animals disembark, and may be responsible for the dairy cow outbreak, officials said.
Infected animals can cause outbreaks at destinations such as livestock auctions, and commercial food supplies often attract older, sicker, or smaller animals. Such auctions “would be the perfect place for the H5N1 virus to move from cattle to pigs,” Linder said.
Pigs are of particular concern. It's possible to be infected with multiple types of influenza at the same time, and different strains can exchange genetic material and new versions of the virus can arise.
The global trade in live pigs has accelerated the evolution of swine flu by sending pigs carrying one influenza virus into regions of the world where different influenza viruses are endemic. A new and harmful bacteria, Streptococcus suis, that can sicken both pigs and humans, emerged through a similar process.
The global pig trade has “increased the diversity of pathogen strains around the world,” said Gemma Murray, an evolutionary geneticist at University College London who has studied streptococcus.
gaps and loopholes
Although the Department of Agriculture has the authority to restrict interstate movement of livestock, there are actually few barriers to interstate transportation. “I think the Department of Agriculture, for the most part, wants to make the lifecycle journey as seamless as possible,” Linder said.
Under federal law, first passed in 1873, livestock transported for more than 28 consecutive hours must be lowered for at least five hours for food, water, and rest. But critics say the 150-year-old law is looser than regulations in comparable countries and is rarely enforced. Over the past 15 years, the federal government has investigated only 12 cases for potential violations, according to the Animal Welfare Institute.
The law also exempts transportation by water or air. Compassion in World Farming documents the use of “cattlemen” to transport calves from Hawaii to the mainland United States on voyages that took more than five days.
Livestock traveling between states must carry a veterinary inspection certificate issued by the state Department of Agriculture or a certified veterinarian declaring the animal to be healthy. However, these visual inspections do not catch infected but asymptomatic animals, which likely play a role in spreading avian influenza to new dairy herds.
Once inspectors identify a sick animal, experts can conduct epidemiological investigations to determine the animal's origin. However, these investigations are not always successful.
Livestock identification and tracking systems that record the movements of individual animals over their lifetime are now mandatory in many European countries. “In today's world, where we are so interconnected, that makes sense,” said Dr. Dirk Pfeiffer, a veterinary epidemiologist at the City University of Hong Kong.
A handful of states, including Michigan, have created similar programs, but none are on a national level. A USDA spokesman defended the U.S. program in an email, noting that the U.S. livestock industry is much larger than many European countries.
A national tracking system could have allowed authorities to quickly trace the path of cows infected with avian influenza, identify affected farms and possibly contain the outbreak, scientists say. said.
“The sooner we have data on where infectious animals may be, the sooner we can implement controls,” Dr. Webb said. “It's really a race against time when trying to control an outbreak.”
Animal rights activists are calling for new livestock transport regulations. One bill proposed by Sen. Cory Booker, D-N.J., would shorten the 28-hour law to eight hours and require stricter record-keeping. Rep. Dina Titus, Democrat of Nevada, plans to introduce another bill that would strengthen enforcement and require compliance with international shipping standards.
“Consumers and Americans should be mindful of how farmed animals are transported because they are sentient creatures and can suffer,” said Dena Jones of the Animal Welfare Institute. Ta. “But also because their health impacts our food and health safety.”
