Farmworker Dave Schillawski milks a cow in Ancramdale, New York, in 2020. Recent cases of H5 flu among dairy cows and poultry are raising concerns about animal disease safety.
Photo by Angela Weiss, courtesy AFP/Getty Images
“It’s the idea that ‘it can’t happen here,’ and that these are things that happen in other countries far away and not risks that we generate here at home in the good old USA.”
— Dale Jamieson
From COVID-19 and mpox to avian flu and severe acute respiratory syndrome, most major human disease outbreaks all have one thing in common: they are believed to have spread from animals to humans.
With avian flu spreading in the U.S. from dairy cows and poultry to farmworkers, zoonotic disease experts are warning that the next pandemic could start close to home.
“The evidence we have, in terms of the emergence and spread of past pandemics, very much supports that a pandemic could start in the U.S.,” Jennifer Nuzzo, DrPH, a professor of epidemiology and director of the Pandemic Center at Brown University School of Public Health, told The Nation’s Health.
From pigs to poultry to pets, the U.S. is home to a vast, complex and diverse network of animal industries, including nearly 3,000 species of native wildlife and a food system of more than 10 billion animals. A 2023 report from Harvard Law School and New York University warned that the scale and diversity of high-risk interactions between humans and animals in the U.S. is greater than in almost any other country, making the nation uniquely vulnerable to diseases that can jump from animals to humans.
The huge scale and diversity of the nation’s human-animal interactions and the inadequacy of the regulatory structure are among the many reasons a pandemic from animals could start in the U.S., Ann Linder, JD, MS, the report’s lead author, told The Nation’s Health.
For example, the U.S. Department of Agriculture does not regulate on-farm production of livestock, “and slaughterhouse inspections are cursory, with each inspector tasked with examining more than 600 animals per hour for signs of disease,” the report said.
The overall light regulation of animal industries for outbreak potential puts the nation at high risk, said Linder, associate director of policy and research at Harvard Law School’s Brooks McCormick Jr. Animal Law and Policy Program.
“We have a really diverse array of different forms of animal industries, and those include really big industries, like industrial animal agriculture, as well as industries that most Americans may have never heard of, including things like captive hunting, roadside zoos, animal auctions and camel farming,” she told The Nation’s Health.
The U.S. is also one of the world’s largest producers of pigs and poultry, two important carriers of influenza viruses that scientists believe are most likely to produce a large-scale human pandemic.
Pigs in particular have long been considered a kind of “doomsday species for influenza transmission,” Linder said, noting that pigs act somewhat as mixing vessels for new forms, “which is very concerning, given the amount of pigs, and the density of pig farming operations in the U.S.”
Some of the 36 animal industries covered in the report, such as white-tailed deer farming, were unfamiliar even to public health officials interviewed for report research, she said. White-tailed deer are raised in captivity and then released for hunting on game ranches.
But white-tailed deer have been shown to be carriers of disease. In a study in Nature Communications last year, researchers detected SARS-CoV-2 in free-ranging white-tailed deer in Ohio. Up to 24% of Ohio deer had been infected with COVID-19 at some point.
Many other diseases are still spread occasionally from wildlife to humans in the U.S., such as plague from rodents, histoplasmosis from bats, rabies from raccoons and toxoplasmosis from deer.
“Of all the kind of new disease outbreaks we’ve had in the past, up to two-thirds of them have started in wildlife,” Nuzzo said.
The U.S. is also the largest importer of live wildlife in the world, with more than 220 million wild animals entering the country each year, often without health checks, making them potential flashpoints for zoonotic disease spillover.
About 14% of American households own one or more exotic pets, such as sugar gliders, chinchillas and hedgehogs. Many exotic animals enter the U.S. without ever being visually seen by inspectors. They are sold at pet stores, swap meets and exotic animal auctions and often end up in homes with kids.
The U.S. is also home to hundreds of live animal markets, sometimes called “wet markets,” where customers can pick out an animal such as a bird, goat, pig or calf to be slaughtered on the spot while they wait. New York City alone is home to at least 84 live animal markets, which are hot spots for disease risks. About 25 million birds per year move through live animal markets in the Northeast alone, Linder said.
In some cases, high-risk species such as minks, which are raised for their fur, fall outside the regulatory mandate of USDA and the U.S. Fish and Wildlife Service.
Minks are among the billions of animals farmed in the U.S., raising risks for spread of disease from animals to humans.
Photo by Vital Hil, courtesy iStockphoto
“Mink farms during COVID turned out to be a real hot spot,” said report co-author Dale Jamieson, founding director of the Center for Environmental and Animal Protection at New York University.
The U.S. is home to about 275 mink farms across 23 states, Jamieson said. But there are no federal regulations governing the treatment, health, housing conditions or slaughter of animals raised on fur farms. In fact, when COVID-19 began spreading through mink farms in Wisconsin, the state veterinarian had to go to the mink industry trade association for information about how to contact the farmers, he said.
“They didn’t actually have any registry of (mink farms) because they don’t regulate them at all,” said Jamieson, adding that the nation’s system of regulation, where much is left to states, “doesn’t really work very well when you’re talking about infectious disease.”
In the case of H5N1 bird flu, the Centers for Disease Control and Prevention has worked closely with state public health officials to be on alert for cases among humans. While about 200 dairy herds and 100 million poultry had been affected as of August, only 14 people had been infected, and all had recovered. No person-to-person spread had been reported and risk to the general public was considered low.
That may not always be the case for future disease outbreaks, however. And when they do occur, Jamieson points to another issue that could serve as a barrier to detecting and controlling them on U.S. soil: disbelief.
“It’s the idea that ‘it can’t happen here,’ and that these are things that happen in other countries far away and not risks that we generate here at home in the good old USA,” Jamieson said.
But viruses are without nationalities, Jamieson said.
“They get into biological systems, and they circulate, and they don’t ask for passports when they’re circulating,” he said.
For more information, visit https://animal.law.harvard.edu and www.wp.nyu.edu/ceap.
- Copyright The Nation’s Health, American Public Health Association