Anthrax in Livestock: Natural Occurrence or Terrorism?

Horse owners in most areas of the country would grow wide-eyed if they heard anthrax had been discovered in horses or other livestock in their region. On the other hand, individuals in the Great Plains (North Dakota to Texas) and Intermountain Basin states (Nevada and Utah) regularly vaccinate their animals against anthrax and are used to hearing about cases every few years, if not annually. They also know cases should be reported. Because of these tendencies, government health authorities say it's possible to tell if an outbreak is a usual occurrence or if it's a concern for national security, to which they could respond quickly.

Background on Anthrax
The anthrax agent is a resilient spore-forming bacterium called Bacillus anthracis, which lives in the ground. Livestock become infected when they ingest spores of  B. anthracis when they forage on vegetation growing in infected soil or eat contaminated feed. Horses seem to be more resistant to anthrax than other livestock species, such as sheep or cattle.

B. anthracis was  researched by German scientists as an agent for biological warfare purposes during World War I for use against livestock and draft animals used by the Allied armies. Sean Shadomy, DVM, MPH, is a Medical Epidemiologist in the Centers for Disease Control (CDC), National Center for Infectious Disease, Meningitis and Special Pathogens Branch, in Atlanta, Ga. He says, "Germany was the first place where anthrax was weaponized in the modern sense. It wasn't until World War II that it was researched for (use against) humans. Throughout the course of the Cold War, a number of countries looked at anthrax."

In his job, Shadomy identifies and detects human disease cases such as anthrax and traces them to their possible source. "Anthrax is very hardy--if you look for it, you will find it," he says. "There have been bones that have been found in some of the national parks in Africa that have had anthrax spores … that are well over a century old. It's the same case in building insulation materials using horsehair and things of that nature."

A change from a very rainy season to a drought can promote the natural development of an outbreak in livestock. "The spores are present from previous cases and it's there that they may wash into areas where vegetation will be growing," Shadomy explains. "Livestock will go into there, eat the vegetation, become sick, and basically the cycle of the disease continues." Carcasses of infected animals should be burned and/or buried to reduce the chance of disease spread.

So is it Normal or Suspicious?
Nina Marano, DVM, MPH, Associate Director of Veterinary Medicine and Public Health in the National Center for Infectious Diseases, says, "Historically, CDC and USDA have had their own set of responsibilities, one for human health and one for animal health. Starting with the anthrax letter events in 2001, there's been an increase in awareness on a national level of the need to work more closely together for zoonoses (diseases transmissible from animals to humans) surveillance--anthrax is one example."

But since the disease is considered endemic in livestock, there is no specific anthrax livestock surveillance or recording on a national level, says Suzan Holl, public affairs specialist for the USDA's Animal and Plant Health Inspection Service, speaking on behalf of the agency's Emergency Programs section. Therefore, the responsibility of keeping track of the cases is primarily held by state veterinary health officials.

As West Nile virus and Eastern equine encephalitis have shown, animals are good sentinels for health events that can impact human populations. "Consider the paradigm of the canary in the coal mine," says Marano. "Certain animals are quite sensitive to anthrax, and if it were ever used deliberately where there were areas of large number of grazing cattle, for example, it would be obvious.

"A clue that something is happening is a larger number of affected animals than is usually observed, or over a greater geographic spread, or (occurring) in an area of the U.S. where it isn't endemic," Marano adds. "So, if we were to see an outbreak in Florida or Alabama or Rhode Island, this would be very unusual and it would alert us."

If you think your animals have anthrax, you should contact your veterinarian along with the state veterinarian or animal health authority. Holl adds, "Then, if it looked like this was something that was maybe an intentional bioterrorist attack (the concern would be relayed to USDA's Animal and Plant Health Inspection Service, APHIS) and APHIS would deploy our emergency operation center--we'd work with other state and federal agencies to resolve the issue."

Anthrax in horses is acute, and clinical signs can include fever, chills, severe colic, anorexia, depression, weakness, bloody diarrhea, and swellings in the region of the neck, sternum, lower abdomen, and external genitalia. Equine victims usually die within 2-3 days of onset of the disease.

The CDC, USDA, and other agencies are continuing to work together to find out the best way to coordinate zoonotic disease surveillance and response, "so if something on a grand scale were to occur in the United States, we'd be able to share data to help center the outbreak investigation," Marano says.

"That relies on a lot of trust and coordination between the two agencies, and we are making great strides," she adds.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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