Two days before Christmas 2003, the United States Department of Agriculture announced some terrifying news: The nation's first case of Bovine Spongiform Encephalopathy (BSE) had been confirmed in a cow in Washington State.

Almost immediately after, farms were quarantined, beef was recalled, and new feeding and slaughter protocols for cows in the U.S. were put in place as the USDA scrambled to halt the spread of the disease.

The USDA took swift action—because they had to. Less than ten years earlier, in January 1993, BSE was infecting 1,000 new cows each week in the United Kingdom, causing other countries to ban the import of British meat and forcing farmers to slaughter over three million cattle. In all, the cost of BSE to the taxpayers in the UK topped 4 billion pounds.

BSE—more commonly referred to as “mad cow disease”—is a progressive neurological disease that affects cows. Although the exact mechanism of infection isn't completely known, experts say that cows consume infectious agents, called prions, which then damages the central nervous system. After an incubation period of several years, an infected cow will have trouble walking or standing, then will start to act nervous or aggressive (hence the name “mad cow”).

Because of a strong defense by the USDA and American government, the United States has been home to only a handful of cases of BSE since 2003. And after the height of the outbreak in 1993, the UK was able to curb the spread of disease by exterminating infected cattle and instituting new feeding practices for their livestock.

It was feeding practices, in fact, that caused the spread of the disease in the first place.

“Classical BSE spreads through the ingestion of certain materials, like brain and spine, from infected animals,” Dr. Jose H. Urdaz, an epidemiologist and Senior Staff Veterinarian at the USDA APHIS Cattle Health Center, told The Daily Beast. “The main way BSE spread [in the UK] was due to contaminated animal feed that contained the meat or bone meal of cattle infected with BSE. The feed ban is proven to keep animals from becoming infected from BSE in the first place.”

But it's not just cows who are at risk for the disease. In 1994, despite the British government insisting that the BSE posed no risk to humans, then-18-year-old Stephen Churchill of Great Britain started showing disturbing neurological symptoms and a loss of coordination. Doctors confirmed in January 1995 that Churchill had contracted variant Creutzfeldt-Jakob Disease (v-CJD) from eating meat derived from a BSE-infected cow. Churchill passed away in May of 1995, the first human victim ever of the BSE crisis.

“ The silver lining is that there haven't been many cases. ” — Ryan Maddox, CDC epidemiologist

People who fall sick with v-CJD typically start developing symptoms between three and six years after the initial infection, and typically die after 18 months of progressively worsening symptoms, such as loss of coordination and dementia.

According to Ryan Maddox, an epidemiologist with the Center for Disease Control's Division of High-Consequence Pathogens and Pathology, there are not effective treatments for BSE or v-CJD currently. “The end result is always death at this point, unfortunately,” he said.

“The silver lining is that there haven't been many cases,” said Maddox, thanks to a large “species barrier” that makes it hard for the disease to transmit between cows and humans.

Scientists don't yet understand entirely how the species barrier works, but they do know that it makes cross-contamination between species rare in the wild. In a lab setting, however, scientists have been able to successfully infect other animals such as sheep and cats with BSE by injecting infected prions directly into their brains. The species barrier is difficult to cross, and even more so for humans.

“Considering how many cattle have been infected with BSE, we've only seen 231 cases of v-CJD worldwide since this began,” Maddox said. As for the few cases of v-CJD that have occurred in the US, “we've been able to make the assumption that they were exposed elsewhere, overseas.”

So is the US at risk for an outbreak of BSE—or worse, an outbreak of v-CJD? Experts say it's not likely.

“The US is actively monitoring for this disease,” Urdaz said. “As a result, the rate of newly-reported cases of BSE has greatly decreased in the U.S. over the last decade.” Thanks to the USDA banning mammalian meat-and-bone products in animal feed, as well as maintaining strict import regulations to prevent BSE-tained meat from entering the US, only two cases of BSE have been confirmed in this country in the last seven years, says Urdaz.

And since no vaccine exists to treat BSE or v-CJD once they strike, preventative measures are still the biggest ally in the fight against another outbreak.