NASHVILLE, Tenn. (WKRN) — A case of Bovine Spongiform Encephalopathy (BSE), commonly known as “mad cow disease,” was detected in South Carolina last weekend— marking the first time a cow in the United States has tested positive for the disease since 2018.

The U.S. Department of Agriculture (USDA) announced in a May 19 press release that a 5-year-old cow at a slaughter plant in South Carolina tested positive for an atypical case of the neurological disease. The identification tag on the animal was linked to a herd in Tennessee.

According to the Food and Drug Administration (FDA), BSE is a neurological disease that gradually damages a cow’s central nervous system. A sick cow typically has trouble walking and may act very nervous or violent, which is why BSE is often called “mad cow disease.”

Once a cow starts to show symptoms, it gets sicker and sicker until it dies or is euthanized, usually within two weeks to six months, according to the FDA.

Can people, other animals get ‘mad cow disease’?

Other animals like sheep, goats and deer can also get sick with their own versions of BSE.

According to the FDA, cats are the only known household pet to have a version of BSE, called feline spongiform encephalopathy. However, the disease has not ever been detected in a cat in the United States.

People can also get a version of BSE called variant Creutzfeldt-Jakob disease (vCJD). As of 2019, 232 people worldwide have become sick with vCJD, and according to the FDA, they all have died. Scientists believe they got the disease from eating food made from cows sick with BSE.

Only four people living in the U.S. have gotten sick with vCJD as of 2019, and according to the FDA, those people likely became infected while they were traveling overseas. People cannot get BSE from drinking milk or eating dairy products, even if the products came from a sick cow.

The variant form of CJD is different from the classic form of CJD, which according to the Centers for Disease Control (CDC), is an endemic throughout the world. Most cases of classic CJD haven’t been linked to eating beef.

First case of BSE detected in U.S.

“Mad cow disease” was first discovered in the United Kingdom, where thousands of cows were affected by an outbreak in the mid-1990s. As concern grew overseas, the U.S. banned imports of British beef.

However, according to the USDA, the first North American case of BSE was reported in Alberta, Canada in May 2003. A few months later, a dairy cow that was imported from Canada to Washington State tested positive for BSE.

In response, the USDA’s Animal & Plant Health Inspection Service (APHIS) tested nearly 1 million animals and implemented further preventative measures, such as restricting certain meat collection methods thought to present a risk, as more was learned about the disease.

Many of those safeguards are still in place today, the USDA reported.

How do cows get ‘mad cow disease’?

According to the FDA, most scientists think that BSE is caused by a protein called a prion. For reasons that are not completely understood, the normal prion protein changes into an abnormal prion protein that is harmful to the animal’s brain structure.

The body of the sick cow does not even know the prion is there, and the USDA reports that it can take up to three to six years for clinical signs of infection to appear.

There are two general types of BSE, classical and atypical, but according to the USDA, neither form is contagious. Classical BSE spreads after a cow eats feed containing meat or bone meal from a cow that was sick with “mad cow disease.”

Because of BSE, the FDA banned the use of ruminant protein in feed for ruminants like cattle, sheep, deer and giraffes in 1997. The FDA also prohibited the use of certain high-risk tissues of cattle in feed for all animals in 2009.

The other type of BSE is more of a mystery. According to the USDA, atypical BSE occurs rarely and spontaneously, and is not associated with contaminated feed or consumption of infected materials. Instead, a spontaneous change in the prion protein causes atypical BSE.

Scientists are studying whether genetics or environmental factors may contribute to atypical BSE.

Latest detection of BSE an ‘isolated case’

The latest case of atypical BSE is the nation’s 7th detection of “mad cow disease.” According to the CDC, six out of the seven cases of BSE in the U.S. have been diagnosed as atypical BSE. The only classical case of BSE in the U.S. was in 2003.

In a press release, South Carolina State Veterinarian, Michael Neault, director of Clemson University Livestock Poultry Health, said the detection of BSE in South Carolina was “an isolated case” and that safeguards “prevented entry into the public and animal food supply systems.”

The animal was tested as a part of APHIS’s routine surveillance of cattle that are deemed unsuitable for slaughter, according to the USDA.

APHIS and veterinary officials in South Carolina and Tennessee are still gathering more information in an ongoing investigation, but the latest detection is not expected to have any trade or health impacts.