This form of bovine spongiform encephalopathy can't be transmitted between cattle, says the USDA, or from cattle to humans. 

By Amanda MacMillan
August 30, 2018

The U.S. Department of Agriculture (USDA) announced yesterday that a case of bovine spongiform encephalopathy (BSE), also known as mad cow disease, was recently identified in a cow being raised for beef in Florida. But there’s no reason to freak out, the USDA says: The animal “never entered slaughter channels, and at no time presented a risk to the food supply, or to human health,” according to a statement from the agency.

Let’s be honest: Mad cow disease sounds pretty terrifying, especially because it’s been linked to a fatal neurological condition in humans called Creutzfeldt-Jakob disease (CJD). Thankfully, the type discovered in this Florida cow is not the type that can be transmitted to people, says Brian Appleby, MD, director of the National Prion Disease Pathology Surveillance Center at Case Western Reserve University. Since mad cow is back in the headlines, however, here’s what he wants everyone to know about BSE, CJD, and food safety in the wake of this news.

What is bovine spongiform encephalopathy?

BSE is a neurologic disease that affects the brain structure of infected cattle, according to the USDA. It’s caused by proteins called prions, which cause animals to lose motor skills, develop coordination problems, lose weight, and experience decreased milk production and behavior changes.

There is no vaccine to prevent BSE and no treatment once an animal is infected. Once symptoms develop, its condition deteriorates until it is euthanized or dies from the disease.

There are two types of BSE: classical and atypical. Classical BSE can be spread when other cows ingest certain materials—like brain or spinal tissue—from infected animals. It’s also been associated with CJD in humans who have eaten contaminated meat.

Atypical BSE, on the other hand, occurs when prion proteins in cattle change spontaneously from normal to abnormal. Scientists aren’t sure exactly why these changes occur, but they’re studying whether genetic or environmental factors may play a role. There’s no evidence that atypical BSE can spread from cow to cow, or from cow to human.

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What is Creutzfeldt-Jakob disease?

Humans can’t get mad cow disease, since it can only occur, by definition, in cattle. They can, however, develop a related infection—called variant Creutzfeldt-Jakob disease (vCJD)—by eating contaminated meat. The most well-known outbreak of vCJD occurred in the United Kingdom in the 1980s and 1990s.

Only four cases of vCJD have ever been reported in the United States, and all are suspected to have been acquired outside of the country. “The time that someone is exposed to these agents to the time they become sick can be a decade or more,” says Dr. Appleby. “Two cases were former U.K. residents and the other two we think were traveling outside of the country when they ate infected beef.”

There is another form of Creutzfeldt-Jakob disease, however, known as sporadic CJD (sCJD), that occurs in humans without any known reason. This strain of the disease affects about one per every one million people, according to the Creutzfeldt-Jakob Disease Foundation, which translates to about 320 new cases a year in the United States. There have also been a few reported cases of CJD acquired through contamination during medical procedures.

Sporadic CJD is a rapidly progressive disease, says Dr. Appleby: Once people develop symptoms—including dementia and motor difficulties—they usually die within four to six months. The BSE-related variant strain, however, is slightly different.

“It affects younger people—in the U.K., it was affecting teens and people in their 20s and 30s—and they tend to present more with psychiatric symptoms prior to the usual symptoms,” says Dr. Appleby. Those psychiatric symptoms can include depression, apathy, or even hallucinations.

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What happened in Florida?

The case identified in Florida was one of atypical BSE, which means it arose spontaneously. It occurred in a 6-year-old beef cow being raised in Florida, but it was tested at the Colorado State University Veterinary Diagnostics Laboratory “as part of routine surveillance of cattle that are deemed unsuitable for slaughter,” according to the USDA’s statement.

The USDA and Florida veterinary officials are gathering more information on the case, says the agency’s statement. But it’s not unheard of for a case of BSE to be discovered in beef cattle; this is actually the sixth case detected in the United States. The first, in 2003, was a case of classical BSE in a cow imported from Canada. The rest have been atypical, like this one.

Dr. Appleby says the fact that this story is in the news is no reason to worry; in fact, he finds it reassuring. “It means that we’re looking,” he says. “I’d much rather say that we find a case of atypical BSE once every few years than say that we have no idea.”

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How is our food supply protected?

After the U.K. outbreak of mad cow disease and related vCJD in humans, regulations were put into place to protect cattle, and consumers, from infection. Since 1997, mammalian protein has been prohibited in feed for cattle in the United States. High-risk tissue materials have also been prohibited in all animal feed since 2009.

Because BSE is not contagious in any other way—not through cows sneezing or sharing close quarters, for example—these measures have insured that the disease doesn’t spread through the U.S. food supply, says Dr. Appleby. The World Organization for Animal Health recognizes the United States as having “negligible risk” for BSE—a ranking that won’t be affected by this atypical case, says the USDA.

Ongoing surveillance and testing of cattle is another important safeguard that protects the nation’s food supply, says the USDA. Meanwhile, Dr. Appleby’s lab—which is funded by the Centers for Disease Control and Prevention (CDC)—tests human cases of CJD to make sure they aren't coming from infected beef. “It's an important tactic for tracking mad cow disease," he says. "That’s how we found those four previous cases,” he says.

Funding for Dr. Appleby’s lab was initially cut from President Trump’s proposed 2018 fiscal budget, but was inserted back in before the financials were finalized. “It’s for reasons like these we like to remind people that surveillance is key,” he says, “and that we have to keep it up.”

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