What Causes Mad Cow Disease?

An Explanation of What It Is, How It's Transmitted, and Potential Human Concerns

Portrait of a cow
Tony C French/Getty Images

BSE (known more commonly Mad Cow Disease) was discovered in the United Kingdom in 1986. The first case in the United States was reported on December 23, 2003, in Washington state.

It's very common for people to wonder what causes the disease and how it's transmitted. You might also have concerns about whether people can get it from eating meat. We're going to answer your Mad Cow Disease questions.

What Is Mad Cow Disease?

BSE (bovine spongiform encephalopathy) is an interesting disease from a medical standpoint because of the causative agent, prions (pronounced pree-ons).

A prion is an infectious protein that is similar to a virus, but it's not a virus.

Unlike viruses, prions aren't alive, so they can't be killed with the usual disinfectants. The body does not mount a typical viral immune attack against prions, either. Prion proteins can be denatured, but only at extremely high temperatures or with very strong chemicals. Either way, these treatments are not consistent with animal life, so they are not an option.

Diseases caused by prions are referred to as TSEs, short for Transmissible Spongiform Encephalopathies. In general, TSEs are fatal and progressively affect the central nervous system. The brain of an animal infected by prions will develop tiny holes that make it appear much like a sponge.

How Do Prions Infect Cows?

The most common mode of infection is from feeding cows contaminated feed, particularly feed that contains animal proteins (from sheep or cows).

Researchers are still studying modes of transmission and exploring if genetics plays a role in an individual animals susceptibility to (or protection from) acquiring this disease.

How Is BSE Diagnosed?

BSE is suspected in animals that exhibit neurological problems. Symptoms may include staggering, general loss of motor control, dementia or behavioral changes, increased startle reflex, weakness, weight loss, and decreased milk production.

BSE is diagnosed by examining the brain tissue of the deceased animal and finding the characteristic "moth eaten" appearance of the brain tissue.

How Long Does It Take for BSE to Develop in Cattle?

BSE has a long incubation period, meaning that it can take months or years to show clinical signs. According to the Merck Veterinary Manual, once a cow starts showing signs, it is often terminal within 3 months.

Can Humans Catch Mad Cow Disease?

Technically, people cannot catch BSE because it is a bovine disease. However, there is a human version called Creutzfeldt-Jacob Disease (CJD), but it’s very rare. In particular, it is "variant CJD" and while it's not entirely understood whether or not it's linked to eating infected meat, there have only been a handful of incidents in the U.S.   

For in-depth human health and current political issues concerning BSE, visit with your local health care provider.

Source:

Centers for Disease Control and Prevention. Bovine Spongiform Encephalopathy (BSE), or Mad Cow Disease. 2017.

National Institute of Neurological Disorders and Stroke. Transmissible Spongiform Encephalopathies Information Page. 2017.

Seuberlich T. Overview of Bovine Spongiform Encephalopathy. Merck Veterinary Manual. 2016.