What Causes Mad Cow Disease?

An explanation of what it is, how it's transmitted, and potential human concerns

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Question: What causes Mad Cow disease, and how is it transmitted?

BSE (known more commonly Mad Cow Disease) was discovered in the mid 1980s in the United Kingdom. The first US case was reported on 12/23/03 in Washington state. The purpose of this FAQ is to educate about the disease causative agent, how the disease is transmitted, and potential human concerns. 

Answer: BSE 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 not a typical 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're not an option. Diseases caused by prions are referred to as TSEs — Transmissible Spongiform Encephalopathies.

How do prions infect cows?

The most common mode of infection is via feeding cows contaminated feed — feed that contains animal proteins (from sheep or cows). Researchers are still studying modes of transmission and exploring if heredity/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, such as 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 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. Once a cow starts showing signs, it is often terminal within 3 months (according to Merck Manual, 8th edition).

Can humans catch Mad Cow disease?

Technically, no, since this is a bovine disease. However, there is a human version called Creutzfeldt-Jacob Disease, but it’s very rare. For in-depth human health and current political issues concerning BSE, please visit with your local health care provider or refer to local/national/Internet news sources.