Prion Cause of Mad Cow Disease?

Suspected Pathogens in Bovine Spongiform Encephalopathy BSE

Nov 14, 2007 Tami Port

What causes transmissible SEs? Is the pathogen prion, virus, or something altogether different? See what the experts think about this rare, deadly neurological disease.

What Is Mad Cow Disease?

Mad Cow Disease, also known as bovine spongiform encephalopathy (bo-vine spun-jih-form en-seh-fah-la-puh-thee), is a disease that affects a cow's nervous system, causing the animal to behave abnormally. The unusual, or “crazy,” behavior of infected cows led to the label Mad Cow Disease.

Researchers believe that cows contract this infection when they consume food that contains the remains of dead cows that had the infection. One infected, BSE causes the cow’s brain to waste away. Upon autopsy, this degenerative brain disorder is characterized by microscopic holes in the brain tissue that give the brain a "spongy" appearance.

Why Do Humans Need to Worry about Mad Cows?

As a type of Transmissible Spongiform Encephalopathy, Bovine SE is of concern to humans because it can be transmitted to people who eat meat from a diseased cow. Consuming BSE-infected beef results in increased risk for getting a rare human variety of the spongiform encephalopathy called Creutzfeldt-Jakob (kroits-felt yock-ub) disease, or CJD.

BSE and CJD are not contagious, meaning that transmission of Bovine SE does not occur between living cows nor can CJD be transmitted from person to person. BSE also cannot be transmitted through milk or milk products, only beef that has been exposed to the neurological tissue of infected cows.

These Transmissible Spongiform Encephalopathies typically progress rapidly and end in death over the course of a few months or, at most, a few years.

What Causes Mad Cow Disease?

We are familiar with diseases caused by bacteria (living organisms that can cause infection) or viruses (nonliving, acellular particles that cause infection), but Transmissible Spongiform Encephalopathies may be caused by something even smaller and simpler--a good protein gone bad.

Prions

Stanley Prusiner, a physician at the University of California at San Francisco, won the 1997 Nobel Prize for Medicine for his assertion that Transmissible Spongiform Encephalopathies are caused by misshaped proteins found in mammalian brains. He called these proteinaceous infectious agents prions (say PREE-on).

Prions are thought to be an abnormal form of a normally harmless protein found in mammals. Some believe that these abnormal proteins can enter the brain through infection, usually after being ingested, or can arise from a mutation in the gene that encodes the protein. Prions are unlike all other type of infectious agent in that they lack nucleic acid (DNA or RNA).

Once present in the brain, prions are thought to cause normal proteins to refold into abnormal shapes. As these abnormal proteins multiply, they destroy neurons and eventually cause brain tissue to become riddled with holes.

Arguments against a Prion Cause of TSE

Some researchers disagree with Prusiner, primarily because prions don't behave according to Koch's postulates, the rules for determining whether a specific microbe causes a specific disease.

The problem is that prions are not always found when TSEs are diagnosed. In addition, researchers aren’t sure what constitutes a “good” and a “bad” protein shape are and how proteins transform from one into the other.

The Manuelidis Perspective

Yale University neuropathologist Laura Manuelidis argues that, although prions are involved with TSEs, they aren't the cause. She believes these encephalopathies to be the result of an undiscovered virus.

Very recently Manuelidis and some of her colleagues published and article announcing that they've found the virus: a 25-nanometer diameter particle that looks viral, and has been found in tissue samples with two different types of TSEs.

Manuelidis’ next step is to attempt to isolate these alleged viral particles, and then inject them into healthy cells, and seeing if TSE develops.

Additional Information

For more information on TSE or microbial pathogens in general see the website of the National Institute of Neurological Disorders or Science Prof Online. To learn more about acellular agents of infectious disease see additional Suite101 articles, including: Cells, Viruses, Viroids & Prions, Early Germ Theory of Disease, and Late Germ Theory of Disease.

This article is for informational purposes only and not meant to be used for self-diagnosis of any suspected medical condition. If you believe that you are ill, please see a doctor, not a computer.

Sources

Bauman, R. (2004) Microbiology. Pearson Benjamin Cummings.

Manuelidis L. (2007) "A 25 nm virion is the likely cause of transmissible spongiform encephalopathies." J Cell Biochem. 100, 4.

Park Talaro, K. (2008) Foundations in Microbiology. McGraw Hill.

The copyright of the article Prion Cause of Mad Cow Disease? in Microbiology is owned by Tami Port. Permission to republish Prion Cause of Mad Cow Disease? in print or online must be granted by the author in writing.

What Causes Mad Cow Disease?	Histology Brain Tissue With BSE	Proposed Mechanism of Prion Propagation
Cow with Mad Cow Disease	Global Map of Mad Cow Cases as of 2006