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. Upon autopsy, this degenerative brain disorder is characterized by microscopic holes in the brain tissue that give the brain a "spongy" appearance.
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.
Why Do We Need to Worry about MCD?
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 Bovine SE can’t be transmitted between living cows not 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 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.
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 prions aren't the cause of TSEs. 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 the Virtual Microbiology Classroom. To learn more about acellular agents of infectious disease see additional LesTout articles, including:
- Human Parasite Naegleria fowleri
- Shigellosis – Food Poisoning from Shigella Bacteria
- What Is a Virus?
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. (2005) Microbiology.
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.
