Chapter 9, Problem 1CS

There have been recurring cases of mad-cow disease in the United Kingdom since the mid-1990s. Mad-cow disease is caused by a prion, an infectious particle that consists only of protein. In 1986, the media began reporting that cows all over England were dying from a mysterious disease. Initially, there was little interest in determining whether humans could be affected. For 10 years, the British government maintained that this unusual disease could not be transmitted to humans. However, in March 1996, the government did an about-face and announced that bovine spongiform encephalopathy (BSE), commonly known as mad-cow disease, can be transmitted to humans, where it is known as variant Creutzfeldt-Jakob disease (VCJD). As in cows, this disease eats away at the nervous system, destroying the brain and essentially turning it into a spongelike structure filled with holes. Victims experience dementia; confusion; loss of speech, sight, and hearing; convulsions; coma; and finally death. Prion diseases are always fatal, and there is no treatment. Precautionary measures taken in Britain to prevent this disease in humans may have begun too late. Many of the victims contracted it over a decade earlier, when the BSE epidemic began, and the incubation period is long (VCJD has an incubation period of 10 to 40 years).

A recent study concluded that 1 in 2,000 people in Great Britain carry the abnormally folded protein that causes VCJD. In spite of these numbers, the death rate from VCJD remains low. It is not clear whether this means that the incubation period for the disease is much longer than previously thought, or whether they may never develop the disease.

How can a prion replicate itself without genetic material?

Summary Introduction

To determine: The way by which prions can replicate itself without genetic material.

Introduction: Viruses can have DNA or RNA as their genetic material. After entering the host body, these agents use host genetic material to synthesize their own genetic material. Prions are able to replicate itself without the aid of genetic material.

Explanation of Solution

Prions are infectious agents that do not contain any genetic material. As an infectious agent, prions contain misfolded proteins. Misfolded proteins act as an infectious agent in prions and cause several diseases in humans like mad cow disease and Creutzfeldt-Jacob disease. Prions use non-essential genes of the host to synthesize their misfolded proteins.

Therefore, prions replicate itself by using non-essential genes of the host.