When viruses were discovered, scientists believed they had found the smallest infectious particles. However, in recent years, that perception has changed. Scientists have discovered an apparently new class of disease agents, virus like agents called prions. To better understand this term “prions”, we begin with a story of a mysterious illness that broke up in 1986 in Great Britain. At that time, farmers found out that some of their cattle were losing weight and losing control over their muscles. Majority of the animal became aggressive. Eventually, all of them died. The disease was dubbed mad cow disease, and the scientists thought that it was caused by a virus. Mad cow disease or bovine spongiform encephalopathy (BSE) is a neurological, transmissible degenerative disease that in most cases is alleged to be caused by a proteinaceous infectious particle referred to as prion. Many animal and human neurological diseases are attributed to prions (Chiras 28-29).


Mad cow disease is a fatal brain disorder. Infected animals develop sponge-like holes in their brains (spongiform) where brain cells have been destroyed in large numbers. The infectious agent appears to be a mutant misfolded protein, or prion, first identified by California neurologist Stanley B. Prusiner. The prion triggers normal proteins to misfold, hence causing the disruption of the cellular function of the brain cells. This thereafter leads to a characteristic degeneration of brain tissue, producing a spongy appearance to the brain. When the disease was first noticed, animals began to suffer neurologic symptoms including aggression, abnormal posture, and inability to walk or even stand up. The animals died within few months of developing these symptoms (Chiras 29). Similar neurological degenerative diseases also have been discovered in other animals and humans. These include the scrapie disease in sheep and goats, wasting disease in deer, and in humans, there is the Creutzfeldt-Jakob disease (CJD). All these are the few examples of diseases called transmissible spongiform encephalopathies (TSEs). This is because, like BSE, they can be transmitted to other animals that are of the same species and possibly to other animal species, including animals.

Conditions it causes

Diseases caused by prions are characterized by long latency periods between the period of infection and when the symptoms begin to appear. The accumulation of misfolded proteins triggered by the prions takes time to develop. The animals infected may take some time to show symptoms and develop severe symptoms over a period of 6 to 12 months. In addition to the above symptoms, the infected animal may also develop gait and other motor problems. Most cows begin to show the symptoms after they are thirty months old. At the beginning of the infection, cows seem more nervous than usual and have trouble walking. Later, they become aggressive, sometimes refusing to be milked and even kicking their owners. They also become increasingly hypersensitive to touch and noise and their heads may shake in an uncontrollable manner. Eventually, the cows’ hind legs become so weak that they are unable to stand. So they lie down all day, refusing to eat.

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The disease may be transmitted through feeding of meat and bone meal from other ruminants. As a result, this practice has been banned (Baker & Lawhead 271). It changed the face of food safety and diminished public trust in politicians and scientists throughout the world. It may also be spread through consumption of the nervous system tissue. However, other regulations have been established to limit the amount of exposure to these tissues. The disease can also occur in other mammals, as a result of consuming infected meat or induced in the laboratory by researchers infecting research animals in order to study the disease. Transfusion of blood contaminated with the CJD agent is also alleged to have been accountable for a few cases of disease in the United Kingdom.

Case study

A veterinary commission announced in 1986 that a new TSE appeared in British cattle. The number of cases of infected cattle increased rapidly, in the peak of 1992-93. Nearly 1,000 new cases occurred weekly; about 50% of dairy herds were affected. Nearly 180,000 cows were confirmed to have BSE by 2001, and millions were slaughtered to prevent further spread. The cases reduced in the 1990s. The government offered to compensate farmers for the loss of revenue by paying them for culling cows that were suspected to be having BSE instead of sending them to the market. The payment was about half a cow’s market price, providing a strong incentive for farmers to sell even suspect cattle to meatpackers.

The British government continued to maintain throughout the 1980s and early 1990s that British beef was safe to eat. The government nonetheless instituted measures in 1995 to protect meat for human consumption from contamination with bovine brain and spinal cord. This may have been too late, since, in March 1996, the government announced that ten young Britons had been diagnosed with a new variant of CJD and that it was linked to the possible consumption of BSE beef. The damage to public confidence was severe, despite actions by the British government to tighten regulations and assure meat safety. A total of 144 cases of CJD occurred in the United Kingdom by 2000, far below a feared epidemic, but still the majority of the 154 total cases reported worldwide (Merz & Greif  291).


Despite recent progress in several issues associated with TSE diseases, an understanding of many fundamental aspects is still lacking. Professionals must have the best information to help them recognize outbreaks of diseases and take action needed to decrease the spread of diseases. In a few countries, for example, the United States, several systems have been proposed to improve on animal identification and tracing capabilities within agricultural supply chains. Some technologies used to trace and monitor the disease have been discovered. They allow a biography to be assembled for each animal that would include origin, location and the health status of the animal as it moves through the chain of supply.

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