Question

What are mad cow disease and scrapie? Explain the cause and of these diseases and their importance to the meat industry?

Answer 1

mad cow disease :-

Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is a neurodegenerative disease of cattle. Symptoms include abnormal behavior, trouble walking, and weight loss. Later in the course of the disease the cow becomes unable to move. The time between infection and onset of symptoms is generally four to five years.Time from onset of symptoms to death is generally weeks to months. Spread to humans is believed to result in variant Creutzfeldt–Jakob disease.

BSE is thought to be due to an infection by a misfolded protein, known as a prion.Cattle are believed to have been infected by being fed meat-and-bone meal (MBM) that contained the remains of cattle who spontaneously developed the disease or scrapie-infected sheep products.The outbreak increased throughout the United Kingdom due to the practice of feeding meat-and-bone meal to young calves of dairy cows.Cases are suspected based on symptoms and confirmed by examination of the brain. Cases are classified as classic or atypical, with the latter divided into H- and L types. It is a type of transmissible spongiform encephalopathy (TSE).

Cause :-

BSE is an infectious disease believed to be due to a misfolded protein, known as a prion.Cattle are believed to have been infected from being fed meat and bone meal (MBM) that contained the remains of other cattle who spontaneously developed the disease or scrapie-infected sheep products. The outbreak increased throughout the United Kingdom due to the practice of feeding meat-and-bone meal to young calves of dairy cows.

Prions replicate by causing other normally folded proteins of the same type to take on their misfolded shape, which then go on to do the same, leading to an exponential chain reaction. Eventually, the prions aggregate into an alpha helical, beta pleated sheet, which is thought to be toxic to brain cells.

The agent is not destroyed even if the beef or material containing it is cooked or heat-treated. Transmission can occur when healthy animals come in contact with tainted tissues from others with the disease. In the brain, the agent causes native cellular prion protein to deform into the misfolded state, which then goes on to deform further prion protein in an exponential cascade. This results in protein aggregates, which then form dense plaque fibers. Brain cells begin to die off in massive numbers, eventually leading to the microscopic appearance of "holes" in the brain, degeneration of physical and mental abilities, and ultimately death.

Scrapie :-

It is a fatal, degenerative disease affecting the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), and as such it is thought to be caused by a prion.Scrapie has been known since 1732 and does not appear to be transmissible to humans.

The name scrapie is derived from one of the clinical signs of the condition, wherein affected animals will compulsively scrape off their fleeces against rocks, trees or fences. The disease apparently causes an itching sensation in the animals. Other clinical signs include excessive lip smacking, altered gaits and convulsive collapse.

Scrapie is infectious and transmissible among conspecifics, so one of the most common ways to contain it (since it is incurable) is to quarantine and kill those affected. However, scrapie tends to persist in flocks and can also arise apparently spontaneously in flocks that have not previously had cases of the disease. The mechanism of transmission between animals and other aspects of the biology of the disease are only poorly understood, and are active areas of research. Recent studies suggest prions may be spread through urine and persist in the environment for decades.

Scrapie usually affects sheep around three to five years of age.The potential for transmission at birth and from contact with placental tissues is apparent.

Cause :-

The cause of scrapie, as with other transmissible spongiform encephalopathies, is unknown and is a matter of debate;the agent is very difficult to destroy with heat, radiation and disinfectants, does not evoke any detectable immune response, and has a long incubation period of between 18 months and 5 years. The agent is thought to be much smaller than the smallest currently known virus and the prevailing theory is that it is caused by a misfolded protein called a prion. Prions multiply by causing normally folded proteins of the same type to take on their abnormal shape, which then go on to do the same, in a kind of chain reaction. These abnormal proteins are gradually accumulated in the body, especially in nerve cells, which subsequently die.