The Relationship Between Bovine Spongiform Encephalopathy, Creutzfeldt-Jakob Disease and Prions
Bovine Spongiform Encephalopathy (BSE) or Mad Cow Disease is a chronic, progressive degenerative, neurological disease of cattle that has been linked to a form of Creutzfeldt-Jakob disease (CJD), a fatal degenerative brain disease in humans. BSE belongs to a family of diseases known as the transmissible spongiform encephalopathies (TSEs). TSE animal diseases found in the United States include scrapie in sheep and goats, chronic wasting disease in deer and elk, transmissible spongiform encephalopathy in mink, feline spongiform encephalopathy in cats, and in humans: kuru, both classic and variant Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker syndrome, and fatal familial insomnia.
In November 1986, the first reported cases of BSE occurred in Britain. During the period 1989 to early 2001, more than 1 million cases of BSE were identified. Other countries around the world at this same time also reported similar cases of BSE. These countries included Denmark, France, Germany, Italy, Ireland, Belgium, The Netherlands, Spain, Portugal, Spain and Switzerland, Canada, the Falkland Islands and Oman.
Symptoms of BSE in cattle
Symptoms of BSE in cattle include loss of muscular coordination, inability to stand up, listlessness, decreased milk production, and loss of body weight. Affected animals also show signs of behavioral change, for example, nervousness, aggression and a lack of interest in surroundings. The period from infection to onset of the disease, known as the incubation period, is from two to eight or more years. Once symptoms develop, animals progressively deteriorate and die within several months.
Where is the BSE agent found in cattle?
Autopsies of diseased cattle brains revealed anatomical and morphological changes consistent with that of spongy like texture, similar to that of Swiss cheese. Current scientific research confirms that BSE infectivity occurs in the brain, trigeminal ganglia, tonsils, spinal cord, dorsal root ganglion, and distal ileum of the small intestine of cattle experimentally infected with the BSE agent. Research also confirms that BSE infectivity is in the brain, spinal cord, and retina of the eyes of cattle infected with the agent under field conditions. Although bone marrow has demonstrated infectivity in experimentally infected cattle, these findings are not conclusive.
What causes BSE?
The general consensus among scientists and researchers is that the causative agent believed to cause BSE is an abnormal form protein called prion. This abnormal protein is found in brain, spinal cord, tonsils and small intestines of cattle. The exact origin of the causative agent, prion, is somewhat controversial. Some researchers believe that prions come from cattle bones, hide and other inedible tissue after slaughter. While others believe that the origin of prions came from sheep. Yet other sources recently indicated that prions may be of human origin.
Irregardless of the origin of prions, cattle and other ruminants can become infected only after consuming contaminated feed containing recycled animal tissues and prions. Prions are extremely resistant to heat, ionizing radiation, normal sterilization process and common disinfectants that normally inactivate viruses and bacteria. This may explain why rendered recycled animal tissue may still be infective after processing.
Can BSE be transmitted from one cow to another cow or ruminant?
BSE is not a contagious disease. There is no evidence that the disease is transmitted through direct contact or animal-to-animal spread. The primary means by which animals become infected is through consumption of feed contaminated with the infectious BSE agent or prions.
Is BSE transferable to humans?
Since the initial report of the disease, there has been much speculation that it might be transferable to humans through beef products. The appearance of CJD in several dairy farmers in Britain in the early 1990s heightened the alarm. In March 1996 the British Ministry of Health announced the discovery of ten cases of a unique type of CJD, called new variant CJD or vCJD.
This type of CJD differs from the classical form in that victims are all under the age of 42 (the classical form of the disease typically develops around age 65), the victims display unusual psychiatric problems, distinct brain tissue changes are identified during an autopsy, and the victims have no family history of the disease. The British government found that the victims may have contracted the disease through contact with BSE-infected cattle before the eradication of suspected animals had taken effect.
What causes vCJD?
Since 1996, a number of studies have confirmed that BSE in cattle can be transmitted to humans and cause vCJD. Studies have linked the time and location of the BSE epidemic in cattle to more than 94 human cases of vCJD found in Britain, France, and Ireland.
In studies in which scientists injected monkeys and mice with brain tissue from BSE-infected cows or brain tissue from vCJD-infected humans, the animals develop the same type of brain degeneration. This degeneration is distinguishable from the degeneration following injection with brain tissue from cases of the classical form of CJD. The British government in 1996 announced that BSE may be transmitted to humans.
Creutzfeldt-Jakob Disease (CJD) form of human spongiform encephalopathy caused by an infection of the brain, probably by a particle called a prion. The disease causes fatal degradation of brain tissue and produces a dementia that affects men and women, often between the ages of 50 and 65. Some 90 percent of cases progress to death within one year, sometimes within one month.
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