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Other spongiform encephalopathies

Scrapie:

This was first recognised in 1730 and is a disease of sheep, so named after the habit of affected animals to repeatedly scrape themselves against objects. Eventually, the animals become unsteady on their feet, uninterested in their surroundings, and stop feeding. Examination of the brains of affected sheep after death shows many of the same changes that are found in people with Creutzfeldt-Jakob disease.

Kuru:

This is a disease of the Fore people in the mountains of New Guinea, and results in an illness similar to Creutzfeldt-Jakob disease. The tribe practised cannibalism during funerals. It is believed that the disease was passed to other tribe members during this ritual. Now that cannablism has died out in this tribe, so has Kuru.

BSE:

Bovine spongiform encephalopathy is a disease of cows which was first described in 1987. The animals affected become unsteady on their feet, lose weight and often assume a fearful disposition. The term "mad cow disease" is not always appropriate as many animals do not become overtly aggressive, and towards the end, may lose interest in their surroundings, and become too unsteady to even stand.

OTHERS:

Spongiform encephalopathies have been now recognised in a number of other species; The disease has been transmitted to one pig which had an extract of BSE-affected cow brain injected into its abdomen, bloodstream, and brain, all at the same time, but there have been no natural cases in the pig.



Tests performed and their meaning:

CT scan:

Also known as a "CAT" scan, which stands for computerized axial tomography. It is a form of specialised x-ray where it is possible to look at the brain, although it is not possible to see "spongy" change which is microscopic. The usual reason for obtaining a scan is to rule out any other cause of the illness.

MRI scan:

MRI stands for magnetic resonance imaging and is a way of looking at the brain without x-rays. Again it is not possible to see the "spongy" change.

EEG:

This is short for electroencephalogram. By putting a number of small electrodes on the scalp, it is possible to record the electrical activity of the brain itself. In many diseases of the brain this becomes altered and can be interpreted by a doctor. In Creutzfeldt-Jakob disease, there can be a characteristic disturbance of the brainwave pattern which can help to make the diagnosis more certain.

Lumbar puncture:

Under local anaesthesia, a thin hollow needle is inserted in the patient's back and a small amount of fluid which surrounds the spinal cord is removed for examination. This test is often done to ensure there is no infection of the brain which could be treated.

The only way in which the diagnosis can be made with certainty is to examine the brain after death, and this can take 2-3 months before all the results of the microscope tests are available. During life, the priority is to ensure that the person does not have a condition which could be easily treated such as liver or kidney failure, vitamin deficiency, or brain tumour, and so most of the tests are planned with this in mind. It is particularly important to remember that there is no blood test or x-ray which can diagnose Creutzfeldt-Jakob disease with absolute certainty.

Research into spongiform encephalopathies

There are presently a large number of doctors and scientists carrying out various research projects on the spongiform encephalopathies, including diseases of both man and animals. The first major finding was in 1967, when brain extract from a person from the Fore tribe who had died of Kuru was injected into the brain of a monkey. Within a few years, the monkey developed a disease similar to Kuru, and when its brain was examined microscopically, it showed similar spongy changes. It was therefore shown that the disease could be transmitted from one species to another, at least artificially. It was already well known that sheep affected with scrapie could pass the condition to other members of the flock, and experimental transmission of scrapie had been documented many years previously. In 1968 Creutzfeldt-Jakob disease was transmitted to laboratory animals by inoculating extracts of brain from a person who had died of the condition. This research led to the conclusion that all these diseases were related in that they caused the same type of illness, looked the same under the microscope, and were caused by agents which had infectious properties, but were different from normal bacteria and viruses. The next step forward was the identification of a protein normally produced by the brain cells which had become altered. The function of this protein is not known, even in its normal form. When produced by the brain cells in cases of Creutzfeldt-Jakob disease, it was produced in larger than normal amounts. Under a very powerful microscope, the scientists were able to see the protein as it clumped together to form minature stick-like structures which were named "scrapie-associated-fibrils" or "prion rods". The exact significance of these fibrils is unknown, although when they are found in brain tissue specimens, they can help to diagnose the condition. Some scientists believe that the protein forms part of the infectious agent that causes the condition, where its function is rather like a "coat" around the agent itself. Others believe that it is simply a by-product of the illness. It is still not possible to see the actual particle which causes these diseases and we are only able to see the effects on the body. Since the agent which causes Creutzfeldt-Jakob disease is obviously very small, some scientists believed that it could be a virus. However, if this was the case it should have been able to detect some reaction of the body to it, in the same way that the body forms antibodies. It should also have been possible to see the virus using powerful electron microscopes. Neither of these occurred. Therefore it was assumed that this was some very minute virus (a "virino"), or perhaps a virus that had become altered in some way. As yet, this theory remains unproven.