Biology 202, Spring 2005
First Web Papers
On Serendip

Transmissible spongiform encephalopathies (TSE) are infrequent, incurable brain conditions that have affected sheep and goats since around 1730 when their presence was first described by farmers in Britain and Europe. The disease in sheep was called Scrapie, and has never been found in any other species. It was the only TSE on record for almost 200 years until the discovery of human TSE, Creutzfeldt-Jakob disease (CJD), was made by scientists in Germany in 1920. In 1985, the first instance of bovine spongiform encephalopathy (BSE) was discovered to have caused the fatalities of several cows in the United Kingdom, and the "Mad Cow Disease" outbreak began (7). Until the discovery of variant CJD, the varieties of TSE which affected the different species appeared to be related through their symptoms, but unable to be transferred between species (4).

TSE is characterized by the appearance of the brain which has been contaminated by a form of TSE. Under the microscope, the brain is revealed to be full of holes and resembles a sponge. It was originally thought that a virus or bacteria caused the condition, but the virus or other organism has never been able to be isolated, nor has it been affected by any prescribed medications which usually have an impact on viruses and bacteria. It is believed that prion proteins, a normal form of protein found in animal cells, can mutate into an infectious form that starts a chain reaction, thus causing other prions to morph and clump together. These aggregates are believed to lead to the neuron loss and other damage to the brain as can be seen in affected animals. How this damage occurs exactly is still unknown. It is very difficult to spread TSE, most specifically CJD because it cannot be transmitted through air or casual contact, and in no instances has a patient who has received blood transfusions contracted CJD from a blood donor ((1).

A wide variety of physical and neurological symptoms occur when a human has been infected by CJD. They do not include a fever or any flu symptoms, and can easily be confused for other neurological disorders such as Alzheimer's or Huntington's disease. Early symptoms include the impairments of memory, judgment and thinking, behavioral changes, lack of coordination, impaired vision and visual disturbances. Victims may also suffer depression, insomnia and unusual sensations (5). Later, mental impairment becomes progressively more severe, and the patient experiences involuntary muscle jerks, blindness, weakness of extremities and hallucinations. Eventually, the person who suffers from CJD loses the ability to move and speak and enters into a coma (1).

Diagnosing CJD is a very trivial task, because there is no single test which can confirm the presence of the disease unless the patient is deceased. The presence of CJD cannot be confirmed without a brain biopsy or autopsy after the victim has passed away. When a neurosurgeon removes a portion of the patient's brain to be studied in a biopsy, there is a chance that an infected portion of the brain will not be isolated and therefore CJD will go undiagnosed. A biopsy is considered a risky procedure, and because there is no treatment for CJD even if it is diagnosed, the procedure is usually discouraged. If a doctor believes a patient to be suffering from CJD, he or she can only be sure of ruling out other treatable brain disorders such as encephalitis or chronic meningitis. This can be done by performing standard diagnostic tests such as a spinal tap, an electroencephalogram (EEG) or with magnetic resonance imaging (MRI). Frequently, CJD will go undiagnosed until the patient dies and an autopsy is done ((1).

There are four types of CJD, the most recent of which, variant CJD, was discovered in 1994. Iatrogenic CJD is the least common form today. It is transmitted accidentally during medical or surgical treatments such as neurosurgery, cornea transplants, human dura mater implants and the use of human cadaveric growth hormone (hGH) and human pituitary gonadotrophin (hGNH). Cases of iatrogenic CJD are identified chiefly from the patient's recent history of such a procedure. Genetic CJD is the variety that affects five to ten percent of CJD cases. In this form, the sufferer inherited an abnormal gene. These cases are most easily identified if a family history of the disease has been recorded. Variant CJD (vCJD) is believed to be caused by ingesting food contaminated with the BSE agent. Aside from few cases found in France, Ireland, Italy and the USA, this strain of CJD has been confined to the United Kingdom. The most common form is sporadic CJD (sCJD). SCJD accounts for 85 percent of CJD cases and has been found in every country in which it has been tested for. For sCJD to occur, it is believed that the prion mutates spontaneously to the abnormal form, resulting in the disease (6).

There are subtle differences between the forms of CJD. The age of onset is on average between 50 and 75 years old. Sufferers of variant CJD, however, are on average 27. Those diagnosed with sporadic CJD most often affects middle-aged and elderly persons. The gestation period of the two forms is also quite different. Variant CJD cases have may take a year or more to take full effect. Sporadic CJD usually has a duration period of a few months, or in some cases, only a few weeks. There are several exceptions to each of these generalizations, however, so they cannot be used to categorize the two types of CJD (6).

As was previously stated, there is no treatment or cure for CJD. Scientists all over the world are searching for an answer to the fatal disease. In San Francisco it was reported in 2004 that a 20-year-old female who was diagnosed with vCJD and treated in a pioneer drug trial recovered fully from her condition. Two likely candidates for the treatment of CJD are quinacrine and pentosan polysulphate (PPS). Both are being further investigated as remedies for CJD sufferers, but must still undergo a great deal of research before they can be prescribed (3).

References

1)Creutzfeldt-Jakob fact sheet, general information on CJD

2)Monthly Creutzfeldt-Jakob disease statistics, chart of CJD diagnoses, deaths

3)Potential treatments for Creutzfeldt-Jakob disease, an essay on possible cures for CJD

4)20/20Hindsight, an essay on BSE

5)Creutzfeldt-Jakob disease fact sheet, more general information on CJD

6)The National Creutzfeldt-Jakob disease surveillance unit, resource from the UK

7)BSE - bovine spongiform encephalopathy "mad cow disease", resource from University of Chicago at Urbana-Champaign


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