Causative agent
CJD is a degenerative, rare, invariably lethal brain disorder. It causes cognitive impairment and with the progression of the illness, the deterioration of the mental health occurs leading to blindness, incontinence, involuntary movement, and extreme weakness, coma and death.
CJD is caused by the aggregation of the toxic proteins called the prions. Prions are proteinaceous infectious particles that are caused due to the abnormal folding of the proteins. Prion protein can occur in normal form and are present in the body of the animals and they normally play a protective part in the cells and help the cells to respond to the oxygen deficiency1. The normal prion protein in a body may suddenly change in to infectious form which may cause neurodegenerative disease. But the abnormally folded protein infects the brains and form holes in the brain, which looks like sponges under the microscope.
The sporadic CJD, the hereditary CJD and acquired CJD.
Figure 1.
Diagram Of Normal Brain Vs Cjd Brain (Sikorska B, Knight R, Ironside JW, Liberski PP. Creutzfeldt-Jakob disease. Neurodegenerative Diseases. 2012)
CJD was identified first in 1920 by German neuroscientists namely Hans Gerhard Creutzfeldt and Alphons Maria Jakob. Creutzfeldt and Jakob identified five similar cases of fatal dementia. Later on through microscopic examination followed by many tests the confirmation about the presence of prions are accepted. They discovered that the brain undergoes spongiform changes that lead to neurodegenerative disorders.
Previously the researchers used to believe that CJD is caused by some slow virus, although they were never been able to isolate any form of bacteria or virus from the brain tissue. Furthermore it was identified that causative agent behind the CJD does not contain any genetic information like the DNA or RNA. By 1960, the scientist had already discovered the spongiform structure of the diseased brain. They found that the disease is almost similar to the disease that has occurred in the people dying from ‘kuru’. Kuru was known to be a result of cannibalism in the tribe of Papua New Guinea. CJD was also found to be transmissible. Later on scientists found that a small amount of abnormal prion could generate more abnormal prions by the abnormal folding. By 1980 it was found that CJD can be transmitted to the patients through the grafts of the dura matter as well as through the hormones prepared from the deceased people infected with CJD. Later on it was also discovered that the cattle are also susceptible to the infected proteins, causing ‘mad cow disease’ in the cattle. Later on by the year 2013, the effect of the variant CJD seemed to be over or very few cases have been found worldwide.
It has been reported that the disease is rare and it is caused in about one person in every one million population in the world3. It occurs in the late 50’s or about 60 and it has been reported that about 90 percent of the infected individual dies within a year. CJD was first discovered in United Kingdom. In the Libyan Jews the rates are higher. Since then up to 2011, 175 cases have been reported all over the world. 25 in France and Spain, 4 in Ireland, 3 in Netherland and United States , few in Italy , Portugal, Japan , Saudi Arabia, Taiwan has been found.
Figure 2. Notifications, Referrals And Cjd Cases By Year (Andréoletti O, Litaise C, Simmons H, Corbière F, Lugan S, Costes P, Schelcher F, Vilette D, Grassi J, Lacroux C. Highly efficient prion transmission by blood transfusion. PLoS pathogens. 2012)
Studies up to now have confirmed that humans are the only known reservoir of the disease.
CJD is not transmitted through direct contact or through air. Exposure of brain tissue and the spinal cord fluid from the infected individual may cause the transmission of this disease. In some cases it has been found that CJD can spread through the grafts of the dura matter2. Cornea transplants, implantation of the improperly sterilized electrodes in the brain, administration of the contaminated pituitary growth hormones taken from the deceased people having CJD infection.
CJD is a rare, lethal neurodegenerative disorder. It is so rare that it occurs one in a million. It is similar to the other neurodegenerative illness like the “Kuru” and “Scrapie”. Kuru is a human brain disorder and Scrapie is found in cattle5. This disease is also termed as spongiform encephalopathy, because the brain resembles a sponge as the neuronal cells are destroyed and the brain tissue are filled with holes.
According to the hypothesis by Griffith, Prion consists of a conformational isomer of the normal prion protein encoded by the host, which can be converted in to other lethal forms auto catalytically. This disease occurs without the involvement of any nucleic acid genome. The normal host prion protein PrPc is converted to abnormal PrPsc. It involves only conformational change as the amino acid sequencing shows no difference between the abnormal and the normal form. PrPsc is deposited as plaques in the brain and the lymphoid tissues. Prion disease can also be formed out of genetic mutation in certain genes.
It causes cognitive impairment and with the progression of the illness, the deterioration of the mental health occurs leading to blindness, incontinence, involuntary movement, and extreme weakness7. Individuals may experience muscular jerks and prolonged spasms rigidity in the limbs. Impairment of speech occurs and they lose the capacity of moving and finally enter the coma, which may lead to multiple organ failure and death.
The incubation period for the prion disease may last from 15 years to 30 years. Once the symptoms are recognizable, the progression of the disease is rapid, causing death within 2 years.
Diagnosis
There is practically no treatment of this disorder, but there are certain procedures to assess the neurological function of the brain. It can be done by Spinal tap and electroencephalography. Diagnosis can also be done by brain biopsy, where a small section of tissue is taken from the brain and are examined in the laboratory8. Test can also be done for the detection of Prion proteins in the blood and the cerebrospinal fluid. Early diagnosis of the Prion protein screening is necessary for the transfusion of blood.
Treatment
There is practically no treatment of this disease. Progression of this disease can also not be delayed by any medicine or surgery. Researchers have tested many drugs like amantidine, acyclovir, antibiotics and several antiviral agents, but none of this has shown any such satisfactory results. Treatment mainly aims on reducing the pain and the discomfort of the patient.
In the Lancet medical journal it was reported that CJD can be transmitted by blood transfusion. It was reported that the UK government banned any individual who have received any blood transfusion since 1980 January. In fact manufacturing of proteins like albumin were being banned. In 2002, the United States food and drug administration introduced a policy where blood donations were not accepted from the individuals who have spent more than three months in the UK. Many policies were taken by the health care organization of all the countries. It was reported that at that time In U.S, the FDA had imposed a ban on the donation of sperm due to the risk of the CJD.
Different measures can be taken while purifying artificial hormones, while installation of the electrodes in the brain, cornea transplants.
References
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