Clinical signs among others include personality changes, psychiatric problems, lack of coordination, steady gait, involuntary jerking movements, unusual sensations, insomnia, confusion and severe mental impairment in the later stages.
Those known to infect other vertebrate animals include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cows, chronic wasting disease in American elk and deer, transmissible mink encephalopathy in mink and feline spongiform encephalopathy in cats (Jeffrey, Goodbrand & Goodsir 1995).
One of the primary risk factors identified in relation to prion diseases is age. Studies suggest that a general mechanism might produce the remarkable reduction in disease risk as age increases. For example, in a study of scrapie outbreaks, it is observed that incidence of clinical cases peaked in sheep with age ranging from 2 to 3 years. The same age range has been noted in cattle with mad cow and deer with chronic wasting disease (Heisey 2004).
In terms of its prevalence in the human population, it is estimated that 1 in 10,000 people are infected with CJD at the time of death. The actual prevalence of prion diseases are very difficult to ascertain due to overlapping symptoms that may lead to misdiagnosis. (Heaphy 2003)
Research pertaining to prion diseases is deemed limited by the fact that studying them is substantially hampered by the unconventional properties of the presumed etiologic agent. Moreover, the long incubation period ranging from 34 to 41 years ("Mad cow could be dormant in people" 2006) of the diseases make them more difficult to detect. Moreover, the standard laboratory methods utilized for studying viruses and bacteria may not be applicable in this case (Belay & Telling).
However, following reports of the outbreak of BSE, commonly termed as "mad cow" disease, in many European countries coupled with the estimated economic and medical implications of the said epidemic, the scope and nature of research on prion diseases has developed rapidly. This paper focuses on the current advancements in the study of prion diseases specifically in terms of modes of transmission, diagnosis methods, possible treatment and prevention.
Modes of Transmission
The manner of transmission of prion diseases is of primary concern in view of the protein nature of the prions. Note that unlike other types of infectious diseases which are spread by microbes, prion diseases are caused by misshaped protein, dubbed as prion protein, which transmits the disease between individuals causing brain deterioration (Belkin 2003).
Based on recent studies, prion diseases have been considered unique as these can be inherited, sporadically occur or spread through infection. Majority of the prion disease cases are said to occur spontaneously, hence, animals with no prion protein mutation were observed infected. (Collinge 2001)
On the other hand, inherited prion disease occurs in animals carrying a rare mutant prion allele. The disease is transmitted when healthy animal consume tainted tissues of other infected animals. The "mad cow" epidemic has been attributed to this mode of transmission as practice of feeding the cattle with processed remains of other cattle, which may have been infected already, became common. (Weissmann 2004)
In humans, as in the cases of CJD, the