PRIONS-SMALLEST INFECTIOUS AGENT

Introduction:

• Prion is smallest proteinaceous infectious agent And does not contain DNA or RNA. A prion is composed of protein in a mis­fold­ed form. When a prion enters a healthy or­gan­is­m, it induces ex­ist­ing, properly folded proteins to convert into the dis­ease-as­so­ci­at­ed, prion form; the prion acts as a template to guide the mis­fold­ing of more proteins into prion form.

 

• Prion is the infectious agent which is most resistant to sterilization. The smaller the agent, the more dif­fi­cult it is to destroy it. Prions are quite re­sis­tant to pro­teas­es, heat, ra­di­a­tion, and formalin treat­ments. 134°C (274°F) for 18 minutes in a pres­sur­ized steam au­to­clave may not be enough to de­ac­ti­vate the agent of disease. Prions may last for decades in the en­vi­ron­men­t.

 

 

• Prion causes diseases that are the most difficult to cure. All known prion diseases affect the struc­ture of the brain or other neural tissue and all are cur­rent­ly un­treat­able and uni­ver­sal­ly fatal.

 

 

Some diseases caused by prions: Prions cause neurodegenerative disease by aggregating extracellularly within the central nervous system to form plaques known as amyloid, which disrupt the normal tissue structure. The human forms of prion disease are most often the names:

 

 

1. CREUTZFELDT-JAKOB DISEASE(CJD):- CJD captured public attention in the 1990s when some people in the United Kingdom developed a form of the disease — variant CJD (vCJD) — after eating meat from diseased cattle. However, “classic” Creutzfeldt-Jakob disease hasn’t been linked to contaminated beef.  CJD is the most common prion disease in humans with an approximate occurrence of one in a million. Creutzfeldt-Jakob disease is a degenerative brain disorder that leads to dementia and, ultimately, death.

 

2. KURU: – Kuru is a neurological disease that mainly affected the Fore people of Papua New Guinea. They called the diseasekuru, which means “shivering” or “trembling”. Tribe’s people contracted the disease by eating brains of dead family members as part of funeral rites. Its highest prevalence occurred during the 1950s and 1960s .The disease primarily hit adult women and children younger than 8 years old. In some villages, there were almost no young women left. The symptoms of the disease include muscle twitching and loss of coordination.

 

3. FATAL FAMILIAL INSOMNIA (FFI):- Fatal Familial Insomnia (FFI) is a rare sleep disorder and inherited prion disease that mainly affects the thalamus. It begins as a sudden and unexplained sleeplessness sometime during middle age. The first symptoms of FFI usually begin in mid-life and may include progressive insomnia, weight loss, lack of appetite, too high or too low body temperature, and rapidly progressive dementia.

 

 

4. GERSTMANN-STRAUSSLER-SCHEINKER SYNDROME(GSS):- Gerstmann Straussler Scheinker disease is a rare, fatal condition and is classed as a prion disease or a transmissible spongiform encephalopathy. The syndrome was first described in 1936 by the Austrian neurologists Josef Gerstmann (), Ernst Sträussler (), and I. Scheinker. Degeneration of the nervous system usually starts in the fourth or fifth decade of life with slowly developing dysarthria (difficulty speaking) and cerebellar ataxia (wobbliness) and later the progressive dementia become evident. Death usually occurs within 10 years of the onset of symptoms. Usually, the first symptoms are clumsiness and unsteadiness when walking.

 

 

5. VARIABLY PROTEASE-SENSITIVE PRIONOPATHY(VPSPR):– Variably protease sensitive prionopathy is a rare prion disease, identified in 2008. And first described in 2010 by Zou W.Q. and coworkers from the United States National Prion Disease Pathology Surveillance Center. Patients present with psychiatric symptoms, speech deficits (aphasia and/or dysarthria), and cognitive impairment. Ataxia and Parkinsonism can develop. Average age at onset is 70 year, and duration of survival is 24 months. About 40% of patients have a family history of dementia.