"Mad cow" disease is caused by?
Ans. D. Prions. (Ref. Robbin's pathology 8th/pg. 880)Prion Diseases# This includes sporadic, familial, iatrogenic and variant forms of Creutzfeldt-Jakob disease (CJD).# Several animal diseases from this group are also known, including scrapie in sheep and goats and bovine spongiform encephalopathy in cattle ("mad cow" disease).6# All these disorders are associated with abnormal forms of a normal cellular protein, termed prion protein (PrPc).# The unique pathogenesis of prion diseases is related to changes in the conformation of PrP from its native PrPc form to an abnormal configuration called either PrPsc (for scrapie) or PrPres (for protease resistant).Creutzfeldt-Jakob Disease# CJD is a rare but well-characterized prion disease that manifests clinically as a rapidly progressive dementia.# It is sporadic in about 85% of cases, with a worldwide annual incidence of about 1 per million; familial forms also exist.# The disease has a peak incidence in the seventh decade.# There are well-established cases of iatrogenic transmission by deep implantation electrodes and contaminated preparations of human growth hormone.# The clinical presentation begins with subtle changes in memory and behavior that rapidly progress to dementia. The disease is uniformly fatal, with an average duration of only 7 months.# Morphology:- On microscopic examination, the pathognomonic finding is a spongiform transformation of the cerebral cortex and deep gray matter structures (caudate, putamen); this consists of a multifocal process that results in* the uneven formation of small, apparently empty, microscopic vacuoles of varying sizes within the neuropil and sometimes in the perikaryon of neurons.* In advanced cases, there is severe neuronal loss, reactive gliosis, and sometimes expansion of the vacuolated areas into cystlike spaces ("status spongiosus").* No inflammatory infiltrate is present.- In all forms of prion disease, immunohistochemical staining demonstrates the presence of proteinase K-resistant PrPsc in tissue.- Western blotting of tissue extracts after partial protease digestion allows detection of diagnostic PrPsc.
HIV virus
Mycoplasma
Chlamydia
Prions
Infection