ACCESSION NO:  96-97-1643
       TITLE:  The Science Behind BSE
      AUTHOR:  ANONYMOUS
     JOURNAL:  Science Spectra
    CITATION:  1996: 10-14.
        YEAR:  1996
    PUB TYPE:  Article
 IDENTIFIERS:  PRION DISEASES; PRION PROTEIN; BOVINE SPONGIFORM 
               ENCEPHALOPATHY (BSE); CREUTZFELD-JAKOB DISEASE (CJD); 
               NEUROLOGICAL DISEASES; DISEASE TRANSMISSION; SCRAPIE; FOOD 
               CHAIN
    ABSTRACT:       Prion diseases cause a massive loss of neurons and 
               synapses and the development of amyloid plaques in the brain. 
               The diseases, known as spongiform encephalopathies, cause a 
               range of neurological symptoms including loss of balance and 
               dementia. These encephalopathies are inherited and 
               transmissible. Transmission may be due to prion proteins 
               found, highly conserved, in all mammalian brains. The disease 
               may be caused by abnormal prion isoforms.
                    Prion diseases affect many mammals including sheep and 
               cows. Experimental evidence does indicate that transmissible 
               spongiform encephalopathies can pass between species. 
               Although no evidence suggests that scrapie (a form common in 
               sheep) can pass to humans, there is fear that bovine 
               spongiform encephalopathy (BSE) can be transmitted to humans. 
               BSE is known in the U.K., Ireland, France, Switzerland, and 
               the Falkland Islands where cattle were fed protein from 
               rendered animals including sheep that are affected by 
               scrapie.
                    Human forms of prion disease may be inherited, caused by 
               somatic mutation, or transmitted. Creutzfeld-Jakob disease 
               (CJD) is uncommon, with an estimated worldwide incidence of 
               0.5 cases per million person years. Classic CJD has a long 
               incubation period, affects victims between 55-70 yr. of age, 
               and progresses rapidly causing death within 9 mo. Ten cases 
               of a new strain of CJD have been reported in the U.K. This 
               new form affects people under 42 yr. of age, causes illness 
               that lasts longer, and the disturbances are behavioral rather 
               than neurological with extensive plaque formation. No proven 
               link between the two yet exists.
                    Prion diseases all involve the conversion of a normal 
               cell protein (PrP) into an abnormal isoform (PrPP) and an 
               accumulation of that isoform in the central nervous system. 
               PrP is encoded by a normal cellular gene located on 
               chromosome 20. It is expressed throughout life and is 
               necessary for basic cell functioning. In the affected brain, 
               the protein forms plaques between and within cells. Pathology 
               results from the alteration to the prion gene to produce an 
               abnormal protein, or from changes in the post translational 
               processing leading to an abnormal protein.
                    It is accepted that cows infected with BSE entered the 
               human food chain before the introduction of controls in 1988 
               and 1989. The risk of disease transmission between cows and 
               humans, the number of infective units needed to initiate 
               disease, and any link between BSE and the new strain of CJD 
               are currently unknown.