JOURNAL OF PATHOLOGY, VOL. 160: 283-285 ( 1990) EDITORIAL BOVINE SPONGIFORM ENCEPHALOPATHY: THE NEED FOR KNOWLEDGE, BALANCE, PATIENCE, AND ACTION In November I986 a discovery was made that was to pose one of the most serious threats to the well- being of the British cattle industry this century. Pathologists at the Ministry of Agriculture's Central Veterinary Laboratory at Weybridge had, as a result of the animal health surveillance activities of the State Veterinary Service. identified a scrapie- like disease of cattle. a condition which previously had been confined. in food animals, to sheep and goats. They named the disease bovine spongiform encephalopathy (BSE).' That the disease. characterized by brainstem lesions of spongiform change in grey matter neuro- pi1 and neuronal vacuolation, was scrapie-like was supported by the clinical presentation as a sporadic. slowly progressive, fatal, neurological disorder embracing abnormalities of behaviour, sensation. posture, and gait. The findings suggested that BSE might be the latest member of the group of diseases known as the subacute. transmissible. spongiform encepha- lopathies (SSEs) caused by unconventional agents. The unconventionality is due to the fact that infec- tion results in no detectable immunological re- sponse and the agents are extraordinarily resistant to heat, ultra-violet, and ionizing radiation and many common disinfectants. The SSE group con- sists of scrapie in sheep and goats, transmissible mink encephalopathy. chronic wasting disease of captive mule deer and elk, and in humans, kuru, Creutzfeldt-Jakob disease (CJD) and Gerstmann- Straussler-Scheinker (GSS) syndrome. Conclusive evidence that BSE was a new member of the group was provided by workers at Weybridge and at the Institute for Animal Health, Neuro- pathogenesis Unit (NPU) in Edinburgh. First. fibrils were found in detergent-treated brain extracts only of BSE-affected cattle.' These were shown to share morphological,' chemical. and immuno- logical properties with scrapie-associated fibrils (SAFs) which are found in all other members of the disease group.' The second important study was the transmissibility of BSE from cattle brain to mice' following intracerebral and intraperitoneal inocu- lation. This study also established mice as a suitable species for assay of infected cattle tissues and prod- ucts, for identifying putative sources of BSE and strain typing of the agent responsible. Studies on the transmissibility of BSE to cattle. sheep. goats, pigs. hamsters, and marmosets are in progress and others are planned. Further studies on the post-translationally altered. host-coded fibril protein (PrP). and particu- larly the production of anti-PrP serum in rabbits. have enabled researchers to detect PrP by immuno- blotting of brain extracts4 and immunocyto- chemistry in brain sections. Currently, BSE diagnosis is confirmed by conventional paraffin histology of the brain. These immunological tech- niques, when developed further, may, however. per- mit more sensitive and preclinical detection of PrP in brain tissue. and. perhaps, in extraneural sites. The current absence of any practical test for identi- fying infection in individuals pre-clinically is a serious deficit restricting development of measures to control the condition. Amongst the theories of unconventional agent structure is that a small nucleic acid is responsible for scrapie or BSE infectivity but which so far has evaded detection. This requires intensified research effort for success and may lead to identification of the agent pre-clinically. and in tissues. without the need for animal inoculation and assay. All disease results from the interaction of en- vironmental or genetic factors. In the case of scrapie. we know at least 20 strains exist with differ- ing biological and physical properties, but it is too early to say if this is true of the BSE agent. Of equal or greater importance is the genetic control of BSE disease expression in cattle. We know that in murine and ovine scrapie a single gene (Sinc in mice and Sip in sheep) exerts a large measure of control over clini- cal disease expression by control of the incubation period.'.' These major genes are closely associated or identical with the PrP gene. Research at NPU has enabled identification of Sip alleles in sheep by a 0022-341 7/90/040283-03 $05.00 0 1990 by John Wiley 8i Sons, Ltd
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
