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CLASSIFICATION

Learn how viruses are classified into families based on structure and genome, and explore the significance of conserved and variable antigens on virus proteins in this informative guide. Understand the importance of antigenic fingerprinting for epidemiologists.

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CLASSIFICATION

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  1. CLASSIFICATION PETER H. RUSSELL, BVSc, PhD, FRCPath, MRCVS Department of Pathology and Infectious Diseases, The Royal Veterinary College, Royal College Street, London NW1 OTU. E-mailWeb site

  2. ObjectivesStudents should be able to: • describe in outline how viruses may be classified into families using a number of different criteria including structure and genome. • compare and contrast conserved and variable antigens on virus proteins

  3. Viruses are classified into families based on appearance and into species based on the host and disease.

  4. Within a species there are different isolates e.g. the Newmarket 1976 isolate of equine influenza virus.

  5. Classification of viral families • presence or absence of an envelope (tested by ether sensitivity), • capsid symmetry • size and shape of particle, • RNA or DNA, and now their sequence, • The number and polarity (sense) of strands of nucleic acid. • enzymes

  6. Classical terms in classification refer to Virus morphology, Location, Lesion; Virus enzyme:

  7. Antigens

  8. Large numbers of different monoclonal antibodies (mAb) have been made to these different epitopes e.g. 40 -400 for a particular virus.

  9. Antigenic variation

  10. Genetic variation is more common in RNA compared to DNA viruses.

  11. Conserved antigens are on many isolates.

  12. The closer isolates are related the more antigens they will share and this is the basis for antigen fingerprinting with monoclonal antibodies

  13. Antigenic fingerprinting is useful to epidemiologists and MAFF eg for tracing the spread of influenza viruses and choosing which vaccines to use

  14. Conserved epitopes involved in neutralisation make for a successful vaccine e.g. for canine distemper.

  15. Summary • Families are classified by their structure and genomic sequence. • Isolates of a species are classified by their antigens and sequence • Conserved antigens are shared between isolates. • Variable antigens are on some but not other isolates.

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