Download HERPESVIRIDAE

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-mail
Web site
Objectives
Students 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
Viruses are classified into
families based on appearance and
into species based on the host
and disease.
Within a species there are
different isolates
e.g. the Newmarket 1976 isolate
of equine influenza virus.
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
Classical terms in classification
refer to Virus morphology,
Location, Lesion; Virus enzyme:
Antigens
Large numbers of different
monoclonal antibodies (mAb)
have been made to these different
epitopes e.g. 40 -400 for a
particular virus.
Antigenic variation
Genetic variation is more
common in RNA compared to
DNA viruses.
Conserved antigens are on many
isolates.
The closer isolates are related the
more antigens they will share and
this is the basis for antigen
fingerprinting with monoclonal
antibodies
Antigenic fingerprinting is
useful to epidemiologists and
MAFF eg for tracing the spread
of influenza viruses and choosing
which vaccines to use
Conserved epitopes involved in
neutralisation make for a
successful vaccine
e.g. for canine distemper.
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.