Transcript HERPESVIRIDAE

ORTHOMYXOVIRIDAEINFLUENZA VIRUSES
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:
• realise that most isolates of influenza
viruses are species-specific
• define antigenic shift and drift and
comment on the mechanisms of each.
• explain how vaccines are made and why
they become out of date.
• describe in outline the pathogenesis and
control of equine influenza.
Introduction
Influenza viruses cause epidemics of
respiratory disease in most species (but
not dogs or cows). New antigenic
variants can infect recovered or
vaccinated hosts. This is why these
fragile viruses have not been eliminated
by vaccination.
Antigens
1. Type specific.
2. Subtype specific antigens on H and N.
3. Antigenic drift - variation of H within a
subtype within a host species
4. Antigenic shift - change of subtype of H
within a host species.
1.Type specific antigenic.
2.Subtype specific antigens on
H and N detected by HI and
NI tests.
3.Antigenic drift evolution of a variant within a
subtype, meaning imperfect
protection by old vaccines
4.Antigenic shift.
Complete change of H molecule meaning
no protection by old vaccines. Shift
occurs by a) gene reassortment, b) change
of species specificity
Vaccines
Virus is grown to high titre in millions of
hens eggs then inactivated with 1/4000
betapropiolactone. BPL was once used to
polymerise bakelite e.g for brown radio
facias. It is now used to polymerise
nucleic acid during vaccine production.
The vaccine is purifed by differential
centrifugation and mixed with an
adjuvant for injection.
EQUINE INFLUENZA
Introduction
Clinical equine influenza (stable cough) used to be
a problem in cities. Equine 1 (H7N7) has been
absent from the UK since 1977. In 1998 an
American-like isolate of equine 2 (H3 N8) caused
an outbreak in UK/EU. Both are controlled by a
vaccination scheme administered by the jockey
club.
EQUINE INFLUENZA
Immunity and epidemiology:
As with most viruses the period of virus excretion
from nasal secretions is during the first 10 days
following infection before spec-immunity kicks in.
Vaccinated animals can excrete virus without
disease and have carried the virus between
countries eg to South Africa from USA.
As with other resp viruses spread is by personnel
and instruments (which most vets do not realise) as
well as by aerosol eg at race meetings. No zoonotic
risk.
EQUINE INFLUENZA
Control:
Isolate coughing horses to minimise
spread and use disposable syringes
when treating them.
EQUINE INFLUENZA
References
Duration of protective efficacy of equine
influenza immunostimulating complex/
tetanus vaccines. Mumford et al., Vet Rec
(1994) 134 158- 162
Equine influenza in the UK in 1998.
Newton et al., Vet Rec (Oct 16th 1999)
145, 449-52.
SWINE INFLUENZA
H1N1 variant 1992. This is the primary
pathogen of current concern, others cause
little disease.
Bronchiolitis with
interstitial
pneumonia
giving
consolidation of lungs and 'meaty'
appearance. Jerky respiration (USA, the
thumps).
SWINE INFLUENZA
Diagnosis
Clinical pneumonia is suggestive.
Paired serum samples to show
seroconversion by HI.
AVIAN INFLUENZA
BOVINE INFLUENZA
INFECTIOUS SALMON
ANAEMIA
(and haemorrhagic kidney
syndrome)
Summary
 Antigenic shift and drift of H is crucial to
immunity.
Virulence and tissue tropism are
controlled by the cleavage site of H0. Vaccines are
grown in eggs.
 Equine influenza is diagnosed by ELISA but
isolates are characterised by the growth of virus
collected in transport medium. Coughing is
prevented by vaccination.
 A more virulent isolate of porcine influenza is now
circulating in the UK, no vaccine is licensed in the
UK.