Transcript HERPESVIRIDAE

Togaviridae,
Flaviviridae and
Arteriviridae
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
Objective
Students should be able to:
• describe in detail how louping ill of sheep is
transmitted from shrews and grouse to end
hosts (eg ruminants, dogs and man) by Ixodes
ricinus
• define the salient features associated with
equine viral arteritis and porcine respiratory
and reproductive syndrome (PRRS).
• explain why antigenic variation and
persistence make control difficult
Family TOGAVIRIDAE
• These are medium sized (70nm),
icosahedral, enveloped, single-stranded
positive-sense RNA viruses with 2-3
glycoproteins as spikes.
Genus ALPHAVIRUS
EQUINE
ENCEPHALOMYELITIS
VIRUS
Genus ALPHAVIRUS
EQUINE
ENCEPHALOMYELITIS
VIRUS (cont.)
Family FLAVIVIRIDAE
These are like the togaviruses but
smaller.
Genus FLAVIVIRUS,
LOUPING ILL
Cattle, sheep, deer, dogs and man are all
end hosts.
Ixodes ricinus is the vector.
Shrews and grouse are reservoir hosts.
Genus FLAVIVIRUS,
LOUPING ILL
Diagnosis
Clinical. Virus isolation, serology and
histopath to confirm.
Genus FLAVIVIRUS,
LOUPING ILL
Control
Genus FLAVIVIRUS
WEST NILE VIRUS
Family ARTERIVIRIDAE
These enveloped RNA viruses have
the morphology of togaviridae and
the nested
mRNAs of the
coronaviridae.
PORCINE REPRODUCTIVE AND
RESPIRATORY SYNDROME
(Lelystad virus, Blue ear)
The virus was first detected at the Central Veterinary
Institute in Lelystad (Holland) in 1990.
The European isolates will only grow in cultures of
alveolar macrophages, which as with FIPV and feline
macrophages, delayed their discovery.
Considerable antigenic heterogeneity in Europe.
Additional isolates occur in the USA.
Isolates of low virulence have now evolved.
PORCINE REPRODUCTIVE AND
RESPIRATORY SYNDROME
(Lelystad virus, Blue ear)
Epidemiology:
PRRS is highly contagious and
disseminated by fomites, wind and AI.
EQUINE VIRAL ARTERITIS
(Equine abortion virus) (EVA or
EAV)
EQUINE VIRAL ARTERITIS
(Equine abortion virus) (EVA or EAV)
(cont.)
EQUINE VIRAL ARTERITIS
(Equine abortion virus) (EVA or EAV)
Epidemiology
Carrier animals are important sources of venereal
as well as oro/nasal transfer.
The virus survives well outside the host on
fomites (greek for wood).
EQUINE VIRAL ARTERITIS
(Equine abortion virus) (EVA
or EAV)
(cont.)
Summary
• Mosquitoes transmit the viral equine encephalitides; and
these can be fatal for man – so that all horses and personnel
should be vaccinated in areas where the virus is endemic in
reservoir hosts.
• Louping Ill is a problem giving rise to CNS disorders in
sheep (and grouse) reared in areas where ticks exist. It can
be reduced both by vaccination and by tick control. It is a
zoonosis.
• PPRS is now endemic in the UK pig population and the
majority of current strains appear to be avirulent. It can
cause respiratory disease, and reproductive failure in sows.
• EVA has entered the UK but remains rare. The persistently
infected stallion sheds virus intermittently in semen and
can be a source of outbreaks of abortion.