(RNA VIRUSES) Lesson 15: Togaviridae Flashcards
General description of Togaviridae
- 60–70 nm in diameter
- Enveloped, RNA viruses with icosahedral symmetry
- Replicate in cell cytoplasm
- Labile in the environment
- Two genera, Alphavirus and Rubivirus
The family name Togaviridae e is taken from the Latin word ______.
toga
toga meaning
cloak or mantle
is a reference to the viral envelope of Togaviridae
cloak or mantle
Togaviridae: Enveloped or Non-enveloped
Enveloped
Togaviridae Replicate in
cytoplasm
Two genera of Togaviridae
Alphavirus and Rubivirus
in common with certain members of the Flaviviridae, Reoviridae, Rhabdoviridae and Bunyaviridae
Alphaviruses
Alphaviruses, in common with certain members of the Flaviviridae, Reoviridae, Rhabdoviridae and Bunyaviridae, are termed _________ indicating that they are arthropod- borne.
arboviruses
Alphaviruses / Genus Alphavirus cause what diseases
a. eastern equine encephalitis (EEE)
b. western equine encephalitis (WEE)
c. Venezuelan equine encephalitis (VEE)
major cause of zoonotic infections under Togaviridae
Alphaviruses / Genus Alphavirus
The majority of these viruses are found in tropical developing countries and have a
distinct geographical distribution.
arboviruses
The majority of arboviruses are found in ______ developing countries and have a
distinct geographical distribution.
tropical
Togaviridae
Ecological factors limiting the distribution of particular arboviruses include:
✓ temperature
✓ rainfall
✓ distribution of both vertebrate reservoir host and of the
arthropod vector
Togaviridae
The most important arthropod vectors.
The vector remains infected for life.
mosquitoes
midges
ticks
sandflies
Togaviruses of veterinary importance
1) Venezuelan
equine
encephalitis virus
(VEEV)
2) Eastern equine
encephalitis virus
(EEEV)
3) Western equine
encephalitis virus
4) Getah virus
Common arthropod vector of Togaviruses
Mosquito
Present in Central and South America with
occasional outbreaks in southern USA.
Venezuelan
equine
encephalitis virus
(VEEV)
Geographical distribution of Venezuelan
equine
encephalitis virus
(VEEV)
Central and South America w/
occasional outbreaks in southern USA
Venezuelan
equine
encephalitis virus
(VEEV) causes disease in
horses, donkeys and
man
Present in eastern USA, Caribbean and
South America
Eastern equine
encephalitis virus (EEEV)
Eastern equine
encephalitis virus
(EEEV) causes disease in
pheasants, horses and
man
Present throughout much of the Americas.
Western equine
encephalitis virus
(WEEV)
Western equine
encephalitis virus
(WEEV) causes disease in
horses and man
Milder disease than EEEV
Western equine
encephalitis virus
(WEEV)
Sporadic cause of disease in horses; fever,
urticaria and hind-limb oedema.
Getah virus
Getah virus: Sporadic cause of disease in these animals; fever,
urticaria and hind-limb oedema.
horses
Infection common in pigs but significance
unclear.
Getah virus
Present in Australia and southeast Asia
Getah virus
are important causes of nervous disease in horses in the New World which produce similar clinical signs
✓ Venezuelan equine encephalitis viruses (VEEV)
✓ Eastern equine encephalitis viruses (EEEV)
✓ Western equine encephalitis viruses (WEEV)
Several epidemiological features are common to the three diseases.
✓ Venezuelan equine encephalitis viruses (VEEV)
✓ Eastern equine encephalitis viruses (EEEV)
✓ Western equine encephalitis viruses (WEEV)
Togaviruses: The peak of disease incidence coincides with the time of maximum vector numbers in late
summer or following the rains
The Venezuelan equine encephalitis (VEE) complex comprises several viral species, divided into six subtypes I to VI
ENUMERATE
1) Subtype 1: have 5 serotypes (AB -F)
2) Subtype II : Everglades virus
3) Subtype III: Mucambo virus
4) Subtype IV: Pixuna virus
5-6) The viruses are maintained in sylvatic cycles involving rodents such as spiny rats (Proechimys chrysaeolus) and mosquitoes of the Culex (Melanoconion) and Aedes (Ochlerotatus) taeniorhynchus subgenus
Subtype 1 of Venezuelan equine encephalitis (VEE) complex
have 5 serotypes (AB - F)
Subtype II of Venezuelan equine encephalitis (VEE) complex
Everglades virus
Subtype III of Venezuelan equine encephalitis (VEE) complex
Mucambo virus
Subtype IV of Venezuelan equine encephalitis (VEE) complex
Pixuna virus
The viruses (Everglades virus, Mucambo virus, Pixuna virus) are maintained in what cycles?
sylvatic cycles
The viruses (Everglades virus, Mucambo virus, Pixuna virus) are maintained involving rodents such as spiny rats (Proechimys chrysaeolus) and mosquitoes of the Culex (Melanoconion) and Aedes (Ochlerotatus) taeniorhynchus subgenus
sylvatic cycles
The viruses are maintained in sylvatic cycles involving the two organisms
✓ rodents such
as spiny rats
✓ mosquitoes
SN of spiny rats
Proechimys chrysaeolus
SN of Culex
Melanoconion
SN and subgeus of Aedes
✓ Ochlerotatus
✓ taeniorhynchus
is found principally in Atlantic
coastal areas of the USA, Canada, Michigan, the Caribbean Basin and South
America.
Eastern equine encephalitis virus (EEEV)
Two distinct lineages of EEEV
✓ North American (pathogenic group I)
✓ South American (Groups IIA, IIB and III)
Lineage of EEEV pathogenic group I
North American
Lineage of EEEV under Groups IIA, IIB and III
South American
The virus is maintained in cycles of infection involving passerine
birds and the irrigation ditch mosquito Culiseta melanura
Eastern equine encephalitis virus (EEEV)
SN of irrigation ditch mosquito
Culiseta melanura
Western equine encephalitis virus (WEEV) cycle of infection involves
_______
✓ mosquitoes, mainly Culex tarsalis
✓ wild birds
cycle of infection involves
mosquitoes, mainly Culex tarsalis, and wild birds
Western equine encephalitis virus (WEEV)
Western equine encephalitis virus (WEEV) cycle of infection involves
mosquitoes, mainly __________, and wild birds.
Culex tarsalis
these animals are infected by WEEV incidentally and are dead-end hosts, developing
only low titres of virus in the blood.
Horses
A related virus of WEEV, occurs in the eastern United
States and causes encephalitis in horses rarely.
Highlands J virus
A related virus of WEEV, Highlands J virus, causes what?
encephalitis in horses rarely
A related virus of WEEV, Highlands J virus, causes encephalitis rarely in what animals?
horses
incubation period of Togaviruses
1-9 days
clinical
signs of Togaviruses usually last for how many days?
4-9 days
Replication of Togaviruses occurs where
✓ near the site of inoculation by a feeding mosquito
✓ local draining lymph nodes
TOGAVIRUSES
Viraemia ranging from barely detectable to an exceedingly high titre
follows. This is accompanied by fever.
In severe cases the Togavirus invades the _______
resulting in neuronal necrosis, perivascular cuffing and interstitial mononuclear inflammatory infiltration.
central nervous system
In severe cases the Togaviruses invades the central nervous system
resulting in
✓ neuronal necrosis
✓ perivascular cuffing
✓ interstitial
mononuclear inflammatory infiltration (IMII)
Clinically, the diseases caused by the three togaviruses are very similar
The 3 togaviruses vary in severity from mild signs of fever and depression to a
fatal febrile encephalomyelitis.
The case fatality rate is highest for EEE at ____%.
90%
case fatality rate is ___% for
VEE
50–80%
case fatality rate is ___% for WEE
20–40%
The case fatality rate is highest for this togavirus at 90%
EEE
Recovered horses (affected by togaviruses) are usually normal but a few may have residual
nervous signs.
Laboratory work with these viruses (VEEV, EEEV, WEEV) should only be carried out by
________ in ________ following containment level ____
procedures.
immunized personnel
biosafety cabinets
level 3
definitive diagnostic technique if togaviruses is
virus isolation (lab animal inoculation, embryo inoculation, cell culture)
TOGAVIRUSES
Specimens to be collected:
✓ whole blood
✓ brain
tissue
✓ cerebrospinal fluid (CSF)
TOGAVIRUSES
Specimens to be collected: whole blood during what stage?
pyrexic stage
TOGAVIRUSES
Specimens to be collected for horses which died following
nervous disease
brain
tissue or CSF
Diagnosis of Togaviruses
✓ RT-PCR
✓ Serology
• ELISA
• plaque reduction neutralization assay
• complement
fixation
• haemagglutination inhibition