2. Properties of Togaviruses
Toga means- Cloak
Virus first time isolated from brain of horse in California
Size-70 nm in diameter
Positive-sense, single-stranded RNA (Reo, Birna)
Virions are spherical in shape,
Enveloped, (Picorna, Calci, Astro, Reo, Birna- NE)
Icosahedral nucleocapsid, (Picorna, Calci, Astro, Reo,
Birna, Togo, Flavi, Retro)
3. Contt..
5' end of the genomic RNA is capped whereas the 3' end is
polyadenylated
Replication - cytoplasmic, (Borna, Orthromyxo-Nucleus)
Maturation occurs via budding from the plasma membrane
Agglutination goose & Chicks erythrocyte
4.
5. Classification
1. Alphavirus (Arthropod born virus)
2. Rubivirus / Rebella virus (Human pathogen)
Alphaviruses are transmitted b/w vertebrates by mosquitoes
and certain hematophagous arthropods.
Alphaviruses have wide host range ,
Rubiviruses infects humans only
(Virus belong to Togaviridae are trans. by insect only)
7. Arboviruses / Arthropod-borne Viruses
Arthropod-borne viruses (arboviruses) are viruses that can be
transmitted to man by arthropod vectors.
Biological transmission of disease between susceptible
vertebrate hosts by hematophagous arthropods or through
transovarian or venereal transmission in arthropods.”
8. Arthropod-borne Viruses
Arboviruses belong to four families:
1. Togaviruses e.g. EEE, WEE, and VEE
2. Bunyaviruses e.g. Sandfly Fever, Rift Valley Fever, Crimean-Congo
Haemorrhagic Fever
3. Flaviviruses e.g. Yellow Fever, dengue, Japanese Encephalitis
4. Reoviridae (Orbivirus- BT, African horse sickness,
Coltivirus- Colorado tick fever)
9. Transmission Cycles
Man - arthropod -man
e.g. dengue, urban yellow fever.
Reservoir may be in either man or arthropod vector.
Animal - arthropod vector - man
e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever.
The reservoir is in an animal.
14. Animal Reservoirs
In many cases, the actual reservoir is not known. The following animals
are implicated as reservoirs
Birds Japanese encephalitis, St Louis encephalitis,
EEE, WEE
Pigs Japanese encephalitis
Monkeys Yellow Fever
Rodents VEE, Russian Spring-Summer encephalitis
15. Diseases Caused
Fever and rash - this is usually a non-specific illness resembling a
number of other viral illnesses such as influenza, rubella, and
enterovirus infections. The patients may go on to develop
encephalitis or haemorrhagic fever.
Encephalitis - e.g. EEE, WEE, St Louis encephalitis, Japanese
encephalitis.
Haemorrhagic fever - e.g. yellow fever, dengue, Crimean-Congo
haemorrhagic fever.
16. Diagnosis
Serology - usually used to make a diagnosis of arbovirus
infections.
Culture - a number of cell lines may be used, including
mosquito cell lines.
Direct detection tests - e.g detection of antigen and nucleic
acids are available but again there are safety issues.
17. Prevention
Surveillance - of disease and vector populations
Control of vector - pesticides, elimination of breeding grounds
Personal protection - screening of houses, bed nets, insect
repellants
Vaccination - available for a number of arboviral infections
e.g. Yellow fever, Japanese encephalitis, Russian tick-borne
encephalitis
19. Viral Encephalitis
Western equine encephalitis (WEE) –Alpha / Toga
Eastern equine encephalitis (EEE) –Alpha / Toga
Venezuelan equine encephalitis (VEE)–Alpha / Toga
St. Louis encephalitis (SLE)
La Crosse encephalitis (LAC) Flavi virus
West Nile virus (WNV)
Center for Food Security and Public Health Iowa State University -
2004
21. History
1925
First arbovirus identified in the U.S. (Sendflies)
Vesicular stomatitis
1930
WEE virus isolated in California
Karl Meyer isolated agent from horse brain
Center for Food Security and Public Health Iowa State University -
2004
22. History
1932
St. Louis encephalitis identified in causing human disease
1933
St. Louis encephalitis virus isolated from human brain
Eastern equine encephalitis virus Isolated from equine
brains
Center for Food Security and Public Health Iowa State University -
2004
25. Estern, Western, Venezulean produce similar clinical sign
Major outbreak- VEEV
VEEV- Six sub type (I to VI)
Highly virulent (IAB & IC)
Other non pathogenic to horse
26. Pathogenesis
Outbreak during late summer and heavy rain fall season
Pathogenesis
Virus enter in to body through mosquito
Replication at local site of biting
Viremia
Sign
27. Sign
I.P-9 days
Fever
Encephalomyelitis
Blindness
Circling
Head pressing
Neurological sign most severe in EEEV
28. Lab Diagnosis
History & Clinical sign
Virus Isolation ( Blood, Brain, CS fluid)
Cell culture- Vero, BHK 21- Produce CPE
C6/36 (Aedes albopictus) grow but do not produce CPE
Anomal inoculation
ELISA
VN
RT PCT
32. Animal EEE
Incubation period: 1-8 days
Severe disease
Horses, pheasants, quail, ostriches, emus, puppies
Clinical signs in horses
Fever, anorexia, weight loss, depression
CNS signs
Wide stance, droopy ears, flaccid lips, hanging head
Death in horses within 4 days
Center for Food Security and Public Health Iowa State University -
2004
35. Animal WEE
Asymptomatic
Blacktail jackrabbit, kangaroo rat, Western gray squirrel,
prairie dog, horse
Horses with clinical signs
Fever, depression, altered mentation, head pressing,
ataxia, dysphagia
Progress to paralysis, convulsions, death
Mortality rate 20-50%
Center for Food Security and Public Health Iowa State University -
2004
37. Viral Strains
Subtype Cycle Pathogenic
I-A
I-B
I-C
Epizootic/
Epidemic
Highly virulent for
equines
I-D II
I-E III
I-F IV
V
VI
Enzootic/
Endemic
Not for horses
Limited cases in
humans
Center for Food Security and Public Health Iowa State University -
2004
41. Management of
Mosquito-Borne Diseases
Center for Food Security and Public Health Iowa State University -
2004
Source reduction
Surveillance
Biological control
Chemical control
Larvicide
Adulticide
Educating the public
How to protect themselves
42. VEE as a Biological Weapon
50 kg virulent VEE particles
Aerosolized over city of 5 million people
150,000 people exposed
30,000 people ill
300 deaths
Center for Food Security and Public Health Iowa State University -
2004
