Togaviruses are a family of viruses that includes alphaviruses and rubiviruses. Key points about togaviruses are that they are spherical, enveloped viruses with positive-sense RNA genomes that replicate cytoplasmically. Alphaviruses are transmitted by mosquitoes and have a wide host range, while rubiviruses only infect humans. Important alphaviruses that can cause encephalitis in horses and humans include Eastern equine encephalitis virus, Western equine encephalitis virus, and Venezuelan equine encephalitis virus. These viruses are maintained in transmission cycles between arthropod vectors and vertebrate hosts like birds, pigs, and rodents.

1. Togaviridae

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

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)

6. Genus ; Alphavirus (Arthropod borne virus)
 Eastern equine encephalitis virus –Aedes Culiseta
 Western equine encephalitis virus –Culex, Culiseta
 Venezuelan equine encephalitis virus- Aedes ,Culex
 Sindbis virus
 Chikungunya virus- Aedes
 Highlands virus
 Igho Ora virus
 Ross River virus
 Semliki forest virus
 Barmah Forest virus
 Getah virus

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.

10. Man-Arthropod-Man Cycle

11. Animal-Arthropod-Man
Cycle

12. Arthropod Vectors
1. Mosquitoes (Aedes, Culex, Culeseta like)
Japanese encephalitis, dengue, yellow fever, St. Louis encephalitis,
EEE, WEE, VEE etc.
2. Ticks (Soft tick / hard tick etc )
Crimean-Congo haemorrhagic fever (Hyaloma), various tick-borne
encephalitides etc.
3. Sandflies
Sicilian sandfly fever, Rift valley fever.

13. Examples of Arthropod Vectors
Aedes Aegyti
Assorted Ticks
Phlebotmine Sandfly
Culex Mosquito

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

18. Viral 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

20. History

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

23. Transmission

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

29. Control
 Vaccination- Monovalent, Bivalent, Trivalent
 Vector control

30. Eastern Equine Encephalitis
(EEEV) / Sleeping sickness

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

33. Western Equine Encephalitis
(WEEV)

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

36. Venezuelan Equine Encephalitis
(VEEV)
PESTE LOCA, DERRENGADERA

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

40. Prevention and
Control

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