1. Togaviruses and Flaviviruses

2. Unique features of Togaviruses & Flaviviruses
Enveloped
Positive sense
ssRNA
Togaviruses replicate in the cytoplasm and bud at the plasma membranes
Flaviviruses replicate in the cytoplasm and bud at internal membranes

3. Togaviruses and Flaviviruses
Virus group
Human pathogens
Togaviruses
Alphavirus
Rubivirus
Arterivirus
Flaviviruses
Flaviviridae
Hepaciviridae
Pestivirus
Arboviruses
Rubella virus
None
Hepatitis C virus

4. Togaviruses and Flaviviruses
Alphavirus and Flavivirus are discussed together because of similarities in the diseases that they cause, as well as in epidemiology.
Most are transmitted by arthropods and are therefore arboviruses (arthropod-borne viruses).
They differ in size, morphology, gene sequence, and replication.

5. Togaviruses and Flaviviruses
The alphaviruses and flaviviruses:
These viruses have a very broad host range, including vertebrates (e.g., mammals, birds, amphibians, reptiles) and invertebrates (e.g., mosquitoes, ticks). Diseases spread by animals or with an animal reservoir are called zoonoses.

6. Togaviruses Alphavirus, Rubivirus, and Arterivirus.
No known arteriviruses cause disease in humans, so this genus is not discussed further.
Rubella virus is the only member of the Rubivirus group; it is discussed separately, because its disease manifestation (German measles) and its means of spread differ from those of the alphaviruses.

7. Togaviruses and Flaviviruses
The Flaviviridae include the flaviviruses, pestiviruses, and hepaciviruses (hepatitis C and G viruses).
Hepatitis C and G are discussed inhepatitis viruses.

8. Arboviruses Disease Vector Host Distribution disease Alphaviruses
Sindbis
Semliki forest
Venezuelan equine enceph.
Eastern equine encep.
Western equine encep.
Aedes & other mosquitos
Aedes, Culex
Aedes, Culiseta
Culex, Culiseta
Birds
Rodents,horses
Africa,Australia,India
East and west Africa
North,South,&Central America
North&South America, Caribbean
North & South America
Subclinical
Mild systemic,severe encephal.
Mild systemic,encephal.

9. Arboviruses Disease Vector Host Distribution disease Alphaviruses
Chikungunya
Aedes
Humans,Monkeys
Africa, Asia
Fever, Arthralgia, arthritis

10. Arboviruses Disease Vector Host Distribution disease Flaviviruses
Dengue
Yellow fever
Aedes
Humans, Monkeys
Humans, monkeys
Worldwide,esp. Tropics
Africa, South America
Mild systemic; break-bone fever, dengue hemorrhagic fever, and dengue shock syndrome
Hepatitis, hemorrhagic fever

11. Arboviruses Disease Vector Host Distribution disease Flaviviruses
Japanese encephalitis
West Nile encephalitis
St. Louis encephallitis
Russian spring-summer encephalitis
Powassan encephalitis
Culex
Ixodes & dermocentor ticks
Ixodes ticks
Pigs, birds
Birds
Small mammals
Asia
Afr.,Eur.,CentralAsia,N.Amer
N. America
Russia
Encephalitis
Fever, encep., hepatitis

12. Togaviruses & Flaviviruses/Clinical syndromes
Alphavirus disease is usually characterized as low-grade disease
Can progress to encephalitis in humans
Flavivirus infections are relatively benign
Serious aseptic meningitis, encephalitis, hemorrhagic disesase can occur

13. Togaviruses & Flaviviruses/Clinical syndromes
Hemorrhagic disesases
Dengue
Yellow fever viruses

14. Togaviruses & Flaviviruses/Clinical syndromes
Hemorrhagic disesases
Dengue virus
Major worldwide problem
100 million cases of dengue fever/year
cases of dengue hemorrhagic fever/y
Dengue shock syndrome

15. Togaviruses & Flaviviruses/Clinical syndromes
Hemorrhagic disesases
Yellow fever viruses
Severe systemic disease
Degeneration of the liver, kidney, heart + hemorrhages
“JAUNDICE”
Mortality rate: ~ 50% during epidemics

16. Togaviruses & Flaviviruses/Laboratory diagnosis
Cell culture vertebrate and mosquito cell lines difficult
IF, hemadsorbtion
RT-PCR
Serology
ELISA HI LA

17. Togaviruses & Flaviviruses/Treatment, Prevention, and Control
No treatment!
“The easiest means of preventing the spread of any arbovirus is elimination of its vector and breeding grounds”
Vaccines
Yellow fever live vaccine (17D strain)
EEE, WEE, Japanese, Russian SSE killed vaccines

18. Rubella virus
Same structural properties and mode of replication as the other toga’s
Rubella is a respiratory virus
Does not cause readily detectable cytopathologic effects

19. Rubella One of the 5 classic childhood exantems Measles Roseola
Fifth disease
Chickenpox

20. Rubella Rubella: “little red” in Latin “German measles”
Infects URT local lymphe nodes viremia
Shedding respiratory droplets
Only one serotype
Natural infection lifelong protective immunity

21. Congenital Rubella “Serious congenital abnormalities in the child”
If the mother does not have antibody
The virus can replicate in most tissues of the fetus
The normal growth, mitosis, and chromosomal structure of the fetus’s cells can be altered by the infection

22. Congenital Rubella
The normal growth, mitosis, and chromosomal structure of the fetus’s cells can be altered by the infection
Improper development of the fetus, small size of the infected baby, and the teratogenic effects

23. Congenital Rubella The nature of the disorder is determined by
The tissue affected
The stage of development disrupted

24. Congenital Rubella
~20% of women of childbearing age escape infection during childhood and are susceptible to infection unless vaccinated

25. Rubella/Clinical syndromes
Rubella disease
Normally benign
3 day of maculopapular or macular rash and swollen glands
More severe in adults

26. Rubella/Clinical syndromes
Congenital disease
The fetus is at major risk until the 20th week of pregnancy
Most common manifestations:
Cataracts
Mental retardation
deafness

27. Rubella/Laboratory diagnosis
Anti-Rubella IgM by ELISA
Avidity test: Low avidity
4x increase in IgG
Antibodies to rubella are assayed early in pregnancy to determine the immune status of the woman

28. Rubella/Treatment, Prevention, and Control
No treatment
Vaccination (live)
MMR vaccine