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Togaviruses and Flaviviruses

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Presentation on theme: "Togaviruses and Flaviviruses"— Presentation transcript:

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

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