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Togaviruses and Flaviviruses

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

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Togaviruses and Flaviviruses

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  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

  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

  9. Arboviruses

  10. Arboviruses

  11. Arboviruses

  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 • 250 000 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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