2 Unique features of Togaviruses & Flaviviruses EnvelopedPositive sensessRNATogaviruses replicate in the cytoplasm and bud at the plasma membranesFlaviviruses replicate in the cytoplasm and bud at internal membranes
3 Togaviruses and Flaviviruses Virus groupHuman pathogensTogavirusesAlphavirusRubivirusArterivirusFlavivirusesFlaviviridaeHepaciviridaePestivirusArbovirusesRubella virusNoneHepatitis 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 SindbisSemliki forestVenezuelan equine enceph.Eastern equine encep.Western equine encep.Aedes & other mosquitosAedes, CulexAedes, CulisetaCulex, CulisetaBirdsRodents,horsesAfrica,Australia,IndiaEast and west AfricaNorth,South,&Central AmericaNorth&South America, CaribbeanNorth & South AmericaSubclinicalMild systemic,severe encephal.Mild systemic,encephal.
10 Arboviruses Disease Vector Host Distribution disease Flaviviruses DengueYellow feverAedesHumans, MonkeysHumans, monkeysWorldwide,esp. TropicsAfrica, South AmericaMild systemic; break-bone fever, dengue hemorrhagic fever, and dengue shock syndromeHepatitis, hemorrhagic fever
11 Arboviruses Disease Vector Host Distribution disease Flaviviruses Japanese encephalitisWest Nile encephalitisSt. Louis encephallitisRussian spring-summer encephalitisPowassan encephalitisCulexIxodes & dermocentor ticksIxodes ticksPigs, birdsBirdsSmall mammalsAsiaAfr.,Eur.,CentralAsia,N.AmerN. AmericaRussiaEncephalitisFever, encep., hepatitis
12 Togaviruses & Flaviviruses/Clinical syndromes Alphavirus disease is usually characterized as low-grade diseaseCan progress to encephalitis in humansFlavivirus infections are relatively benignSerious aseptic meningitis, encephalitis, hemorrhagic disesase can occur
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”VaccinesYellow fever live vaccine (17D strain)EEE, WEE, Japanese, Russian SSE killed vaccines
18 Rubella virusSame structural properties and mode of replication as the other toga’sRubella is a respiratory virusDoes not cause readily detectable cytopathologic effects
19 Rubella One of the 5 classic childhood exantems Measles Roseola Fifth diseaseChickenpox
20 Rubella Rubella: “little red” in Latin “German measles” Infects URT local lymphe nodes viremiaShedding respiratory dropletsOnly one serotypeNatural infection lifelong protective immunity
21 Congenital Rubella “Serious congenital abnormalities in the child” If the mother does not have antibodyThe virus can replicate in most tissues of the fetusThe normal growth, mitosis, and chromosomal structure of the fetus’s cells can be altered by the infection
22 Congenital RubellaThe normal growth, mitosis, and chromosomal structure of the fetus’s cells can be altered by the infectionImproper 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 affectedThe 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 diseaseNormally benign3 day of maculopapular or macular rash and swollen glandsMore severe in adults
26 Rubella/Clinical syndromes Congenital diseaseThe fetus is at major risk until the 20th week of pregnancyMost common manifestations:CataractsMental retardationdeafness
27 Rubella/Laboratory diagnosis Anti-Rubella IgM by ELISAAvidity test: Low avidity4x increase in IgGAntibodies to rubella are assayed early in pregnancy to determine the immune status of the woman
28 Rubella/Treatment, Prevention, and Control No treatmentVaccination (live)MMR vaccine