TOGAVIRIDAE

• STRUCTURE: ss (+) RNA, spherical, enveloped, infectious.

• REPLICATION: Polymerase is at the 5' end and structural proteins are at the 3' end.

  • First, the 5' end of the genome is translated, making some non-structural proteins and RNA-Dependent RNA Polymerase.

  • RNA-Dependent Polymerase then makes a minus-strand out of the plus strand, and then uses that to make more plus-strands.

  • Then the 3' end is translated, forming structural proteins that are packaged together with the new RNA strands.

• ALPHAVIRUS: All are arboviruses, transmitted by insect-vector.

  • STRUCTURE: All share serological reactivity, i.e. cross-reactive for some internal viral antigens.

  • EASTERN EQUINE ENCEPHALITIS VIRUS (EEEV):

    • The deadliest of the encephalitis viruses.

    • The rarest of the encephalitis viruses.

    • Fatality: 30-50%

  • WESTERN EQUINE ENCEPHALITIS VIRUS (WEEV): The next deadliest.

    • TRANSMISSION: Horse-mosquito. Man is dead-end host.

    • Fatality: 3-5%

  • VENEZUELAN EQUINE ENCEPHALITIS (VEEV):

  • SINDBIS VIRUS:

    • MANIFESTATIONS: Standard common viremia symptoms: fever, myalgia, rash, vomiting. May see maculopapular rash.

• RUBIVIRUS: RUBELLA -- not an Arbovirus (no arthropod vector)
• STRUCTURE: ss (+) RNA, enveloped.
• DIAGNOSIS: Immunofluorescence on cultured viruses in mammalian cell lines. MANIFESTATIONS: German Measles. Usually a trivial disease
• Incubation Period: 2-3 weeks. Disease most prevalent in Spring.
• Rubella is non-Cytocidal, as compared to the Arboviruses.
• Symptoms:
• Lymphadenopathy and mild conjunctivitis.
• Maculopapular "Rubelliform" Rash that forms small discrete blotches, that do not coalesce, and disappear in 3-5 days.
• Complications: Arthritis and, rarely, post-encephalitis.
• MANIFESTATIONS: Congenital Rubella Syndrome (TORCH). Very few cases seen today, but an outbreak happened recently when people were lax about vaccines.
• Do a Rubella titer for women of child-bearing age.
• Greatest risk when maternal infection is early in pregnancy (first trimester).
• Effects: Blindness, deafness, congenital heart defects, and brain defect are all possible. Rarely fatal (no spontaneous abortion).
• DIAGNOSIS: Look for Anti-Rubella IgM in fetal cord-blood.

• PESTIVIRUS:

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Category: Microbiology Notes