FLAVIVIRIDAE

• STRUCTURE: ss (+) RNA, enveloped

  • Used to be classified with Togaviruses, but now is reclassified, because:

    • Nucleic acid sequences for Yellow Fever virus genome are different.

    • The virus does not utilize a subgenomic mRNA.

    • Alpha viruses bud mainly from the surface plasma membrane, whereas the Flaviviruses bud mainly into internal membranous structures (Golgi).

• ST. LOUIS ENCEPHALITIS VIRUS: It has been the major cause of arboviral-born encephalitis over the last three decades.

  • TRANSMISSION:

    • Urban cycle of man-mosquito-man.

    • Natural cycle of bird-mosquito-bird.

• JAPANESE ENCEPHALITIS VIRUS:

  • VACCINE: Vaccine available before travel to endemic area. Inactivated, purified vaccine given in three subcutaneous doses.

• YELLOW FEVER VIRUS:

  • TRANSMISSION: Monkey-insect-monkey cycle, with occasional transmission to man.

    • Can also have an Urban man-mosquito-man cycle.

  • MANIFESTATIONS: Hemorrhagic Fever with hepatitis. Yellow = jaundice.

  • VACCINE: Live attenuated vaccine is available, recommended before travel.

• DENGUE FEVER VIRUS:

  • TRANSMISSION: Can have an Urban man-mosquito-man cycle.

  • SUBTYPES: Divided into Types 1-4.

  • MANIFESTATIONS: Dengue fever is the most common and (usually) least serious arboviral infection.

    • Fever-arthralgia-rash: Common symptoms of viremia -- Fever, chills, headache, myalgia, rash, nausea, vomiting.

    • Dengue Shock Syndrome: A form of hemorrhagic fever. Thought to be a hypersensitivity reaction with reinfection of a second subtype of Dengue virus.

      • Mechanism involves immune enhancement and extended tissue tropism -- i.e. infecting cells which are not normally infected.

      • Macrophages get infected by the virus whereas they normally are not infected.

• HEPATITIS-C:

  • TRANSMISSION: Primary mode of transmission is parenteral route (blood). In the past has been associated with transfusions.

  • MANIFESTATIONS: Most often leads to chronic hepatitis.

Category: Microbiology Notes