Arboviruses

Arboviruses

 

Mosquito-borne arbovirus human diseases in North America cause a spectrum of disease from a mild viral syndrome to encephalitis.

Epidemiology

  • Incidence
    • Seasonal occurrence – April to October
  • Ages – extremes of age (old, young children) more likely to acquire severe disease
  • Transmission – bite of an insect

Organism

  • Bunyavirus – California encephalitis (CE)
    • La Crosse virus
      • Primarily in upper Mississippi River Valley
    • Jamestown Canyon virus
      • Upper midwestern states, including New York
    • Snowshoe Hare virus
      • Southern Canada
    • Mosquito species
      • Aedes triseriatus
  • Togavirus – Eastern equine encephalitis (EEE)
    • Present in the eastern half of U.S.
    • Mosquito species
      • Aedes, Coquillettidia and Culex
  • Flavivirus – St. Louis encephalitis
    • Present in nearly all of the U.S.
    • Mosquito species
      • Culex pipiens and Culex quinquefasciatus
        • Gulf Coast, Ohio and Mississippi Valley
      • Culex nigripalpus
        • Florida
      • Culex tarsalis
        • Western states
  • Togavirus – Western equine encephalitis (WEE)
    • Present in western and midwestern U.S.
    • Mosquito species
      • Culex tarsalis
  • Flavivirus – West Nile encephalitis (WNV)
    • Endemic in U.S. 
    • Mosquito species
      • Culex tarsalis

Clinical Presentation

  • Nonspecific illness consisting of:
    • Fever
    • Headache
    • Myalgias
    • Nausea, anorexia
    • Respiratory effects
    • Sore throat
  • Acute encephalitis
    • Lasts from a few days to months, with slow and sometimes incomplete recovery
    • Central nervous system involvement by arboviruses is very similar, with the exception of a more abrupt onset and shorter, more severe course found with Eastern equine encephalitis (EEE)
  • WNV
    • Acute flaccid paralysis can also occur in infections from West Nile virus
      • Attributed to peripheral demyelinization process or anterior myelitis
      • Meningoencephalitis occasionally complicates disease
      • Mortality ranges between 5–20% in affected patients
        • Up to 70% in affected patients older than 75 years

Diagnosis

  • Laboratory testing
    • Serum antibody testing
    • Viral isolation is seldom productive; the majority of human cases are diagnosed by serologic means
    • Significant change in sequentially timed specimens (acute and convalescent)
      • The best evidence for infection is a significant change (fourfold difference) in titer on 2 appropriately timed specimens done at the same laboratory
      • IgG usually negative in 1st 2 weeks
      • Single positive titer may represent past or current infection

Differential Diagnosis

  • Herpes encephalitis
  • Brain abscess
  • Viral meningitis
  • Bacterial meningitis
  • Brain tumor

Treatment

  • Supportive
  • Recovery may be prolonged

See Also