West Nile Virus: Surveillance and Clinical Issues

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West Nile Virus Surveillance and Clinical Issues

• Anne Kjemtrup, DVM, MPVM, Ph.D.
• California Department of Public Health
• Vector-Borne Disease Section

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Sequence of WNV detection events in California
relative to human case onset, 2008
Number of human cases
Disease Week of Onset
Jan
Feb
Mar
Jun
Jul
Sep
Oct
Nov
Dec
Apr
May
Aug
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The Clinical Pyramid Picture
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West Nile fever

• Typical clinical manifestations
• Fever
• Headache
• Fatigue
• Muscle weakness
• Muscle aches
• Skin rash on trunk of body
• Anorexia
• Duration of illness3 6 days
• Outcome in general, excellent w/o specific
  treatment

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Watson JT et al. Ann Intern Med 2004 141360-5
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West Nile Neuroinvasive Disease

• Aseptic Meningitis (25-35 WNND cases)
• Fever, headache, malaise, muscle weakness
• Nausea, vomiting, stiff neck, myalgia, cranial
  nerve palsies
• Outcome generally good
• Encephalitis (60 - 70 WNND cases)
• Alternation of consciousness (lethargy ? coma),
  tremors, weakness, brainstem/cranial nerve
  deficits, cerebellar signs/symptoms
• Outcome variable. Fatality-case ratio up to 15
  increases with advanced age. Potential of
  long-term neurologic deficits in some patients.
• WNV Poliomyelitis- a flaccid paralysis syndrome
  (uncommon).
• Acute onset of asymmetric limb weakness or
  paralysis in absence of sensory loss
• Can occur in the absence of fever, headache, or
  other WNV-associated signs.

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Preliminary Univariate Analysis (2006)Risk
Factors for Developing WNND vs. WN Fever
Characteristic WNF n () WNND n () OR 95 CI
Diabetes 9 (7) 12 (20) 3.60 1.43 - 9.10
Age (gt64 years) 24 (13) 25 (31) 2.96 1.56 5.60
Hypertension 36 (26) 26 (44) 2.25 1.19 4.27
Gender (male) 114 (62) 56 (69) 1.36 0.78 - 2.37

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WNV Outcome Picture

• Risk factors for severe disease include
  increasing age, immunosuppression, diabetes, and
  hypertension.
• Though risk of WNV infection higher in children
  than adults, risk of WNND in children lower than
  adults.
• Most WNF patients recover in first few months.
  For some, problems may linger (subclinical
  encephalitis? Other risk factors?). (Encephalitis
  Outcome Study Shilpa Gavali-Jani, VRDL Carson et
  al., CID 2006 Haaland et al EID 2006)

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Were pretty sure its the West Nile virus...
Diagnosis
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West Nile virus Laboratory Testing

• West Nile virus (WNV) testing within the regional
  public health laboratory network is recommended
  on individuals with the following
• A. Encephalitis
• B. Aseptic meningitis (Note Consider enterovirus
  for individuals 18 years of age)
• C. Acute flaccid paralysis atypical
  Guillain-Barré Syndrome transverse myelitis or
• D. Febrile illness
• Illness compatible with West Nile fever and
  lasting 7 days
• Must be seen by a health care provider

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West Nile virus Laboratory Testing

• IgM antibody-capture ELISA for serum collected
  within 8-14 days of illness onset or CSF
  collected within 8 days of illness onset
• IgM in CSF strong suggests CNS infection since
  IgM does not cross blood-brain barrier.
• Plaque-reduction neutralization test (PRNT) used
  to distinguish false-positive results or cross
  reactivity with other arboviruses

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West Nile virus Why test?

• Differentiate from other conditions (enterovirus,
  other arboviral diseases)
• Forewarn of further complications (e.g. flaccid
  paralysis)
• Help with treating/dealing with unexplained
  lingering health issues. Early testing in the
  febrile phase will help determine acute
  infection.
• A febrile positive WNV patient may have older
  family members at risk for serious WNV disease
  (since often acquired near the place of
  residence) - in effect functioning as a local
  sentinel.
• Mosquito control and public health agencies can
  institute proper control measures to save others
  from serious disease.
• Testing by local health departments is FREE!

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Treatment

• Supportive Care
• Experimental Clinical trial of interferon for
  meningoencephalitis patients underway.

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For More Informationwww.westnile.ca.gov
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Mt. Luku Islandmountain
Murchison Falls

• Where it all began
• West Nile Region of Uganda

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• www.game-reserve.com/uganda_murchison_falls.html
• www.min.uni-kiel.de/.../ugandaweb/wnile.html