West Nile Virus: Background and Ecology

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West Nile Virus Background and Ecology
West Nile Virus Background and Ecology

• First isolated in West Nile district, Uganda,
  1937
• Commonly found in humans and birds and other
  vertebrates in Africa, Eastern Europe, West Asia,
  and the Middle East, but has not previously been
  documented in the Western Hemisphere
• Basic transmission cycle involves mosquitoes
  feeding on birds infected with the West Nile
  virus
• Infected mosquitoes then transmit West Nile virus
  to humans and animals when taking a blood meal

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The Japanese Encephalitis Serocomplexof the
Family Flaviviridae
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West Nile Virus Outbreaks

• Israel 1951-1954, 1957, 2000
• France 1962, 2000
• South Africa 1974
• Romania 1996
• Italy 1997
• Russia 1999
• United States 1999-2002

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Spread of West Nile Virus in the U.S. 7/30/02
1999
2000
2001
Humans
2002
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1999 - 2002 Verified WNV Surveillance Results
Reported to ArboNet
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WNV Case-Patient Demographics Mortality United
States, 1999-2001
WNV Case-Patient Demographics Mortality United
States, 1999-2001
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Date of Symptom Onset, West Nile VirusUnited
States, 1999-2001
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1999 and 2000 Serosurvey Results
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Clinical Epidemiology

• Incubation period 3 - 14 days
• 20 develop West Nile fever
• 1 in 150 develop meningoencephalitis
• Advanced age primary risk factor for severe
  neurological disease and death

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West Nile Fever Classic Clinical Description
West Nile Fever Classic Clinical Description

• Mild dengue-like illness of sudden onset
• Duration 3 - 6 days
• Fever, lymphadenopathy, headache, abdominal pain,
  vomiting, rash, conjunctivitis, eye pain,
  anorexia
• Symptoms of West Nile fever in contemporary
  outbreaks not fully studied

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Symptoms of Hospitalized Patients withWest Nile
Virus, New York City, 1999
90
Fever
56
Weakness
53
Nausea
51
Vomiting
47
Headache
46
Change in mental status
27
Diarrhea
19
Rash
2
Lymphadenopathy
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Neurological Presentations of West Nile Virus
Infection

• New York City 1999
• Encephalitis/meningoencephalitis 62
• Meningitis 32
• Complete flaccid paralysis 10
• Confused with Guillain-Barre syndrome
• EMG and nerve conduction velocity studies
  indicating both axonal and demyelinating lesions,
  with axonal lesions most prominent
• Previous series
• Ataxia, extrapyramidal signs, cranial nerve
  abnormalities, myelitis, optic neuritis, seizures

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Neurological Presentations of West Nile Virus
Infection

• Preliminary data 2002
• Complaints of weakness out of proportion to
  evidence on physical exam
• Myoclonus nearly a universal finding
• Some patients have Parkinsonian-like signs

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Outcome of West Nile Virus Infection among
Hospitalized Patients

• At discharge (NY and NJ, 2000)
• More than half did not return to functional level
• Only one-third fully ambulatory
• At one year (NYC 1999 patients)
• Fatigue 67, memory loss 50, difficulty walking
  49, muscle weakness 44, depression 38

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Predictors of Death among West Nile
Virus-Infected Patients

• Change in level of consciousness
• Encephalitis with severe muscle weakness
• Advanced age
• Possibly diabetes mellitus or immunosuppression

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Treatment

• Supportive treatment
• About 25 require ICU care 10 mechanical
  ventilation
• Ribavirin and interferon-a2b
• In-vitro activity in high doses
• One reported comatose patient did not improve
• Worse outcome with ribavirin in open-label trial
  in Israel unclear patient selection

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Risk of West Nile Virus Transmission Through
Blood Transfusion

• Concern most WNV infections have no or only mild
  symptoms, and transient viremia occurs after
  infection
• Transfusion-transmission of WNV or other related
  flaviviruses not reported, but plausible
• Mathematical modeling estimated risk of
  transfusion-transmission was 2 in 10,000 during
  NYC outbreak (Transfusion, Aug 2002)
• WNV should be considered in persons who develop
  unexplained fever, meningitis, or encephalitis
  after transfusion

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Laboratory Findings from WNV Outbreaks in New
York and Israel

• Total leukocyte count normal or slightly elevated
• Hyponatremia occasionally in patients with
  encephalitis
• CSF
• Leukocytes 0 - 1782 cells/mm3, mostly lymphocytes
• Protein universally elevated 51 - 899 mg/dL
• Glucose normal
• CT brain no evidence of acute disease
• MRI in one-third showed enhancement of
  leptomeninges, periventricular areas, or both