UIC School of Public Health
October Dean‟s Forum:
West Nile Virus Update
Dan Tessier Doug Passaro
What is West Nile Virus
(WNV)?
Arbovirus (arthropod-borne virus)
Flavivirus family: Yellow Fever, Dengue,
St. Louis Encephalitis Viruses
Transmitted among various species of birds
primarily through mosquitoes (Culex and
others)
1937: Isolated from blood of woman in
West Nile district, Uganda
What is West Nile Virus
(WNV)?
1957: cause of encephalitis (spinal cord
and brain infection) in elderly patients
during outbreak in Israel.
1960’s: Horse infections Egypt & France
Currently endemic in Africa, the Middle
East, and Southwestern Asia
Human/Equine Epidemics
Israel –1951-54, 57 Congo – 1998
France –1962 Italy – 1998
South Africa –1974 Russia – 1999
Algeria –1994 USA – 1999-02
Romania –1996-97 Israel – 2000
Morocco –1996 France – 2000
A New Disease? NYC, 1999
WNV
• Massive
die-off of
local birds
• Sudden, Bird
unusual Disease
cluster of Birds Humans
same as confirmed confirmed
encephalitis Human
(SLE?) with WNV with WNV
Disease?
August 1999 September 1999
Lanciotti et al.
Science 286:2333-337
Lanciotti et al.
Science 286:2333-337
North Queens
Serosurvey Area
Lessons from NYC Outbreak
Serosurvey ~6 weeks after outbreak peak:
2.6% infected with WNV
0.5% non-specific West Nile fever
~1 of 5 infected persons
0.02% developed West Nile Encephalitis
~1 of 140 infected persons
RISK FACTOR: spending time outdoors near
dawn and dusk
PROTECTIVE: using insect repellent
62
1
14
2000
6
NYC, 2001
= WNV+
dead bird
= Forest
preserve
= WNV+
dead bird
= Forest
preserve
National, through 2001
National, through 2002
National, through 2002
WNV: Spectrum of Illness
Most infections clinically silent
Milder illness: non-specific flu-like symptoms
Prominent myalgias, backaches, arthralgias
Occasional rash (20%), lymph node swelling
Severe illness:
Aseptic meningitis: Fever, headache, stiff neck
Encephalitis: Mental changes coma, death
Myelitis: Polio-like, fever with flaccid paralysis
Elderly/immunocompromised at high risk
Diabetics, Hypertensives
Laboratory Findings
Total WBC usually normal or
Low WBC and anemia also occurrs
Serum sodium sometimes
Examination of cerebrospinal fluid (CSF)
typical for a viral meningoencephalitis
Lymphocytes in CSF
Protein , Glucose normal
Radiographic Imaging
CAT scans mostly normal
Magnetic resonance imaging (MRI)
inflammation of leptomeninges, the
periventricular areas, or both
Diagnosis
West Nile virus or viral RNA in serum,
cerebrospinal fluid, or other tissue.
Isolation from culture (insensitive; 3-7 days)
RNA detection/PCR (insensitive)
West Nile virus protein can be identified in
brain specimens by immunohistochemical
staining (IHC)
Diagnosis
IgM Antibody-Capture Enzyme-Linked
ImmunoSorbent Assay, (MAC-ELISA; 24-36
hrs)
IgM in cerebrospinal fluid confirmatory
IgM in serum not specific
IgG: (PFNR assay) acute & convalescent
serum
Outcomes
Case-fatality rates (hospitalized):
4% Romania,
12% New York,
14% Israel,
Similar (~12%) among Northeast US patients
2000/2001, and IL patients 2002
50 confirmed human cases followed, 5 deaths
Other clusters: Birmingham AB, and Mexico
1975 SLE Outbreak
2,131 documented cases (30 states & D.C.)
578 (27% of total) in Illinois
67 (66%) Illinois counties reported cases
>50% in metropolitan Chicago
Newspaper Headlines
“Sleeping sickness kills four”
“Encephalitis at „epidemic‟ stage in Cook County”
“City, county crews join mosquito war”
Peak Sept 1-2 (68 cases)
1st Chicago case
confirmed
2001: “Déjà vu all over again.”
2001 Illinois dead bird WNV
surveillance 8/02 - 10/02
Crows, blue jays, raptors
138/284 (49%) tested positive
Culex mosquito pools tested in
Cook County
20/81 pools positive
Horses - 2 positive of 9 symptomatic
Number of positives Number of positives
A A
pr pr
50
100
150
200
250
300
0
50
100
150
200
250
300
0
2 2
M 8 M 8
ay ay
19 19
Ju Ju
n n
Ju 9 Ju 9
n n
3 3
Ju 0 Ju 0
l2 l2
A 1 A 1
ug ug
11 11
Week
Week
1- 1-
Se Se
22 p 22 p
-S -S
e e
13 p 13 p
-O -O
ct ct
Horses
Dead birds
Mosquito Pools
Humans-AM/ENC
Preliminary Positive WNV Test Results, Illinois,2002
Differences Between
SLE and WNV
WNV better adapted to northern
temperatures: Ontario; grows 2X
faster than SLE
WNV may produce higher viremia
in birds
WNV kills many birds and horses
WNV identified in many non Culex
species
Risk of WNV Illness
# of mosquitos X
Prevalence in mosquitos (0.5-5%) X
# of bites per mosquito‟s life X
Risk that a bite transmits wnv X
Risk of severe illness if infected (1/150) =
~1/30,000 bites??