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
West Nile Virus Outbreaks
–
1951-1954, 1957, 2000
 France –
1962, 2000
 South Africa –1974
 Romania –
1996
 Italy –
1997
 Russia –
1999
 U. S. A. –
1999-2002
 Israel
Spread of West Nile Virus in the U.S.
7/30/02
1999
2000
2001
2002
Humans
WNV Case-Patient Demographics & Mortality
United States, 1999-2001
1999 - 2000
83
2001
66
65
5 - 90
68
19 - 90
Males
54%
65%
CFR
11%
14%
Number
Age (yr)
median
range
Date of Symptom Onset, West Nile Virus
United States, 1999-2001
2001
2000
1999
Number of cases
30
25
20
15
10
5
0
Week ending
Clinical Epidemiology
 Incubation
 20%
1
period 3 - 14 days
develop “West Nile fever”
in 150 develop meningoencephalitis
– Advanced age primary risk factor for
severe neurological disease and death
West Nile Fever: Classic Clinical Description
• Mild flu-like illness of sudden onset
• Duration 3 - 6 days
• Fever, swollen lymph nodes, headache,
abdominal pain, vomiting, rash, conjunctivitis,
eye pain, anorexia
• Symptoms of West Nile fever in contemporary
outbreaks not fully studied
Symptoms of Hospitalized Patients with
West Nile Virus
Fever
Weakness
Nausea
Vomiting
Headache
Change in mental status
Diarrhea
Rash
Swollen Lymph Nodes
90%
56%
53%
51%
47%
46%
27%
19%
2%
West Nile Virus
Mosquitoes
 Usually
Culex Genus
Pipiens or Restuans species are most common
carriers in this area
 Only the females bite
 Males feed on nectar
 Normally only ¼ “ long
 “Huge” mosquitoes are really crane flies

Mosquito Lifecycle

Egg raft
 Up to 300 eggs
 Hatch within 3 days

Larvae
 Wigglers

Pupae
 Tumblers
 Become adults within a few days

Adult
 Males Live one week
 Females live one month
 Flight range up to ½ mile
West Nile Virus
Transmission Cycle
 Mosquito
infects bird while taking a
“blood meal”
 Other mosquitoes pick up the virus
from the infected bird
 Humans and animals (horses) get
the virus from infected mosquitoes
 ONLY MOSQUITOES CAN SPREAD
WEST NILE VIRUS
West Nile Virus
Transmission Cycle
Dead Birds
 Virus
found in over 100 species of
birds
 Predominant species:
– Hawks
– Owls
– Crows
– Blue jays
 Call
1-877-PA HEALTH
 Only five birds are tested weekly
Hawks





Length: 18 inches
Wingspan: 48 inches
Short, dark, hooked
beak
Large, broad-winged,
broad-tailed hawk
Immatures have notably
narrower wings and tail,
and appear slimmer
Dark patagial mark on
underwing, present on
all ages and races, is
unique
Owls






Length: 8 inches
Wingspan: 22 inches
Small, nocturnal,
predatory bird
Large, rounded head
with ear tufts
Yellow eyes
Dense streaking on
underparts with finer
barring
Some birds have rusty
plumage, others dark
gray
Bluejays








Length: 10 inches
Black sturdy bill
Blue crest and
upperparts
Black eyeline and
breastband
Grayish-white throat and
underparts
Bright blue wings with
black bars and white
patches
Long blue tail with black
bars and white corners
Dark legs
Crows




Length: 17 inches
Entirely black
plumage
Squared-off tail
Very common in
urban and
agricultural areas
Washington County
WNV Program
 Surveillance
of known problem areas
 Surveillance of citizen complaints
 Samples sent to PA DOH for analysis
 Positive areas are treated
 Heavily infested areas are treated
 Purpose is not to eradicate the
mosquito population
West Nile Virus Surveillance
Dead Bird Reports
Dead Bird Testing
Live Bird Testing
Mosquito Testing
Equine Cases
Human Cases
Gravid Trap
 Lactalbumin
water is an attractant
 Draws mosquitoes into trap from the
bottom
 Easier to use
 More effective than light traps
Gravid Trap
Light Trap
Carbon dioxide and
light used as
attractants
 Color
 Collection bin
hangs from the
bottom

West Nile Virus – Human Cases
PREVENTION
Mosquito
Control
Personal
Protection
Personal Protection
Clothing
Avoid black and white
Wear long sleeves
Wear long pants
Personal Protection
Avoidance
•Home needs to be “Bug Tight”
•Stay indoors at dusk and dawn
•Use insecticides at dusk and dawn
•Use white incandescent lights
•Vitamin “B”, “Bug Zappers”, and
“ultrasonic” devices are ineffective
Personal Protection
•Repellant
Deet
Bite Blocker
Avon Skin So Soft
•Read and understand label
directions
•Apply lightly to skin and clothing
Mosquito Control
Mosquito Control
Habitat Elimination
Adulticiding
Larviciding
Adulticiding
 Malathion
 Organophosphate
 Applied
in “Ultra Low Volume”
 Can be toxic to humans
 Originally,
only done for positive test
areas
 Will be done for heavy infestations
Larviciding
Preferred method of control
 Microbial – BTI, CG, and WDG




Methoprene



Growth regulating hormone
Applied to ditches, ponds, marshes
Temephos



Naturally occurring bacteria
Non-toxic to humans and animals
Organophosphate pesticide
Can pose a human health hazard
Monomolecular films & Oils


Causes larvae and pupae to drown
Poses little risk to humans, wildlife, and the
environment
Natural Predators
 Purple
Martins
 Bats
 Mosquito
fish
 Other breeds of mosquitoes
Mosquitoes
of choice
are not the meal
Habitat
Catch basins
 Clogged bodies of
water
 Construction
depressions
 Flooded Flower pots
 Public dumps
 Birdbaths
 Unfiltered swimming
pools

Cemetery urns
 Clogged rain gutters
 Boats
 Rain barrels
 Hoof prints
 Swamps
 Tree holes
 Tin cans
 Tires

Control Breeding Sites
 Turn
over pools and wheel barrows
 Dispose of things that can hold water
i.e. tires, tin cans, broken toys, etc.
 Drill holes in permanent containers
 Clean clogged roof gutters
 Empty accumulated water from boats
 Keep outdoor water fresh
 Landscape your property
 Keep grass cut and weeds pulled
QUESTIONS?
THANK YOU!