West%20Nile%20Virus

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West Nile Virus
Epidemiology of the North American outbreak

• Mira J. Leslie
• State Public Health Veterinarian
• Washington State Department of Health

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Learning Objective

• West Nile virus is established in North America.
  The magnitude of the ongoing WNV outbreak is
  extraordinary and our knowledge is incomplete.
• Definitions
• Arbovirus arthropod-borne virus
  Epizootic epidemic in animals

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Do you remember when?Encephalitis- NYC 1999

• SLE cases reported in Queens
• Active ph surveillance identified additional
  cases of encephalitis
• Causative agent unknown in many cases

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Bronx Zoo

• Zoo collection birds and birds in community
  (crows) dying.
• Veterinary pathologist pursued testing.
• West Nile virus isolated for the first time in
  Western Hemisphere.

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Initial outbreak
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West Nile virus history

• June 10, 323BC Alexander the Great died in
  Babylon. (www.cdc.gov/ncidod/EID/vol9no12/03-0288.
  htm)

• 1937 First identified (human illness) West Nile
  district of Uganda.
• 1937- 1990s Mild disease/ meningoencephalitis
  Middle East and Africa
• 1996 1999 Severe neurologic disease in
  Romania, Israel, Russia

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West Nile Virus- the organism
2000-2004
Davis CT, Beasley DWC, Guzman H, Raj P, DAnton
M, Novak RJ, et al. Genetic variation among
temporally and geographically distinct West Nile
virus isolates, United States, 2001, 2002. Emerg
Infect Dis 2003 Nov
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History of Arbovirus Outbreaks in North America
Year Virus neuro cases (approx) deaths (approx) CFR
1933 SLE 1400 280 20
1975 SLE 2000 170 8
2003 WN 2866 264 9
CDC data
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Distribution of WNV activity, 1999-2003
1999
2002
2000
2003
2001
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West Nile Virus, Human Cases
2002 epicenter
2003 epicenter
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West Nile Virus in the US How did it get
here?Possible Pathways of Introduction

• Infected human host
• Human-transported vertebrate host
• Legal
• Illegal
• Human-transported vector(s)
• Storm-transported vertebrate host (bird)
• Intentional introduction (terrorist event)-not

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West Nile virus transmission cycle
Vector mosquito
Incidental hosts
Reservoir host -birds
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Mosquitoes WNV vectors

• 37 species of native mosquitoes have tested
  positive in the U.S. 1999-2003.
• Some mosquitoes are more competent vectors than
  others. Environmental factors including climate
  play a role.
• Culex species including Culex tarsalis in the
  west are principal arbovirus vectors.

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Birds WNV reservoir hosts

• More than 225 species have been reported to be
  infected with WNV.
• Crows and jays predominate with a high fatality
  rate.
• Variable experiences Chicago vs. Connecticut.

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Learning about avian reservoirs of WNV

• Most competent reservoirs Blue jay, Common
  grackle, House finch, American crow, House
  sparrow
• Transmission routes mosquitoes, ingestion, and
  bird-bird contact.
• Some birds have persistent infection in many
  organs including skin.
• Komar et al. Experimental Infection of North
  American birds with the New York 99 strain of
  West Nile Virus, Emerg Infect Dis, Vol 9, No. 3,
  March 2003

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Dead birds as early indicators of WNV activity
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Horses

• In 2002, an intense epizootic of equine WNV
  infection occurred (gt 14,500 reported cases).
• Two new vaccines are licensed for use in horses.
• Horses do not develop sufficient viremia to
  amplify the virus.

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In addition to humans,bugs, birds, and horses

• Bats
• Squirrels, Chipmunk
• Skunk Rabbit
• Goat, sheep, llama, deer
• Zoo animals
• Harbor seal
• (Non-human) Primates
• Farmed Alligators.

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West Nile infection, U.S., 2003

• Human illness 9862 Fatality 264
• Corvid (crow, jay) 10,200 Other bird 1866
• Mosquito pools 8384
• Equine 5145
• Sentinel flocks 1956
• Other animals 48
• Canine 37 Squirrel 20 Feline 1

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West Nile virus
WNV activity, U.S. Jan 1- June 1, 2004
Cases States
Humans 2 2
Birds 133 15
Mosq. pools 35 5
Equine 7 3
Flocks 55 3
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WNV Seasonality
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West Nile virus Surveillance/Response
Partnerships

• Public Health agencies
• Health care providers, laboratories
• Blood banks
• Wildlife agencies and orgs
• Zoos
• Entomologists, ecologists, cartographers
• Veterinarians, veterinary laboratories
• Universities
• The public, the media, and others .

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Arbonet, CDC
Human cases, 2004

• Tracking the virus in real-time
• Secure web-based reporting
• Compiles data on humans, birds, mammals, sentinel
  flocks, mosquitoes, etc.
• Humans recorded by syndrome and status
• Real-time mapping-USGS

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Take home messages

• West Nile virus
• Established ecological niche in North America
• WNV outbreaks are unpredictable and our
  understanding is rudimentary.
• Management flexibility, coordination,
  partnerships
• Plan surge capacity.

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Who is this human?
QUESTIONS?
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West Nile virus-important issues

• Laboratory testing
• Public health labs,commercial labs
• Veterinary labs
• Test development
• Communications
• Health Alert messaging
• Prevention messaging
• Strategies and target audiences