West Nile VirusMira J. LeslieState Public Health VeterinarianWashington State Department of Health Epidemiology of the North American outbreak

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

Do you remember when?Encephalitis- NYC 1999SLE cases reported in Queens

Active ph surveillance identified additional cases of encephalitis

Causative agent unknown in many cases

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

Initial outbreak

West Nile Virus in NYC

- 2000 Rushton Young

1999: 62 human cases 7 deaths

West Nile virus: history

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

Epidemic/Epizootic West Nile Virus

1937 first case identification in Uganda

1950-75

1994 - 2001

WorldWNV.ppt

West Nile Virus- the organism

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

2000-2004

History of Arbovirus Outbreaks in North AmericaCDC data

YearVirus# neuro cases(approx)# deaths(approx)CFR1933SLE140028020%1975SLE20001708%2003WN28662649%

JAMA August 18, 1945

Human Encephalitis in the Yakima Valley, Washington, 1942

1942 was fourth year of summer outbreaks peak in August28 cases Western Equine and St. Louis encephalitis types, 2 fatal (7.2%)44 strains of WEE and 5 strains of SLE virus isolated from mosquitoes

JAMA August 18, 1945

Distribution of WNV activity, 1999-200320002001200220031999

States with WNV (46 + DC)

WNV has also been spreading westward across Canada.

States with WNV 4

States with WNV (44 + DC)

WNV has also been spreading westward across Canada.

States with WNV (12 + DC)

States with WNV (27 + DC)

West Nile Virus, Human Cases2003 epicenter2002 epicenter

Reported WNV Disease Cases in Humans,United States, 1999-2003

Year# CasesOnset Date Range

1999622 AUG 24 SEP

20002120 JUL 27 SEP

20016613 JUL 7 DEC

20024,15619 MAY 19 DEC

20039,86228 MAR 3 DEC

West Nile Virus in the US How did it get here?Possible Pathways of Introduction

Infected human hostHuman-transported vertebrate hostLegalIllegalHuman-transported vector(s)Storm-transported vertebrate host (bird)Intentional introduction (terrorist event)-not

West Nile virus transmission cycle

Incidental hostsVector mosquitoReservoir host -birds

Mosquitoes: WNV vectors37 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.

Birds: WNV reservoir hostsMore 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.

Learning about avian reservoirs of WNVMost 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

Dead birds as early indicators of WNV activity

Timing of WNV-Positive Dead Bird Collection and Human WNV Case Onset, By County, United States, 2003*

* Reported as of 1/29/2004

Counties Reporting Bird and Human Surveillance (n=725)

Human illness before bird collection (n=188, (26%))

Bird collection before human illness (n=537, (74%))

* Reported as of 1/20/2004

Regional Differences in WNV Surveillance, 2003*

RegionArea(hundred mi2)(A)# dead birdstested(B)Ratio(B/A)

East3,40011,8143.5

Central6,6105,0310.8

West9,3015,6020.6

HorsesIn 2002, an intense epizootic of equine WNV infection occurred (> 14,500 reported cases).

Two new vaccines are licensed for use in horses.

Horses do not develop sufficient viremia to amplify the virus.

U.S. Counties Reporting Equine WNV Disease Cases, 2002*

12,038 cases1,678 counties39 states

In addition to humans,bugs, birds, and horsesBatsSquirrels, ChipmunkSkunk; RabbitGoat, sheep, llama, deerZoo animalsHarbor seal(Non-human) PrimatesFarmed Alligators.

West Nile infection, U.S., 2003Human illness: 9862 Fatality: 264

Corvid (crow, jay): 10,200 Other bird: 1866

Mosquito pools: 8384Equine: 5145Sentinel flocks: 1956Other animals: 48Canine: 37 Squirrel: 20 Feline: 1

West Nile virusWNV activity, U.S.Jan 1- June 1, 2004:

CasesStatesHumans22Birds13315Mosq. pools355Equine73Flocks553

WNV Seasonality

Human WNV Disease Cases, by Week of Onset, Northern vs. Southern United States, 2003*

* Reported as of 1/20/2004

West Nile virus Surveillance/Response: PartnershipsPublic Health agenciesHealth care providers, laboratoriesBlood banksWildlife agencies and orgsZoosEntomologists, ecologists, cartographers Veterinarians, veterinary laboratoriesUniversitiesThe public, the media, and others .

Arbonet, CDCTracking the virus in real-timeSecure web-based reporting

Compiles data on humans, birds, mammals, sentinel flocks, mosquitoes, etc.Humans recorded by syndrome and status

Real-time mapping-USGSHuman cases, 2004

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

Who is this human?QUESTIONS?

West Nile virus-important issuesLaboratory testingPublic health labs,commercial labsVeterinary labsTest development

CommunicationsHealth Alert messagingPrevention messagingStrategies and target audiences

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