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
.