Six Years of West Nile Virus in Tarrant County, Texas

Tarrant County Public HealthTarrant County Public HealthNorth Texas Regional LaboratoryNorth Texas Regional Laboratory

Six Years of West Nile Virus in Six Years of West Nile Virus in Tarrant County, TexasTarrant County, Texas

Guy C. Dixon, Ph.D.Guy C. Dixon, Ph.D.


West Nile Virus BackgroundWest Nile Virus Background


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• Family: Family: FlaviviridaeFlaviviridae

• Genus: FlavivirusGenus: Flavivirus

• Over seventy identified viruses in the Over seventy identified viruses in the genus and includes the medically genus and includes the medically important arthropod borne viruses important arthropod borne viruses (arboviruses) such as Dengue, Yellow (arboviruses) such as Dengue, Yellow fever, Japanese encephalitis and St. Louis fever, Japanese encephalitis and St. Louis encephalitisencephalitis


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• Flaviviruses are 40 to 50 nm in diameter Flaviviruses are 40 to 50 nm in diameter and have a spherical nucleocapsid and have a spherical nucleocapsid surrounded by a lipid bilayer envelopesurrounded by a lipid bilayer envelope

• The flavivirus genome is a positive sense, The flavivirus genome is a positive sense, single-stranded RNA genome of about single-stranded RNA genome of about 11,000 nucleotides11,000 nucleotides

• The envelope (E) proteins mediate host The envelope (E) proteins mediate host receptor binding and are thus a major receptor binding and are thus a major factor in virus virulencefactor in virus virulence


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• WNV was first isolated from a human WNV was first isolated from a human patient with a fever in Uganda in 1937patient with a fever in Uganda in 1937

• WNV host range is broad and includes WNV host range is broad and includes birds, horses and humansbirds, horses and humans

• Historically, WNV was found in Europe, Historically, WNV was found in Europe, Africa, the Middle East and AsiaAfrica, the Middle East and Asia

• In 1999, WNV emerged in North America In 1999, WNV emerged in North America and arrived in Texas in 2002and arrived in Texas in 2002


66


• WNV is typically WNV is typically transmitted by transmitted by CulexCulex mosquitoes with wild mosquitoes with wild birds serving as the birds serving as the viremic hostsviremic hosts

• Humans, horses, and Humans, horses, and dogs are incidental hosts dogs are incidental hosts and do not develop a and do not develop a significant enough significant enough viremia to perpetuate viremia to perpetuate transmissiontransmission


West Nile Virus SurveillanceWest Nile Virus Surveillance

20022002


88



99



1010


• June 2002: WNV detected in two blue jays June 2002: WNV detected in two blue jays in Harris Countyin Harris County

• June 2002: First WNV detection in a June 2002: First WNV detection in a mosquito in Tarrant Countymosquito in Tarrant County

• July 2002: WNV detected in a bird from July 2002: WNV detected in a bird from Tarrant CountyTarrant County

• July 2002: First case of human WNV in July 2002: First case of human WNV in Texas is detected in man from Orange Texas is detected in man from Orange CountyCounty


1111


• August 2002: First case of human WNV August 2002: First case of human WNV detected in Tarrant Countydetected in Tarrant County

• September 2002: First case of equine September 2002: First case of equine WNV detected in Tarrant CountyWNV detected in Tarrant County


Tarrant County WNV ProjectTarrant County WNV Project

2003 - 20082003 - 2008


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• In 2003, Tarrant County Public Health In 2003, Tarrant County Public Health implemented a comprehensive WNV implemented a comprehensive WNV surveillance project that included the surveillance project that included the collaborative efforts of the Epidemiology, collaborative efforts of the Epidemiology, Environmental Health, and Laboratory Environmental Health, and Laboratory divisions.divisions.

• Epidemiology received and tracked the Epidemiology received and tracked the human caseshuman cases


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Tarrant County WNV ProjectTarrant County WNV Project• Environmental Health coordinated the efforts of Environmental Health coordinated the efforts of

local municipalities to collect mosquito samples, local municipalities to collect mosquito samples, assisted with vector control activities, and assisted with vector control activities, and provided public educationprovided public education

• Laboratory staff performed RT-PCR testing of Laboratory staff performed RT-PCR testing of mosquito poolsmosquito pools

• The Public Information Office provided regular The Public Information Office provided regular updates to media outletsupdates to media outlets

• The local Public Health Authority and Public The local Public Health Authority and Public Health Director provided media interviews and Health Director provided media interviews and briefingsbriefings


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• Environmental Health Environmental Health purchased gravid purchased gravid traps to distribute to traps to distribute to local municipalities local municipalities with grant funds from with grant funds from Texas DSHSTexas DSHS

• The first training The first training session was held on session was held on March 27, 2003, for March 27, 2003, for participating local participating local municipalitiesmunicipalities


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• Around 29 cities Around 29 cities participated in the first participated in the first year of mosquito year of mosquito surveillancesurveillance

• 565 mosquito pools were 565 mosquito pools were submitted for testing with submitted for testing with WNV detected in 127 WNV detected in 127 pools pools

• 23 of the 29 participating 23 of the 29 participating cities had WNV positive cities had WNV positive mosquitoes detectedmosquitoes detected


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1818


• Environmental Health Environmental Health received the mosquito received the mosquito samples and sorted samples and sorted the frozen mosquitoes the frozen mosquitoes into tubes for testinginto tubes for testing

• Lab staff Lab staff homogenized the homogenized the mosquito samples mosquito samples prior to RNA prior to RNA extraction extraction


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• The laboratory then The laboratory then performed real-time performed real-time polymerase chain polymerase chain reaction using the Roche reaction using the Roche LightCyclerLightCycler

• West Nile and St. Louis West Nile and St. Louis encephalitis virus were encephalitis virus were eventually multiplexed so eventually multiplexed so that both results are that both results are available from a single available from a single reaction well or tubereaction well or tube


2020


• Environmental Health Environmental Health used GIS to map the used GIS to map the location of mosquito location of mosquito sampling sitessampling sites


2121



2222


• In 2004, the West Nile virus surveillance In 2004, the West Nile virus surveillance project received a Best Practice Award project received a Best Practice Award from the Texas Association of Countiesfrom the Texas Association of Counties

• Also in 2004, the Tarrant County WNV Also in 2004, the Tarrant County WNV project was recognized by NACCHO as a project was recognized by NACCHO as a Model Public Health PracticeModel Public Health Practice


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• In 2005, In 2005, Environmental Health Environmental Health added Mosquito Fish added Mosquito Fish ((Gambusia affinisGambusia affinis) as ) as an additional means an additional means of biological control of biological control available to available to participating citiesparticipating cities


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• After a large number After a large number of human cases and of human cases and deaths in 2006 the deaths in 2006 the public information public information office prepared office prepared several mini several mini brochures aimed at brochures aimed at reducing the risk of reducing the risk of exposure to WNVexposure to WNV


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Tarrant County WNV TrendsTarrant County WNV Trends

2002 - 20082002 - 2008


2727


565

445 478

378338

210

127

21 60 39 30 7

0

200

400

600

2003 2004 2005 2006 2007 2008

Year

WNV Mosquito Pool Data

WNV Positive Pools

Total Mosquito Pools


2828


5

22

5

23

53

2214

1 0 0 07

0 00

20

40

60

2002 2003 2004 2005 2006 2007 2008

Year

WNV Human Cases

Deaths Total Cases


Tarrant County WNV Tarrant County WNV Geographical InformationGeographical Information

2003 - 20082003 - 2008


3030

Tarrant County WNV GeographyTarrant County WNV Geography


3131



3232



3333



3434



3535



3636



3737



3838



3939



4040



4141



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ConclusionsConclusions

• The biology of the virus and its interactions The biology of the virus and its interactions with the host and the environment is very with the host and the environment is very complexcomplex

• The Northeast quadrant of Tarrant County The Northeast quadrant of Tarrant County appears to consistently have more positive appears to consistently have more positive mosquitoes and more human cases mosquitoes and more human cases appear in the eastern half of the countyappear in the eastern half of the county


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Future OpportunitiesFuture Opportunities

• Research utilizing additional geographic and Research utilizing additional geographic and climatological information to better understand climatological information to better understand the ecology of the vector and host interactionthe ecology of the vector and host interaction

• Research using the mosquito sample bank to Research using the mosquito sample bank to explore genetic changes in virulence factorsexplore genetic changes in virulence factors

• Assess the role of sampling bias in trap locations Assess the role of sampling bias in trap locations and the relevance to positive trap locationsand the relevance to positive trap locations


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AcknowledgementsAcknowledgements

• Michelle Markham, Environmental Health - Michelle Markham, Environmental Health - GISGIS

• Kaylene Ryza, Environmental HealthKaylene Ryza, Environmental Health

• Dr. Anita Kurian, EpidemiologyDr. Anita Kurian, Epidemiology

• Vanassa Joseph, Public Information OfficeVanassa Joseph, Public Information Office

• Jason Nagati, North Texas Regional Jason Nagati, North Texas Regional LaboratoryLaboratory

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Six Years of West Nile Virus in Tarrant County, Texas

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