Mosquito-borne Zoonotic DiseasesMosquito-borne Zoonotic Diseases

CMED/EPI 526CMED/EPI 526Spring Quarter 2009Spring Quarter 2009

Anthony A Marfin, MD, MPH, MAAnthony A Marfin, MD, MPH, MAState EpidemiologistState Epidemiologist

Washington Department of HealthWashington Department of Health

April 15, 2009April 15, 2009University of WashingtonUniversity of WashingtonSchool of Public HealthSchool of Public Health

OverviewOverview

Zoonotic diseasesZoonotic diseases Definitions for vector-borne diseaseDefinitions for vector-borne disease Role of dipterans in vector-borne diseasesRole of dipterans in vector-borne diseases Japanese encephalitis serocomplexJapanese encephalitis serocomplex West Nile virus in North AmericaWest Nile virus in North America ArboNET surveillanceArboNET surveillance Mosquito-borne viruses in the blood supplyMosquito-borne viruses in the blood supply Disease controlDisease control

Zoonoses refer to diseases & infections Zoonoses refer to diseases & infections

naturally transmitted between vertebrate naturally transmitted between vertebrate

animals & man with or without an arthropod animals & man with or without an arthropod

intermediate (WHO, 1956)intermediate (WHO, 1956)

Why worry about vector-borne zoonoses?Why worry about vector-borne zoonoses?

Negative impact on commerce, travel, & economies (e.g., Rift Negative impact on commerce, travel, & economies (e.g., Rift

Valley fever, yellow fever)Valley fever, yellow fever)

Explosive debilitating outbreaks (e.g., yellow fever)Explosive debilitating outbreaks (e.g., yellow fever)

Developing nations, diseases of major public health significance Developing nations, diseases of major public health significance

(e.g., yellow fever, leishmaniasis)(e.g., yellow fever, leishmaniasis)

Preventable cause of human illness & deathPreventable cause of human illness & death

Human impact on environment can Human impact on environment can ↑ incidence (e.g., Japanese ↑ incidence (e.g., Japanese

encephalitis)encephalitis)

Mosquito-borne diseases that are Mosquito-borne diseases that are NOTNOT zoonotic zoonotic

Human is only vertebrate hostHuman is only vertebrate host Question if there is a “sylvatic” reservoir (e.g., non-Question if there is a “sylvatic” reservoir (e.g., non-

human primate species)human primate species) Examples include:Examples include:

• Malaria (protozoa) – Malaria (protozoa) – AnophelesAnopheles spp. spp.• Dengue (flavivirus) – Dengue (flavivirus) – Aedes aegyptiAedes aegypti, , Ae. albopictusAe. albopictus• Filiriasis (nematode) – Filiriasis (nematode) – Aedes aegyptiAedes aegypti• Chikungunya (alphavirus) – Chikungunya (alphavirus) – AedesAedes spp. spp.

Vector-Borne Infectious Diseases Vector-Borne Infectious Diseases Are More ComplexAre More Complex

Multiple interconnected & complex cyclesMultiple interconnected & complex cycles Pathogens adapted to vertebrate & Pathogens adapted to vertebrate &

invertebrate speciesinvertebrate species Vector interacts with host & agentVector interacts with host & agent Environment affects vector abundance & Environment affects vector abundance &

ability to transmit infectionability to transmit infection Multiple “host” speciesMultiple “host” species

Commonalities of Mosquito-Borne ZoonosesCommonalities of Mosquito-Borne Zoonoses

Humans rarely develop high titer of pathogens Humans rarely develop high titer of pathogens

in blood, CSF, or tissue (i.e., do not amplify*).in blood, CSF, or tissue (i.e., do not amplify*). Large outbreaks rare but can be explosiveLarge outbreaks rare but can be explosive Clinical cases usually severeClinical cases usually severe High mortalityHigh mortality Finding source of infection (“reservoir”) Finding source of infection (“reservoir”)

important for disease control (source reduction, important for disease control (source reduction,

depopulation)depopulation)

* Excluding yellow fever virus

Big Concepts & Definitions Unique to Big Concepts & Definitions Unique to Vector-Borne DiseasesVector-Borne Diseases

VectorVector – Does not itself cause disease. Instead, vectors – Does not itself cause disease. Instead, vectors transmit infection by moving pathogen from one host to transmit infection by moving pathogen from one host to another. Infection generally lasts vector’s life & can kill vector.another. Infection generally lasts vector’s life & can kill vector.

Bridging vectorBridging vector – Mosquito feeds on amplifying hosts & other – Mosquito feeds on amplifying hosts & other species causing infections in other hosts. “Bridge” between species causing infections in other hosts. “Bridge” between one cycle & another.one cycle & another.

“Bridging”

““Bridging” mosquito species in yellow feverBridging” mosquito species in yellow fever

Different Types of HostsDifferent Types of Hosts Amplifying hostAmplifying host – Host (usually vertebrate) in which – Host (usually vertebrate) in which

pathogens replicate to high levels (“titer”) leading to pathogens replicate to high levels (“titer”) leading to infection of more vectors. infection of more vectors.

Reservoir hostsReservoir hosts – Host that allows persistence of – Host that allows persistence of pathogen in nature when active transmission is not pathogen in nature when active transmission is not occurring. occurring.

““Dead-end” hostsDead-end” hosts – Host that does not develop high titer of – Host that does not develop high titer of pathogens. Consequently, will not infect vectors. AKA pathogens. Consequently, will not infect vectors. AKA “incidental hosts.”“incidental hosts.”

Definitive hostDefinitive host – Host in which pathogen reaches – Host in which pathogen reaches “maturity” (generally applies to protozoal & nematodal “maturity” (generally applies to protozoal & nematodal infections, not viral & bacterial infections)infections, not viral & bacterial infections)

““Advanced knowledge” of mosquito-borne Advanced knowledge” of mosquito-borne zoonotic diseaseszoonotic diseases

Extrinsic incubation periodExtrinsic incubation period – Time interval between – Time interval between

infection of vector & first transmission of pathogen by infection of vector & first transmission of pathogen by

vector.vector. Transovarial transmissionTransovarial transmission – Infection of eggs in – Infection of eggs in

ovaries of an infected female vector leading to new ovaries of an infected female vector leading to new

vector infection (“vertical transmission”)vector infection (“vertical transmission”) Mosquito Infection Rate (MIR)Mosquito Infection Rate (MIR) – Minimum estimate – Minimum estimate

of number of infected mosquitoes. Usually expressed of number of infected mosquitoes. Usually expressed

“per 1,000 mosquitoes.”“per 1,000 mosquitoes.”

““Over-wintering” mechanisms: Over-wintering” mechanisms: Viral persistence strategies Viral persistence strategies

Allow re-emergence of pathogen in next year Allow re-emergence of pathogen in next year despite unfavorable environmental conditions:despite unfavorable environmental conditions:• Reintroduction by migratory birdsReintroduction by migratory birds• Alternate arthropod vectorsAlternate arthropod vectors• Long-term survival of infected, dormant Long-term survival of infected, dormant

femalesfemales• Continued feeding & transmission year-aroundContinued feeding & transmission year-around• Chronic infection of vertebrate hostsChronic infection of vertebrate hosts• Transovarial transmissionTransovarial transmission

Factors that strongly affect pathogen Factors that strongly affect pathogen transmission by mosquitoestransmission by mosquitoes

Vector competence (ability to get infected & transmit)Vector competence (ability to get infected & transmit) Extrinsic incubation period (influenced by temperature)Extrinsic incubation period (influenced by temperature) Vector contact with critical hostVector contact with critical host Population indices of vector & hostsPopulation indices of vector & hosts Diurnal feeding habits of vectorDiurnal feeding habits of vector Pathogen replication in host (intrinsic incubation period)Pathogen replication in host (intrinsic incubation period) Host feeding preferencesHost feeding preferences Vector longevityVector longevity Precipitation – flooding & droughtPrecipitation – flooding & drought TemperatureTemperature Proximity of vectors/reservoirs to human populationsProximity of vectors/reservoirs to human populations

Dipteran Vectors of Human DiseaseDipteran Vectors of Human Disease

InsectsInsects ““True flies” (True flies” (di + ptera = “two wings”di + ptera = “two wings”)) ~240K ~240K sppspp of mosquitoes, sandflies, & black flies of mosquitoes, sandflies, & black flies MajorMajor insect orders for human health & economies insect orders for human health & economies Example: mosquitoes are primary vectors for Example: mosquitoes are primary vectors for

malaria, dengue, West Nile virus, yellow fever, & malaria, dengue, West Nile virus, yellow fever, &

multiple viruses causing encephalitismultiple viruses causing encephalitis

Mosquitoes, Sandflies, & Black fliesMosquitoes, Sandflies, & Black flies (Order (Order Diptera, Diptera, Suborder Suborder Nematocera)Nematocera)

““Primitive flies”Primitive flies” Not common house flyNot common house fly Aquatic larval forms (important for control)Aquatic larval forms (important for control) Vectors other than mosquitoes in suborder disease:Vectors other than mosquitoes in suborder disease:

• Black flies - Black flies - Onchocerca volvulusOnchocerca volvulus, nematode causing “river , nematode causing “river

blindness”blindness”

• Deer flies - Deer flies - Francisella tularensisFrancisella tularensis (tularemia, “rabbit fever”) (tularemia, “rabbit fever”)

• Phlebotamine sandflies – Toscana, SFF Sicily, & SFF Naples Phlebotamine sandflies – Toscana, SFF Sicily, & SFF Naples

viruses (viruses (Phlebovirus, Phlebovirus, Bunyaviridae)Bunyaviridae)

• Biting midges – Blue tongue virus (Biting midges – Blue tongue virus (OrbivirusOrbivirus, Reoviridae) & other , Reoviridae) & other

diseases of livestockdiseases of livestock

Infectious Disease Transmission:Infectious Disease Transmission:The “Epi-Triangle”The “Epi-Triangle”

Agent

EnvironmentHosts

MosquitoesSand fly

VirusesBacteriaProtozoansNematodes

“Vectors”

Vertebrates – Humans, horses, rodents, birds,& reptiles

Temperature, humidity, rainfall

Mosquitoes, Sandflies & Human DiseaseMosquitoes, Sandflies & Human Disease

Infectious Disease AgentsInfectious Disease Agents

Vector generaVector genera VirusVirus BacterialBacterial ProtozoalProtozoal

AnophelesAnopheles Onyong-n’yong (Alphavirus)Onyong-n’yong (Alphavirus) ????PlasmodiumPlasmodium

(Malaria)(Malaria)

Aedes / OchlerotatusAedes / Ochlerotatus

((StegomyiaStegomyia))

Yellow fever & DengueYellow fever & Dengue

(Flavivirus)(Flavivirus)

Chikungunya virusChikungunya virus

(Alphavirus)(Alphavirus)

Francisella tularensis*Francisella tularensis* ????

CulexCulex

West Nile virusWest Nile virus

Japanese encephalitis virusJapanese encephalitis virus

St. Louis encephalitis virusSt. Louis encephalitis virus

Francisella tularensis*Francisella tularensis* ????

Phelbotomus Phelbotomus & & LutzomyiaLutzomyiaSandfly FeverSandfly Fever

(Phlebovirus)(Phlebovirus)

BartonellaBartonella

(Oroya Fever)(Oroya Fever)

LeishmaniaLeishmania

(Kala Azar)(Kala Azar)

* Mechanical transfer of bacteria

Today’s DiscussionToday’s DiscussionInfectious Disease AgentsInfectious Disease Agents

Vector generaVector genera VirusVirus BacterialBacterial ProtozoalProtozoal

AnophelesAnopheles

Aedes/OchlerotatusAedes/Ochlerotatus

((StegomyiaStegomyia))

CulexCulexJapanese encephalitis Japanese encephalitis

serocomplexserocomplex

(Flaviviruses)(Flaviviruses)

PhelbotomusPhelbotomus

Japanese encephalitis serocomplex (14 viruses)Japanese encephalitis serocomplex (14 viruses)

Viruses that cause human encephalitisViruses that cause human encephalitis

• Japanese encephalitis virusJapanese encephalitis virus

• West Nile virus (Variant: Kunjin)West Nile virus (Variant: Kunjin)

• St. Louis encephalitis virusSt. Louis encephalitis virus

• Murray Valley encephalitis virus (Variant: Alfuy)Murray Valley encephalitis virus (Variant: Alfuy)

• Rocio virusRocio virus

• Ilheus virusIlheus virus

• Bussuquara virus (?)Bussuquara virus (?) Viruses that do not cause human encephalitis but may cause animal Viruses that do not cause human encephalitis but may cause animal

infections/illnessesinfections/illnesses

• Usutu (?), Cacipacore, Koutango, Yaounde, & Stratford virusesUsutu (?), Cacipacore, Koutango, Yaounde, & Stratford viruses

Commonality of Viruses in JE SerocomplexCommonality of Viruses in JE Serocomplex Human infections:Human infections:

• Most asymptomaticMost asymptomatic• Small number of rash-fever or febrile illness casesSmall number of rash-fever or febrile illness cases• < 1% associated with central nervous system illness< 1% associated with central nervous system illness• Very low virus titer in human serum & CSF:Very low virus titer in human serum & CSF:

No human-mosquito-human transmissionNo human-mosquito-human transmissionNo human-to-human transmissionNo human-to-human transmission

Surface Surface EEnvelope protein similar across complexnvelope protein similar across complex CulexCulex mosquitoes are vectors mosquitoes are vectors Amplifying hosts: BirdsAmplifying hosts: Birds

• JE & MVE – Ardeid birdsJE & MVE – Ardeid birdsIn JE, pigs also serve as amplifying hostsIn JE, pigs also serve as amplifying hosts

• WNV & SLE – Passerine birdsWNV & SLE – Passerine birds

“…“…West Nile virus was first West Nile virus was first isolated in 1937 from the isolated in 1937 from the

blood of a febrile woman in blood of a febrile woman in the West Nile province of the West Nile province of

Uganda…”Uganda…”

Endemic transmission with periodic epidemicsEndemic transmission with periodic epidemics First recorded epidemic: Israel, 1951-1954 & 1957First recorded epidemic: Israel, 1951-1954 & 1957 France – 1962France – 1962 South Africa – 1974 South Africa – 1974

• Massive (~75K), 1 case of encephalitis reportedMassive (~75K), 1 case of encephalitis reported Romania – 1996 Romania – 1996 Italy – 1998Italy – 1998 Russia – 1999Russia – 1999

• ↑ ↑ rate of WNND, ↑ case fatality raterate of WNND, ↑ case fatality rate

West Nile Virus EpidemicsWest Nile Virus Epidemics

West Nile VirusWest Nile VirusApproximate Geographic Range in 1998Approximate Geographic Range in 1998

1999: 11999: 1stst WNV outbreak in North America WNV outbreak in North America

New York City, June – October 1999New York City, June – October 1999 Initially, two separate investigationsInitially, two separate investigations

• Epizootic beginning June 1999Epizootic beginning June 1999• Epidemic beginning August 1999Epidemic beginning August 1999

Begins with the “astute clinician…”Begins with the “astute clinician…”• Veterinary & medical cliniciansVeterinary & medical clinicians• Tracey McNamara, Bronx ZooTracey McNamara, Bronx Zoo• Debbie Asnis, Flushing Hospital Debbie Asnis, Flushing Hospital

Links between investigations established in Links between investigations established in

September 1999September 1999

June & July 1999:June & July 1999:

• Epizootic begins, dead crow reportsEpizootic begins, dead crow reports

• Veterinarian (Flushing/Brooklyn) finds crows with signs of Veterinarian (Flushing/Brooklyn) finds crows with signs of nervous system disordersnervous system disorders

• No human illnesses identified (retrospective review)No human illnesses identified (retrospective review) August 1999:August 1999:

• Epizootic: Epizootic: Bronx zoo birds die (~8/25).Bronx zoo birds die (~8/25). Samples to NYS Samples to NYS Department of Environmental Conservation (DEC)Department of Environmental Conservation (DEC)

• Epidemic begins in 1Epidemic begins in 1stst week week 8/2 – First human infection (retrospective)8/2 – First human infection (retrospective) 8/12 – First case admitted to Flushing hospital8/12 – First case admitted to Flushing hospital 8/23 – 58/23 – 5thth case admitted, Hospital contacts NYC-DOH case admitted, Hospital contacts NYC-DOH 8/31 – Samples arrive at NYS-DOH lab8/31 – Samples arrive at NYS-DOH lab

West Nile Virus, New York City, 1999, Timeline

September 1999:September 1999:• Epizootic:Epizootic:

Avian samples to USGS & USDA. Unidentified virus isolated.Avian samples to USGS & USDA. Unidentified virus isolated. Connecticut: Virus isolated from crow brainConnecticut: Virus isolated from crow brain Isolates sent to CDCIsolates sent to CDC

• Epidemic:Epidemic: 9/1 NYS-DOH lab: Antibody to Flavivirus (SLE?)9/1 NYS-DOH lab: Antibody to Flavivirus (SLE?) 9/3 CDC DVBID confirms SLE; NYC starts vector control9/3 CDC DVBID confirms SLE; NYC starts vector control Autopsy samples to UC IrvineAutopsy samples to UC Irvine

Late September 1999 – Late September 1999 – Investigations come togetherInvestigations come together• Virus identified as Flavivirus by CDC (WNV-like) & UC Irvine Virus identified as Flavivirus by CDC (WNV-like) & UC Irvine

(Kunjin)(Kunjin)• Repeat serology, high-titer antibody against WNVRepeat serology, high-titer antibody against WNV• Complete sequence identifies West Nile virus from birds/humansComplete sequence identifies West Nile virus from birds/humans• WNV identified from mosquitoes collected in NYCWNV identified from mosquitoes collected in NYC

WNV in NYC in 1999WNV in NYC in 1999

Lanciotti et al. 1999. Origin of the West Lanciotti et al. 1999. Origin of the West Nile virus responsible for an outbreak Nile virus responsible for an outbreak

of encephalitis in the northeastern U.S. of encephalitis in the northeastern U.S. Science 286:2333-337.Science 286:2333-337.

NYC 1999 isolate essentiallyidentical to 1998 isolate from Israel

(Epidemic transmission)

(Low level, zoonotic transmission)

October 1999:October 1999:• Equine outbreak on Long Island reportedEquine outbreak on Long Island reported• WNV-positive dead crow found in WNV-positive dead crow found in

BaltimoreBaltimore Jan-Feb 2000:Jan-Feb 2000:

• WNV found in overwintering dormant WNV found in overwintering dormant female female Cx. pipiensCx. pipiens in NYC in NYC

WNV in NYC in 1999WNV in NYC in 1999

Enzootic vector (Maintenance/Amplification)

Amplifying hostsAmplifying hosts

WNV transmission (Eastern U.S.)WNV transmission (Eastern U.S.)

Enzootic vectorEnzootic vectorCulex quinquefasciatusCulex quinquefasciatusCulex pipiensCulex pipiens

Primary Enzootic Cycle

Enzootic vector

Amplifying hostsAmplifying hosts

Incidental hostsIncidental hostsHumansHumansHorsesHorses

Other mammalsOther mammals

Bridge vectorsBridge vectors**Cx salinariusCx salinarius

Cx nigripalpusCx nigripalpusOchlerotatus sollicitansOchlerotatus sollicitans

Oc taeniorhynchusOc taeniorhynchusAedes vexansAedes vexansAe albopictusAe albopictusCx tarsalisCx tarsalis

* Epidemic potential* Epidemic potential

WNV transmissionWNV transmission

Enzootic vectorEnzootic vector

What About Crows?What About Crows?

High mortality throughout regionHigh mortality throughout region Short time from infection to deathShort time from infection to death Intermediate virus titerIntermediate virus titer Unlikely to be amplifying host driving Unlikely to be amplifying host driving

epidemic & epizooticepidemic & epizootic Unlikely to be reservoir host allowing Unlikely to be reservoir host allowing

seasonal persistenceseasonal persistence

“I love the smell of malathion in the morning”

West Nile Virus Human Illness West Nile Virus Human Illness

West Nile neuroinvasive West Nile neuroinvasive disease(WNND)disease(WNND)

Encephalitis, meningitis, myelitisEncephalitis, meningitis, myelitis

Increased risk with age & co-morbid Increased risk with age & co-morbid conditionsconditions

Reportable conditionReportable condition

<1% infections<1% infections

WNF (10-30%)

West Nile fever (WNF) West Nile fever (WNF)

No “overt” CNS involvementNo “overt” CNS involvement

Fever, rash, headache, myalgia, arthralgiaFever, rash, headache, myalgia, arthralgia

Not a reportable conditionNot a reportable condition

10 -30% infections10 -30% infections

Asymptomatic WNAsymptomatic WNinfection (70-90%)infection (70-90%)

Asymptomatic infectionAsymptomatic infection

Not reportable conditionNot reportable condition

Same virus / antibody kinetics Same virus / antibody kinetics

Life-long immunityLife-long immunity

Potential problem for blood Potential problem for blood banking & organ donationbanking & organ donation

70-90% infections70-90% infections

ClinicalClinical Spectrum of WNV Spectrum of WNV Illness: RevisedIllness: Revised

WN EncephalitisWN Encephalitis

WN “Poliomyelitis”WN “Poliomyelitis”Inflammatory NeuropathyInflammatory NeuropathyRadiculopathy / plexopathyRadiculopathy / plexopathy

WN FeverWN FeverWN MeningitisWN Meningitis

• Weather conditions (temperature & precipitationWeather conditions (temperature & precipitation• Wild-bird population:Wild-bird population:

• Sick/dead birds – test for virus (WNV, Usutu)Sick/dead birds – test for virus (WNV, Usutu)• Healthy birds – test for antibodiesHealthy birds – test for antibodies

• Sentinel chicken flocks – test for antibodiesSentinel chicken flocks – test for antibodies• Mosquito collections – test for virusMosquito collections – test for virus• Horses – encephalitis – test for antibodiesHorses – encephalitis – test for antibodies• Human illnessesHuman illnesses• Viremic blood donors (WNV)Viremic blood donors (WNV)

Surveillance for mosquito-borne zoonosesSurveillance for mosquito-borne zoonoses

WNV Disease SurveillanceWNV Disease Surveillance

http://diseasemaps.usgs.gov/

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

West Nile Virus Neuroinvasive Disease West Nile Virus Neuroinvasive Disease Cases in United States (by year)Cases in United States (by year)

0

500

1000

1500

2000

2500

3000

19

99

20

00

20

01

20

02

20

03

20

04

20

05

20

06

20

07

20

08

*

WNND Cases

Average = 1295/yr

(*As of 11/18/2008)

Regional epidemics

First Reported WNV Activity by State, 1999-2008First Reported WNV Activity by State, 1999-2008

200120001999

20022003

2004

Average Annual Incidence of WNND,Average Annual Incidence of WNND,by County, U.S., 2004-2007by County, U.S., 2004-2007

Clallam

Grays Harbor

Pacific

Cowlitz

Clark(1

human)

Island

King(1 human)

Lewis

Mason

Pierce (2 humans)

Skagit

Snohomish

Thurston

Whatcom

Adams

Benton

Chelan

Columbia

FranklinGarfield

GrantKittitas

Klickitat

Lincoln

Okanogan

Spokane

Walla Walla

Whitman

Yakima(2 humans)

Douglas

Ferry

Stevens

PendOreille

Asotin

SkamaniaWahkiakum

JeffersonKitsap

San Juan

WNV-infected human identified in county

Human WNV Cases in Human WNV Cases in Washington State, 2006-2008Washington State, 2006-2008

Culex tarsalisCulex tarsalis

• “The” vector of irrigated lands in arid west• Efficient WNV transmitter in lab• Long distance flier• Feed equally on birds & mammals• High infection rates in 2003

Estimated Number of WNV Infections & Estimated Number of WNV Infections & Fever Cases, U.S., 1999-2008Fever Cases, U.S., 1999-2008

Reports of WNV fever vary widely Reports of WNV fever vary widely WNND best indicator of WNV transmission among WNND best indicator of WNV transmission among

humanshumans 11,807 cases of neuroinvasive disease in 10 years11,807 cases of neuroinvasive disease in 10 years Based on serosurveys:Based on serosurveys:

• 140 WNV infections per 1 WNND case140 WNV infections per 1 WNND case

• 28 WNV fever cases per 1 WNND case28 WNV fever cases per 1 WNND case

140 x 11,807 WNND = ~1.65 million infections140 x 11,807 WNND = ~1.65 million infections

28 x 11,807 WNND = ~331,000 WNV fever28 x 11,807 WNND = ~331,000 WNV fever

West Nile Virus - The most widespread of the JE West Nile Virus - The most widespread of the JE serocomplex flavivirusesserocomplex flaviviruses

Transmission of WNV Without Transmission of WNV Without MosquitoesMosquitoes

InfectionInfection

Illness onsetIllness onset

D4 – D6 illnessD4 – D6 illness 1Y after illness1Y after illness

ViremiaViremia

Serum & CSF IgM AbSerum & CSF IgM Ab

IgG & Nt AbIgG & Nt Ab

D14 – D21 illnessD14 – D21 illness

Co

nc

entr

ati

on

Co

nc

entr

ati

on

WNV-CNS tissueWNV-CNS tissue

Incubation: 2-15 daysIncubation: 2-15 days

Surveillance for Asymptomatic Surveillance for Asymptomatic WNViremic Blood DonorsWNViremic Blood Donors

23 transfusion-associated WNV infections 23 transfusion-associated WNV infections identified in 2002identified in 2002

Beginning 2003, all blood donations screened Beginning 2003, all blood donations screened using NATusing NAT

““Presumed Viremic Donors” (PVD) reported to Presumed Viremic Donors” (PVD) reported to state health departments which report cases to state health departments which report cases to ArboNETArboNET

WNV Transfusion- & Transplantation-WNV Transfusion- & Transplantation-Associated DiseaseAssociated Disease

2002-2008, 32 transfusion (TFX)-associated WNV 2002-2008, 32 transfusion (TFX)-associated WNV

illnesses reportedillnesses reported

Last documented TFX-associated cases in 2006Last documented TFX-associated cases in 2006

2002-2008, 7 transplantation-associated WNV 2002-2008, 7 transplantation-associated WNV illnesses reportedillnesses reported• 4 cases in 2002, 3 cases in 20054 cases in 2002, 3 cases in 2005

Last documented TFX-associated cases in 2005Last documented TFX-associated cases in 2005

Disease ControlDisease Control

Strategies to prevent arboviral infectionsStrategies to prevent arboviral infections Alter environment:

• Reduce mosquito breeding habitats• Screen windows/doors

Kill mosquitoes:• Larvicide/ Bacillus thuringienis applications• Aerial spraying (“adulticide”)• Tailor to habits of specific vector• Mosquito fish & copepods

Humans & personal protection: • Restrict outdoor activity at dawn & dusk• Wear long-length clothing• Mosquito repellant use

Human-Driven Ecological Changes That Alter Human-Driven Ecological Changes That Alter Incidence of Mosquito-Borne ZoonosesIncidence of Mosquito-Borne Zoonoses

DeforestationDeforestation Large-scale water projectsLarge-scale water projects Global climate changeGlobal climate change UrbanizationUrbanization Industrial agriculture practicesIndustrial agriculture practices Industrial animal husbandry practicesIndustrial animal husbandry practices Widespread use of pesticidesWidespread use of pesticides Water pollutionWater pollution Introduction of exotic speciesIntroduction of exotic species Tendency towards monocultureTendency towards monoculture

Environmental Change & Potential Changes Environmental Change & Potential Changes to Mosquito-Borne Zoonotic Diseasesto Mosquito-Borne Zoonotic Diseases

Increase amplifying hostsIncrease amplifying hosts• Example: Hog farms that Example: Hog farms that ↑ ↑ Japanese Japanese

encephalitis virus transmission in Southeast encephalitis virus transmission in Southeast AsiaAsia

• Example: Rice monoculture in peri-urban Example: Rice monoculture in peri-urban areas of SE Asian citiesareas of SE Asian cities

Increase vector speciesIncrease vector species• Example: Irrigation practices that Example: Irrigation practices that ↑ ↑ West Nile West Nile

virus transmission in CO & NEvirus transmission in CO & NE