Protecting Yourself from Protecting Yourself from Mosquito-borne Infections: Mosquito-borne Infections:

West Nile VirusWest Nile Virus

Dr. Richard M. HousemanDr. Richard M. HousemanDepartment of EntomologyDepartment of Entomology

University of MissouriUniversity of Missouri

“When unable to defend herself by the sword, Rome could defend herself by means of the fever.”

Godfrey of Viterbo, 1167

Mosquito-Borne InfectionsMosquito-Borne Infections

• FilariaFilaria– HeartwormHeartworm– ElephantiasisElephantiasis

• ProtozoaProtozoa– MalariaMalaria

• VirusVirus– Yellow FeverYellow Fever– Dengue Dengue – SLE, WEE, WNVSLE, WEE, WNV

West Nile VirusWest Nile Virus

• Encephalitis-type virus identified in Encephalitis-type virus identified in Uganda (1937)Uganda (1937)

• Commonly found in humans and birds Commonly found in humans and birds throughout much of the worldthroughout much of the world– Historically Europe, Africa, Middle East.Historically Europe, Africa, Middle East.

• Has been in North America since 1999Has been in North America since 1999– First found in New York CityFirst found in New York City– Now permanently established in Western HemisphereNow permanently established in Western Hemisphere

                                                

                                  

                                                

                                  

Human WNV Reports in 2003Human WNV Reports in 2003

West Nile Virus SymptomsWest Nile Virus Symptoms

• Most human infections have none or Most human infections have none or mild symptoms (West Nile Fever)mild symptoms (West Nile Fever)– Recovery in >99% of casesRecovery in >99% of cases– No long-term effectsNo long-term effects

• <1% with symptoms develop <1% with symptoms develop encephalitisencephalitis– Disorientation, weakness, paralysis, comaDisorientation, weakness, paralysis, coma

• Hospitalization for support therapyHospitalization for support therapy– Intravenous fluids, ventilator, monitoringIntravenous fluids, ventilator, monitoring

West Nile Virus TransmissionWest Nile Virus Transmission

• Birds are primary hosts, others are Birds are primary hosts, others are incidentalincidental– Human infections are rare Human infections are rare

• In temperate areas (24In temperate areas (24ºº-66-66ºº latitude) latitude) virus transmission is seasonalvirus transmission is seasonal– Summer to early fallSummer to early fall– Cases appear 3-4 weeks following infectionCases appear 3-4 weeks following infection

140 species

Dogs, cats, bats, squirrels, skunks, chipmunks, rabbits

20 species

Mosquito Vectors of WNVMosquito Vectors of WNV

• Of the ~20 known vector species…Of the ~20 known vector species…– 14 have been collected in Missouri14 have been collected in Missouri– 12 are found in all areas of the state12 are found in all areas of the state– 8 are common or abundant8 are common or abundant– 7 inhabit temporary/human-created water7 inhabit temporary/human-created water– 7 inhabit permanent water7 inhabit permanent water– 7 bite at dawn/dusk7 bite at dawn/dusk– 5 overwinter as fertilized females5 overwinter as fertilized females

All mosquitoes are not All mosquitoes are not created equalcreated equal• Different habitat preferencesDifferent habitat preferences

– Water conditions Water conditions – Activity periodsActivity periods

• Different movement patternsDifferent movement patterns• Different host preferencesDifferent host preferences

– Warm-bloodedWarm-blooded– Different groupsDifferent groups

‘‘Urban’ MosquitoesUrban’ Mosquitoes

• Breeding occurs and hosts available in Breeding occurs and hosts available in human-dominated environmentshuman-dominated environments

• Important urban speciesImportant urban speciesCulex pipiens Culex pipiens (common house)(common house)

Aedes aegypti Aedes aegypti (yellow fever)(yellow fever)

Aedes albopictusAedes albopictus (Asian tiger) (Asian tiger)

‘‘Suburban’ MosquitoesSuburban’ Mosquitoes

• Breed in non-human-dominated Breed in non-human-dominated environments and move to locate hostsenvironments and move to locate hosts– Highly vagile adults (ie. up to 17 miles)Highly vagile adults (ie. up to 17 miles)

• Important urban ‘invading’ speciesImportant urban ‘invading’ speciesCulex tarsalis Culex tarsalis (western encephalitis) (western encephalitis)

Aedes vexansAedes vexans (inland floodwater) (inland floodwater)

‘‘Rural’ MosquitoesRural’ Mosquitoes

• Breed in non-human-dominated Breed in non-human-dominated environments and feed to a lesser environments and feed to a lesser extent on man.extent on man.– Less vagile (ie. <1 mile)Less vagile (ie. <1 mile)

• Important rural speciesImportant rural species– Anopheles quadrimaculatusAnopheles quadrimaculatus (eastern (eastern

malaria)malaria)

Life Cycle of MosquitoesLife Cycle of Mosquitoes

• WaterWater– Eggs, larvae, pupaeEggs, larvae, pupae

• LandscapeLandscape– AdultsAdults

• HostHost– AdultsAdults

• Back to WaterBack to Water– AdultsAdults

egg

adult

pupa

larva

In the WaterIn the Water

• Standing waterStanding water– Pollution Pollution – Decaying organic matterDecaying organic matter– Emergent vegetation (intersection line)Emergent vegetation (intersection line)

• Containers, puddles, drains, etc.Containers, puddles, drains, etc.– Small or large amounts of waterSmall or large amounts of water– Decaying organic matter for Decaying organic matter for

hatching/feedinghatching/feeding

In the WaterIn the Water

• Eggs (2d)Eggs (2d)– Oviposition, hatching, breathing system Oviposition, hatching, breathing system

• Larvae (10d)Larvae (10d)– Feed actively, breathing, mobilityFeed actively, breathing, mobility

• Pupae (2d)Pupae (2d)– Non-feeding, breathing, mobilityNon-feeding, breathing, mobility

In the WaterIn the Water

• Feeding on microbes and small Feeding on microbes and small nematodes nematodes

• High mortality rates High mortality rates – No fish in temporary and/or filthy water No fish in temporary and/or filthy water – Cannibalistic mosquitoes Cannibalistic mosquitoes

• ((ToxorhynchitesToxorhynchites) )

– Predaceous insects Predaceous insects • (Gyrinidae, Dytiscidae, Gerridae, Notonectidae) (Gyrinidae, Dytiscidae, Gerridae, Notonectidae)

In the LandscapeIn the Landscape

• Protected locations that minimize dryingProtected locations that minimize drying• Vertical surfaces used frequentlyVertical surfaces used frequently• Landmarks Landmarks

– Near waterNear water– Often used by multiple generations, year Often used by multiple generations, year

after yearafter year

In the LandscapeIn the Landscape

• Development continues (2d)Development continues (2d)– Cuticle hardening, sexual developmentCuticle hardening, sexual development

• Feeding Feeding – plant nectars and honeydew plant nectars and honeydew – BloodBlood

• Resting and digestingResting and digesting

In the LandscapeIn the Landscape

• MatingMating– Swarming and copulationSwarming and copulation

• Avoiding predatorsAvoiding predators– dragonflies, ants, lizards, and batsdragonflies, ants, lizards, and bats

On the HostOn the Host

• Mostly warm-blooded vertebratesMostly warm-blooded vertebrates– Host preferences varyHost preferences vary

• Carbon dioxide, lactic acid, body heat Carbon dioxide, lactic acid, body heat signalssignals

• Activity/biting period variesActivity/biting period varies– Sleeping or active hostSleeping or active host

On the HostOn the Host

• Locating a host Locating a host – movement, chemical/temperature stimulimovement, chemical/temperature stimuli

• FeedingFeeding– Probing for arterioles, venulesProbing for arterioles, venules– Salivating and suckingSalivating and sucking

• Getting awayGetting away

Back to the WaterBack to the Water

• Resting and DigestingResting and Digesting– Humid, protected locationsHumid, protected locations– Predator avoidancePredator avoidance

• ExcretionExcretion– Peritrophic membrane surrounds mealPeritrophic membrane surrounds meal– Elimination of liquid portion of bloodElimination of liquid portion of blood

Back to the WaterBack to the Water

• Survival to reproduction almost a Survival to reproduction almost a miracle miracle

• Locating oviposition sitesLocating oviposition sites– Visual and olfactoryVisual and olfactory– Fermenting stimuli of nutrient-rich waterFermenting stimuli of nutrient-rich water

• One clutch of eggs most commonOne clutch of eggs most common– Two, or even three rarelyTwo, or even three rarely

• Death from various causesDeath from various causes

“If you would see all of nature gathered up at one point, in all her loveliness, and her skill, and her deadliness, and her sex, where would you find a more exquisite symbol than the mosquito?”

Havelock Ellis, 1920

Missouri WNV UpdateMissouri WNV Update

• 2002 Reports2002 Reports– 169 human cases in 29 169 human cases in 29

countiescounties• Age ranged from 4-92 Age ranged from 4-92

yearsyears• Attack rate of 3 per Attack rate of 3 per

100,000 (0. 003%)100,000 (0. 003%)

– 5 human fatalities5 human fatalities• Age ranged from 61-88 Age ranged from 61-88

yearsyears

– 819 horses in 103 819 horses in 103 countiescounties

– 277 birds in 82 counties277 birds in 82 counties

• 2003 Reports2003 Reports– 61 human cases in 25 61 human cases in 25

countiescounties• Age ranged from 6-85 Age ranged from 6-85

yearsyears• Attack rate of ~1 per Attack rate of ~1 per

100,000 (0. 001%)100,000 (0. 001%)

– 6 human fatalities6 human fatalities• Age ranged from 69-83 Age ranged from 69-83

yearsyears

– 130 horses in 53 130 horses in 53 countiescounties

– 144 birds in 54 counties144 birds in 54 counties

Human WNV in MissouriHuman WNV in Missouri

Comparison of Cumulative Numbers of Human West Nile Virus Cases in Missouri

Date

JUL1 JUL2 JUL3 JUL4 AUG1 AUG2 AUG3 AUG4 SEP1 SEP2 SEP3 SEP4 OCT1 OCT2 OCT3 OCT4 OCT5 NOV1 NOV2 NOV3 NOV4 DEC1

Nu

mb

er o

f C

ase

s

0

20

40

60

80

100

120

140

160

180

20022003

Relative Numbers of Human WNV Cases Reportedin Missouri and Surrounding States (2002-2003)

State

MO NE IA IL KY TN AR OK KS

Hu

man

WN

V c

ases

0

200

800

1000

1200

1400

1600

1800

20022003

West Nile Virus cases in Missouri and surrounding states. States below the line had more cases in 2002, while those above the line had more cases in 2003.

2002

0 200 800

2003

0

200

400

1400

1600

ILMO

AR

TNKY

NE

IA

KSOK

Avian WNV in U.S.Avian WNV in U.S.

2002 2003

Minimizing the Risk of WNVMinimizing the Risk of WNV

• Avoid mosquito bitesAvoid mosquito bites

– Reduce mosquito populationsReduce mosquito populations– Personal Protective measuresPersonal Protective measures

Minimizing the Risk of WNVMinimizing the Risk of WNV

• Reducing Mosquito PopulationsReducing Mosquito Populations– Eliminate temporary mosquito breeding Eliminate temporary mosquito breeding

habitatshabitats• Regular surveillanceRegular surveillance• Empty containers and clutterEmpty containers and clutter

– Monitor permanent breeding habitatsMonitor permanent breeding habitats• ‘‘dip’ countsdip’ counts• rising and receding waterrising and receding water• Insecticide or oil application when presentInsecticide or oil application when present

Minimizing the Risk of WNVMinimizing the Risk of WNV

• Personal Protective MeasuresPersonal Protective Measures– Limit outdoor activity during peak bite timesLimit outdoor activity during peak bite times

• Dawn, duskDawn, dusk• Prevent mosquitoes from coming indoorsPrevent mosquitoes from coming indoors

– Wear long-sleeved shirts, long pantsWear long-sleeved shirts, long pants• Permethrin or DEET may be appliedPermethrin or DEET may be applied

– Apply insect repellent containing DEET Apply insect repellent containing DEET – Possible vaccinePossible vaccine

MU Extension ResourcesMU Extension Resources