Protecting Yourself from Mosquito-borne Infections: West Nile Virus

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Protecting Yourself from Mosquito-borne
Infections West Nile Virus

• Dr. Richard M. Houseman
• Department of Entomology
• University of Missouri

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When unable to defend herself by the sword,
Rome could defend herself by means of the
fever. Godfrey of Viterbo, 1167
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Mosquito-Borne Infections

• Filaria
• Heartworm
• Elephantiasis
• Protozoa
• Malaria
• Virus
• Yellow Fever
• Dengue
• SLE, WEE, WNV

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West Nile Virus

• Encephalitis-type virus identified in Uganda
  (1937)
• Commonly found in humans and birds throughout
  much of the world
• Historically Europe, Africa, Middle East.
• Has been in North America since 1999
• First found in New York City
• Now permanently established in Western Hemisphere

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Human WNV Reports in 2003
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West Nile Virus Symptoms

• Most human infections have none or mild symptoms
  (West Nile Fever)
• Recovery in gt99 of cases
• No long-term effects
• lt1 with symptoms develop encephalitis
• Disorientation, weakness, paralysis, coma
• Hospitalization for support therapy
• Intravenous fluids, ventilator, monitoring

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West Nile Virus Transmission

• Birds are primary hosts, others are incidental
• Human infections are rare
• In temperate areas (24º-66º latitude) virus
  transmission is seasonal
• Summer to early fall
• Cases appear 3-4 weeks following infection

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20 species
140 species
Dogs, cats, bats, squirrels, skunks, chipmunks,
rabbits
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Mosquito Vectors of WNV

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

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All mosquitoes are not created equal

• Different habitat preferences
• Water conditions
• Activity periods
• Different movement patterns
• Different host preferences
• Warm-blooded
• Different groups

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Urban Mosquitoes

• Breeding occurs and hosts available in
  human-dominated environments
• Important urban species
• Culex pipiens (common house)
• Aedes aegypti (yellow fever)
• Aedes albopictus (Asian tiger)

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Suburban Mosquitoes

• Breed in non-human-dominated environments and
  move to locate hosts
• Highly vagile adults (ie. up to 17 miles)
• Important urban invading species
• Culex tarsalis (western encephalitis)
• Aedes vexans (inland floodwater)

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Rural Mosquitoes

• Breed in non-human-dominated environments and
  feed to a lesser extent on man.
• Less vagile (ie. lt1 mile)
• Important rural species
• Anopheles quadrimaculatus (eastern malaria)

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Life Cycle of Mosquitoes

• Water
• Eggs, larvae, pupae
• Landscape
• Adults
• Host
• Adults
• Back to Water
• Adults

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In the Water

• Standing water
• Pollution
• Decaying organic matter
• Emergent vegetation (intersection line)
• Containers, puddles, drains, etc.
• Small or large amounts of water
• Decaying organic matter for hatching/feeding

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In the Water

• Eggs (2d)
• Oviposition, hatching, breathing system
• Larvae (10d)
• Feed actively, breathing, mobility
• Pupae (2d)
• Non-feeding, breathing, mobility

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In the Water

• Feeding on microbes and small nematodes
• High mortality rates
• No fish in temporary and/or filthy water
• Cannibalistic mosquitoes
• (Toxorhynchites)
• Predaceous insects
• (Gyrinidae, Dytiscidae, Gerridae, Notonectidae)

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In the Landscape

• Protected locations that minimize drying
• Vertical surfaces used frequently
• Landmarks
• Near water
• Often used by multiple generations, year after
  year

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In the Landscape

• Development continues (2d)
• Cuticle hardening, sexual development
• Feeding
• plant nectars and honeydew
• Blood
• Resting and digesting

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In the Landscape

• Mating
• Swarming and copulation
• Avoiding predators
• dragonflies, ants, lizards, and bats

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On the Host

• Mostly warm-blooded vertebrates
• Host preferences vary
• Carbon dioxide, lactic acid, body heat signals
• Activity/biting period varies
• Sleeping or active host

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On the Host

• Locating a host
• movement, chemical/temperature stimuli
• Feeding
• Probing for arterioles, venules
• Salivating and sucking
• Getting away

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Back to the Water

• Resting and Digesting
• Humid, protected locations
• Predator avoidance
• Excretion
• Peritrophic membrane surrounds meal
• Elimination of liquid portion of blood

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Back to the Water

• Survival to reproduction almost a miracle
• Locating oviposition sites
• Visual and olfactory
• Fermenting stimuli of nutrient-rich water
• One clutch of eggs most common
• Two, or even three rarely
• Death from various causes

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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
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Missouri WNV Update

• 2002 Reports
• 169 human cases in 29 counties
• Age ranged from 4-92 years
• Attack rate of 3 per 100,000 (0. 003)
• 5 human fatalities
• Age ranged from 61-88 years
• 819 horses in 103 counties
• 277 birds in 82 counties

• 2003 Reports
• 61 human cases in 25 counties
• Age ranged from 6-85 years
• Attack rate of 1 per 100,000 (0. 001)
• 6 human fatalities
• Age ranged from 69-83 years
• 130 horses in 53 counties
• 144 birds in 54 counties

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Human WNV in Missouri
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NE
IA
IL
MO
KS
OK
TN
KY
AR
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Avian WNV in U.S.
2002
2003
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Minimizing the Risk of WNV

• Avoid mosquito bites
• Reduce mosquito populations
• Personal Protective measures

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Minimizing the Risk of WNV

• Reducing Mosquito Populations
• Eliminate temporary mosquito breeding habitats
• Regular surveillance
• Empty containers and clutter
• Monitor permanent breeding habitats
• dip counts
• rising and receding water
• Insecticide or oil application when present

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Minimizing the Risk of WNV

• Personal Protective Measures
• Limit outdoor activity during peak bite times
• Dawn, dusk
• Prevent mosquitoes from coming indoors
• Wear long-sleeved shirts, long pants
• Permethrin or DEET may be applied
• Apply insect repellent containing DEET
• Possible vaccine

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MU Extension Resources