Organism Organism History



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Organism

  • Organism

  • History

  • Epidemiology

  • Transmission

  • Disease in Humans

  • Disease in Animals

  • Prevention and Control

  • Actions to Take



Eastern equine encephalitis (EEE)

  • Eastern equine encephalitis (EEE)

  • Western equine encephalitis (WEE)

  • Venezuelan equine encephalitis (VEE)





EEE, WEE, and VEE viruses

  • EEE, WEE, and VEE viruses

    • Family Togaviridae
    • Genus Alphavirus
  • Mosquito-borne

  • Disease

    • Encephalitis in humans and horses
    • Other mammals and birds are occasionally affected






Four-stage life cycle

  • Four-stage life cycle

    • Egg, larva, pupa, adult
  • Aedes species

    • Lay single eggs
    • Damp soil, later flooded
  • Culex species

    • 100-300 eggs in raft
    • Lay eggs at night on water surface
  • Survival requires wind protection

  • Overwinter in egg stage



Larvae live upside down in water; “wriggler”

  • Larvae live upside down in water; “wriggler”

    • Breathe via siphon tube
    • Molt 4 times
  • Pupal stage is restful, non-feeding; “tumbler”

    • Breathe via “trumpets”
    • Splits to allow adult to emerge


Newly emerged adult rests

  • Newly emerged adult rests

  • Female takes blood meal

    • Only females bite
    • Attractants for biting
      • Carbon dioxide, temperature, moisture, smell, color, movement
  • Mating occurs a few days after flight

  • Lifespan varies from 4 to 30 days





Distribution, Magnitude, and Outcomes

  • Distribution, Magnitude, and Outcomes





Eastern equine encephalitis

  • Eastern equine encephalitis

    • Elderly most at risk
    • Case fatality rate: 33%
  • Western equine encephalitis

    • Children <1 year most at risk
    • Case fatality rate: 3%
  • Venezuelan equine encephalitis

    • Children most often affected
    • Fatalities are rare


Case-fatality rate in horses

  • Case-fatality rate in horses

    • EEE ~ 90%
    • VEE ~ 50 to 90%
    • WEE ~ <30%
  • Vaccine available in the U.S





1831

  • 1831

    • Unknown encephalomyelitis virus affects horses in Massachusetts
  • 1933

    • EEE first isolated from a horse
  • 1937

    • EEE identified in ring-necked pheasants
  • 1938

    • EEE first isolated from human brain


1942-1943

  • 1942-1943

    • Michigan epidemic
  • 1947

    • Southern Louisiana and Texas
    • 14,000 cases
    • 83% case fatality rate
  • 1951

    • Isolated from Culiseta melanura




1964-2010

  • 1964-2010

    • 270 cases total
    • Average 6 cases each year
    • Average 1 to 2 deaths each year
  • Case-fatality rates

    • Human: 30 to 70%
    • Equine: 90%
  • Equine cases usually appear first

    • Serve as sentinels for human disease










Incubation period: 4 to 10 days

  • Incubation period: 4 to 10 days

    • Mild disease uncommon
    • Fever, myalgia, headache, nausea, vomiting, abdominal pain, and photophobia
    • Seizure and coma in severe cases
  • Longer fever and flu-like symptoms before CNS signs results in a better outcome



Survival rates associated with age

  • Survival rates associated with age

    • Highest in young adults: 70%
    • Lower in children: 60%
    • Lowest in elderly: 30%
  • Recovery can result in permanent brain damage

  • Diagnosis by serology

  • Treatment is supportive care



Incubation period: 5 to 14 days

  • Incubation period: 5 to 14 days

  • Clinical signs in horses

    • Fever, anorexia, depression
    • CNS signs
      • Hypersensitivity, aimless wandering, head pressing, circling, ataxia, paresis, paralysis
  • Death may occur within days

  • Asymptomatic or mild infections also occur

  • Equine vaccine available



Asymptomatic in most bird species

  • Asymptomatic in most bird species

  • Clinical signs

    • Depression, tremors, leg paralysis, somnolence
    • Emus, ostriches
      • Hemorrhagic enteritis, emesis
    • Death 24 hours after onset
  • Vaccination

    • Some birds are vaccinated for EEE


Ante mortem: serology

  • Ante mortem: serology

    • Virus neutralization
    • Hemagglutination inhibition
    • ELISA
    • Complement fixation
    • Virus isolation
  • Post mortem

    • Virus identified in tissues (brain)
    • Immunohistochemistry, ELISA, RT-PCR




1930

  • 1930

    • Isolated from horse brain
    • California; 50% case fatality rate
  • 1933

    • Aedes aegypti experimentally infected with WEE
      • Virus transmitted to guinea pigs
      • Virus transmitted to horses (1936)
  • 1938

    • Isolated from human brain


1941

  • 1941

    • Natural infection found in mosquito Culex tarsalis
    • Epidemic in Canada and northern U.S.
  • 1942

    • Culex tarsalis identified as the vector
  • 1943

    • Confirmed as mosquito-borne disease
    • Birds identified as reservoir host






Culex tarsalis

  • Culex tarsalis

    • High populations in mid- to late-summer
    • Epidemics associated with cool, wet spring
    • Wind can carry mosquitoes 800 miles in less than 24 hours
  • Cases appear in June-August

    • 639 cases since 1964
    • 1989-1997: No human deaths






Incubation: 5 to 10 days

  • Incubation: 5 to 10 days

  • Resembles EEE but usually asymptomatic or mild in adults

  • Clinical signs

    • Sudden onset of fever, headache, nausea, vomiting, anorexia, malaise
    • CNS signs in children less than 1 year
      • Altered mental status, weakness, irritability, stupor, coma


Prognosis

  • Prognosis

    • Poor for young clinical patients
    • Case-fatality rate: 3 to 15%
    • Death within one week of clinical onset
  • Diagnosis difficult from blood, CSF

    • Post mortem virus isolation from brain
  • Treatment is supportive care

  • Vaccine available for military personnel only



Asymptomatic

  • Asymptomatic

    • Blacktail jackrabbit, kangaroo rat, Western gray squirrel, prairie dog, birds
  • Horses with clinical signs

    • Fever, depression, altered mentation, head pressing, ataxia, dysphagia
    • Progress to paralysis, convulsions, death
    • Mortality rate <30%


Diagnosis

  • Diagnosis

    • Serology
      • Can differentiate EEE and WEE using the virus neutralization or ELISA tests
    • Post mortem
      • Immunohistochemistry, ELISA, RT-PCR
  • Treatment is supportive care

  • Vaccine available







Epizootic/Epidemic

  • Epizootic/Epidemic

    • I-A, I-B, and I-C
    • Disease in humans and horses
    • Transmission by many mosquito species
    • Natural reservoir unknown
    • Horses and donkeys act as amplifiers


1938

  • 1938

    • Isolated from horse brain
  • 1962-1964

    • Outbreak in Venezuela
      • 23,000 human cases
  • 1967

    • Outbreak in Colombia
      • 220,000 human cases
      • Over 67,000 horse deaths


1969-1971

  • 1969-1971

    • Largest recorded outbreak
    • Covered area from Costa Rica to Rio Grande Valley in Texas
    • Thousands of human encephalitis cases
    • Over 100,000 horses died
  • 1995

    • Venezuela and Colombia
    • Over 90,000 human cases






Incubation period: 1 to 6 days

  • Incubation period: 1 to 6 days

  • Usually acute, mild, systemic disease

  • Clinical signs

    • Fever, chills, headache, myalgia
    • Coughing, vomiting, diarrhea
    • CNS signs
      • Encephalitis occurs in 4% of children
      • Less than 1% of symptomatic adults
  • Death is rare



Pregnant women

  • Pregnant women

    • Fetal encephalitis, placental damage, abortion/stillbirth, congenital disease
  • Diagnosis

    • Paired sera with rising titer
    • ELISA IgG or IgM
  • Treatment

    • Supportive care
  • No vaccine available



Incubation period: 1 to 5 days

  • Incubation period: 1 to 5 days

  • Horses most susceptible

    • Fever, anorexia, depression, flaccid lips, droopy eyelids and ears, incoordination, and blindness
    • Death 5 to 14 days after clinical onset
  • Case-fatality rate: 50 to 90%

  • In utero transmission results in abortion, stillbirth



Most domestic animals do not show clinical signs or amplify the virus

  • Most domestic animals do not show clinical signs or amplify the virus

  • Experimentally

    • Infected rabbits and dogs die after inoculation
    • Laboratory animals susceptible
      • Act as sentinels
      • Guinea pigs, mice, hamsters
  • Enzootic strains do not cause disease in animals



Diagnosis

  • Diagnosis

    • Virus isolation
    • Serology
      • Paired sera with rising titer
      • ELISA IgG or IgM
  • Treatment

    • Supportive care
  • Vaccine available for horses



Aerosolized VEE

  • Aerosolized VEE

  • Human and equine disease occur simultaneously

  • Flu-like symptoms in humans

  • Possible neurological signs in horses

  • Large number of cases in a given geographic area





Source reduction

  • Source reduction

  • Surveillance

  • Biological control

  • Chemical control

    • Larvicide
    • Adulticide
  • Educating the public

    • How to protect themselves


Mosquito habitats

  • Mosquito habitats

    • Make unavailable or unsuitable for egg laying and larval development
  • Minimize irrigation and lawn watering

  • Punch holes in old tires

  • Fill tree holes with cement

  • Clean bird baths, outside waterers, fountains



Drain or fill temporary pools with dirt

  • Drain or fill temporary pools with dirt

  • Keep swimming pools treated and circulating

    • Avoid stagnant water
  • Open marsh water management

    • Connect to deep water habitats and flood occasionally
    • Fish access


Sentinel chicken flocks

  • Sentinel chicken flocks

    • Blood test and ELISA to monitor seroconversion


Predators, natural and introduced, to eat larvae and pupae

  • Predators, natural and introduced, to eat larvae and pupae

    • Mosquito fish
      • Gambusia affinis, G. holbrooki
      • Fundulus spp., Rivulus spp., killifish
  • Other agents have been used but are not readily available

  • Copepods



Essential when:

  • Essential when:

    • Source reduction not effective
    • Surveillance shows increased population of virus-carrying mosquitoes
  • Requires properly trained personnel

  • Larvicides, adulticides

  • Toxic to many birds, fish, wildlife, aquatic invertebrates, honeybees

  • Human exposure is uncommon



Federal Food Drug and Cosmetic Act limits the quantity of adulticide used

  • Federal Food Drug and Cosmetic Act limits the quantity of adulticide used

    • Due to wind drift onto agricultural crops
  • Method used varies

    • Type of target mosquito
    • Type of targeted habitat
    • Aerial spraying covers wide area
  • Funding provided by state or local government

    • Rarely federal


Use when source reduction and biological control not feasible

  • Use when source reduction and biological control not feasible

  • More effective and target-specific

  • Less controversial than adulticides

  • Applied to smaller geographic areas

    • Larvae concentrate in specific locations




Necessary when other control measures unsuccessful

  • Necessary when other control measures unsuccessful

  • Least efficient

  • Proper type and time of application helps efficacy

    • Ultra low volume (ULV) foggers
      • 1 ounce per acre
    • Small droplets contact and kill adults




Stay inside during the evening when mosquitoes are most active

  • Stay inside during the evening when mosquitoes are most active

  • Wear long pants and sleeves

  • Use mosquito repellent when necessary



Make sure window and door screens are "bug tight"

  • Make sure window and door screens are "bug tight"

  • Replace your outdoor lights with yellow "bug" lights

    • Bug zappers are not very effective
  • ULV foggers for backyard use

  • Keep vegetation and standing water in check around the dwelling



CDC Division of Vector Borne Infectious Diseases-Arboviral Encephalitides

  • CDC Division of Vector Borne Infectious Diseases-Arboviral Encephalitides

    • http://www.cdc.gov/ncidod/dvbid/arbor/


Development of this presentation was made possible through grants provided to the Center for Food Security and Public Health at Iowa State University, College of Veterinary Medicine from

  • Development of this presentation was made possible through grants provided to the Center for Food Security and Public Health at Iowa State University, College of Veterinary Medicine from

  • the Centers for Disease Control and Prevention, the U.S. Department of Agriculture, the Iowa Homeland Security and Emergency Management Division, and the Multi-State Partnership for Security in Agriculture.

  • Authors: Radford Davis DVM, MPH; Danelle Bickett-Weddle, DVM, MPH, PhD, DACVPM; Anna Rovid Spickler, DVM, PhD

  • Reviewers: Jean Gladon, BS; Katie Spaulding, BS ; Kerry Leedom Larson, DVM, MPH, PhD, DACVPM; Glenda Dvorak, DVM, MPH, DACVPM




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