Organism Organism History

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

• Follow label directions
• DEET
• Do not use on pets

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