Eastern Equine Encephalitis Virus Detected in Florida

Several sentinel chickens in the same flock have tested positive for Eastern Equine Encephalitis infection thus increasing risk of transmission to humans.

Several sentinel chickens of the same flock have tested positive for the mosquito-borne virus that causes Eastern Equine Encephalitis Virus (EEEV) infection, thus increasing the risk for transmission to humans, according to officials from the Florida Department of Health in Orange County.

Sentinel chickens are fowl routinely tested for EEEV and West Nile virus. Despite having a detectable viral load, infected chickens are predominantly asymptomatic. The Centers for Disease Control and Prevention (CDC) has stated that residents and visitors of areas with reported EEEV activity are at risk of infection, particularly those individuals engaging in outdoor work and recreational activities. Individuals aged >50 and <15 years are at greatest risk for severe disease when infected. Approximately 4% to 5% of human EEEV infections result in encephalitis, and only about 7 cases in humans are reported in the United States each year.

Symptomology of EEEV Infection

EEEV infection results in one of two types of illness: systemic or encephalitic. According to the CDC, systemic infections present with an abrupt onset of fever, chills, malaise, arthralgia, and myalgia. Illness lasts for 1 to 2 weeks and recovery is complete when central nervous system involvement is no longer present.

Manifestations of the encephalitic type of infection are stratified by age: in infants, it is characterized by abrupt onset of signs associated with cerebral inflammation, while in older children and adults, encephalitis manifests after a few days of systemic illness. Signs and symptoms of encephalitic infection include fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions, and coma.

Diagnosis of EEEV Infection

Preliminary diagnosis of an infection with EEEV is based on clinical features, travel history, activities, and epidemiologic history of the location where infection occurred. The primary method of diagnosis is serologic testing of serum or cerebrospinal fluid to detect virus-specific IgM and neutralizing antibodies. Any suspected cases should be reported to local public health authorities.

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Sequelae of EEEV Infection

Of those who become infected, 30% die within 2 to 10 days of symptom onset; among survivors, disabling and progressive mental and physical sequelae can occur. Severe EEEV sequelae has been linked to mortality within a few years of original infection. At present, there is no human vaccine against EEEV infection or specific antiviral treatment for clinical infections.

Recommendations to Prevent EEEV Infection

The Florida Department of Health in Orange County has indicated that they, along with mosquito control agencies, will continue surveillance and prevention efforts. However, officials have indicated that the most effective way to prevent infection from EEEV is to prevent bites and limit exposure to mosquitoes. Clinicians should encourage patients in endemic areas to wear shoes, socks, and long pants/sleeves when working in areas with mosquitoes present. The use of insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin and/or clothing should be advised. The repellent permethrin can be used on clothing to protect through several washes. In addition, the use of secure screens on windows and doors may aid in keeping mosquitoes out of enclosed areas, and emptying standing water from flower pots, buckets, barrels, and other containers may reduce the number of mosquito breeding sites.


1. Donahue K. Health officials issue mosquito-borne illness advisory. Florida Department of Health in Orange County website. http://orange.floridahealth.gov/newsroom/2019/07/mosquito-borne.html. July 25, 2019. Accessed July 31, 2019.

2. Eastern Equine Encephalitis. Centers for Disease Control and Prevention website. https://www.cdc.gov/easternequineencephalitis/index.html. Reviewed December 17, 2018. Accessed July 31, 2019.