After a six year absence, the St. Louis encephalitis virus (SLEV) has reappeared in Florida. On August 31, Pinellas County officials confirmed that four sentinel chickens in the county tested positive for SLEV. The chickens, used around the state to detect early signs of mosquito-borne disease, came from Clearwater and Seminole. Officials first suspected the disease on August 18 but did not receive laboratory confirmation until this week. There have been no reported human cases of SLEV.
SLEV is transmitted to humans through bites by infected mosquitoes. Symptoms include fever, headache, nausea, vomiting and fatigue; however, most of those infected will be asymptomatic. Symptoms generally appear within 5-15 days. Encephalitis, or inflammation of the brain, is rare and generally occurs only in older adults. In extreme cases, SLEV can result in long-term disability or death. Pinellas County residents are urged to take precautions against mosquito bite, such as wearing mosquito repellent and draining any standing water near their homes.
Historically, SLEV has usually been found in the central and eastern states of the United States. The US experienced a large outbreak in 1975 in the Ohio-Mississippi River Basin, when nearly 2,000 cases were reported. Annual cases have generally been under 300 since then. The states with most cases are since 1964 are Illinois, Ohio, Mississippi, and Florida.