Saint Louis Encephalitis

Over the summer there have been mentions of Saint Louis encephalitis virus (SLEV) in regards to Pinellas County. This virus is a flavivirus – a group that includes West Nile – and has the potential to cause severe illness or death in older adults. The name of this disease comes from a particularly extensive outbreak that occurred in St. Louis, Missouri and the surrounding St. Louis County in 1933. Due to the high number of cases NIH was able to investigate and isolate this previously unknown virus. It is thought to have originated in northern Mexico and have been carried north by birds. Pinellas County Mosquito Control uses sentinel chickens to monitor for Saint Louis encephalitis and other arboviruses, since birds are usually the source of infection for mosquitos. Blood is drawn from the chickens weekly and tested for antibodies to the viruses of concern. Fortunately for the chickens they do not develop any symptoms, although once they test positive they have to be removed from the program since they will always carry the antibodies. Sentinel chickens from Pinellas County have tested positive for Saint Louis encephalitis in late July as well as August and into September. Regions with confirmed SLEV include Cross Bayou, Walsingham Park, Sawgrass Lake Park, and Lake Maggiore. While it is more common during hot and humid months, Saint Louis encephalitis can occur year round. Most individuals that are infected have no symptoms, but in rare cases it can manifest with such signs as fever, headache, nausea, vomiting, and fatigue. Severe infections can result in high fever, neck stiffness, disorientation, confusion, tremors, coma, and sometimes convulsion, spastic paralysis, and death. Older adults are at a greater risk for fatal disease. Since there is no cure for Saint Louis encephalitis the only treatment available is supportive care. If you or anyone you know shows symptoms of this disease be sure to talk to your health care provider for proper diagnosis. Since this virus is spread by mosquitos you should take the appropriate precautions. Wear insect repellent and protective clothing and be sure to avoid areas with high mosquito populations. Drain standing water, change pets’ water dishes and birdbaths regularly, and maintain your pool’s water balance to prevent mosquitos from breeding. If you use rain barrels be sure to cover them with fine mesh. Ornamental ponds can be stocked with fish that eat the mosquito larvae and any ornamental bromeliads should be flushed with fresh water regularly and treated with a larvicide. Mosquito Control field technicians can respond to concerns by use of the Mosquito Control Request form found on the Pinellas County website. http://www.pinellascounty.org/forms/mosquito_form.htm