St. Louis Encephalitis (SLE)

St. Louis Encephalitis (SLE) is mosquito-borne viral infection. The virus is known to occur in natural enzootic bird-mosquito cycles. The primary mosquito species responsible for transmitting the infection is the common house mosquito, Culex pipiens, in the northeastern United States. This mosquito will readily feed on avain hosts allowing for efficient build up of the virus in local bird populations. Occasionally, these mosquitoes will feed on a variety of mammals, including humans; thereby, transmission of the virus can occur from infected mosquitoes that had previously fed on infected birds. Culex pipiens breeds in stagnant water that collects in a variety of places, including catch basins, dis-repaired pools, buckets and other containers, and roadside ditches. The virus is thought enter new areas through migrating birds because these mosquitoes do not normally fly very far from their breeding sources.

After being bitten by an infected mosquito, symptoms of SLE may appear within 5 to 15 days. These symptoms include, but are not limited to, fever, headache, nausea, drowsiness, and brain inflammation. Most individuals infected with SLE virus recover quickly within several weeks. However in the elderly, infants and immuno compromised people, the disease can continue to progress and is fatal in 10% to 15% of the cases. There are an average of nearly 200 cases of SLE reported each year in the United States, making it the most commonly reported mosquito-borne disease in the country. Most of these cases occur in southeastern and midwestern states. The last case reported from New Jersey was in 1975.

For more information on SLE visit these other websites:

Frequently Asked Questions about St. Louis Encephalitis (The Centers for Disease Control and Prevention)
SLE Fact Sheet (The Centers for Disease Control and Prevention)
SLE Fact Sheets and Alerts (The New Jersey Department of Health and Senior Services)
St. Louis Encephalitis Information (


Page Last Updated: 4/5/2016 2:57:00 PM

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