St. Louis Encephalitis Virus Detected in Tranquility, CA


FIREBAUGH, CALIFORNIA – The Fresno Westside Mosquito Abatement District has received confirmation that mosquito samples collected north of the census-designated place of Tranquility, in Western Fresno County have tested positive for St. Louis Encephalitis virus (SLEV). SLEV is transmitted via the bite of Culex mosquitoes (the same mosquitoes which can transmit West Nile virus). Most people that contract St. Louis Encephalitis will show few to no symptoms. Others will show mild flu-like symptoms and severe cases can cause neurological problems such as, headache, confusion, disorientation, and dizziness. Some cases can result in paralysis, coma, or death. The elderly and those with weakened immune systems are more at risk for severe infections of St. Louis Encephalitis.

The mosquito samples that tested positive for SLEV are the first detection of the virus in Fresno County since 1992, when it was detected in sentinel chickens. The mosquitoes were trapped at a location that has already produced mosquito samples positive for West Nile virus (WNV) this summer. As such, the area is subject to extensive ongoing control efforts for both larval and adult mosquitoes. The detection of SLEV comes amidst a heavy season for the more common WNV, with 89/393 mosquito samples submitted by the District testing positive for that virus to date.

To reduce the risk of being bitten by mosquitoes and exposed to mosquito-borne viruses such as SLEV or WNV, residents are urged to take the following precautions:
1) Drain all sources of standing water around your home. Remove unnecessary objects from around your home that can potentially hold water.
2) Report observed sources of standing water (i.e. unmaintained swimming pools) to the Fresno Westside Mosquito Abatement District (559) 659-2437 or at
3) Irrigation water on farms and other lands should not be allowed to stand for more than three days.
4) Report dead birds to 877-WNV-BIRD (877-968-2473) or
5) Repair window and door screens to prevent mosquitoes from entering buildings.
6) Wear long sleeves and pants if outdoors when mosquitoes are present.
7) Use a repellent containing DEET, oil of lemon eucalyptus, picaridin or IR3535, as recommended by the U.S. Centers for Disease Control and Prevention. Always read and follow the repellent label instructions..
8) Stock mosquitofish in domestic water features, such as backyard ponds and horse troughs. The District will place mosquitofish, at no cost, in backyard mosquito breeding sources.

For more information on St Louis Encephalitis Virus:

Center for Disease Control:

Download Press Release:

FWMADSLEPressRelease9302016 .pdf

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