Health officials in Las Vegas say mosquitoes infected with St. Louis encephalitis have been found in several Las Vegas areas, but no human cases have been reported.
The Southern Nevada Health District says there haven't been any cases of St. Louis encephalitis in Clark County since 2007.
It's similar to West Nile virus, because it's usually spread by bites from infected mosquitoes.
Most people infected by the strain of encephalitis never get sick or have mild illness with fever and headache.
The infected mosquitoes were found in pools in the 89104 and 89120 postal Zip codes southeast of downtown; the 89146 area southwest of the Strip; and the 89191 area in northeast Las Vegas.
The health district says it hasn't found any mosquitoes with West Nile virus this season.