Las Vegas health officials are warning of a spike in the number of mosquitoes infected with St. Louis encephalitis, though no human cases have been reported.
The Southern Nevada Health District said Wednesday that more than 4,300 mosquitoes have tested positive for the virus since its discovery in tested pool water was noted earlier this month.
There haven't been any cases of St. Louis encephalitis in Clark County since 2007.
Most people infected by the strain of encephalitis either never get sick or have mild illness with fever and headache.
The virus is similar to West Nile virus because it's usually spread by bites from infected mosquitoes.
The health department said it so far hasn't found any mosquitoes with West Nile or mosquitoes known to spread the Zika virus.