The Southern Nevada Health District’s Vector Surveillance Program has identified a sharp increase in St. Louis Encephalitis-positive mosquitoes since it first reported positive mosquito pools earlier this month.


Currently, 124 submission pools totaling 4,380 mosquitoes have tested positive for the virus. While there have been no reports of human cases of St. Louis Encephalitis in Clark County since 2007, the increase of the virus in the mosquito population raises concern for the potential of disease transmission to humans. The Vector Surveillance Program monitors mosquitoes that are known to spread diseases to people.

“This increase in St. Louis Encephalitis-positive mosquitoes serves as an important reminder to our community that we do indeed have mosquitoes in Southern Nevada, and it is important for people to take steps to eliminate breeding sources and to protect themselves from mosquito bites,” said Dr. Joe Iser, Chief Health Officer for the Health District.

St. Louis Encephalitis (SLE) is transmitted from birds to man and other mammals by infected mosquitoes (mainly some Culex species). SLE is found throughout the United States, but most often along the Gulf of Mexico, especially Florida.

Most persons infected with SLEV have no apparent illness. Initial symptoms of those who become ill include fever, headache, nausea, vomiting, and tiredness. Severe neuroinvasive disease (often involving encephalitis, an inflammation of the brain) occurs more commonly in older adults. In rare cases, long-term disability or death can result.