LAS VEGAS – 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. Updated information on positive mosquito submission pools and mosquitoes that are tested in Clark County will be posted on the Health District’s website.

“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.

“While most people who get infected with St. Louis Encephalitis virus may not know it, or may only get mild symptoms, some people may develop a more serious form of the disease. Children and especially the elderly are more at risk for complications,” said Iser.

The mild infections are characterized by fever and headache. Symptoms of more severe illness can include dizziness, nausea, stiff neck, confusion, tremors, coma, and in rare cases long-term disability or death.

No West Nile virus-positive mosquitoes have been identified this season in Clark County. Ongoing surveillance by the Health District has not detected Aedes albopictus or Aedes aegypti, the species known to spread the Zika virus as well as chikungunya and dengue. For information about prevention tips, visit the Health District’s Mosquito Surveillance page.

In addition to Zika, West Nile Virus, and St. Louis Encephalitis, the Southern Nevada Health District’s Vector Surveillance Program regularly tests mosquito pools for Western Equine Encephalitis, which is occasionally identified in Clark County. Residents can report green swimming pools and standing or stagnant water sources to local code enforcement agencies. Contact information for local jurisdictions’ code enforcement is available on the reporting resources section of the Health District website.


The Health District and the CDC advise everyone to take the following steps at home or if traveling:

  • Wear long-sleeved shirts and long pants.
  • Stay in places with air conditioning and window and door screens.
  • Sleep under a mosquito bed net if you are overseas or outside and are not able to protect yourself from mosquito bites.


    • Use Environmental Protection Agency (EPA)-registered insect repellents with one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol. When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breast-feeding women.
  • To protect your child from mosquito bites:


    • Do not use insect repellent on babies younger than 2 months old.
    • Do not use products containing oil of lemon eucalyptus or para-menthane-diol on children younger than 3 years old.
    • Dress your child in clothing that covers arms and legs.
    • Cover crib, stroller, and baby carrier with mosquito netting.
    • Do not apply insect repellent onto a child’s hands, eyes, mouth, and cut or irritated skin.
    • Adults: Spray insect repellent onto your hands and then apply to a child’s face.
  • Treat clothing and gear with permethrin or purchase permethrin-treated items.
  • Treated clothing remains protective after multiple washings. See product information to learn how long the protection will last.
  • If treating items yourself, follow the product instructions carefully.
  • Do NOT use permethrin products directly on skin. They are intended to treat clothing.

For more information on eliminating breeding sources, visit the CDC’s Controlling Mosquitoes at Home page for a list of tips, including:

  • Eliminate standing or stagnant water sources to eliminate mosquito breeding.
  • Store wading pools on their sides.
  • Check and repair window screens for tears.

Access information about the Southern Nevada Health District on its website: Follow the Health District on Facebook:, YouTube:, and Twitter: The Health District is available in Spanish on Twitter: Don’t have a Twitter account? Follow the Health District on your phone by texting “follow SNHDinfo” to 40404. Additional information and data can be accessed through the Healthy Southern Nevada website: