/Health District detects St. Louis Encephalitis in mosquitoes

Health District detects St. Louis Encephalitis in mosquitoes

June 10, 2016

LAS VEGAS – The Health District’s Vector Surveillance Program has identified St. Louis Encephalitis (SLE)-positive mosquito pools in the 89104, 89120, 89146, and 89191 zip codes. There have been no reports of human cases of St. Louis Encephalitis in Clark County since 2007. To date, no West Nile virus-positive mosquitoes have been identified this season in Clark County. For information about prevention tips, visit the Health District’s Mosquito Surveillance page.

Like West Nile Virus, St. Louis Encephalitis (SLE) is most often spread by the bite of an infected mosquito. Most people infected with SLE have very mild illness or may never become sick. The mild infections are characterized by fever and headache. In rare cases people may develop a more serious form of the virus, St. Louis Encephalitis virus. Symptoms include fever, headache, dizziness, nausea, and malaise.

Since 2014, the Health District’s Vector Surveillance Program has been doing surveillance for Aedes albopictus and Aedes aegypti, the mosquito species known to spread the Zika virus as well as chikungunya and dengue. To date, these mosquitoes have not been identified in Southern Nevada.

“Each summer, we encourage our residents to ‘fight the bite’ by taking steps to prevent mosquito bites and eliminate mosquito breeding sources. These steps can help protect you against illnesses such as St. Louis Encephalitis, West Nile virus infection and limit potential places to breed for the mosquitoes that can transmit the Zika virus,” said Dr. Joe Iser, Southern Nevada Health District Chief Health Officer. “By preventing mosquito bites, everyone can protect themselves whether they are at home or if they are traveling this summer. While diseases that are transmitted by mosquitoes are mild in many cases, they can be severe with serious complications for some.”

The Health District reminds Southern Nevadans to protect themselves against mosquito bites to avoid Zika virus if traveling this summer to areas where there is virus transmission. The CDC has information regarding areas with Zika transmission as well as information for pregnant women and tips for travelers to reduce their risk on the Prevention section of its website.

“We encourage everyone to use insect repellants, wear protective clothing, and limit outdoor activity when mosquitoes are most active,” said Iser.

The Southern Nevada Health District’s Vector Surveillance Program regularly tests mosquito pools for West Nile, Saint Louis Encephalitis, and Western Equine Encephalitis, which is routinely 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 Health District website at: www.southernnevadahealthdistrict.org/forms/mosquito.php.

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.


The Southern Nevada Health District serves as the local public health authority for Clark County, Boulder City, Henderson, Las Vegas, Mesquite and North Las Vegas. The agency safeguards the public health of the community’s residents and visitors through innovative programs, regulations, and initiatives focused on protecting and promoting their health and well-being. More information about the Health District, its programs, services, and the regulatory oversight it provides is available at www.SNHD.info.