/Health District reports first St. Louis Encephalitis

Health District reports first St. Louis Encephalitis

August 26, 2016

LAS VEGAS – The Southern Nevada Health District is reporting its first human case of St. Louis Encephalitis in Clark County since 2007. The individual is male over the age of 50 who had the more serious neuroinvasive form of the illness. He was hospitalized and has been released. The Health District will not be providing additional details regarding this individual. Additional case counts will be updated on the Health District’s website as they occur.

Most people who are infected with St. Louis Encephalitis virus have mild symptoms or might never become sick. Symptoms typically develop between five and 15 days after being bitten by an infected mosquito. Mild infections are characterized by fever and headache without other apparent symptoms. Some people will experience severe illness, especially older adults. Symptoms of the more serious form of the illness include headache, high fever, neck stiffness, confusion, shaking, seizures and/or paralysis, and even coma. The illness is diagnosed through a blood test and laboratory confirmation. There is no specific treatment for St. Louis Encephalitis virus disease, and mild cases resolve on their own. People with the more serious form of the illness are often hospitalized.

“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 the more serious forms of the disease. Children and especially the elderly are more at risk for complications,” said Dr. Joe Iser, Southern Nevada Health District Chief Health Officer. “With the increased number of St. Louis Encephalitis-positive mosquitoes in Southern Nevada this season, we are not surprised to receive confirmation of a human case of the illness. It is another reminder to the community to protect themselves from bites and check their homes and yards for mosquito breeding sources.”

The Southern Nevada Health District’s Vector Surveillance Program identified a sharp increase in St. Louis Encephalitis-positive mosquitoes in more than 30 ZIP codes in Clark County. To date, St. Louis Encephalitis-positive mosquitoes have been identified in the 89002, 89005, 89011, 89012, 89014, 89030, 89074, 89081, 89101, 89103, 89104, 89107, 89108, 89117, 89118, 89119, 89120, 89121, 89122, 89123, 89128, 89130, 89131, 89134, 89135, 89143, 89144, 89145, 89146, 89147, 89149, and 89191 ZIP codes.

In 2016, the Vector Surveillance Program has submitted a total of 1,236 mosquito pools totaling 33,276 mosquitoes to the Nevada Department of Agriculture. Of those, 177 submission pools and 5,555 mosquitoes were positive for St. Louis Encephalitis. The 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 are posted on the Health District’s Mosquito Surveillance page.

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.