West Nile Virus

West Nile Virus is the leading cause of mosquito-borne disease in the continental United States. It is most commonly spread to people by the bite of an infected mosquito. Cases of West Nile Virus occur during mosquito season, which starts in the summer and continues through fall. There are no vaccines to prevent or medications to treat West Nile Virus in people.

How is it spread?

Infected mosquitoes: West Nile Virus is spread by the bite of an infected mosquito. Mosquitoes are West Nile Virus carriers ("vectors") that become infected when they feed on infected birds. Infected mosquitoes can then spread West Nile Virus to humans and other animals when they bite.

Who is at risk?

Anyone living in an area where West Nile Virus is present in mosquitoes can get infected. The risk of infection is highest for people who work outside or participate in outdoor activities, because of greater exposure to mosquitoes.

People of any age can get West Nile Virus. However, people over age 65 and underlying medical conditions are at the greatest risk for severe disease.

How Can I Reduce the Risk?

Exposure to mosquito bites and West Nile virus can be reduced by practicing the "Three Ds":

  • DEET - Apply insect repellent containing DEET, picaradin, oil of lemon eucalyptus, or IR3535 according to label instructions. Repellents keep the mosquitoes from biting. DEET can be used safely on infants and children 2 months of age and older. Use an EPA-registered insect repellent.

  • DAWN AND DUSK - The mosquitoes that transmit West Nile Virus bite in the early morning and evening, so it is important to wear proper clothing and repellent if outside during these times. Make sure doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.

  • DRAIN - Mosquitoes lay their eggs on standing water. Eliminate or drain all sources of standing water around homes and properties, including buckets, old car tires, rain gutters, birdbaths, and pet bowls. If a swimming pool is not being properly maintained, please contact the local mosquito and vector control agency.

Residents are urged to report unusual numbers of mosquitoes or day-biting mosquitoes to the local vector control agency.

  • In Stanislaus County:
    • East Side Mosquito Abatement District - (209) 522-4098
    • Turlock Mosquito Abatement District - (209) 634-1234

For additional information about protection from mosquito borne diseases including Zika, please visit the Centers for Disease Control and Prevention website for mosquito control.

Symptoms, Diagnosis & Treatment

Most people infected with mosquito-borne viruses don't get sick. For people who do, the time between the mosquito bite and the start of symptoms can be from 2 to 14 days.

  • Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
  • Recovery from severe illness might take several weeks or months. Some effects to the central nervous system might be permanent.
  • About 1 out of 10 people who develop severe illness affecting the central nervous system die.
If you think you or a family member is sick with West Nile Virus, call your health care provider. Your healthcare provider can order tests to look for West Nile virus infection.

There is no treatment for the virus other than supportive care, and there is no vaccine to prevent it. Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms.

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