County of Marin Health and Human Services

West Nile Virus

Mosquitoes and West Nile virus

Marin Health and Human Services and the Marin/Sonoma Mosquito and Vector Control District (MSMVCD) remind residents to do their part in preventing mosquito breeding and mosquito-borne disease.

Protect Yourself: Follow the Four D’s

To keep families and neighbors safe from diseases such as West Nile Virus, practice the four D’s of mosquito protection (Dawn, Dusk, DEET and Drain):

►DAWN and DUSK are when some mosquitoes are most active. Avoid going out at those times during mosquito season or prepare accordingly. If outdoors during these times, dress in long sleeves, long pants and light-colored, loose-fitting clothing.

►DEET is an effective repellent. Always use Environmental Protection Agency (EPA)-registered insect repellents with one of the active ingredients such as DEET, picaridin, IR3535, or oil of lemon eucalyptus (OLE). When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breastfeeding women.

►DRAIN water from containers—tires, buckets, planters, toys, kid pools, birdbaths, flowerpots, animal water bowls or trash cans—at least twice per week. It only takes as little as one bottle cap of water for mosquitoes to breed and multiply.

Eliminate Mosquito Breeding Areas Around your Home:

  • Stock permanent water features with mosquitofish (available for free from MSMVCD)
  • Be sure to properly screen and/or secure lids on rain barrels or water storage containers
  • Do not over-water lawns
  • Clean out bird baths and animal waterboow
  • Keep swimming pools and hot tubs properly chlorinated
  • Make sure that septic tank lids are properly sealed and vent pipes are screened
  • Report mosquito problems at 707-285-2200 or online at www.msmosquito.org

Mosquito Borne-Disease

  • West Nile virus (WNV) is the leading cause of mosquito-borne disease in the continental United States.  It is most spread to people by the bite of an infected mosquito. Cases of WNV occur during mosquito season, which starts in the summer and continues through fall. There are no vaccines to prevent or medications to treat WNV in people. Fortunately, most people infected with WNV do not feel sick. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. [learn more]
  • Saint Louis encephalitis (SLE) is spread to people by the bite of an infected mosquito. Most people infected with SLE virus 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. There are no vaccines to prevent nor medications to treat SLE. While SLE reemerged in California in 2015, it has not been detected in Marin County.
  • Zika virus is transmitted through mosquito bites, sexual transmission, or from a pregnant woman to her fetus. Many people infected with Zika virus wont’ have symptoms or will only have mild symptoms. Symptoms include fever, rash, headache, joint pain, read eyes, and muscle pain. Symptoms can last for several days to a week. People usually don’t get sick enough to go to the hospital, and they very rarely die of Zika. Once a person has been infected with Zika, they are likely to be protected from future infections.  Zika poses the greatest risk for pregnant women. Zika infection during pregnancy can cause a birth defect of the brain called microcephaly and other severe brain defects. It is also linked to other problems, such as miscarriage, stillbirth, and other birth defects. There have also been increased reports of Guillain-Barré syndrome, an uncommon sickness of the nervous system, in areas affected by Zika. If you must travel to an area with risk of Zika, take steps to protect yourself. Pregnant women should avoid traveling to areas of Zika outbreaks.  While Zika has been found in areas around the United States, they have not been detected in Marin County.

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