West Nile Virus

West Nile Virus (WNV) is a mosquito-borne virus first reported in Africa, West Asia, the Middle East and now recently identified in the United States in 1999.  Primarily a bird disease, it can also affect mammals including humans.  It is in the same virus family as the St. Louis Encephalitis virus, also found in Florida.

Infected mosquitoes transmit the virus from birds to humans. The virus undergoes a reproductive cycle inside the mosquito, in which it must multiply in many tissues, and accumulates in the salivary glands of the mosquito. Mosquitoes salivate every time they bite, and are capable of transmitting the virus 10-14 days after feeding on an infected bird, so bites after that time are infectious. Many mosquito species have been identified with West Nile Virus including: Culex, Aedes, and Ochlerotatus spp. C. pipiens, the northern house mosquito.  These includes species active at dawn and dusk, and those active during the day.

Mosquito Prevention and Control

  • Dispose of any materials that can hold water such as tin cans and used tires.
  • Drill holes in the bottom of recycling containers and check uncovered junk piles for standing water.
  • Clean clogged roof gutters, check storm drains, and repair leaky outdoor faucets and window wells.
  • Empty accumulated water from wheelbarrows, boats, pet dishes, toys, ceramic pots.  Turn items over so they don't accumulate water.
  • Do not allow water to stagnate in birdbaths, ornamental pools, water gardens, and swimming pools.
  • Alter the landscape of your property to eliminate standing water.  Mosquitoes can breed in any puddle of water. Larvicides can be used when standing water cannot be eliminated.

Reduce Your Risk to West Nile Virus

  • Make sure window screens are "bug tight."
  • Use the proper type of lighting outside: incandescent lights attract mosquitoes, whereas fluorescent lights neither attract or repel mosquitoes.
  • Staying indoors at dawn and dusk when mosquitoes are most active.
  • Wearing long sleeved shirts and long pants when outdoors.
  • Spray exposed skin and clothing with repellents containing permethrin or DEET (mosquitoes can bite through thin clothing).  Be sure to follow label directions before applying.  For children use a repellent containing no more than 10 percent DEET.


Most persons infected with WNV have no symptoms.  A small percentage of individuals develop mild symptoms that include fever, headache, body aches, swollen lymph glands, and a body rash.  Severe symptoms include headache, high fever, neck stiffness, disorientation, tremors, convulsions, paralysis, and coma.  Encephalitis develops in less than 1% of infected people.  If you experience these symptoms contact your physician immediately.

Dead birds may indicate the presence of West Nile Virus in an area.  If you find a dead or dying bird report it to the Monroe County Health Department, Office of Environmental Health, Lower Keys 293-7524, Middle Keys 289-2721, or Upper Keys 853-1900.

To report a mosquito problem, contact Florida Keys Mosquito Control at 305-292-7190 or call 800-276-7493. 

More Information on the West Nile Virus: