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Environmental Health

West Nile Virus

What is the West Nile Virus?

West Nile virus (WNV) is the leading cause of mosquito-borne disease in the United States.  It is spread to people by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds and then pass the virus to other birds, animals, and people. Cases of WNV occur during mosquito season, which starts in the summer and continues through fall.

West Nile Virus Symptoms and Treatment

Most people who are bitten by a mosquito with WNV never develop symptoms. Some people may have mild febrile illness symptoms such as fever with headache, body aches, joint pains, vomiting, diarrhea, and/or rash. Most people with febrile illness due to West Nile virus recover completely, but fatigue and weakness can sometimes last for weeks or months.

A small number of people infected with West Nile Virus develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).

  • Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
  • Severe illness can occur in people of any age; however, people over 60 years of age are at greater risk for severe illness if they are infected (1 in 50 people). People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.
  • 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.

There is no vaccine or treatment for WNV. Rest, fluids, and over-the-counter pain medications may relieve some symptoms. In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

Ways to protect yourself against West Nile Virus

The best way to prevent West Nile Virus is to protect yourself from mosquito bites. Here are ways you can protect yourself and your family:

  • Limit evening outdoor activity when mosquitos are most active.
  • Use insect repellent. Click here for the Environmental Protection Agency (EPA) registered insect repellents. You can also use the EPA’s Search Tool to find the right repellent for you.
  • Wear long-sleeve shirts and long pants.
  • Treat clothing and gear such as boots, pants, socks, etc. with 0.5 permethrin or buy permethrin-treated clothing and gear.
  • Use mosquito nets correctly. Follow the instruction label for the best results.
  • Use screens on windows and doors and make sure there are no holes in the screens.
Ways to reduce the mosquito population around your home
  • Clean clogged roof gutters on an annual basis. Roof gutters are easily overlooked and can be an ideal breeding ground for mosquitos.
  • Aerate ornamental pools or stock them with fish. Water gardens are major mosquito producers if allowed to stagnate.
  • Dispose of tin cans, ceramic pots, old tires or similar water holding containers on your property.

For more prevention tips, click here

How to Protect pets and livestock against West Nile Virus

There is no vaccine for dogs and cats. However, horse owners should ensure their horses are vaccinated against West Nile virus (WNV), Eastern Equine Encephalitis (EEE) and Western Equine Encephalitis (WEE). Consult your veterinarian for more details.

Can dead birds be tested for West Nile Virus?

 Washoe County Health District Vector-Borne Disease Prevention Program collects some dead birds for testing of West Nile virus. For a bird to be testable it must be recently deceased and in good overall condition.  The program does not test pigeons or doves.  

 Nevada Department of Agriculture also collects some dead birds for testing. Call 775-353-3709 for more information on specimen collection and handling. 

Nevada Department of Wildlife provides information on reporting any sick or dead wildlife and provides a link to report sick or dead wildlife online. The public can also call 775-688-1500 for reporting. 

If you want to dispose of a bird, you may use rubber or latex gloves to pick it up and put it in a plastic bag. Or, if gloves are not available, use a plastic bag turned inside out and pick up the carcass with your protected hand. With your other hand, wrap the bag around the bird, tie off the bag and place it inside a second plastic bag that you can again tie off or zip lock shut. Double bagging prevents cross-contamination and leakage. Place the double bag inside of an outside garbage can or dumpster.

Where can I get more information on West Nile Virus?