Mosquitos and West Nile Virus

First reported in the United States in 1999, West Nile Virus has since spread rapidly. It typically appears in the summer until fall.

For 20 percent of those who become infected, the virus causes a mild, flu-like illness. It is considered a public health concern because there is a risk of contracting a potentially fatal brain infection in about one percent of cases. The severity of the virus is greater for persons over age 50 and for persons whose immune systems are compromised.

West Nile Virus is transmitted by mosquitoes, which means the best way to reduce your chance of becoming infected is to avoid getting bitten. Here’s how:

  • When you are outside, use insect repellent such as DEET (no more than 10 percent formula for children; not intended for use on infants under two months old) or natural oil of lemon eucalyptus (not intended for use on children under age three) on clothing and skin. For details on insect repellents and CDC usage guidelines go here.
  • Eliminate mosquito breeding sites by draining sources of standing water, inserting mosquito larvae pellets in drains, maintaining clean gutters and keeping fountain waters flowing.
  • Cover up as much as possible when you are outdoors; wear long-sleeve shirts and pants.
  • Stay inside between sunset and sunrise, when mosquitoes are more active.
  • Install or repair screens on doors and windows to keep mosquitoes out.
  • Never handle dead birds with your bare hands (precautionary measure to prevent disease).
  • Investigate and support your community’s mosquito-control program. Many communities practice integrated pest management. For details, see

Identifying Mild and Severe Symptoms

  • About one in five persons who become infected show any signs of illness, and usually these symptoms are mild. Most infected people will experience fever, headache, fatigue, aches and pains and, in some cases, swollen lymph nodes and a skin rash on the trunk of the body.
  • These symptoms generally last for a few days, but in some cases can linger for a few weeks.
  • Symptoms of serious infection include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis.
  • Symptoms of the most severe infections include West Nile encephalitis (inflammation of the brain), meningitis (inflammation of the tissue surrounding the brain and spinal cord) and West Nile poliomyelitis (inflammation of the spinal cord that causes sudden weakness and/or paralysis in the limbs and/or breathing muscles).

Because there is no specific treatment available for West Nile Virus infection, prevention of mosquito bites is critical.

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