West Nile Virus

When summer is in full swing, you can bet that people will want to be outdoors. Unfortunately, it's also the time that mosquitoes come out. You should take care to protect yourself from West Nile virus, one of many germs that mosquitoes can carry. The insects pick up the virus by feeding on infected birds and transmit the disease when they bite other animals. The virus has been found in many different species, including horses, cats, squirrels, and, of course, humans.

Humans usually catch the disease from mosquitoes, though, not from infected people, birds, horses, or pets. However, researchers at the Centers for Disease Control and Prevention have confirmed that four organ transplant patients developed the disease in 2002 after receiving organs from the same infected donor, and one of the patients died.

Outbreaks of West Nile virus seem to affect birds first. In many areas, an early warning sign for residents is an abundance of dead crows. The CDC urges people to call local animal control officers to report dead or sick birds so that they may be tested for the virus.

Why is West Nile virus dangerous?

In the worst-case scenario, the virus travels through the bloodstream and infects the brain. The infection can lead to encephalitis, or acute inflammation of the brain. It can also cause meningitis, which is inflammation of the brain's outer covering.

However, serious complications such as encephalitis are extremely rare in people under 50. Although anyone can become infected from a mosquito bite, the elderly are much more likely to become sick. Fortunately, the worst-case scenario is unlikely. Data from the CDC shows that about half of all West Nile cases result in encephalitis or meningitis and 2 percent are fatal. But when factoring in that only the worst cases are reported to the CDC, the agency estimates that less than 1 percent of all cases develop serious complications.

There's no cure for the virus itself, but most people are able to fight it off easily. Many who contract the virus have symptoms so mild, and their recovery is so fast, that they might not be aware of ever having the disease. As reported in the Annals of Internal Medicine, about one in five infected people develops a mild fever. Other common symptoms include muscle pain, joint pain, fatigue, headache, swollen lymph glands, and a skin rash on the trunk. These symptoms generally last for just a few days.

What are the warning signs?

If you live in an area where there's a West Nile outbreak, you should know the warning signs of this potentially serious disease. If you develop a high fever, confusion, severe headache, or muscle weakness, the CDC urges you to call a doctor immediately.

You should also seek immediate medical care if you get a sudden headache and stiffness in the neck, which are possible symptoms of encephalitis.

Other symptoms of encephalitis include tremors, convulsions, hearing or vision problems, confusion, drowsiness, vomiting, unusual sensitivity to light, lack of muscle coordination or difficulty walking, irritability (and other mental disturbances), poor responsiveness, trouble speaking coherently, or coma. If you or someone you know develops these symptoms, especially in combination with a sudden headache or stiff neck, seek emergency care right away. A single mosquito bite -- or even several -- is no cause for alarm. Even if there is an outbreak in your area, only a tiny percentage of mosquitoes carry the germ. Unless you start developing symptoms of an infection, there's no reason to worry.

What precautions should you take?

There's no human vaccine against West Nile virus (although there is a vaccine for horses). The best way to avoid the disease is to guard against mosquito bites. Being cautious during the summer and fall when mosquitoes are especially prevalent may not be enough. Some areas in the south have mosquitoes all year long, and the CDC reports that one species of mosquito known to carry the virus is able to survive winter weather. One of the first things to do is make sure your house has tight-fitting window screens. The CDC and other health officials offer these additional tips for preventing mosquito bites:

  • When possible, wear long pants and long-sleeved shirts sprayed lightly with the chemical DEET (short for N, N-diethyl-m-toluamide), Picaridin (KBR 3023), or oil of lemon eucalyptus (p-menthane 3, 8-diol [PMD]).
  • The best protection against mosquitoes (short of staying indoors) is a repellent containing DEET or Picaridin, according to the CDC. The CDC says that recent research shows oil of lemon eucalyptus, a plant-based repellent, may also provide similar protection. The agency recommends applying one of these substances on all exposed skin of adults and children age 3 and older.
  • Stay inside during dawn, dusk, and early evening, the times when mosquitoes are most active.
  • Don't let your house become a mosquito breeding ground. Remove standing water from flowerpots, buckets, clogged rain gutters, old bottles and cans, and birdbaths. Drain water from pool covers and make sure that pools and hot tubs are clean and chlorinated.

Repellents like DEET can irritate the eyes and mouth, so keep it off of children's hands. If you're wearing light clothing, like a T-shirt, you may have to spray that also. (You can give other natural fiber clothing a light spray as well.) A few other cautions from the manufacturer: Don't soak clothing or bedding in DEET, never spray it on broken skin or in anyone's face, and avoid using it on children under 2 months of age. For all children, the American Academy of Pediatrics recommends using DEET in concentrations of less than 30 percent.

Interestingly, DEET and other repellents don't kill mosquitoes. Instead, they make it impossible for them to find you for several hours. Mosquitoes locate their human prey through the carbon monoxide given off by our skin and breath, and repellents disrupt their ability to target us by following our scent and exhalations.

Last, read the product label carefully, because the repellent comes in different concentrations. If you plan to be outdoors for more than three hours, you may need to reapply it or use a higher concentration. Avoid using any pesticide on your body that's designed to kill mosquitoes. These simple steps will save you from itchy, annoying bites -- and you'll also have some peace of mind.

References

Centers for Disease Control and Prevention. West Nile virus: Questions and answers. February 25, 2010.

Centers for Disease Control and Prevention. West Nile virus update. August 4, 2003.

Centers for Disease Control and Prevention. West Nile virus. Fight the Bite! December 28, 2010.

Centers for Disease Control and Prevention. West Nile Virus Case Count. December 28, 2010.

Petersen LR and AA Marfin. West Nile virus: A primer for the clinician. Annals of Internal Medicine. August 6, 2002. 137(3): 173-179.

New York City Department of Health and Mental Hygiene. West Nile virus: Symptoms and care. July 2002.

West Nile Seen Scarier Than SARS for U.S., Canada. Reuters Health Information. May 15, 2003.

American Academy of Pediatrics. Follow Safety Precautions When Using DEET on Children.

Centers for Disease Control and Prevention. Insect Repellent Use and Safety. May 2008.

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