Know the Facts About West Nile Virus

By John Spinosa, M.D., Ph.D., Scripps Memorial Hospital La Jolla

Not too long ago, the biggest risk from an encounter with a mosquito was an itchy, swollen bite. In recent years, however, a disease known as West Nile virus has elevated mosquitoes from simple pests to the source of a potentially serious infection.

West Nile virus is a seasonal epidemic that generally peaks from August to October. Most often, it is spread to humans and other animals by the bite of an infected mosquito, which gets the virus from feeding on infected birds. In rare cases, the virus also has been spread through blood transfusions, organ transplants, breastfeeding and from mother to baby during pregnancy. It is not spread through casual contact such as touching, kissing or sharing utensils.

Like many viruses, West Nile has several forms. So far, the majority of West Nile cases seen this year in Southern California are the neuroinvasive form, which is a more severe strain that can affect the brain.

And like many viruses, West Nile can make some people very sick while only mildly affecting others. About 80 percent of people who contract West Nile virus have no symptoms at all. In the other 20 percent, symptoms usually develop from three to 14 days after infection and may include mild, flu-like reactions such as fever, headache and body aches, nausea, swollen glands and a skin rash. These symptoms can last from a few days to a few weeks.

For very few people —about one in 150—the virus leads to serious illness with severe symptoms such as a high fever, neck stiffness, disorientation, tremors, convulsions, muscle weakness, vision loss, numbness, paralysis and coma. Symptoms may last several weeks, while the neurological damage may be permanent. People over age 50 are more likely to have severe symptoms than younger people. If you develop anything other than mild symptoms, call your doctor right away or go to the emergency room.

There is no specific treatment for West Nile virus infection. As with the flu, milder cases clear up on their own over time. People who suffer more severe symptoms may need hospital care, such as intravenous fluids and nursing support.

Prevention and Treatment

In recent weeks, health officials in California have warned that the risk of contracting West Nile virus from mosquito bites is the highest it has been since 2004, when 710 people were infected, 21 fatally. Anyone is at risk: the virus has affected people between six months and 96 years of age.

The best way to avoid West Nile virus is to avoid the source: mosquitoes. So far in 2008, over 300 mosquito samples and more than 500 dead birds in Southern California have tested positive for the virus. Mosquitoes are most active at dusk and dawn; if you can’t stay indoors during these times, be sure to use insect repellant and wear long pants and sleeves if possible. Any time you do go outdoors, use insect repellent containing a long-lasting, EPA-registered active ingredient such as DEET, Picaridin, Oil of Lemon Eucalyptus or IR3535. Use as directed on the package and remember to reapply if you go swimming, perspire, etc.

Keep mosquitoes out of your home with screens on your windows and doors, and eliminate sources of standing water such as flower pots, buckets, bird baths and pet water dishes. If your child has a wading pool, empty it when it isn’t being used. In Southern California, the increase in home foreclosures has left many backyard swimming pools unused—a perfect breeding ground for mosquitoes.

In addition, avoid dead birds and teach children to steer clear as well. If you find one, don’t touch it with your bare hands; instead, call your local health department for instructions. Officials may want to test the bird for the virus.

Although medical procedures can spread West Nile virus, the risk is very low. Donated blood is screened for the virus, and infection is rarely contracted through organ transplants. If you are having surgery and have concerns, talk to your doctor.

John Spinosa, M.D., Ph.D., is a pathologist and chief of staff at Scripps Memorial Hospital La Jolla. For more wellness tips or for a physician referral, please call 1-800-SCRIPPS (1-800-727-4777).