West Nile Virus: What To Know

By Michelle Abbo, MD, Scripps Health

As if it isn’t bad enough that mosquitoes leave itchy, swollen welts on their victims that can last for days, this summer’s swarms have brought another problem: West Nile virus. A blood-borne disease that can cause symptoms ranging from mild to life-threatening, West Nile virus has been especially widespread this year. In an average year, about 300 cases are reported; according to the Centers for Disease Control (CDC), more than 1,100 cases have been reported so far in 2012, and 41 people have died.

West Nile is most often transmitted to humans, horses, squirrels and other animals by the bite of an infected mosquito, which acquires the virus from feeding on infected birds. Since donated blood is tested for the virus, blood transfusions are unlikely to spread it.  It is not transmitted through casual contact such as touching, kissing or sharing towels.

The virus can make some people very sick yet not affect others at all. About 80 percent of those who get the virus have no symptoms. In the other 20 percent, symptoms usually develop within a few days to two weeks after being bitten and usually include fever, headache, body aches, and swollen glands. Some people may develop a skin rash. Most symptoms go away within a few weeks. 

However, for about one in 150 people, West Nile virus becomes a serious illness, with severe symptoms such as high fever, neck stiffness, disorientation, convulsions, swelling of the brain, coma and paralysis. In rare cases, brain damage can be permanent, and the disease can be fatal.

There is no specific treatment for the infection; like the flu, mild cases resolve on their own within a week or two. More severe symptoms may require medical support such as intravenous fluids and nursing care. If you develop symptoms that cause concern, call your doctor or go to an urgent care center or emergency department.

While this year’s outbreak is the largest seen in the U.S. so far since the virus was first detected in the country in 1999, San Diego County has not had any reports of serious human cases of the disease. The County uses helicopters and back-pack devices to drop and spread larvicide, a type of insecticide that targets mosquitoes in the larvae stage, on local waterways. The larvicide is not harmful to people or pets. 

Not all mosquitoes carry West Nile virus, but since there is no way to tell which ones are infected just by looking at them, the best defense is to avoid them as much as possible. Here are a few tips to keep yourself and your family virus-free:

• Stay indoors at dusk and dawn, when mosquitoes are most active. If you do go outdoors, wear long pants and sleeves and use an insect repellent with an EPA-registered active ingredient such as DEET, Picaridin, Oil of Eucalyptus or IR3535.
• Put screens on open windows and doors to keep mosquitoes out of the house. Check screens for tears or poor fit.
• Standing water is the ideal breeding ground for mosquitoes, so empty anything in your yard that holds such as bird baths, unused planters, rain gutters, and water dishes for pets. Empty kiddie pools when not in use. The County of San Diego can supply mosquito-eating fish for fountains and decorative pools.
• Report dead birds, hawks and owls, as well as unused or green swimming pools, to the County Health Department.
• Avoid dead birds, squirrels and other animals and never touch them with bare hands. Report them to the health department, which may want to test them for the virus.

Michelle Abbo, MD, is an internal medicine physician with Scripps. For a referral to a Scripps physician, call 1-800-SCRIPPS (1-800-727-4777).