Dear Doctors: I keep seeing on the news that we are having a lot more cases of West Nile virus here in Los Angeles than we used to. It seems like there are more mosquitoes here each year, so it does make sense. How do you know if you have West Nile, and what is the treatment? Is there a vaccine?
Dear Reader: West Nile virus is the leading cause of mosquito-borne illness in the contiguous United States. This has been the case since it first emerged in this country in 1999. Mosquitoes acquire the virus when they feed on an infected bird, and then they can pass it along to a subsequent host. Thanks to migratory patterns and the prevalence of mosquitoes throughout the world, the virus has seen a rapid spread. At this time, West Nile virus is not spread through ordinary person-to-person contact.
As is happening in many areas of the U.S., Southern California is seeing an increase in the number of cases of West Nile virus this year. Data collected by local health agencies shows a rise in the number of mosquito samples infected with the virus and a significant increase in the number of human cases. This is being driven, in part, by warmer and more humid summer weather, which helps mosquitoes thrive.
In the majority of people, the virus does not cause symptoms. Of the 20% who do become sick, the illness is typically mild. The most common symptoms are mild to moderate fever and a flu-like illness. Treatment focuses on supportive care, including rest, hydration and over-the-counter medications for fever and pain. However, for a small percentage of people, West Nile virus can become neuroinvasive. That means it has infected the central nervous system, which includes the spinal cord and the brain. People 65 and older and those of all ages who are immunocompromised are at greatest risk of this escalation.
Symptoms of neuroinvasive illness with West Nile include severe headache, stiff neck, sensitivity to light, changes to vision, sudden muscle weakness or an altered mental state. If any of these occur, the person must seek immediate emergency medical care. In mild disease, treatment consists of supportive care. However, in neuroinvasive disease, this is intensive, hospital-based care. It can include IV fluids to maintain electrolyte balance, antiseizure medications, respiratory support, and pain and fever management.
There is no approved West Nile vaccine for humans at this time. That makes it important to take steps to decrease contact with mosquitoes. Do a check of your property and address any places water can collect. Mosquitoes need standing water to breed, and just a few tablespoons can be enough. Protect yourself with an insect spray. For adults, products that contain 30% DEET are known to be extremely effective. When using insect repellents on children, be sure to choose age-specific products and closely follow directions on the product label.
With these simple precautions, you can lower your risk of infection and even enjoy spending time outdoors during mosquito season.
(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
