What is West Nile Virus?

Mosquito (Credit: tanakawho/Creative Commons)

Have you heard the recent news about West Nile Virus? In the last couple weeks, Texas has experienced a fairly large number of cases in the counties surrounding Dallas and it doesn’t seem to be getting any better. The state has reported 336 cases of human infection and 14 deaths as of August 11, 2012. Dallas County declared a state of emergency due to the number of cases and has authorized a city-wide spraying of insecticide.

West Nile virus is a classified as a flavivirus. The family Flaviviridae contains West Nile virus as well as St. Louis encephalitis virus, dengue virus and yellow fever virus. They all can cause encephalitis, which is an irritation and swelling of the brain.

According to the Centers for Disease Control, 43 states have reported cases of West Nile virus infecting humans in 2012.

West Nile Virus is spread by mosquitoes, with the peak season for West Nile virus is during late August to early September. As the weather cools and the mosquitoes die off for the year, the number of cases goes down.

West Nile virus is common in temperate and tropical regions of the world. It was first identified in Uganda in 1937 and the first cases in the United States were discovered in the summer of 1999. Since then, the virus has become widespread in the United States.

Most people who become infected will never know it. The majority of infected people won’t notice symptoms or develop severe disease. The people most at risk are immunocompromised, very young or very old, or pregnant. The minority that does develop symptoms will notice flu-like symptoms of abdominal pain, diarrhea, fever, headache, muscle aches, etc. Serious infections will result in confusion, loss of consciousness or coma.

In order to positively diagnose a patient with West Nile virus, blood or cerebrospinal fluid (CSF) is drawn and a serology test is used to check for antibodies against the virus.

For more information and updates about West Nile virus, please see the CDC website.