West Nile virus first emerged in the United States in the New York metropolitan area in the fall of 1999. Since then, the virus, which can be transmitted to humans by the bite of an infected mosquito, has quickly spread across the country.

In 2002, the state's first human cases and deaths from West Nile disease were recorded and all but two of the state's 102 counties eventually reported a positive, human, bird, mosquito or horse case.

The Louisiana Department of Public Health (LDOPH) maintains a sophisticated disease surveillance system to monitor animals and insects that can potentially carry the virus: dead crows and blue jays, mosquitoes and horses. Mosquitoes can either carry the virus or get it by feeding on infected birds.

Mild cases of West Nile infections may cause a slight fever or headache. More severe infections are marked by a rapid onset of a high fever with head and body aches, disorientation, tremors, convulsions and, in the most severe cases, paralysis or death. Usually symptoms occur from three to 14 days after the bite of an infected mosquito. Persons at the highest risk for serious illness are those 50 years of age or older.