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Human Information

West Nile virus is an Arthropod-borne virus, i.e., Arboviruses, maintained in nature when susceptible vertebrate hosts become infected when the infected arthropod (mosquitoes, ticks, etc.) take a blood meal. These viruses are usually found in small mammals or birds and are transmitted to humans through mosquitoes. Humans are incidental hosts because only in very few specific cases do humans produce enough viremia to cause vector infection. The term 'arbovirus' has no taxonomic significance.

There are currently over 100 arboviruses distributed worldwide. The four main virus agents of encephalitis in the United States include St. Louis encephalitis (SLE), California serogroup (primarily LaCrosse (LAC)) encephalitis, western equine encephalitis (WEE) and eastern equine encephalitis (EEE), all of which are transmitted to humans by the bite of an infected mosquito. In the United States, West Nile virus (WNV) was first recognized in 1999 as the cause of an encephalitis outbreak in New York state.

The surveillance program consists of human West Nile virus patient surveillance, mosquito trapping and identification, identification of equine West Nile virus cases, reporting dead birds and testing of dead birds for WNV.