Seminar in Geography: West Nile

West Nile virus was first detected in the United States in New York City in 1999 and quickly spread across the country within a few years. West Nile virus was first identified in Ohio birds and mosquitoes in 2001. The following year, the first human cases and deaths were reported. By the end of 2002, all but one of the state's 88 counties reported positive humans (441 total human cases), mosquitoes, birds or horses. West Nile virus is now established in Ohio where cases occur each year and seasonal epidemics can flare up under certain conditions in the summer and continue into the fall.

Cases of West Nile virus (WNV) have been reported in states across the continental United States. WNV activity typically occurs during the summer months and into the fall. The annual number of reported WNV disease cases can fluctuate widely, as a result of periodic epidemics. All residents of and visitors to areas where WNV activity has been identified are at risk of WNV infection, particularly people who engage in outdoor work and recreational activities.

Mosquito-based arbovirus surveillance data are useful in tracking virus activity. The most basic form of mosquito-based surveillance data presentation – and that currently used by CDC’s ArboNET system – is the number of positive mosquito pools found in collections of a particular mosquito species over a defined time period and area.