Why the West in West Nile virus infections

West Nile virus (WNV) was initially isolated and identified in 1937 in Uganda (Africa). Over the ensuing decades, outbreaks of WNV were infrequent, usually associated with mild febrile illnesses, and most commonly found in west Asia, Africa and the Middle East (1,2). However, WNV was identified in North America in 1999 following an outbreak of viral encephalitis in New York City (USA) that resulted in 62 confirmed human cases with seven deaths (3). Within the next five years, WNV emerged as an important human, avian and equine disease in the United States (2–7). Following this outbreak in New York City, several Canadian provinces implemented enhanced surveillance for human cases of WNV encephalitis, but none were detected. The first WNV-infected bird was detected in Ontario in 2001, and the first confirmed human cases of WNV infection endemic to Canada occurred in Quebec and Ontario in 2002 (8). During the summer of 2003, WNV became firmly established within the Canadian ecology and a total of 1493 human cases of illness (14 deaths) due to WNV infection were reported, with the majority occurring in western Canada (9). The ensuing three years were relatively quiet with only 26 cases reported in 2004, 225 cases in 2005 and 151 cases in 2006. However, 2007 has seen a record 2035 human cases reported in Canada as of September 15, with more than 99% of the cases occurring in the three Prairie provinces (9).