West Nile virus range expansion into British Columbia.

In 2009, an expansion of West Nile virus (WNV) into the Canadian province of British Columbia was detected. Two locally acquired cases of infection in humans and 3 cases of infection in horses were detected by ELISA and plaque-reduction neutralization tests. Ten positive mosquito pools were detected by reverse transcription PCR. Most WNV activity in British Columbia in 2009 occurred in the hot and dry southern Okanagan Valley. Virus establishment and amplification in this region was likely facilitated by above average nightly temperatures and a rapid accumulation of degree-days in late summer. Estimated exposure dates for humans and initial detection of WNV-positive mosquitoes occurred concurrently with a late summer increase in Culex tarsalis mosquitoes (which spread western equine encephalitis) in the southern Okanagan Valley. The conditions present during this range expansion suggest that temperature and Cx. tarsalis mosquito abundance may be limiting factors for WNV transmission in this portion of the Pacific Northwest.

Use of geographic information systems to assess the feasibility of ground- and aerial-based adulticiding for West Nile virus control in British Columbia, Canada.

Geographic Information Systems (GIS) analysis of 34 forecasted high West Nile virus (WNV) risk communities in British Columbia (BC), Canada was useful to assess feasibility and planning of the operational logistics of an emergency spray event in advance of a WNV outbreak. The geographic coverage and operational time required to perform ground- and aerial-based ultra-low volume (ULV) adulticiding were calculated using GIS. The mean geographic coverages of the ground-, aerial-, and combination of ground- and aerial-based adulticiding strategies were 39%, 61%, and 69%, respectively. The driving distance, driving time, and number of treatment nights required to perform ground-based spraying of an entire community were also calculated. Due to the large variability of treatment coverage estimates within and among the communities, no single treatment method was identified as the best strategy for province-wide ULV adulticiding in BC. Instead, the strategy for each community should be examined individually with local knowledge and expertise.