West Nile virus surveillance and diagnostics: A Canadian perspective

Abstract

A surveillance program has been in place since 2000 to detect the presence of West Nile virus (WNV) in Canada. Serological assays are most appropriate when monitoring for human disease and undertaking case investigations. Genomic amplification procedures are more commonly used for testing animal and mosquito specimens collected as part of ongoing surveillance efforts. The incursion of WNV into this country was documented for the first time in 2001 when WNV was demonstrated in 12 Ontario health units during the late summer and fall. In 2002 WNV activity was documented by avian surveillance in Ontario by mid-May with subsequent expansion of the virus throughout Ontario and into Quebec, Manitoba, Saskatchewan and Nova Scotia. Human cases were recorded in both Ontario and Quebec in 2002 with approximately 800 to 1000 probable, confirmed and suspect cases detected. The possible recurrence and further spread of WNV to other parts of Canada in 2003 must be anticipated with potential risk to public health. The continued surveillance and monitoring for WNV-associated human illness is necessary and appropriate disease prevention measures need to be in place in 2003.

Keywords: Corvids; Diagnostics; Humans; Mosquitoes; Surveillance; West Nile virus.

Figure 1

West Nile virus diagnostic platforms (including biocontainment levels at which procedures are performed). *The manipulation of bird tissue may require level 3 (L3) containment. This is advised due to high viral load in infected corvids and other bird species. Ag Antigen; HI Hemagglutination inhibition; IHC-IFA Immunohistochemistry-immunofluorescence assay; L2 Level 2; NASBA Nucleic acid sequence based amplification; NATs nucleic acid amplification tests; PCR Polymerase chain reaction; PRNT plaque-reduction neutralization test