West Nile Virus and other mosquito-borne diseases in Canada
Annual national surveillance report - 2017
West Nile Virus
During the 2017 West Nile virus (WNV) season, six provinces (Québec, Ontario, Manitoba, Saskatchewan, Alberta, and British Columbia) reported West Nile virus activity to the Public Health Agency of Canada (PHAC) (Figure 1).
In total, 193 human clinical cases (both confirmed and probable) were reported: Québec (26), Ontario (154), Manitoba (4), Saskatchewan (1), Alberta (7), and British Columbia (1). Of these, eighty-six (45%) were classified as WNV Neurological syndrome, seventy-one (37%) as WNV Non-neurological syndrome and thirty-six (19%) as unclassified (Figure 2, Table 1). Eight deaths associated with WNV were reported in the 2017 season. In addition, seven WNV asymptomatic infections were reported by four provinces: Québec (1), Ontario (4), Manitoba (1), and British Columbia (1).
In the 2017 season, 17,374 mosquito pools were tested for WNV in four provinces: Québec (1,849), Ontario (14,076), Manitoba (1,028), and Saskatchewan (421). Of these, 544 (3.13%) tested positive for West Nile virus: 84 in Québec (15%), 409 in Ontario (75%), forty-one in Manitoba (8%), and ten in Saskatchewan (2%) (Table 2).
The Canadian Wildlife Health Cooperative (CWHC) reported a total of 236 dead wild birds that were tested for WNV. Of these, 146 (62%) were positive for WNV: Québec (87), Ontario (46), Manitoba (2), and Saskatchewan (11). Overall, WNV activity was detected in wild birds from June to early December in Canada (Figure 3).
Detections of WNV in wildlife during the 2017 season relied mainly on the CWHC National Scanning Surveillance Program; the detection of WNV in wild birds in Manitoba was done by Manitoba Agriculture, Food and Rural Initiatives. Further details on surveillance data can be accessed via the CWHC website: http://www.cwhc-rcsf.ca/.
Fifty-four (54) horses with WNV infection were reported to the Canadian Food Inspection Agency from the following six provinces: Québec (7), Ontario (23), Manitoba (1), Saskatchewan (8), Alberta (11), and British Columbia (4). In addition, cases of WNV in other domestic animals were reported: pheasant (1 case in Québec), alpacas (1 case in Ontario, 1 case in Québec).
Other mosquito-borne diseases
During the WNV season, samples collected for testing that were negative for WNV were regularly assessed for other select mosquito-borne diseases that could be locally acquired in Canada. Findings regarding these other mosquito-borne diseases are highlighted below.
Eastern Equine Encephalitis Virus
In 2016, Canada reported its first locally acquired human case of Eastern Equine Encephalitis (EEE) virus. During 2017, no human cases of EEE were reported to PHAC.
During 2017, two horses tested positive for EEE virus in Ontario and were reported by the Canadian Food Inspection Agency based on testing at private animal health laboratories.
California Serogroup Viruses
In 2017, a total of 122 human laboratory confirmed cases/exposures of California serogroup virus were diagnosed by the National Microbiology Laboratory in the following eight provinces: Nova Scotia (2), New Brunswick (4), Québec (100), Ontario (1), Manitoba (1), Saskatchewan (10), Alberta (3), and British Columbia (1). Of these, eighty-nine (89) were further classified as Jamestown Canyon virus and eleven (11) as Snowshoe Hare virus.
Most of the samples were initially collected for testing for West Nile virus; WNV-negative samples were further assayed for non-West Nile virus mosquito-borne agents. During the 2017 season, enhanced surveillance for the detection of California serogroup viruses was carried out in Quebec.
Figure 2 - Text Equivalent
A total of 200 human clinical cases and asymptomatic infections were reported to the Public Health Agency of Canada (PHAC): 27 in Quebec, 158 in Ontario, 5 in Manitoba, 1 in Saskatchewan, 7 in Alberta and 2 in British Columbia.
|Province / Territory||Report WeekFootnote ±||Total|
|WNV Clinical CasesFootnote 1|
|Province/Territory||Neurological syndrome||Non-neurological syndrome||Unclassified/ Unspecified||Total clinical casesFootnote 1||Travel-related casesFootnote 2||Asymptomatic infectionsFootnote 3|
|Province/Territory||2017 West Nile virus seasonFootnote *|
|Number of positive mosquito pools||Number of mosquito pools tested||Percentage of positive mosquito pools (%)|
Figure 3 - Text Equivalent
In 2017, there were a total of 146 WNV cases in birds in Canada
- Footnote *
Not all provinces are conducting dead wild bird surveillance as part of their own WNV surveillance program. However, WNV positive dead wild birds may be identified through the National Wildlife Disease Surveillance Program of the CWHC.
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