West Nile Virus and other mosquito-borne diseases in Canada

Annual national surveillance report - 2017

West Nile Virus

Humans

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).

Mosquitoes

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).

Wild Birds

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/.

Domestic Animals

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

Humans

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.

Domestic Animals

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 1 - Text Equivalent

Map showing geographic distribution of West Nile virus (WNV) in Canada.

Geographical distribution of human cases of West Nile virus (WNV) in Canada.

During the 2017 West Nile Virus (WNV) season, six provinces (Quebec, Ontario, Manitoba, Saskatchewan, Alberta and British Columbia) reported West Nile virus activity to the Public Health Agency of Canada (PHAC).

A total of 200 human cases were reported: 27 in Quebec, 158 in Ontario, 5 in Manitoba, one in Saskatchewan, 7 in Alberta, and 2 in British Columbia

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.

Table showing human clinical cases and asymptomatic infections associated with WNV in Canada, by province or territory and by week monitoring, 2017

Province / Territory	Report WeekFootnote ±																												Total
	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50
SaskatchewanFootnote *	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1
Québec	2	2	2	5	1	3	3	2	1	2	1	1	1	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	27
Alberta	0	0	0	0	0	0	0	0	0	0	1	4	1	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	7
Manitoba	0	0	0	0	0	0	0	0	0	0	0	3	0	1	0	0	0	0	0	0	0	1	0	0	0	0	0	0	5
British Columbia	0	0	0	0	0	0	0	0	0	0	0	2	0	0	0	0	0	0	0	0	0		0	0	0	0	0	0	2
Ontario	0	0	1	0	1	1	7	3	6	8	23	17	29	21	10	14	6	6	3	0	0	1	0	0	0	0	0	1	158
Total	2	2	3	5	2	4	10	5	7	10	25	27	31	25	10	14	6	6	3	0	0	2	0	0	0	0	0	1	200
Footnote 1 WNV clinical cases and asymptomatic infections are grouped by report week, based on episode date. Episode date could include one of the following: onset date, diagnosis date, lab sample date or reporting date. Return to footnote ± referrer Footnote 2 Saskatchewan provides counts of WNV neurological syndrome cases only. Return to footnote * referrer

Table 1: WNV human clinical cases and asymptomatic infections in Canada, 2017 season

WNV Clinical CasesFootnote 1
Province/Territory	Neurological syndrome	Non-neurological syndrome	Unclassified/ Unspecified	Total clinical casesFootnote 1	Travel-related casesFootnote 2	Asymptomatic infectionsFootnote 3
Québec	24	2	0	26	0	1
Ontario	55	63	36	154	31	4
Manitoba	3	1	0	4	0	1
SaskatchewanFootnote 4	1	-	-	-	-	-
Alberta	2	5	0	7	2	0
British Columbia	1	0	0	1	0	1
Total	86	71	36	193	33	7
Footnote 1 Total clinical cases are the sum of confirmed and probable: WNV neurological and non-neurological syndromes, along with any unclassified or unspecified cases. Return to footnote 1 referrer Footnote 2 Likely related to travel outside the Province/Territory. These cases are included in either the total clinical cases or WNV asymptomatic infections. Return to footnote 2 referrer Footnote 3 Satisfies WNV diagnostic test criteria in the absence of clinical criteria. This category could include asymptomatic blood donors whose blood is screened using a nucleic acid amplification test, by blood operators (i.e. Canadian Blood Services or Hema-Quebec) and is subsequently brought to the attention of public health officials. Blood operators in Canada perform a supplementary WNV specific nucleic acid amplification test following any positive donor screen test result. Return to footnote 3 referrer Footnote 4 Saskatchewan provides counts of WNV neurological syndrome cases only. Return to footnote 4 referrer

Table 2: Number of mosquito pools tested for WNV and number of positive mosquito pools in Canada, 2017 season

Province/Territory	2017 West Nile virus seasonFootnote *
	Number of positive mosquito pools	Number of mosquito pools tested	Percentage of positive mosquito pools (%)
Québec	84	1,849	4.54
Ontario	409	14,076	2.91
Manitoba	41	1,028	3.99
Saskatchewan	10	421	2.38
Total	544	17,374	3.13
Footnotes Footnote * In 2017, mosquito surveillance was conducted by the following four provinces: Quebec, Ontario, Manitoba, and Saskatchewan. Return to footnote * referrer

Figure 3 - Text Equivalent

In 2017, there were a total of 146 WNV cases in birds in Canada

Table showing the reported number of dead birds tested positive for WNV in Canada, by province/territory and by report week, 2017 season.

Province	April	May				Jun					Jul				Aug					Sep				Oct				Nov					Dec		Total
	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50
Québec	0	0	0	0	0	0	0	0	0	0	0	5	3	9	10	7	8	10	16	6	4	4	2	1	0	0	1	1	0	0	0	0	0	0	87
Ontario	0	0	0	0	0	0	0	0	3	1	1	0	0	2	6	1	8	4	3	5	1	0	2	2	1	1	1	1	0	0	1	0	0	2	46
Manitoba	0	0	0	0	0	0	0	0	0	0	0	0	0	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	2
Saskatchewan	0	0	0	0	0	0	0	0	0	0	0	0	0	0	2	0	4	3	1	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	11
Total	0	0	0	0	0	0	0	0	3	1	1	5	3	13	18	8	20	17	20	12	5	4	4	3	1	1	2	2	0	0	1	0	0	2	146