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Mosquito-borne disease surveillance report: August 30 to September 12, 2020 (Week 36 and 37)

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Organization: Public Health Agency of Canada

Date published: 2020-10-09

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Year-to-date snapshot
Year-to-date snapshot - Text equivalent

Between January 1 and September 12, 2020, thirty-four human cases of West Nile virus in Canada have been reported to the Public Health Agency of Canada (PHAC). Twenty-six WNV-positive birds, and 183 WNV-positive mosquito pools have also been reported.

Figure 1. Geographic distribution of WNV human clinical cases and asymptomatic infections in Canada, 2020
Figure 1 - Text equivalent

Between January 1 and September 12, 2020, thirty-four human cases associated with West Nile virus acquired in Canada were reported to PHAC.

West Nile

Human epidemiology

As of surveillance week 37, ending on September 12, 2020, thirty-four human cases of West Nile virus (WNV) have been reported to the Public Health Agency of Canada (PHAC) (Table 1).

Table 1. West Nile virus human cases, by disease classification and province (January 1-September 12, 2020)
Province Clinical cases Total of clinical cases Footnote 1 Asymptomatic infections Footnote 2 YTD grand total Rate (per 100,000) Footnote 3
Neurological Non-neurological Unclassified
Ontario 2 13 9 24 1 25 0.09
Quebec 4 0 2 6 3 9 0.06
Total 6 13 11 30 4 34 0.05
Footnote 1

Clinical cases are the sum of confirmed and probable: WNV neurological and non-neurological syndromes, along with any unclassified.

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Footnote 2

Satisfies WNV diagnostic test criteria in the absence of clinical criteria (i.e., asymptomatic blood donors whose blood is screened by blood operators, Canadian Blood Services or Héma-Québec.

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Footnote 3

Calculated with grand total of clinical and asymptomatic cases, using Statistics Canada 2020 Q1 population estimates.

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Mosquito, wild bird and equine epidemiology

As of week 36 and 37, PHAC has been notified of 14,268 mosquito pools tested for WNV in Canada. Of these, there have been five WNV-positive mosquito pools identified in Manitoba, 166 in Ontario, and twelve in Québec (Table 2).

Twenty-six dead wild birds have tested positive for WNV, by the Canadian Wildlife Health Cooperative fourteen in Ontario and twelve in Québec (Table 3).

Since the start of this season, the Canadian Food Inspection Agency (CFIA) has identified five equine case that tested positive for WNV in two in Saskatchewan, one in Ontario, one in Quebec and one in Manitoba (Table 3).

Figure 2. (A) WNV human clinical cases and asymptomatic infections, (B) positive WNV birds, and (C) percent positive mosquito pools by episode or report week, in Canada, 2020
(A) (B) (C)
Figure 2 - Text equivalent

Between January 1 and September 12, 2020, thirty-four human cases associated with West Nile virus acquired in Canada were reported to PHAC. A total of twenty-six birds and 1.28 % of mosquito pools have tested positive for WNV in Canada and reported to PHAC.

Figure 2 footnotes

Footnote 1

Human cases includes clinical cases and asymptomatic infection.

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Footnote 2

Episode week is based on symptom onset or best available date including: diagnosis, lab sample or date reported.

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Footnote 3

Episode week is based off date of death or best available date including: date found, submitted, or received.

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Table 2. Year-to-Date WNV positive pools and percent positive by province and nationally (January 1- September 12, 2020)
ProvinceFootnote 1 Positive pools Total pools tested Percent positive
Saskatchewan 0 71 0.00 %
Manitoba 5Footnote * 1264 0.40 %
Ontario 166 11770 1.41 %
Québec 12 1163 1.03 %
Total 183 14268 1.28 %
Footnote 1

Mosquito surveillance data is reported by the following 4 provinces: Saskatchewan, Manitoba Ontario and Quebec.

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Footnote 2

No WNV infected mosquito pools have been found as part of Manitoba Health’s West Nile virus surveillance program, which submits information to PHAC, however two (2) positive mosquito pools were detected by another surveillance program in the Prairie Mountain Health Region.

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Table 3. Number of WNV positive equine and birds by province and nationally (January 1- September 12, 2020)
Province Wild birds Footnote 1 Equine
British Columbia 0 0
Alberta 0 0
Saskatchewan 0 2
Manitoba 0 1
Ontario 14 1
Quebec 12 1
Maritime provinces 0 0
Territories 0 0
Total 26 5
Footnote 1

Not all provinces conduct dead wild bird surveillance as part of their respective WNV surveillance program. However, WNV positive dead wild birds may be identified through the National Wildlife Disease Surveillance Program, CWHC or by specific provinces.

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California serogroup

As of September 12, 2020, no human exposures or cases of California serogroup virus have been reported by the National Microbiology Laboratory.

Eastern equine encephalitis

No human cases of EEEV have been reported to PHAC since the beginning of the 2020 transmission season.

The CFIA has reported two horses testing positive for Eastern Equine Encephalitis virus (EEEV) in Ontario.

Provincial/territorial and international surveillance links

Data reported to PHAC is subject to change and may differ from provincial webpages due to reporting timelines. To obtain the latest arbovirus surveillance data, please refer to the following jurisdictional/regional webpages:

Provincial

International

Notes

Thank you to all our partners for participating in the National WNV/MBD surveillance program.

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