Mosquito-borne diseases surveillance report: July 19 to August 1, 2021 (Week 29 to 30)

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Organization: Public Health Agency of Canada

Date published: 2021-08-18

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

Between January 1 and August 1, 2021, one human case of West Nile virus in Canada has been reported to the Public Health Agency of Canada (PHAC). Two WNV-positive birds, and 45 WNV-positive mosquito pools have also been reported.

Figure 1. Geographic distribution of WNV human clinical cases and asymptomatic infections in Canada, 2021
Figure 1 - Text equivalent

Between January 1 and August 1, 2021, one human case associated with West Nile virus acquired in Canada was reported to PHAC. Two positive birds have also been reported.

West Nile

Human epidemiology

As of surveillance week 30, ending on August 1, 2021, one human case of West Nile virus (WNV) has 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 – August 1, 2021)
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 0 0 1 1 0 1 0.003
Total 0 0 1 1 0 1 0.003
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 30, PHAC has been notified of 8,979 mosquito pools tested for WNV in Canada. Of these, there have been 29 WNV-positive mosquito pools identified in Manitoba and 16 in Ontario (Table 2).

One wild bird has tested positive for WNV in Ontario, by the Canadian Wildlife Health Cooperative. Province of Québec reported one wild bird that has tested positive for WNV (Table 3).

Since the start of this season, the Canadian Food Inspection Agency (CFIA) has not identified any equine cases that tested positive for WNV (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, 2021
(A)

(B)

(C)
Figure 2 - Text equivalent

Between January 1 and August 1, 2021, one human case associated with West Nile virus acquired in Canada was reported to PHAC. Two birds and 0.50% of mosquito pools have tested positive for WNV in Canada and reported to PHAC.

Figure 2 - Legend

A

Human cases includes clinical cases and asymptomatic infection.

B

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

C

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

Table 2. Year-to-Date WNV positive pools and percent positive by province and nationally (January 1 – August 1, 2021)
ProvinceFootnote 1 Positive pools Total pools tested Percent positive
Saskatchewan 0 170 0.00 %
Manitoba 29 925 3.14 %
Ontario 16 7,229 0.22 %
Québec 0 655Footnote 2 0.00 %
Total 45 8,979 0.50 %
Footnote 1

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

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Footnote 2

Number of tested mosquito pools is until Week 28.

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Table 3. Number of WNV positive equine and birds by province and nationally (January 1 – August 1, 2021)
Province Wild birds Footnote 1 Equine
Ontario 1 0
Quebec 1 0
Total 2 0
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.

Return to footnote 1 referrer

California serogroup

As of August 1, 2021, 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 2021transmission season.

The CFIA has reported one horse 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:

Notes

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

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