Mosquito-borne diseases surveillance report: September 13 to September 26, 2021 (Week 37 to 38)

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Organization: Public Health Agency of Canada

Date published: 2021-10-12

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

Between January 1 and September 26, 2021, 13 clinical human cases of West Nile virus in Canada has been reported to the Public Health Agency of Canada (PHAC). 24 WNV-positive birds and 230 WNV-positive mosquito pools have also been reported.

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

Between January 1 and September 26, 2021, 13 clinical human cases and one asymptomatic case associated with West Nile virus acquired in Canada were reported to PHAC. 24 positive birds have also been reported.

West Nile

Human epidemiology

As of surveillance week 38, ending on September 26, 2021, 13 clinical human cases and one asymptomatic human case 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 26, 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
Manitoba 1 2 2 5 1 6 0.43
Ontario 2 1 5 8 0 8 0.05
Total 3 3 7 13 1 14 0.04
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 2021 Q1 population estimates.

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Mosquito, wild bird and equine epidemiology

As of week 38, PHAC has been notified of 18,349 mosquito pools tested for WNV in Canada. Of these, there have been 2 WNV-positive mosquito pools identified in Québec, 103 Ontario, 116 in Manitoba and 9 in Saskatchewan (Table 2).

21 wild birds have tested positive WNV by the by the Canadian Wildlife Health Cooperative, 14 in Québec and seven in Ontario (Table 3). The province of Manitoba reported three birds tested positive for WNV.

Since the start of this season, the Canadian Food Inspection Agency (CFIA) has identified equine cases that tested positive for WNV in Alberta (1), Saskatchewan (9) Manitoba (7) and Ontario (1) (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 September 26, 2021, 13 clinical human cases and one asymptomatic human case associated with West Nile virus acquired in Canada were reported to PHAC. 24 birds and 1.25% 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 – September 26, 2021)
ProvinceFootnote 1 Positive pools Total pools tested Percent positive
Saskatchewan 9 360 2.50 %
Manitoba 116 1,446 8.02 %
OntarioFootnote * 103 13,093 0.79 %
Québec 2 3,450 0.06 %
Total 230 18,349 1.25 %
Footnote 1

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

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Footnote *

Additional two mosquito pools were detected by another surveillance program (First Nations Community of Walpole Island); however these numbers were not aggregated into the counts in this table.

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Table 3. Number of WNV positive equine and birds by province and nationally (January 1 – September 26, 2021)
Province Wild birds Footnote 1 Equine
Ontario 7 1
Quebec 14 0
Saskatchewan 0 9
Manitoba 3 7
Alberta 0 1
Total 24 18
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 26th, 2021, one human case of California serogroup virus was diagnosed by the National Microbiology Laboratory in Canada: Ontario (1). The case was further classified as Jamestown Canyon virus.

Eastern equine encephalitis

No human cases of Eastern Equine Encephalitis virus (EEEV)  have been reported to PHAC since the beginning of the 2021 transmission season.

The CFIA has reported seven horse cases testing positive for EEEV in Ontario.

Province of Ontario reported two positive EEEV mosquito pools. Furthermore, another surveillance program in the Wahta Mohawks territory detected additional two mosquito pools.

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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