Mosquito-borne disease surveillance report: July 26 to August 15, 2020 (Week 31, 32 and 33)

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Organization: Public Health Agency of Canada

Date published: 2020-08-28

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

Between January 1 and August 15, 2020, two human cases of West Nile virus in Canada have been reported to the Public Health Agency of Canada (PHAC). Eight WNV-positive birds, and 99 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 August 15, 2020, two human cases associated with West Nile virus acquired in Canada were reported to PHAC. Eight positive birds have also been reported.

West Nile

Human epidemiology

As of surveillance week 33, ending on August 15, 2020, two 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-August 15, 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
Quebec 0 1 0 1 1 2 0.00
Total 0 1 0 1 1 2 0.00
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 33, PHAC has been notified of 11764 mosquito pools tested for WNV in Canada. Of these, there have been 98 WNV-positive mosquito pools identified in Ontario and one in Québec (Table 2).

Eight dead wild birds have tested positive for WNV, by the Canadian Wildlife Health Cooperative five in Ontario and three in Québec (Table 3).

Since the start of this season, the Canadian Food Inspection Agency (CFIA) has not reported any domestic animals 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, 2020
Figure 2 - Text equivalent

Between January 1 and August 15, 2020, two human cases associated with West Nile virus acquired in Canada were reported to PHAC. A total of eight birds and <1% 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- August 15, 2020)
ProvinceFootnote 1 Positive pools Total pools tested Percent positive
Saskatchewan 0 24 0.00 %
Manitoba 0Footnote * 1027 0.00 %
Ontario 98 8374 1.17 %
Québec 1 2339 < 1 %
Total 99 11764 < 1 %
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- August 15, 2020)
Province Wild birds Footnote 1 Equine
British Columbia 0 0
Alberta 0 0
Saskatchewan 0 0
Manitoba 0 0
Ontario 5 0
Quebec 3 0
Maritime provinces 0 0
Territories 0 0
Total 8 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.

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California serogroup

As of August 15, 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 not reported any horses testing positive for Eastern Equine Encephalitis virus (EEEV) in Canada.

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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