2005 Surveillance for West Nile virus in Manitoba

Positive Surveillance Indicators
Surveillance Indicator 2005* 2004 2003 2002
Corvids 12 16 134 86
Mosquito Collections (Adult) 193 57 290 15
Horse Cases 4 0 47 236
Human Cases 58 3 143** 0

* As of December 9, 2005.

** Updated in 2005 after receiving a late report on a Manitoba resident with WNV who was investigated in Saskatchewan in 2003.

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Corvid Surveillance by Regional Health Authority 2005*

Regional Health Authority

Number of birds
submitted for testing

Number of birds
that tested positive

Winnipeg

35

1

Parkland

3

1

Interlake

38

2

Assiniboine

18

1

Central

30

3

North Eastman

16

1

South Eastman

22

1

Brandon

9

2

Nor-Man

3

0

Burntwood

5

0

Churchill

0

0

Total

179

12

* As of September 30, 2005. (Corvid surveillance ended on this date.)

Birds from the crow family (corvids) are very susceptible to WNV. Many die soon after becoming infected. Testing dead crows and other corvids provides an early indication of the presence of infected mosquitoes in an area.

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Culex tarsalis Mosquito Trap Catch by Regional Health Authority 2005*
Average Adult Culex tarsalis Mosquitoes per Weekly Trap Catch
Regional Health Authority June 5 - 11 June 12 - 18 June 19 - 25
Assiniboine 0 0 1
Brandon 0 <1 1
Central <1 <1 10
Interlake <1 <1 11
North Eastman 0 0 23
Parkland 0 0 <1
South Eastman <1 <1 25
Winnipeg <1 <1 31
Regional Health Authority June 26 -
July 2
July 3 -
July 9
July 10 -
July 16
Assiniboine 4 4 270
Brandon 5 6 229
Central 28 40 2118
Interlake 9 6 478
North Eastman 4 4 231
Parkland <1 <1 23
South Eastman 23 15 1429
Winnipeg 31 12 2210
Regional Health Authority July 17 -
July 23
July 24 -
July 30
July 31 -
Aug. 6
Assiniboine 562 1289 416
Brandon 367 205 1359
Central 854 944 1342
Interlake 484 356 439
North Eastman 356 185 211
Parkland 59 37 47
South Eastman 1158 605 997
Winnipeg 1670 1847 1602
Regional Health Authority August 7 -
August 13
August 14 -
August 20
 August 21 - August 27
Assiniboine 943 70 10 
Brandon 718 35   4
Central 944 142   6
Interlake 218 22   1
North Eastman 314 20   1
Parkland 89 6   <1
South Eastman 482 77   3
Winnipeg 823 115   4
Regional Health Authority August 28 -
September 3
September 4 -
September 10
 
Assiniboine 2 <1  
Brandon 3 <1  
Central 4 3  
Interlake <1 <1  
North Eastman <1 <1  
Parkland 0 0  
South Eastman <1 1  
Winnipeg 5 7  

* As of September 10, 2005. (Routine mosquito trapping ended on this date.)

Permanent mosquito traps are set up in 30 community areas in southern Manitoba to monitor Culex tarsalis mosquitoes, the mosquitoes that are most likely to transmit West Nile virus to humans in Manitoba. The above table represents the average number of Culex tarsalis mosquitoes per trap catch for the week by Regional Health Authority (RHA) and  provides a relative measure of the activity levels of Culex tarsalis from one RHA to another and over time. This measure is an indicator as to whether Culex tarsalis mosquito populations are rising or falling or staying steady. It should be noted that these RHA averages provide an approximate indication of the number of Culex tarsalis in the RHA, counts in specific locations within the RHA will vary depending on local conditions, temperature, precipitation, etc.

Note:  Normally, two or three Centers for Disease Control (CDC) mosquito traps baited with carbon dioxide are run for one or two nights each week in each Manitoba community except Winnipeg and Brandon (where proportionately more traps are used because of larger community size). 

The average number of Culex tarsalis per trap catch (a trap catch – may also be called a “collection”- represents the mosquitoes collected by one trap during one night from approximately one hour before sunset until approximately one hour after sunrise) is calculated by dividing the total number of Culex tarsalis collected for the whole week in a given RHA by the number of collections.

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Positive Mosquito Collections (Adult) by RHA 2005
Positive Mosquito Collections (Adult) by RHA 2005* July 10 -
July 16
July 17-
July 23
July 24-
July 30
July 31-
Aug. 6
Assiniboine 1 3 11 6
Brandon 0 1 2 2
Central 7 2 3 6
Interlake 0 1 1 3
North Eastman 0 0 1 2
Parkland 0 0 1 0
South Eastman 1 4 2 14
Winnipeg 4 3 2 5
Total 13 14 23 38
 
Positive Mosquito Collections (Adult) by RHA 2005* August 7-
August 13
Aug. 14 -
Aug. 20
Aug. 21 - Aug. 27  Aug. 28 - Sept. 3
Assiniboine 24 17 2 0
Brandon 0 0 1 0
Central 16 9 0 0
Interlake 3 1 0 0
North Eastman 4 0 0 0
Parkland 3 0 0 0
South Eastman 11 3 0 1
Winnipeg 5 3 0 1
Total 66 33 3 2
 
Positive Mosquito Collections (Adult) by RHA 2005* Sept. 4-
Sept. 10
     
Assiniboine 1      
Brandon 0      
Central 0      
Interlake 0      
North Eastman 0      
Parkland 0      
South Eastman 0      
Winnipeg 0      
Total 1      

*  As of September 10, 2005. (Routine mosquito trapping ended on this date.)

Mosquito samples from the following communities have tested positive for WNV:
Altona, Beausejour, Boissevain, Brandon, Carberry, Carman, Deloraine, East St. Paul, Killarney, Morden, Morris, Neepawa, Niverville, Oakbank, Roblin, Russell, Sandy Bay First Nations, St. Andrews, Ste. Anne, Selkirk, Souris, Steinbach, Stonewall, Stony Mountain, West St. Paul, Winkler, Winnipeg, Virden.

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WNV Human Cases by Regional Health Authority 2005*

Represents the Regional Health Authority of residence of the patient.

Regional
Health
Authority

Asymptomatic

West Nile Virus Non-Neurological Syndrome

West Nile Virus
Neurological Syndrome

Under Investigation

TOTAL

Assiniboine 0 12 3 0 15
Brandon 0 3 1 0 4
Central 1 10 1 0 12
Interlake 0 4 1 0 5
N. Eastman 0 2 0 0 2
Parkland 0 0 0 0 0
S. Eastman 1 2 0 0 3
Winnipeg 1 12 4 0 17
Total

3

45

10

0

58

* As of December 9, 2005.

West Nile Related Deaths:  In 2005, there was one human death related to a West Nile virus infection in Manitoba.

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Severity of WNV Disease By Age 2005*
Age in Years Asymptomatic West Nile Virus Non-Neurological Syndrome West Nile Virus
Neurological Syndrome
Under Investigation Total
  0 -   9 0 2 0 0 2
10 - 19 0 2 1 0 3
20 - 29 0 1 0 0 1
30 - 39 0 9 1 0 10
40 - 49 1 14 2 0 17
50 - 59 1 9 3 0 13
60 - 69 1 4 2 0 7
Over 70 0 4 1 0 5
Total 3 45 10 0 58

Average age (West Nile virus Neurological Syndrome):  52
Average age (West Nile virus Non-Neurological Syndrome): 46.3

* As of December 9, 2005.

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WNV Disease by Gender 2005*
Gender Asymptomatic West Nile Virus Non-Neurological Syndrome West Nile Virus
Neurological Syndrome
Under
Investigation
Total
Male 2 19 7 0 28
Female 1 26 3 0 30
Total 3 45 10 0 58

* As of December 9, 2005.

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Additional information and maps are available at the Public Health Agency of Canada website.


For WNV health concerns, contact your doctor or call:

Health Links - Info Santé
204-788-8200
(Winnipeg) or toll-free 1-888-315-9257