2007 Surveillance for West Nile virus in Manitoba


Positive Surveillance Indicators*
Surveillance Indicator 2007* 2006 2005 2004 2003 2002
Corvids 1 __ __ 12 16 134 86
Mosquito Collections (Adult) 948 171 193 57 290 15
Horse Cases 2 8 1 4 0 47 236
Human Cases (Classified) 582** 51 58 3 1433 0

* As of February 14, 2008.

** 2007 human case classifications include both final and preliminary classifications and may be subject to change as further information becomes available.

1 The West Nile virus dead corvid pick up program is not in effect in 2007. Dead corvids are no longer needed as an early indicator of West Nile virus in Manitoba or to determine geographic distribution. Larval sampling, mosquito sampling and testing in addition to other factors (temperature, etc.) will be used to guide the assessment of risk of West Nile virus exposure.

2 Other animals and birds that have tested positive for WNV in 2007 include: one blue jay, one magpie, one seagull, and one snowy owl.

3 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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Culex tarsalis Mosquito Trap Catch by Regional Health Authority 2007*
Average Adult Culex tarsalis Mosquitoes per Weekly Trap Catch
Regional Health Authority June 3-9 June 10-16 June 17-23
Assiniboine 48 43 69
Brandon 9 40 47
Central 65 252 381
Interlake 3 71 44
North Eastman 14 63 46
Parkland 0 <1 24
South Eastman 19 108 63
Winnipeg 25 389 148
Manitoba 31 158 126
 
Regional Health Authority June 24-30 July 1-7 July 8-14
Assiniboine 661 4481 1311
Brandon 279 790 586
Central 3155 1904 878
Interlake 240 563 338
North Eastman 1931 582 377
Parkland 34 247 384
South Eastman 1534 1381 551
Winnipeg 2579 1467 437
Manitoba 1548 1954 691
 
Regional Health Authority July 15-21 July 22-28 July 29-
August 4
Assiniboine 921 3749 3861
Brandon 82 3029 2853
Central 277 1326 2347
Interlake 36 516 420
North Eastman 103 471 323
Parkland 30 1102 932
South Eastman 83 657 657
Winnipeg 134 1040 994
Manitoba 304 1634 1760
 
Regional Health Authority August 5-11 August 12-18 August 19-25
Assiniboine 454 284 43
Brandon 395 124 20
Central 240 84 8
Interlake 79 30 2
North Eastman 77 26 3
Parkland 88 41 5
South Eastman 83 19 1
Winnipeg 119 43 7
Manitoba 237 99 14
 
Regional Health Authority August 26-September 1 September 2
-September 8
September 9
-September 15
Assiniboine 7 3 <1
Brandon 3 2 0
Central 2 2 <1
Interlake <1 <1 0
North Eastman <1 <1 0
Parkland 3 0 0
South Eastman 1 0 <1
Winnipeg 2 <1 0
Manitoba 3 1 <1
 
Regional Health Authority September 16-September 22    
Assiniboine <1    
Brandon 0    
Central <1    
Interlake 0    
North Eastman 0    
Parkland <1    
South Eastman <1    
Winnipeg <1    
Manitoba <1    

* As of January 17, 2008.
(Routine mosquito trapping was discontinued the week ending September 22, 2007.)

Permanent mosquito traps are set up in 37 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 will represent 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 Centers for Disease Control (CDC) mosquito traps baited with carbon dioxide are run for 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 2007
Positive Mosquito Collections (Adult) by RHA 2007
Assiniboine 378
Brandon 73
Central 172
Interlake 79
North Eastman 28
Parkland 17
South Eastman 32
Winnipeg 169
Total 948

* As of January 17, 2008.
(Routine mosquito trapping was discontinued the week ending September 22, 2007.)

Mosquito samples from the following communities have tested positive for WNV in 2007: Altona, Beausejour, Boissevain, Brandon, Carberry, Carman, Dauphin, Deloraine, East St. Paul, Gimli, Headingley, Killarney, Minnedosa, Morden, Morris, Niverville, Oakbank, Peguis First Nation, Portage la Prairie, Roblin, Russell, St. Andrews, Ste. Anne, Sandy Bay First Nation, Selkirk, Sioux Valley First Nation, Souris, Steinbach, Stonewall, Stony Mountain, Virden, West St. Paul, Winkler, Winnipeg, and Winnipeg Beach.

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WNV Human Cases by Regional Health Authority 2007*

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

Unclassified Positive
Test
Results

TOTAL

Assiniboine
3
142
17
0
162
Brandon
0
65
6
1
72
Central
2
95
8
2
107
Interlake
1
38
5
1
45
North Eastman
1
19
3
0
23
Parkland
0
14
3
0
17
South Eastman
1
25
2
1
29
Winnipeg
1
103
28
0
132
Total
9
501
72
5
587
Out of Province
0
0
1
0
1^

West Nile Related Deaths:  In 2007, there were four human deaths related to a West Nile virus infection in Manitoba. All four were male individuals.  Three were in their sixties or older and one was in his forties. One was a resident of Assiniboine health region, one of Central health region, one of Interlake health region, and one of Winnipeg health region.

* As of February 14, 2008.

Note: For the above table and the two following tables, 2007 human case classifications include both final and preliminary classifications and may be subject to change as further information becomes available.

The most likely locations of exposure have been determined for at least one human case in each of the following municipalities: RM of Alexander, RM of Bifrost, RM of De Salaberry, RM of East St. Paul, RM of Lac du Bonnet, Town of Morden, Town of Morris, RM of North Norfolk, RM of Park, RM of Portage la Prairie, RM of St. Clements, RM of Ste. Rose, RM of Stanley, City of Steinbach, RM of Tache, City of Winkler, City of Winnipeg, Town of Winnipeg Beach.

Further information on most likely locations of exposure will be added as it becomes available. The risk of WNV, however, exists throughout all of southern Manitoba and is not limited to the communities listed. WNV has been identified in this or previous years within the boundaries of all regional health authorities except for NOR-MAN, Burntwood, and Churchill.

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Severity of WNV Disease By Age 2007*
Age in Years Asymptomatic West Nile Virus Non-Neurological Syndrome West Nile Virus
Neurological Syndrome
Unclassified Positive
Test
Results
Total
  0 -   9 0 1 1 0 2
10 - 19 0 27 4 1 32
20 - 29 2 45 5 0 52
30 - 39 0 69 5 1 75
40 - 49 2 130 9 1 142
50 - 59 3 116 11 2 132
60 - 69 2 66 20 0 88
Over 70 0 47 17 0 64
Total 9 501 72 5 587

Average Age - Asymptomatic West Nile Virus: 47
Average Age - West Nile Virus Non Neurological Syndrome : 48
Average Age - West Nile Virus Neurological Syndrome: 56

* As of February 14, 2008.

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WNV Disease by Gender 2007*
Gender Asymptomatic West Nile Virus Non-Neurological Syndrome West Nile Virus
Neurological Syndrome
Unclassified Positive
Test
Results
Total
Male 7 281 43 3 334
Female 2 220 29 2 253
Total 9 501 72 5 587

* As of February 14, 2008.

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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