2006 – west nile virus in the region of peel - dead bird … · 2010. 3. 30. · include blue...

2006 – West Nile Virus in the Region of Peel

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Dead Bird Surveillance

Historically, the sudden appearance of dead birds has been the first indicator of the presence of WNV in an area. The corvid species (crows, blue jays) and hawks are particularly sensitive to the effects of WNV and are the most likely to die once infected. For this reason, the Region of Peel maintains a Dead Bird Surveillance program.

Dead Bird Surveillance Highlights for 2006

• 1,037 dead birds were reported to Customer Contact Centre/Environmental Health duty desk – a decrease of 3% from 2005 and the lowest number since 2002

• Approximately 61% of the dead birds were reported from the City of Mississauga, 31% from the City of Brampton and 8% from the Town of Caledon

• The number of target birds (crows, blue jays) reported decreased by 27% over 2005. As was the case in 2005, most were from the City of Mississauga.

• The first WNV-positive bird was observed in late July - the second consecutive year that a positive bird finding was preceded by positive mosquitoes

• 41% of birds tested were positive for WNV o 4 positive birds in Mississauga (3 in South Mississauga) o 4 positive birds in Brampton o 3 positive birds in Caledon

• Brampton Ward 5 had the highest density of bird sightings per square kilometre (0.480 to 0.599 per square kilometre)

• In 2006, there was a 15% decrease in WNV positive birds in Ontario (from 300 to 256).

• Across Ontario, Peel Region had the third highest number of WNV positive birds (11); only Toronto and Thunder Bay had more at 13 and 12, respectively; however, Peel Region ranked 7th in the percentage of birds testing positive

• Nationally, the number of dead birds decreased by approximately 39% - Ontario and Alberta had the highest percentage of birds testing positive for WNV (26% and 14%) compared to the national average of 8.9%.

• All seven Great Lake States reported WNV positive birds with the State of Minnesota reporting the most at 378 followed by New York State at 262.


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Telephone calls reporting dead birds are received by the Customer Contact Centre (CCC) on weekdays and by the staff at the Environmental Health duty desk on weekends. A dead bird surveillance form is completed for every call. Dead bird surveillance started in 2000 with the inclusion of only crows but has since changed to include blue jays. Hawks were included for testing in 2004 for study purposes only. Testing of dead birds for WNV is conducted by the Canadian Cooperative Wildlife Health Centre (CCWHC) located in Guelph, Ontario. Not every target bird is suitable for testing due its physical condition. Also, the bird testing program is suspended by the CCWHC after the virus has been established in the bird population in all three municipalities in Peel Region. Therefore, not every dead target bird reported within the season is tested.

Figure 3 American Crow Source: Greg Gough – reproduced with permission

A private pest control company is contracted by Peel Public Health to pick up dead crows and blue jays for testing. In some previous years local animal control in the City of Mississauga, City of Brampton and Town of Caledon provided the dead bird pick up service. Reports of other dead birds species are noted and mapped but Peel Public Health does not collect or test these birds for WNV. As shown in Figure 5, the total numbers of dead birds (all species) reported in 2006 was the fewest since the start of Peel’s bird surveillance program in 2002. There were 1,037 dead bird calls to Customer Contact Centre in 2006. This represents a 74% decrease in dead bird reports since 2003. This decline in the number of reports may be due to several factors including a general population decline of birds, especially those species sensitive to WNV that may have been significantly impacted in previous years.


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Figure 4 Blue Jay Source: Jerry Acton, 2006 – reproduced with permission Figure 5 Number of Dead Birds Reported to Customer Contact

Centre/Environmental Health Duty Desk, Region of Peel, 2002-2006

1,436

3,919

2,078

1,071 1,037

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Breakdown for 2006:Mississauga = 636Brampton = 317Caledon = 84

*In 2002 all dead bird reports are assumed to be crows. Map 3 illustrates the geographic location for all species of dead birds reported to Customer Contact Centre and the Environmental Health duty desk in 2006 across Peel Region. Mississauga reported approximately 61% of the dead birds in the Region of Peel. The majority were found in locations south of Highway 401 with a small cluster in the northeast community of Malton. Thirty one percent of the dead birds were from Brampton, most from central Brampton. Approximately 8% of the dead bird reports were from Caledon where a greater dispersion of dead bird reports across the municipality was observed, with a small cluster in Bolton. This small clustering effect may reflect the fact that there is a greater population density in Bolton and therefore more opportunity to notice and report dead birds.


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Table 5 shows the number of dead bird reports for the target species, crows and blue jays over the five-year period 2002 to 2006. There were 1,436 dead crows reported in 2002 in comparison to 112 dead crows and blue jays combined, in 2006. Eighty-six of the 112 were crows and 26 were blue jays. This represents a 27% decrease in the number of target birds reported over the previous year but was approximately the same as in 2004. Comparisons with 2002 and 2003 can only be conducted using the dead crow data. There was a significant decrease in dead crows reported from 2002 through to 2006 from 1436 to 86, respectively. The number of dead crows in 2006 (86) was similar to 2005 (87). When separating the reports based on the local municipality the greatest number of reports were from Mississauga (41%) followed by Brampton (32%) and Caledon (27%). A similar distribution was observed in 2005 but differs from 2004 when the greatest proportion of the target birds (53%) was from Caledon. Table 5 Number of Dead Bird Reports for Target Species by Municipality -

Region of Peel, 2002-2006

2002* 2003* 2004† 2005† 2006†

Brampton 485 37 25 41 36

Caledon 48 54 58 41 30

Mississauga 903 59 27 72 46

TOTAL 1436 150 110 154 112 *Target Birds were crows only †Target Birds were crows and blue jays Source: Region of Peel, 200511

Figure 6 illustrates the temporal trend across the Region of Peel for dead target birds for each year of the program. As noted previously, the number of target birds being reported in 2002 was significantly greater than other years. The large numbers of dead target birds (crows) were observed starting in July (weeks 29, 30 and 31) and continued with high numbers throughout September. In one week (week 34) there were close to 250 reports. The temporal trend throughout the 2006 reporting season was similar to 2005, although the number of dead target birds in any given week in 2006 did not exceed any value observed in 2005. Similar to previous years (except 2002) the weekly report of dead target birds did not exceed 20. Figure 7 illustrates the 2003, 2004, 2005 and 2006 temporal trends in the Region of Peel (2002 excluded). The patterns of target bird reports differed in 2006 where the first reports occurred later in the season (mid-June, week 24) compared to early May for the previous three years.


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The weekly trend of target bird reports from 2004-2006 is fairly similar. As observed in As observed the three previous years, the number of dead birds reported weekly in 2006 remained below 10 birds except for week 32 (August 6 – August 12) when 11 target birds were reported. The greatest number of target birds reported, 16, since 2003 occurred in 2005 during the same period. In 2006, the peak in number of reported target birds occurred in the latter part of July and throughout August. This differs slightly from 2003 where peaks were seen earlier in June and later in September.


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Map 3 West Nile Virus - Bird Surveillance (All Birds), Region of Peel, 2006 (Week 19-39)


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Figure 6 Total Target Birds* by Week - Region of Peel, 2002-2006

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Target Bird in 2002: CrowTarget Bird in 2003: CrowTarget Birds in 2004: Crow and Blue Jay, Hawk (1Positive, wk38)Target Birds in 2005: Crow and Blue JayTarget Birds in 2006: Crow and Blue Jay

* Defined as positive, negative, pending and sighting

Figure 7 Total Target Birds* by Week - Region of Peel, 2003-2006

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Target Bird in 2003: CrowTarget Birds in 2004: Crow and Blue Jay, Hawk (1 Positive, wk38)Target Birds in 2005: Crow and Blue JayTarget Birds in 2006: Crow and Blue Jay

* Defined as positive, negative, pending and sighting


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As shown in Table 6, the first WNV positive bird in the 2006 surveillance season was reported in week 31 (July 31, 2005) in the City of Brampton. The reporting the first positive bird in 2006 occurred later than that for any previous year with the exception of 2001. As noted in the section on adult mosquito surveillance in 2006, the first positive mosquitoes in Peel were found in week 30 (July 25, 2006), one week prior to the first positive bird. 2006 was the second consecutive year that WNV-positive mosquitoes were found earlier than the first WNV-positive bird. In 2002, WNV positive birds were observed as early as mid-May. Table 6 Date and Location of First Positive Target Bird (Crow or Blue Jay) -

Region of Peel, 2001-2006

Year Date Location

2001 August 14, 2001 Mississauga

2002 May 19, 2002 (week21) Mississauga

2003 July 4, 2003 (week 27) Caledon

2004 July 6, 2004 (week 27) Brampton

2005 July 24, 2005 (week 30) Mississauga

2006 July 31, 2006 (week 31) Brampton In 2006, the total number of WNV positive birds in the Region of Peel was 11. There were four positives in Brampton, three in Caledon and four in Mississauga. Of the 11 WNV positive birds, 10 were crows and one was a blue jay. Table 7 shows a decrease in the number of WNV positive birds in 2006 when compared to 2005. However, the number of positive birds for 2006 is comparable to 2004 and 2003. The number of birds sent for testing in 2006 was dramatically less than previous years. Table 7 does not represent a true measure of the rate of WNV infection in birds because the number of birds accepted for viral testing in a given week is capped towards the end of the season, with the exception of 2005 where there was no maximum. This maximum has not been applied consistently across all five years and therefore comparisons from year to year should be made with caution. In 2006, the cap was applied earlier than ever before (August 18, 2006).


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Table 7 Annual Comparison of the Total Number of WNV Positive Birds - Region of Peel, 2002-2006

Year # of

birds tested

# of positive birds

Per cent positive

2002 71 20 28.2 2003 58 12 20.7 2004 60 16 26.7 2005 75 33 44.0 2006 27 11 40.7 Sources: CCWHC, 200613; Region of Peel, 200511

Map 4 illustrates the geographical distribution of the target birds and their viral status (positive, negative and sighting). In Mississauga, reports of dead crows and blue jays were distributed across the City. However, the positive birds reported in Mississauga were predominantly found in south Mississauga - three out of four WNV positive birds found in Mississaugai. This observation is consistent with what has been seen in previous years. It forms the basis for the stratified analysis and informs the annual prevention and control plan. Dead bird reports in Brampton tended to cluster mostly around the centre of Brampton. In Caledon, dead bird reports were dispersed throughout the town. Map 5, 6, and 7 present the data for each of the three local municipalities.

i Highway 403 is the dividing line between North and South Mississauga


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Map 4 West Nile Virus - Bird Surveillance (Crows & Blue Jays), Region of Peel – 2006 (Week 19-39)


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Map 5 West Nile Virus - Bird Surveillance (Crows & Blue Jays), Caledon, 2006 (Week 19-39)


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Map 6 West Nile Virus - Bird Surveillance (Crows & Blue Jays), Brampton, 2006 (Week 19-39)


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Map 7 West Nile Virus - Bird Surveillance (Crows & Blue Jays), Mississauga, 2006 (Week 19-39)


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Dead bird reports across the Region of Peel were mapped by municipal ward (Map 8). This allows for a density analysis of the number of target bird sightings (positives) per square kilometre. Ward 5 in the City of Brampton had the highest density, with 0.480 to 0.599 dead birds per square kilometre in the Region of Peel. In a number of wards across all three municipalities an intermediate density, 0.240 to 0.359 per square kilometre, was observed. An intermediate density range in 2006 corresponds to a low density range in 2005. This observation is a function of the overall decrease in the number of target birds reported. Bird Surveillance in other Ontario Health Units Table 8 presents the data collected by the CCWHC on the birds tested and those that were positive for WNV in each Ontario health unit in 2006. There was a 15% decrease in the total number of birds positive for WNV in Ontario – 300 positive birds in 2005 compared to 256 in 200611. The number of positive birds in 2006 compares well with 2004 when there were 250 positive birds in Ontario. Peel Region had their bird testing suspended at 27 birds compared to 75 in 2005. Northwestern (15), Toronto (13) and Thunder Bay (12) had more WNV-positive birds than the 11 found in the Region of Peel. Table 8 also presents the proportion of positive birds to the total number of birds tested. The overall positive rate across Ontario was 26.3% (range 6.3% to 87.6%) which is a slight increase from 2005 at 23%. In 2006, the highest positive bird rate, 87.6%, was observed in Middlesex-London. Peel Region ranked seventh in Ontario with a 40.7% positive rate compared to sixth in 2006. When comparing to adjacent municipalities Peel Region ranked second only to the City of Toronto which had a 50% positive rate.


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Map 8 Density of Dead Crow & Blue Jay Sightings by Municipal Ward, Region of Peel, 2006


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Table 8 Dead Bird Results by Ontario Health Unit - Ontario, 2006

Health Unit Total Submitted

Not Tested Tested Total

PositivePer

Cent Positive

ALGOMA 31 0 31 8 25.8BRANT 19 0 19 11 57.9CHATHAM - KENT 8 0 8 3 37.5DURHAM 52 0 52 7 13.5EASTERN ONTARIO 17 1 16 3 18.8ELGIN - ST.THOMAS 6 0 6 3 50.0GREY - BRUCE - OWEN SOUND 29 0 29 8 27.6HALDIMAND - NORFOLK 12 1 11 4 36.4HALIBURTON - KAWARTHA 39 2 37 8 21.6HALTON 19 0 19 6 31.6HAMILTON - WENTWORTH 31 1 30 6 20.0HASTINGS - PRINCE EDWARD 50 0 50 10 20.0HURON COUNTY 20 0 20 5 25.0KINGSTON, FRONTENAC 19 0 19 3 15.8LAMBTON 15 0 15 7 46.7LEEDS, GRENVILLE, LANARK 16 0 16 1 6.3MIDDLESEX - LONDON 8 0 8 7 87.5NIAGARA REGION 42 1 41 5 12.2NORTH BAY 43 0 43 6 14.0NORTHWESTERN 37 0 37 15 40.5OTTAWA - CARLETON 44 0 44 6 13.6OXFORD COUNTY 14 0 14 5 35.7PEEL REGIONAL 27 0 27 11 40.7PERTH DISTRICT 15 0 15 8 53.3PETERBOROUGH 42 0 42 12 28.6PORCUPINE 20 1 19 2 10.5RENFREW DISTRICT 27 1 26 6 23.1SIMCOE COUNTY 57 1 56 11 19.6SUDBURY 51 1 50 11 22.0THUNDER BAY 21 1 20 12 60.0TIMISKAMING 18 0 18 2 11.1TORONTO 27 1 26 13 50.0WATERLOO 29 0 29 10 34.5WELLINGTON - DUFFERIN - GUELPH 36 2 34 5 14.7WINDSOR - ESSEX COUNTY 10 0 10 5 50.0YORK REGIONAL 34 0 34 10 29.4

Total: 986 14 972 256 26.3Red - highest per cent positive rate

Blue - Ontario health units adjacent to the Region of Peel Yellow - Region of Peel Source: adapted from CCWHC, 200613


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Bird Surveillance across Canada Table 9 presents the dead bird data from the Canadian provinces and territories for 2006. A total of 3,157 birds were submitted for testing in 10 provinces and territories. Nunavut, Quebec and Newfoundland and Labrador did not submit any dead birds for testing. Manitoba submitted only one bird for testing. Approximately 8.9% of all the birds submitted across Canada tested positive for WNV. This is a decrease of approximately 39% over the previous year.11 Ontario and British Columbia submitted the greatest number of birds with 986 and 841 birds, respectively. Approximately 26% of the birds from Ontario were positive for WNV representing a three per cent increase in positives from the previous year. As was the case in 2005, there were no positive birds submitted from British Columbia.11 Other provinces with positive birds were Saskatchewan and Alberta with the rate of positive birds of 0.8% and 14%, respectively. While the total number of birds submitted from Alberta decreased substantially from 215 in 2005 to 86 in 2006, the percentage of WNV positive birds in Alberta increased from 2.8% to 14%.11 Table 9 Dead Bird Results by Province - Canada, 2006

Province Total Submitted

# not Tested Tested West Nile Status

Total Positive Per cent Positive

AB 86 0 86 12 14.0BC 841 32 809 0 0MB 1 0 1 0 0NB 325 17 308 0 0NS 132 1 131 0 0NT 10 1 9 0 0ON 986 14 972 256 26.3PE 109 10 99 0 0SK 658 2 656 5 0.8YT 9 0 9 0 0

Total: 3157 77 3080 273 8.9Source: adapted from CCWHC, 200613

Bird Surveillance in Great Lake States Table 10 presents the numbers of WNV-positive birds reported for each of the Great Lake states.12 In 2006, bird surveillance programs in all seven Great Lake states reported WNV positive birds with every state except Illinois observing an increase in the number of WNV positive birds. Minnesota had the greatest number of positive birds in 2006 and had the largest increase in positive birds compared to other states – increased from 93 to 378.11 The state of New York followed with 262 WNV positive birds. Pennsylvania was once again the Great Lake state with the fewest WNV positive birds (55).


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Most Great Lake states had fewer numbers of WNV positive birds when compared to the province of Ontario with two exceptions: Minnesota had 378 and New York had 262 compared to 256 WNV positive birds in Ontario in 2006. Table 10 Great Lake States - Number of WNV Positive Birds - United States,

2006

Great Lake State # of WNV positive birds reported

Illinois 161 Indiana 81 Minnesota 378 New York 262 Ohio 126 Pennsylvania 55 Wisconsin 135 Source: USGS, 200612

Other Bird Species Corvid birds are particularly sensitive to WNV. The CCWHC tests many species including crows and blue jays. Figure 8 illustrates the various species tested and number of positive birds across Canada organized by species. Two hundred and thirty-three American Crows, 36 Blue Jays, two Black-billed Magpie, one Common Raven and one other bird tested positive for WNV in Canada in 2006.


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Figure 8 Dead Bird Reports by Species - Canada, 2006

Source: adapted from CCWHC, 200613 When evaluated temporally throughout the surveillance season (May through October), American Crows and Black-billed Magpies were the first specimens to be submitted in 2006 (Figure 9). American Crows continued to be submitted throughout the season. A similar pattern was observed in 2005, especially as it relates to American Crows (Figure 10). There was also a 21% decline in the total number of birds submitted to CCHWC in 2006 compared to 2005. The number of American Crows submitted declined by 32%; however, the decline in Blue Jay species was 59% compared to 2005.13 While the overall numbers of birds submitted for WNV testing is declining, there is no authoritative reference that supports a population decline in certain bird species. The annual Christmas Bird Count (CBC) is a non-scientific count of various bird species conducted by volunteers around the world and has reported a decline in some local bird populations. In previous years, the CBC American Crow data for Ontario showed a decline.14 However, in the 106th Christmas Bird Count, occurring between December 14, 2005 to January 6, 2006, showed the highest numbers of American Crows and Blue Jays were reported dispelling the concern of WNV having lasting population effects.15 It must be noted, however, that the CBC relies on volunteers to conduct the count, the number of volunteers will vary from year to year.

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Total Submitted 1 2014 56 256 151 2 602 9

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Figure 9 Bird Species Submitted based on the Week of the Year – Canada, 2006

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American Crow Black-billed Magpie Blue JayCommon Raven Northwestern Crow Other Birds

Source: adapted from CCWHC, 200613

Figure 10 Bird Species Submitted based on the Week of the Year – Canada,

2005

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American Crow Black-billed Magpie Blue Jay Common Raven Northwestern Crow Other Birds

Source: Region of Peel, 200511

2006 – west nile virus in the region of peel - dead bird … · 2010. 3. 30. · include blue...

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