Ontario Ministry of Health and Long-Term Care - Health Care Providers - Program - Public Health - West Nile virus Bulletin - Volume 1 / Issue 3

Public Information

Health Care Providers

News Media

Text Only Version

West Nile virus Bulletin : 2000 Archive
Disease Control Service Public Health Branch	Volume 1 / Issue 3 – August 4, 2000

IN THIS ISSUE

Summary of Ontario Surveillance Activities
WNv Surveillance in Ontario
Sentinel Chicken Surveillance
Human Encephalitis Surveillance

Mosquito Surveillance
Dead Bird Surveillance
Other News

Summary of Ontario Surveillance Activities for the week ending July 14, 2000
Sentinel Chicken Surveillance	All sites negative.
Active Human Surveillance	No cases detected.
Mosquito counts	Culex species present – currently < 35% of female population at all sites.
Dead Bird Surveillance	102 specimens collected – no confirmed case of West Nile virus (WNv).
Summary of surveillance activities in other jurisdictions to date
Canada
No other jurisdictions in Canada have reported confirmed WNv in mosquitoes, birds, sentinel chickens or humans.
U.S.
As of August 8, 2000, one human case of WNv has been confirmed in New York while birds have tested positive for WNv in four states, including New York, New Jersey, Massachusetts, and Connecticut. The human case was a 78-year-old man from the southern section of Staten Island. He first became ill on July 20, and when the incubation of WNv in humans (5 to 15 days) is taken into account, then it would indicate that he was infected prior to the spraying on Staten Island on July 19. The case was hospitalized with a diagnosis of viral meningo-encephalitis but was later released and is recovering at home. As of August 7, 128 birds have tested positive in New York State, involving 20 counties. WNv has spread north and northwest from the epicenter of last year's outbreak, and is now active throughout New York State. The counties across the Ontario border include Franklin, Niagara and Erie. The crow from Erie was found in the town of Tonawanda (immediately east of the Canada U.S. border and east of the Niagara health unit). As of August 7, 53 crows have tested positive for WNv (29 in Bergen, 12 in Middlesex, 2 in Union, 2 in Hudson, 5 in Passaic, 2 in Monmouth and 1 in Essex Counties). Three birds have also tested positive in Massachusetts (north of NYC), specifically in Jamaica Plain, Hopkinton, and Boston City Park. Additionally, 1 crow in the Springdale region of Stamford, Connecticut (northeast of NYC) and one crow from the town of Columbia beyond the Fairfield and New Haven region, Connecticut have tested positive for WNv. In New York State, spraying is being conducted within a two-mile radius in all areas with positive identification of WNv in birds.

WNv Surveillance in Ontario

This is the third issue of the Ontario WNv Bulletin. This bulletin is intended to provide a summary of results of the various surveillance activities in Ontario, as well as update readers on surveillance findings elsewhere in Canada and the U.S.

Sentinel Chicken Surveillance

Another successful week of Sentinel Chicken Surveillance was carried out. All 18 sites located in the six potentially high-risk areas of Brockville (BR), Picton (PI), Guelph (GU), Niagara (NI), Long Point (LP) and Point Pelee (PP) were visited.

For the week ending July 14, blood samples were collected from all 18 sites in all six regions. However, at one site in the Picton region, only 9 of 10 samples were taken. No other difficulties in sampling of chickens have been noted. As of the week ending July 14, all sentinel chicken serums have tested negative for WNv. To date, no sentinel chickens in Ontario have tested positive for WNv.

Human Encephalitis Surveillance

In a mailing sent July 5, 2000, selected specialty programs and all hospitals have been notified about the possibility of WNv infection in Ontario.

As of August 4, all 58 hospitals have agreed to participate in active human meningo-encephalitis surveillance. Eleven suspect cases have been reported from nine sentinel hospital sites. Diagnostic specimens have included acute and convalescent sera and cerebrospinal fluid. None have been confirmed for WNv. Cases of meningo-encephalitis have included a 7-year-old child from the London-Middlesex health unit region, a 29-year-old individual from the Hamilton-Wentworth region, and a 42-year-old case from the Ottawa-Carleton health unit region. Three cases, aged 34, 35 and 54 years, were reported from Peel region and one 43-year-old case was reported from the Halton health unit region. Additionally, 4 cases (aged 2, 11, 32 and 45) were reported from the Toronto health unit region.

Mosquito Surveillance

Surveillance of the composition and abundance of local mosquito populations in 18 sites spread across six regions in Ontario has continued. For the week ending July 14, mosquitoes were collected from all 18 sites.

Analysis of variance of mean mosquito counts at each site within the 18 regions over the 7-week period indicated only one site in the Brockville region (BR1) having a significantly higher count of total mosquitoes compared to the other sites in the same region (p=0.04). In the last issue of the WNv Bulletin Vol. 1, Issue 2, this site in Brockville was reported as having higher, but not statistically significant, counts of mosquitoes than the other sites in the Brockville region. One site in Long Point (LP-3) and one in Picton (PI-3) maintained markedly higher counts of mosquitoes than the other sites within the same region, but these differences are not statistically significant (see Figure 1). There was an increase in total mosquito counts in 10 (55.6%) of the sites when compared to the previous week.

Total mosquito counts from the three sites of each of the six regions were pooled for further analysis. A summary of the first seven weeks of collection is provided in the table below. The regions of Brockville, Niagara, Picton and Point Pelee reported a significant increasing trend of total mosquitoes over the seven-week period (p= 0.04, 0.04, 0.01, 0.03 respectively). No significant increasing trend in the proportion of females was reported in any of the six regions. Only Brockville had a significant increasing trend of the proportion of female mosquitoes that are Culex pipiens (p= 0.01). There were no other significant increases over the seven-week period in proportion of female mosquitoes that are of the genus Aedes in any of the six regions.

7 Week Summary
SITE	Mean Number of Female Mosquitoes Mean (range)	Mean % of Mosquitoes Female	Mean % of Female Mosquitoes Culex pipiens	% of Female Mosquitoes Aedes
Brockville	746.1 (35-1985)	92.6	10.4	88.1
Guelph	399.1 (6-1552)	87.9	20.6	78.4
Long Point	71.4 (1-311)	81.6	34.1	59.5
Niagara	91.0 (8-366)	88.0	26.3	63.2
Picton	640.6 (35-1902)	85.9	21.5	77.0
Point Pelee	218.4 (19-476)	91.0	12.9	85.4

Figure 1

Mean Number of Mosquitoes per Site : June 2 - July 14, 2000

Dead Bird Surveillance

Figure 2 shows the weekly submissions of dead bird carcasses to the week ending July 14. The figure indicates a marked increase in the number of submissions in the first two weeks of July, with 15 submissions in the first week and 26 in the second week. The weekly submissions of carcasses for the first two weeks of July are higher than any other previous week. Health unit participation in dead bird surveillance has increased. As of the week ending July 14, 18 (49%) health units have made a total of 36 submissions (each submission could involve multiple carcasses). This increase in health unit participation is important, since dead bird surveillance is a vital part of Ontario's efforts to detect any virus activity as early as possible.

As of July 14, 102 bird carcasses have been submitted for examination in Ontario. Initial autopsy indicated that 30 (29%) carcasses did not require further diagnosis, and 26 of these had a firm alternative diagnosis. Of the 102 carcasses submitted, 68 required further examination after autopsy. Histology results have indicated a firm alternative diagnosis in 18 of the 68 carcasses, with another 12 not requiring further testing since no indications of WNv lesions were present. Results on a further 26 carcasses are pending. To date histology results are available for 25 (48%) of the specimens requiring further examination. Thus far, no dead bird carcasses submitted in Ontario have been confirmed positive for WNv.

Figure 2

Dead Bird Submissions, Ontario : May 1 - July 14, 2000

Figure 3

Proportion of Dead Birds by Type : May 1 - July 14, 2000

Other News

On July 27, Health Canada released a travel advisory for Canadians travelling to specified areas in the U.S. These areas include New York City, specifically Queens and Richmond, and the surrounding counties in New York State including Orange, Rockland, Suffolk, and Westchester. Fairfield County in Connecticut, Bergen, Hudson and Middlesex Counties in New Jersey and Suffolk County in Massachusetts were also specified as areas of potential exposure to WNv. A full copy of this advisory including precautionary measures may be obtained from Health Canada.



Comments, questions and suggestions about surveillance results in this bulletin should be directed to : Public Health Branch Sheila Artes WNv Surveillance Coordinator Disease Control Service Tel : 416-327-3508 E-mail : sheila.artes@moh.gov.on.ca

| return to program menu |