West Nile Virus Surveillance and Control 2015

Report to: Board of Health

Meeting Date: June 1, 2016

Report Number: BOH Report – BH.01.JUN0116.R10

Prepared by: Shawn Zentner, Manager, Health Protection

Mike Coburn, Public Health Inspector

Sarah Croteau, Health Promotion Specialist

Approved by: Rob Thompson, Director, Health Protection

Submitted by: Dr. Nicola Mercer, Medical Officer of Health & CEO


(a) That the Board of Health receives this report for information.

Infographic discusses background, surveillance and reporting, and prevention activities for 2015 West Nile Virus Program Report. All information in infographic is in the report.


In 2015, Wellington-Dufferin-Guelph Public Health (WDGPH) implemented its 13th consecutive West Nile virus (WNV) prevention program. As in previous years, WDGPH continued with public education, mosquito surveillance and larviciding activities.  In preparation for the implementation of the 2016 WNV program, it is essential to reflect on results and lessons learned from previous years.

The goal of this program is to prevent or reduce human exposure to WNV


WNV is transmitted from mosquitoes to humans (zoonotic transmission) and was first found in Ontario in 2001. Birds of the corvid family (crows, ravens and blue jays) act as the primary reservoir for the virus and mosquitoes are the vectors that spread the virus from infected birds to humans and to other animals.1 Among large animals, horses are especially at risk for WNV infection and disease.1,2

With respect to mosquitos, the species of greatest concern for the transmission of WNV are Culex restuans and Culex pipiens.3 These mosquitoes thrive in urban environments where they breed in small bodies of protected, stagnating water as found in catch basins, abandoned swimming pools, old tires, blocked eaves troughs, storm retention ponds, and bird baths.

It’s estimated that between 70% – 80% of people infected with the virus have no symptoms.4,5 Some people have mild, flu-like symptoms including fever, headache, body aches, mild rash, and swollen lymph glands.5,6  However, in rare cases (<1%) the virus can cause severe symptoms such as inflammation of the brain or spinal cord, which can sometimes be fatal.7 In general, recovery can take a week for mild cases, and months to years for more severe cases. 

People who are over age 50, who have chronic diseases such as cancer, diabetes, alcoholism, or heart disease, or who are immunocompromised, are at higher risk for serious health effects, but WNV can cause severe complications for people of any age or health status.1 It is important to note that there is no specific treatment or vaccine for WNV infection in humans, however, mild symptoms such as fever and body aches can be managed and treated.

In 2002, the first human case of WNV was reported to WDGPH. Since then, WDGPH has implemented a WNV prevention program. The program typically runs from May/June to September/October of each year depending on weather conditions, when humans are most at risk of becoming infected with WNV. It operates in accordance with the Ministry’s West Nile Virus Preparedness and Prevention Plan.8 WDGPH’s 2015 WNV program was aimed to prevent or reduce human exposure to WNV within the community through mosquito surveillance, larviciding, and public education.  These program components remain similar from one year to the next, and can be scaled up or down as needed based on the surveillance being conducted.  In preparation for the 2016 WNV program, it is essential to reflect on results and lessons learned from previous years.  

In April 2015, a public notification was placed in local newspapers regarding upcoming larviciding treatments (Appendix A). This is a mandatory requirement of the Ministry of the Environment and Climate Change. The public was encouraged to have catch basins located on their own properties treated. The larviciding service was offered free-of-charge and promoted through a media release and the WDGPH website. In addition, letters were sent to homeowners who had their catch basins treated in previous years.

In 2015, a total of 22,284 roadside and 150 non-roadside catch basins were treated within the County of Wellington, the County of Dufferin, and the City of Guelph. As part of larviciding efforts, stagnant surface water was also treated. A total area of 6.64 hectares was treated. In addition, the public was encouraged to notify WDGPH of areas of standing water that may be conducive to mosquito-breeding. All larviciding was carried out by the Canadian Centre for Mosquito Management (CCMM) on behalf of WDGPH. Further detail regarding CCMM larviciding can be found in Appendix B. 

As in past years, WDGPH coordinated with the City of Guelph’s Property Standards Inspection Department, which is responsible for enforcing by-law (2003) – 17192. This by­law regulates standing water (i.e., unmaintained artificial ponds, hot tubs, swimming pools, and excavations) within the limits of the City of Guelph. Enforcement of this by-law commenced and concluded based on larval and adult mosquito activity as determined through surveillance.

Surveillance activities included the collection of both adult and larval life stages of the vector species, Culex restuans and Culex pipiens. The presence of larval vector species determined whether or not the standing water in question would be treated. Trapped adults were sent to Entomogen for species identification. Positively identified vector species were tested for the presence of WNV in order to determine the prevalence of the virus in mosquitoes in the WDGPH area. No mosquito pools tested positive for WNV in 2015. A summary of surveillance activities and findings can be found in Appendix C.

Although there were no human cases of WNV reported in 2015 within Wellington, Dufferin or Guelph, WDGPH issued a physician’s advisory in July 2015 in response to a confirmed case in a neighbouring health unit (Region of Waterloo Public Health). 

Public education efforts conveyed that WNV is still a concern, and that simple steps can be taken by the public to reduce their risk of contracting the virus. These messages were delivered through a media release, the WDGPH WNV webpage, and social media.  Key messages included:

Preventing mosquito bites

When outdoors, especially at dawn and dusk when mosquitos are most active:

  • Cover up by wearing light coloured, long-sleeved shirts and pants
  • Use a Health Canada approved mosquito repellent, such as one that contains DEET or Icaridin

Removing standing water on your property to eliminate potential breeding grounds

To decrease the number of mosquitoes on your property, eliminate standing water where mosquitoes lay their eggs:

  • Empty standing water from wheelbarrows, flowerpots, old tires and anywhere else water collects
  • Frequently change water in pet dishes and bird baths
  • Stock your pond with fish, as they will eat mosquito larvae
  • Ensure ponds have good circulation


WNV activity was first reported in Canada in the summer of 2001; the virus was found in dead birds and mosquito pools in southern Ontario. During the following year, the first human cases of WNV were reported in Ontario and Quebec. Throughout 2002, 395 cases of WNV were reported in Ontario. From 2003 through 2011, the number of cases reported annually remained relatively low, ranging from 4 to 101 (Figure 1), until 2012 when 271 confirmed human cases of WNV were reported in Ontario. The 2012 increase in WNV cases across the province served as a reminder that it is difficult to predict virus activity from one year to the next, as it is dependent on many different factors. Thus, it is important to be vigilant with surveillance, larviciding and educational efforts in 2016 and beyond. 

Within WDGPH, a total of six confirmed and suspect cases of WNV have been reported since 2002. Four of these cases were reported during 2011-2013. Since then, and up until the time of writing, no human cases of WNV have been diagnosed. 

Ontario Public Health Standards

Health Hazard Prevention and Management Program Standard

Goal: To prevent or reduce the burden of illness from health hazards in the physical environment. 

The board of health shall develop a local vector-borne management strategy based on surveillance data and emerging trends in accordance with the Infectious Diseases Protocol, 2015.

WDGPH Strategic Directions

Strategic Directions
Health Equity: We will provide programs and services that integrate health equity principles to reduce or eliminate health differences between population groups.                NO
Organizational Capacity: We will improve our capacity to effectively deliver public health programs and services.                 NO
Service Centred Approach: We are committed to providing excellent service to anyone interacting with Public Health.                NO
Building Healthy Communities: We will work with communities to support the health and well-being of everyone.               YES

Health Equity

An important health equity issue is the higher prevalence of WNV found in both mosquitos and humans among low income areas. Research studies have shown that poorer economic conditions may act as a direct surrogate for environmental characteristics related to WNV prevalence.9, 10 Results have shown that low income areas represent habitats that are conducive to WNV amplification in mosquitos, thus leading to a higher occurrence of disease in humans.9, 10 

The WNV prevalence in low income areas is thought to occur due to a combination of three reasons:

Older infrastructure characterized by antiquated runoff systems that contribute to poor drainage and favourable mosquito breeding habitats;
Less likelihood of investment in private property upkeep, leading to a higher density of neglected stagnant water; and
Less education and political involvement, with a lower likelihood of requesting mosquito management in the area.9


Appendix A – Copy of the public notice that was placed in local newspapers to inform the community of upcoming larviciding activities.

Appendix B – The scope of work performed by the Canadian Centre for Mosquito Management (CCMM) has been summarized in the following tables.

Appendix C – Summary of Mosquito Surveillance.


1. Health Canada. Surveillance of West Nile Virus. Healthy Canadians Website, Modified May 1, 2016. Accessed at: http://healthycanadians.gc.ca/diseases-conditions-maladies-affections/di….

2. CDC, Centers for Disease Control and Prevention. Division of Vector-Borne Diseases. West Nile Virus in the United States: Guidelines for Surveillance, Prevention, and Control. 4th Revision. June 14, 2013

3. PHO, Public Health Ontario. Guide for Public Health Units: Considerations for Adult Mosquito Control. Guidance Document. August, 2013.

4. Mostashari F, Bunning M, Kitsutari P et al. Epidemic West Nile encephalitis, New York, 1999: Results of a household-based seroepidemiological survey. Lancet. 2001; 358: 261-264.

5. Zou S, Foster GA, Dodd RY et al. West Nile fever characteristics among viremic persons identified through blood donor screening. J Inf Dis. 202:1354-1361.

6. Watson J, Pertel P, Jones R et al. Clinical characteristics and functional outcomes of West Nile Fever. Ann Intern Med. 2004; 141: 360-365.

7. Hayes E, Sejvar J, Zaki S, Lanciotti R, Bode A, Campbell G. Virology, pathology, and clinical manifestations for West Nile Virus Disease. Emerg Infect Dis. 2005; 11:1174-1179.

8. OMHLTC, Ontario Ministry of Health and Long-Term Care. West Nile Virus Preparedness and Prevention Plan 2008. Toronto ON: Queen’s Printer for Ontario.

9. Harrigan R, Thomassen H, Beurmann W et al. Economic Conditions Predict Prevalence of West Nile Virus. PLoS ONE. 2010; 5(11): e15437.

10. LaDeau SL, Liesnham PT, Biehler D, Bodner D. Higher mosquito production in low-income neighbourhoods of Baltimore and Washington, DC: Understanding ecological drivers and mosquito-borne disease risk in temperate cities. Int J Environ Res Public Health. 2013;     10(4): 1505-1526.

Copy of the public notice that was placed in local newspapers to inform the community of upcoming larviciding activities.

Notice that went into paper about Ground Application For Larval Mosquitoes, dates, where it will be use, and how to contact public health.

APPENDIX B.  The scope of work performed by the Canadian Centre for Mosquito Management (CCMM) has been summarized in the following tables.

Table B1. Larval and Audlt Mosquito Surveillance
Larval Mosquito Surveillance
                                                     Timeframe of surveillance

- Catch basin monitoring timeframe: May 18, 2015 – June 2, 2015 (when treatments began)

- Surface water monitoring timeframe: May 18, 2015 – September 28, 2015

                                                  Adult Mosquito Surveillance
                                                     Timeframe of surveillance

- Catch basin monitoring timeframe: May 18th, 2015 - July 14th, 2015

- Surface water timeframe: May 18th, 2015 – September 28, 2015


Table B2. Treatment Dates of Larvicide Application
Treatment Dates

Wellington-Dufferin-Guelph Public Health Vector-borne Disease Summary

of Larvicide Application Dates 2015

         Site           Product App. #1   App. #2     App. #3 App. #4   Unscheduled Apps. 
Non-ESA CBs*   Altosid®  Pellets June 2-3  June 25-26 July 15-16, 26 Aug. 5-7            N/A
 Non-ESA CBs Altosid® XR Briquets June 3     N/A       N/A    N/A            N/A
   ESA CBs**       Vectolex WSP June 2-3  June 25-26

July 15-26

Aug. 5-7            N/A
 Surface Waters      Vectobac 200G     N/A     N/A        N/A    N/A May 28 – September 28

*Non-Environmentally Sensitive Area Catchment Basins

**Environmentally Sensitive Catchment Basins


Table B3. Treatment Locations of Larvicide Application
Treatment Locations

Wellington-Dufferin-Guelph Public Health Vector-borne Disease Summary

of Product Application Location by Community 2015

Non-ESA CBs w/ Altosid® Pellets & Altosid XR Briquets   ESA CBs w/ Vectolex WSP Stagnant Surface Waters w/ Vectobac 200G
                                     Guelph                Guelph                             Guelph
                               Guelph-Eramosa   Guelph-Eramosa                          Rockwood
                                     Puslinch                   Erin                          Orangeville
                                       Erin              Orangeville                              Fergus
                                 Orangeville                        -                                                  East Garafraxa
                                 Palmerston                        -                              Arthur
                                 Mount Forest                        -                                   -                                       
                                   Harriston                        -                                   -
                                     Fergus                        -                                   -
                                     Elora                        -                                   -
                                  Drayton                        -                                   -
                                   Arthur                        -                                   -


Table B4. Total Amount of Product Used for Larvicide Treatments

Totals: Catch Basin and Standing Water Treatments, and Product Usage 

Wellington-Dufferin-Guelph Public Health Vector-borne Disease Summary

of Non-ESA Catch Basin Larvicide Treatments 2015

         Product         Rounds   App. Rate CBs Treated/Round   Total Prod. Used All Rounds
Altosid®  Pellets           4   0. 7 g/CB          22,284                 58. 9 kg
Altosid® XR Briquets           1 1 Briquet/CB            150               150 Briquets

Wellington-Dufferin-Guelph Public Health Vector-borne Disease Summary

of ESA Catch Basin Larvicide Treatments 2015

          Product         Rounds App. Rate CBs Treated/Round Total Prod. Used All Rounds
       Vectolex WSP          4  1 Pouch/CB              25          100 Pouches/100 CBs

Wellington-Dufferin-Guelph Public Health Vector-borne Disease Summary

of Stagnant Surface Water Larvicide Treatments 2015

          Product Total Treatments  App. Rate      Area Treated Total Prod. Used All Treatments
     Vectobac 200G         711     10 kg/ha        6. 64 ha               66. 4 kg



Table C. Summary of Mosquito Surveillance.

Wellington-Dufferin-Guelph Public Health Vector-borne Disease Summary

of Adult Mosquito Surveillance 2015

Total traps submitted           127
Total mosquitoes submitted          9920
Total mosquitoes identified          4378
Total pools viral tested for WNV           168
Total WNV positive pools             0
Total pools viral tested for EEEV           168
Total EEEV positive pools             0