Vector-borne Diseases in Windsor and Essex County, 2021

Lyme disease is a vector-borne disease caused by the bacterium Borrelia burgdorferi. It is transmitted to humans through the bite of infected blacklegged ticks. Lyme disease occurs in stages. The signs and symptoms of each stage can overlap and varies from person to person. A common symptom is an expanding area of redness on the skin (may not be itchy or painful) that appears at the site of the tick bite about a week after it occurred. It may be circular or oval-shaped or can look like a target or bull's eye. Other early stage symptoms may include fever, headache and tiredness. Lyme disease may present in a later stage without a history of prior signs or symptoms. More severe infections may lead to joint pain, memory problems, severe headaches and increased tiredness  (Government of Canada, 2022).

The WECHU's role is to measure and evaluate the risk of this tick-borne disease in our area. Active surveillance was used to assess the local distribution and incidence of blacklegged ticks in WEC and human case surveillance was used to assess the incidence of Lyme disease.

Active surveillance

Active surveillance involves the dragging of a white cloth through grassy areas whereby ticks attach themselves to the cloth and can be easily spotted. Ticks collected on the cloth are identified by health unit staff and sent to an accredited laboratory for testing. Tick dragging is performed twice yearly in the spring and the fall.

• In 2021, tick dragging was conducted at four sites - Ojibway Prairie Nature Reserve, Chrysler Greenway, Gesstwood Camp and Education Centre and Ruscome Shores Conservation Area - in the spring and in the fall.
• A total of 33 blacklegged ticks were found through tick dragging, with nine of these carrying the infectious agent that causes Lyme disease

Human case surveillance

Lyme disease is a reportable disease in Ontario. The WECHU investigates reported cases of Lyme disease in the region. In 2021, there were seven confirmed cases of Lyme disease in WEC, representing a rate of 1.6 cases per 100,000 population. Figure 1 shows both confirmed and probable cases of Lyme disease from 2009-2021.

As per data reported in the Integrated Public Health Information System (iPHIS,) the top four risk factors reported by WEC Lyme disease cases from 2016-2021 were:

• activities in wooded or tall grass areas (84% of cases)
• not always using insect repellent in wooded or tall grass areas (72% of cases)
• inadequate clothing protection in wooded or tall grass areas (68% of cases)
• exposure to ticks or having a tick bite  (68% of cases)

[[chart-nid:6821,chart-view-mode:full]]

West Nile virus (WNV) is typically spread to humans by infected mosquitoes which receive the virus when they feed on infected birds. The virus is not known to spread through touching, kissing, or caring for someone who is infected.  In very rare cases, WNV can be spread through blood transfusion, organ or tissue transplants, during pregnancy from mother to baby, breast milk, or exposure of laboratory workers to infected medical specimens (Government of Canada, 2022).

The symptoms of WNV can range from mild to severe. Although the majority of infections do not result in any noticeable symptoms, some human cases may develop a fever, headache, vomiting, or a rash. Rare instances of infection may lead to encephalitis or meningitis (Government of Canada, 2022).

The WECHU's WNV program includes human case surveillance, and in collaboration with local municipalities adult mosquito surveillance.

Adult mosquito surveillance

Adult mosquito surveillance is an important component of the vector-borne disease program and involves the deployment of black-light CDC traps at various locations throughout WEC. These traps capture mosquitoes for testing to determine the presence of WNV in our area. The CDC traps are equipped with a light and dry ice  attracts and traps the mosquitoes. The  trapped mosquitoes are counted and tested to identify the species and determine if any of the mosquitoes carry the WNV.

In 2021, WNV positive mosquitoes were also found in BG-Sentinel 2 (BGS-2) traps. These traps are species-specific have traditionally been set up to catch invasive species of mosquitoes (Aedes albopictus and Aedes aegypti) that were identified during routine WNV surveillance in WEC in 2016. BGS-2 traps use a scent lure and dry ice to attract daytime mosquitoes and are set up in high traffic areas (such as near transport routes and industrial cargo areas) as well as in residential homes. The number of CDC and BGS-2 traps deployed for each municipality can be found in Appendix A.

Results for 2021

• In total, 187,918 mosquitoes were caught in CDC and BGS-2 traps combined (see Appendix A)
  • 144,866 mosquitoes were caught in CDC traps
  • 43,052 mosquitoes were caught in BGS-2 traps
• 0.7% (17 of 2,291) mosquito pools tested were WNV positive
  • 0.7% (9 of 1,333) mosquito pools at CDC trap locations tested positive for WNV.
  • 0.8% (8 of 958) mosquito pools at BGS-2 trap locations tested positive for WNV.
• The top three species captured across all traps in 2021 were:
  • Aedes vexans (n = 24,362)
  • Coquillettidia perturbans (n = 15,623)
  • Culex pipiens/restuans (n = 9,314)

[[chart-nid:8742,chart-view-mode:full]]

Human case surveillance

WNV is a reportable disease in Ontario. The WECHU follow-ups on reported cases of WNV in the region.

• In 2021, there were three human cases of WNV in WEC, representing a rate of 0.7 cases per 100,000 population (Figure 3). Ontario overall showed a rate of 0.1 cases per 100,000 population in 2021.
• According to data reported in iPHIS, the top four risk factors reported by WNV cases in WEC from 2016-2021 were:
•  
  • no insect repellent when outdoors (74% of cases)
  • not always using adequate clothing protection (i.e., long sleeves, long pants, covered shoes) when exposed to mosquitoes (72% of cases)
  • exposure to mosquitoes and mosquito bites (72% of cases)
  • camping, hiking, working, or other activities outdoors (69% of cases)

[[chart-nid:6846,chart-view-mode:full]]

Mosquito larviciding

Mosquito larviciding involves applying larvicides to catch basins, standing water sites, and lagoons that hold water where mosquitoes may breed. The WECHU and municipalities contracted a service provider to run larval surveillance beginning in May.

• 118,560 treatments of larvicide were applied at roadside catch basins across WEC in 2021.
• Two treatments of larvicide were applied at one standing water site in 2021.

Data Sources

1. The Windsor-Essex County Health Unit. Internal database [2018-2021].
2. Public Health Ontario. Infectious Disease (ID) Query Tool [2009-2021].
3. Ontario Ministry of Health. Integrated Public Health Information System (iPHIS) [2016-2021].
4. GDG Environment Inc. West Nile Virus Abatement Program. Final Report [2021].

References:

Government of Canada. (2022). Lyme disease: Symptoms and treatment. Retrieved from https://www.canada.ca/en/public-health/services/diseases/lyme-disease.h…

Government of Canada. (2022). West Nile Virus. https://www.canada.ca/en/public-health/services/diseases/west-nile-viru…

Otten, A., Fazil, A., Chemeris, A., Breadner, P., & Ng, V. (2020). Prioritization of vector-borne diseases in Canada under current climate and projected climate change. Microbial risk analysis  v.14, https://doi.org/10.1016/j.mran.2019.100089.

Appendix A: Number and Type of Traps by Municipality

1. The Windsor-Essex County Health Unit. Internal database [2018-2021].
2. Public Health Ontario. Infectious Disease (ID) Query Tool [2009-2021].
3. Ontario Ministry of Health. Integrated Public Health Information System (iPHIS) [2016-2021].
4. GDG Environment Inc. West Nile Virus Abatement Program. Final Report [2021].

References:

Government of Canada. (2022). Lyme disease: Symptoms and treatment. Retrieved from https://www.canada.ca/en/public-health/services/diseases/lyme-disease.h…

Government of Canada. (2022). West Nile Virus. https://www.canada.ca/en/public-health/services/diseases/west-nile-viru…

Otten, A., Fazil, A., Chemeris, A., Breadner, P., & Ng, V. (2020). Prioritization of vector-borne diseases in Canada under current climate and projected climate change. Microbial risk analysis  v.14, https://doi.org/10.1016/j.mran.2019.100089.