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Overview

Vector-borne diseases are caused by the transmission of parasites, viruses and bacteria in humans by vectors. The most common vectors are mosquitoes and ticks. Vectors  can transfer pathogens from one host to another. Public health units are required to conduct vector-borne surveillance to monitor trends for emerging diseases, including factors that influence their occurrence. In addition, surveillance data is translated into evidence-based programs and services to control insect vector populations. The primary focus of Ontario's vector-borne management plan is on tick and mosquito population surveillance. This report summarizes the surveillance activities of the Windsor-Essex County Health Unit (WECHU) as it relates to West Nile Virus (WNV) and Lyme disease.

Lyme disease is an infectious disease spread by ticks. A common symptom is an expanding area of redness on the skin (not itchy or painful) that appears at the site of the tick bite about a week after it occurred. Other early symptoms may include fever, headache and tiredness. More severe infections may lead to joint pain, memory problems, and tiredness for at least six months.

The WECHU's role is to measure and evaluate the risk of this tick-borne disease in our area.  To measure the local distribution and incidence of ticks and Lyme disease cases in Windsor and Essex County (WEC), the following three surveillance techniques were used in 2019 – active surveillance, passive surveillance, and human case surveillance.

Active surveillance

Active surveillance involves dragging a white cloth through grassy areas whereby ticks attach themselves to the cloth and can be easily spotted. Ticks collected on the cloth are sent to an accredited lab for testing. Tick dragging is performed twice yearly to identify areas in WEC that have populations of black-legged ticks, the main vector for Lyme disease.

  • In 2019, tick dragging was conducted at four sites (Chrysler Greenway, Ojibway Prairie Nature Reserve, Gesstwood Camp and Ruscom Shores Conservation Area) in the spring and in the fall.
  • Two black-legged ticks were found through tick dragging, none carrying the infectious agent of Lyme disease.
  • In 2020, tick dragging was not conducted due to the COVID-19 pandemic.

Passive surveillance

Residents submitted ticks to the WECHU for identification and subsequent testing if the tick was identified as a black-legged tick.

  • 329 ticks were submitted to the WECHU in 2019. Tick species were identified for 328 ticks (99.7%) (Figure 1).
    • 38 black-legged ticks were identified to the WECHU (11.6% of identified ticks) (Figure 1).
    • Five black-legged ticks tested positive for Borrelia burgdorferi, the bacteria that causes Lyme disease (Figure 2).
  • In 2020, submission of ticks to the WECHU has been discontinued as the Public Health Agency of Canada suspended their diagnostic testing for black-legged ticks as part of the passive surveillance program. The residents are now directed to submit a photograph of the tick to identify its type on www. etick.ca, which is a free online service.

Figure 1. Ticks submitted to the Windsor-Essex County Health Unit, 2014-2019

Figure 2. Blacklegged ticks submitted to the Windsor-Essex County Health Unit, 2014-2019

Human case surveillance

Lyme disease is a reportable disease in Ontario. The WECHU investigates reported cases of Lyme disease in the region.

  • In 2019, there were four confirmed cases of Lyme disease in WEC, representing a rate of 0.9 cases per 100,000 population (Figure 3).
  • Similarily in 2020, there were four confirmed cases of Lyme disease in WEC, representing a rate of 0.9 cases per 100,000 population (Figure 3).
  • As per data reported in the Integrated Public Health Information System (iPHIS,) the top four risk factors reported by WEC Lyme disease cases between 2016 and 2020 were:
    • activities in wooded or tall grass areas (78% of cases),
    • inadequate clothing protection in wooded or tall grass areas (61% of cases),
    • not checking oneself for ticks after being outdoors in wooded or tall grass areas (61% of cases), and  
    • not always using insect repellant when outdoors in wooded or tall grass areas (61% of cases).

Human cases of Lyme disease in WEC and Ontario, 2009-2020

West Nile virus (WNV) is typically spread by infected mosquitoes, which receive the virus when they feed on infected birds. 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.

[1] Rarely the virus is spread through blood transfusions, organ transplants, or from mother to baby during pregnancy, delivery, or breastfeeding. [2] It otherwise does not spread directly between people. [3] Risks for severe disease include age over 60 and other health problems

In collaboration with local municipalities, the WECHU's WNV program includes both adult mosquito surveillance and human case 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 have a light and dry ice that attracts the mosquitoes. The mosquitoes fly into the trap, get caught in the net, and are then collected for testing. The mosquitoes trapped are counted and tested to identify the species and determine if any of the mosquitoes are carrying the virus.

In 2019 and 2020, WNV positive mosquitoes were also found in BG-Sentinel 2 (BGS-2) traps. These traps have traditionally been set up to catch tropical species of mosquitoes (Aedes albopictus and Aedes aegypti) that were identified during routine WNV surveillance in Windsor and Essex County (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.

Results for 2019

  • In total, 165,369 mosquitoes were caught in CDC and BGS-2 traps combined
    • 127,382 mosquitoes were caught in CDC traps
    • 37,987 mosquitoes were caught in BGS-2 traps
  • 1.6% (18 of 1137) mosquito pools tested were WNV positive
    • 0.7% (7 of 979) mosquito pools at CDC trap locations tested positive for WNV (Figure 4)
    • 7.0% (11 of 158) mosquito pools at BGS-2 trap locations tested positive for WNV.
  • The top three species captured across all traps in 2019 were:
    • Coquillettidia perturbans (n = 11,758)
    • Culex pipiens/restuans (n = 6,473)
    • Aedes vexans (n = 5,796)

Results for 2020

  • In total, 205,569 mosquitoes were caught in CDC and BGS-2 traps combined
    • 177,932 mosquitoes were caught in CDC traps
    • 27,637 mosquitoes were caught in BGS-2 traps
  • 1.5% (30 of 2,052) mosquito pools tested were WNV positive
    • 1.2% (13 of 1,094) mosquito pools at CDC trap locations tested positive for WNV (Figure 4)
    • 1.8% (17 of 958) mosquito pools at BGS-2 trap locations tested positive for WNV.
  • The top three species captured across all traps in 2020 were:
    • Coquillettidia perturbans (n = 23,580)
    • Aedes vexans (n = 9,378)
    • Culex pipiens/restuans (n = 6,238)

Mosquitoes tested for West Nile Virus (WNV) in Windsor and Essex County, 2014-2020

Human case surveillance

WNV is a reportable disease in Ontario. The WECHU follows up on reported cases of WNV in the region.

  • In 2019, there was one human case (confirmed) of West Nile Virus (WNV) illness in WEC, representing a rate of 0.2 cases per 100,000 population (Figure 5).
  • In 2020, there were three human cases (two confirmed, one probable) of WNV, representing a rate of 0.7 cases per 100,000 population (Figure 5).
  • According to data reported in iPHIS, the top four risk factors reported by WNV cases in WEC between 2016 and 2020 were :
    •  not always using adequate clothing protection (i.e., long sleeves, long pants, covered shoes) when exposed to mosquitoes (75% of cases),
    •  no insect repellant when outdoors (75% of cases),
    •  exposure to mosquitoes and mosquito bites (69% of cases), and
    • outdoor activities (i.e., camping, hiking, working) (67% of cases).

Human cases of West Nile Virus illness in Windsor and Essex County (WEC) and Ontario, 2009-2020

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.

  • 137,311 treatments of larvicide were applied at roadside catch basins across WEC in 2019.
    • 201 treatments of larvicide were applied at 52 standing water sites in 2019.
  • 136,042 treatments of larvicide were applied at roadside catch basins across WEC in 2020.
    • 7 treatments of larvicide were applied at 6 standing water sites in 2020.

Data Sources

  1. The Windsor-Essex County Health Unit. Internal database [2014-2020].
  2. Public Health Ontario. Infectious Disease (ID) Query Tool [2009-2020].
  3. Ontario Ministry of Health. Integrated Public Health Information System (iPHIS) [2009-2020].
  4. Pestalto Environmental Health Services Inc. Mosquito Abatement Program for Reduction of West Nile Virus Vectors. 2019 Final Report [2019].
  5. Pestalto Environmental Health Services Inc. Mosquito Abatement Program for Reduction of West Nile Virus Vectors. 2020 Final Report [2020].

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