Protecting Outdoor Workers from West Nile, Zika, and Lyme Disease

Protecting Outdoor Workers from West Nile, Zika, and Lyme Disease

Under the Occupational Health and Safety Act employers must take reasonable precautions for the protection of workers, and this includes protecting outdoor workers from exposure to West Nile virus, Zika virus, and Lyme disease. While you may be thinking that it isn’t possible to protect outdoor workers from naturally occurring workplace hazards, you must recognize that risks to outdoor workers can be mitigated and reduced. It is the employer’s responsibility to ensure that such action is taken.


The Occupational Health and Safety Act, defines occupational illness as “a condition that results from exposure in a workplace to a physical, chemical or biological agent to the extent that the normal physiological mechanisms are affected and the health of the worker is impaired.” Currently, in Ontario, outdoor workers are at risk of exposure to three primary illnesses: West Nile virus, Zika virus, and Lyme disease.


West Nile is a virus spread primarily through mosquito bites. Mosquitos feed on infected birds, then bite humans and pass the virus through their bites. West Nile is less commonly transmitted by blood transfusions, organ transplants, or pregnancy and/or breastfeeding. While the risk of contracting West Nile in Canada is low, it is highest among populations that work outdoors. 80% of people who contract West Nile do not show symptoms. The remaining 20% can experience fevers, joint pain, headaches, flu-like symptoms, and in very rare cases, brain swelling, meningitis, or death (1).


Like West Nile virus, Zika is spread through mosquito bites. Not all mosquitos are infected. In Canada, reported Zika exposure is rare. However, there have been a small number of cases recorded. Most people who contract Zika, experience mild symptoms and recover fully with little or no medical intervention. The danger of Zika exposure lies in the risks it poses to unborn babies. Unborn babies with mothers who have Zika virus are at risk of serious birth defects, including microcephaly. This is a very serious defect of the brain, associated with incomplete development. The risk to outdoor workers includes both pregnant workers and those who may expose pregnant partners to the virus, as Zika virus is also passed through sexual transmission (2).


Unlike West Nile virus and Zika virus, which are passed through infected mosquitos, Lyme is transmitted by black-legged ticks or deer ticks. Not all of these types of ticks are infected. Lyme disease is transmitted only by tick bites, and cannot be passed from person to person, or animal to person; however, animals may carry infected ticks to people. In Ontario, there is a risk of encountering infected ticks almost everywhere, but the risk increases in parks and grassy areas, especially in long grasses, wetlands, and bog areas. Symptoms of Lyme are flu-like. If you’ve been bitten by a tick and do not feel well, you should see a doctor. In order for Lyme to be transmitted, a tick must feed for 24 hours (3).


Workers at risk of being exposed to West Nile, Zika, and/or Lyme disease through mosquito or tick bites can all be protected by following the same general set of guidelines. Insect repellents must contain DEET (a brand of diethyltoluamide, a colorless oily liquid with a mild odor) to be effective. The amount of DEET correlates to the amount of time for which it is effective. For example, a spray containing 4.75% DEET will effectively repel mosquitos and ticks for an hour, where repellent containing 23.8% DEET will work for up to 5 hours. It has been proven that sprays with 50% DEET or more are not effective longer – efficacy for DEET tends to plateau at around 50%. The following tips apply to all outdoor workers, regardless of the exposure hazard that is most prevalent in your area:

  • Wear long sleeved shirts and pants to minimize skin exposed to ticks and mosquitos
  • Tuck your pants into your socks
  • Wear light coloured clothes mosquitos are less attracted to light colours, and ticks are more easily found on light coloured items of clothing
  • Follow all directions on insect repellent sprays
  • Use an insect repellent that contains DEET, and be aware of the amount of time you will be protected
  • Re-apply DEET-containing insect sprays as recommended by the manufacturer

Follow these specific tips to reduce West Nile, Zika, and Lyme disease exposure risks:

West Nile virus:

  • Minimize exposure to mosquito bites by eliminating areas containing standing water in your worksites, such as dump buckets of water or wheel barrows
  • Remove items that could become standing water breeding grounds, such as barrels, old tires, or tarps
  • Take particular care at dusk and dawn, when mosquitos are most active


  • Educate workers with partners who are pregnant or planning to become pregnant
  • Do not allow workers who are pregnant or may become pregnant to work outdoors in Zika-infected areas
  • Consider providing workers with extra PPE, such as gloves and hats with mosquito netting that covers the face

Lyme Disease:

  • Wear a hat if contact might be made with overhead vegetation
  • Avoid long grasses
  • Immediately after work, do a thorough body inspection to check for ticks
  • Inspect gear thoroughly for ticks
  • Report any ticks you find on yourself or your gear to your direct supervisor
  • If you find a tick, place it in a secure container. Any health professional or unit can arrange for the tick to be tested if necessary


Employers must do what is reasonable to protect outdoor workers from exposure to the risk of occupational illnesses such as West Nile, Zika, or Lyme disease. The best way to do this is to develop a policy and safety program that educates outdoor workers on the risks of mosquito and tick bites, and how to avoid them. Leading industry practice suggests that employers with outdoor workers provide insect repellent that contains DEET, and any other PPE deemed reasonable to reduce the risk of exposure.


Workers do have the right to refuse work if they feel that the risk of exposure to mosquito or tick bites is a serious threat to their health and safety. If a worker is concerned about the risk of West Nile, Zika, or Lyme, they must discuss it with their supervisor and the Joint Health and Safety Committee. Rest assured, a reasonable solution can almost always be found. If one cannot be found, the work refusal process must be followed.

Although the risk of exposure to West Nile, Zika, and Lyme is low in our region, employers must be aware that it is their responsibility to protect outdoor workers. In many instances, insect repellent and common sense are all that’s needed to ensure a safe and productive outdoor working experience.

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