West Nile Virus and Lyme Disease in Ottawa

June 7, 2024


Sharing an update from Ottawa Public Health:

West Nile Virus and Lyme Disease in Ottawa

When ticks and mosquitoes are active, they have the potential to spread infections to Ottawa area residents.

What is Lyme disease?

Lyme disease is an infection caused by Borrelia burgdorferi, a bacteria transmitted through the bite of an infected blacklegged tick (Ixodes scapularis), most commonly during the spring, summer and fall months. If a person finds a tick on their body, they should remove it as soon as possible. The risk of Lyme disease increases the longer the tick is attached. Because blacklegged ticks in Ottawa are known to carry this bacteria, Ottawa Public Health (OPH) recommends that, if a person finds a tick on their body that has been attached more than 24 hours, they speak to a healthcare provider or pharmacist. The healthcare provider or pharmacist will provide recommendations on what to do, which may include monitoring for symptoms for the next 32 days and, if appropriate, taking post-exposure prophylaxis (antibiotics). Early signs of Lyme disease occur three to 32 days following a tick bite. This may include an expanding, circular rash, which may look like a “bull’s eye,” but is not present in all cases. Other symptoms can include fatigue (tiredness), fever, headache, swollen lymph nodes, and muscle and joint pain. If untreated, the infection can cause additional rashes on other areas of the body, fatigue, weakness, and may harm the heart, liver, nerves and joints.

What is West Nile virus?

West Nile virus (WNV) is a disease primarily spread to humans by infected mosquitoes. Mosquitoes, especially the Culex type, can become infected after biting a bird with the virus which can then spread the virus to humans by a bite. It can take between three and 14 days before symptoms occur after being bitten by an infected mosquito. Most people infected with WNV will remain asymptomatic, but approximately 20% will develop symptoms of usually mild (through to sometimes debilitating) febrile illness, which may include headache, fatigue, body aches, rash, nausea and vomiting. Less than 1% of those infected may develop severe neurological illness. In Ontario, locally acquired WNV occurs in the summer months, with the majority of cases occurring in August and September.

What is OPH’s Role?

OPH works to prevent Lyme disease and West Nile virus through a variety of measures, including:

  • OPH investigates every report of a person being infected with WNV to identify the likely source of infection and, where appropriate, takes action to minimize further risk to the population.
  • OPH conducts epidemiological surveillance of reported infections of Lyme disease and WNV to identify trends and populations at risk.
  • OPH in partnership with University of Ottawa researchers, conducts surveillance of tick populations to assess for spread and the presence of the bacteria or virus that causes Lyme and other public health relevant diseases spread through ticks.
  • OPH conducts surveillance and management of mosquito populations through its West Nile Virus Prevention Program.
  • OPH provides information to healthcare providers to aid in clinical diagnosis.
  • OPH also conducts public education on tick and mosquito bite prevention.

OPH contracts services to:

Apply Ministry of Environment, Conservation and Parks approved and environmentally-friendly biological larvicides (Bacillus thuringiensis subspecies israelensis – Bti or Bacillus sphaericus) or chemical larvicide (methoprene) to treat for mosquito larvae.

    • Altosid pellets (methoprene), Vectolex pouches (Bacillus sphaericus) or Altosid briquettes (methoprene) placed into catch basins of storm drains in the city.
    • Vectobac (Bacillus thuringiensis israelensis, liquid) or My-Crobe (Bacillus thuringiensis israelensis, liquid) and Vectobac (Bacillus thuringiensis israelensis, granular) or My-Crobe (Bacillus thuringiensis israelensis, granular), applied to ditches and temporary or permanent pools including storm water management ponds within the city if found to contain Culex pipiens/restuans larvae.
    • Vectolex (Bacillus sphaericus, granular) applied to sewage lagoons or similar facilities if found to contain Culex pipiens/restuans larvae.

If necessary, conduct mosquito control using adulticide (malathion), based on assessment of increased transmission and risk. No adulticide treatment has been used to date in the history of OPH’s West Nile Virus Prevention Program.

How can individuals protect themselves from these infections?

  • Apply a Health Canada approved insect repellent containing DEET or icaridin to exposed skin and clothing
  • Wear long pants, a long-sleeved shirt, shoes, and socks to cover exposed skin
  • Tuck your pants into your socks
  • Wear light-coloured clothing to spot ticks more easily; this is also appropriate for mosquitoes as they are attracted to darker colours
  • Stay on the trails when hiking in the woods and other natural areas. Enjoy mowed and maintained areas in parks and playing fields but be mindful of the borders adjacent to natural areas and tall grass that may be suitable tick habitat
  • For ticks, do a “full body” check on yourself, your children, and pets. Pay careful attention around your toes, back of the knees, groin, armpits and scalp
  • For mosquitoes, avoid being outside during dusk and dawn – periods when they are most active – and at any time in shady, wooded areas – remembering to use repellent and protective clothing if you must be out during these periods
  • Make sure all windows and doors in your home have well-fitting screens that are in good condition to prevent mosquitoes from entering
  • Mosquitoes need water to breed.  Decrease mosquito numbers around personal property by reducing or eliminating areas or objects that can accumulate or retain water (e.g., old tires, garbage or recycle containers, flowerpots, toys, bird feeders, ornamental ponds, pool covers, etc.). Empty and refill them regularly, turn them over when appropriate, or dispose of them accordingly.

 For more information about West Nile virus and Lyme disease, visit the OPH website at Insects, Animals and Bites – Ottawa Public Health.


Number of human WNV cases and positive WNV mosquito pools by year in the City of Ottawa; 2003 – 2023


People with confirmed or probable Lyme disease, Ottawa, 2003 to 2023