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Health Professionals Update – Vol. 18, No. 16

July 4, 2025

From:
Nicholas Brandon, MD, MA, MSc, CCFP, FRCPC
Associate Medical Officer of Health

In this issue:

  • Tick-borne disease risk in Peel region
  • Public Health Ontario’s vector-borne disease surveillance tool
  • Tick-borne disease clinical guidance
  • Tick-borne disease testing
  • Tick species identification
  • Tick-borne disease reporting

Key messages:

  • Tick-borne diseases are spread by blacklegged ticks, which are established in Peel region.
  • Consider tick-borne illness as part of the differential diagnosis when patients present with a non-specific febrile illness of unknown origin, if outdoor temperatures are above freezing and the ground isn’t covered with snow.
  • Health care providers and patients can use eTick, an image-based tick identification service for fast, free, and reliable results in approximately 48 hours. 

Tick-borne disease risk in Peel region

Blacklegged ticks (Ixodes scapularis) are established in Peel and much of southern Ontario. Warmer seasonal temperatures have contributed to the expansion of tick populations and rising Lyme disease cases both locally and provincially.

In 2024, Peel experienced a record number of 50 confirmed human cases of Lyme disease. Most of these cases reported tick exposures that occurred outside of Peel region (e.g., eastern Ontario, southern Quebec, Atlantic provinces); however, local exposures to blacklegged ticks are also being reported by cases in Mississauga, Brampton and Caledon. Rates of Lyme disease are lower in Peel region (3.15/100,000) than the provincial average (14.98/100,000).

Anaplasmosis, babesiosis, and Powassan virus infection became reportable in 2023. In 2024, 160 cases of anaplasmosis, four cases of babesiosis and one case of Powassan virus infection were reported in Ontario. The risk of acquiring these diseases in Peel region remains very low, but local exposure is possible, as blacklegged ticks capable of carrying these pathogens are present.

Public Health Ontario’s vector-borne disease surveillance tool

Public Health Ontario has launched a new Vector-Borne Disease (VBD) Tool that provides real-time data of blacklegged tick activity and tick-borne disease risk across the province. Health care providers can use this tool to support patient risk assessments. Features include:

  • Risk area maps for blacklegged ticks
  • Tick positivity rates by region
  • Human case data 

Tick-borne disease clinical guidance 

Consider tick-borne illness as part of differential diagnosis when patients present with a non-specific febrile illness of unknown origin, any time outdoor temperatures are consistently above freezing and the ground is not covered with snow. Ticks are tiny, often no bigger than a poppy seed, and their painless bites are easy to miss. Most people with confirmed Lyme disease don’t recall being bitten. 

Use Health Quality Ontario’s Clinical Guidance Document on the Management of Tick Bites and Investigation of Early Localized Lyme Disease to support diagnosis and treatment decisions, including for:

  • Asymptomatic patients who have had a recent tick bite: The document provides guidance on when antibiotic prophylaxis is warranted.
  • Symptomatic patients: The document provides a decision tree to assist with determining whether testing, treatment, or a combination are warranted.

For additional information on the management and treatment of tick-borne disease, refer to: 

Tick-borne disease testing

Public Health Ontario Laboratory (PHOL) can support with diagnostic test selection and interpretation of test results. Refer to the disease specific test information sheets for details on test methods, testing indications, requisition forms and/or turn-around times. For additional information, contact PHOL’s customer service by phone at 1-877-604-4567 or emailing: Customerservicecentre@oahpp.ca.

Early localized Lyme disease is primarily diagnosed clinically, based on symptoms and exposure risk. Treatment should not be delayed while awaiting test results. Serological testing should only be used to supplement clinical findings, not as a basis for diagnosis of early Lyme disease or to monitor treatment response. 

NOTE: Effective July 2, 2025, a single serum sample submitted to PHOL for anaplasmosis testing will be tested with PCR instead of serology. Serological testing will remain available, but only if both an acute (within 2 weeks of symptom onset) and a convalescent (between 2 to 12 weeks of symptom onset) serum sample are submitted. Refer to the Anaplasmosis test information sheet for more information.

Tick species identification

To assist with clinical risk assessment, patients and providers can submit photos of ticks for identification. Most ticks sent for identification from Brampton and Mississauga are not blacklegged ticks and do not transmit Lyme disease. If species identification confirms the tick is not a blacklegged tick, antibiotic prophylaxis is not recommended.

Tick-borne disease reporting

Lyme disease, anaplasmosis, babesiosis, and Powassan virus are reportable diseases. Report all suspect or confirmed cases by faxing Peel Public Health at (289) 801-0257. This includes cases of Lyme disease that have been diagnosed based on symptoms (e.g. typical or atypical erythema migrans rash > 5cm) and risk of exposure to ticks but have not received additional serological testing.

Contact us

The Health Professionals Update (HPU) is distributed to physician offices in Peel region via fax or email. Share this update with other health professionals in your clinic. 

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