Medical Advisory: Lyme Disease Surveillance and Clinical Guidance

Issued by: Dr. Angela Ma, MD, FRCPC, Associate Medical Officer of Health
Date: July 23, 2026

Niagara region has long been recognized as an established high-risk area for blacklegged ticks. As tick activity increases with warmer weather, health care providers should be on heightened surveillance for patients presenting with signs and symptoms of Lyme disease, and consider prophylaxis for patients presenting with a known tick bite. A total of 47 cases of Lyme disease were reported in Niagara in 2025. Public Health Ontario’s Vector-Borne Disease Tool identifies Niagara as an area with established populations of blacklegged ticks. 

Clinical Assessment 

• Assess patients based on clinical presentation and possible tick exposure, recognizing that a tick bite may not be recalled
• Erythema migrans, the characteristic rash associated with Lyme disease and often described as a bull’s-eye rash, may vary in appearance based on skin tone
• For individuals exposed to black-legged ticks in established risk areas such as Niagara region, the presence of an erythema migrans lesion greater than five centimetres in diameter is considered diagnostic of early localized Lyme disease and should be treated without laboratory confirmation
• Other symptoms may include fever, chills, headache, fatigue, swollen lymph nodes and muscle or joint pain

Lyme Disease Post-Exposure Prophylaxis 

• Doxycycline should be used for post-exposure prophylaxis in adults and children of all ages 
• Post-exposure antibiotic therapy should be considered when all four of these criteria are met:  
  • Tick was attached >24 hours 
  • Tick was removed within the past 72 hours 
  • Tick was acquired in a higher risk area 
  • Doxycycline is not contraindicated (e.g. allergy) 
• Refer to the most recent Ontario Vector-Borne Disease Tool for estimated risk areas  

Other Reportable Tick-Borne Diseases 

In addition to Lyme disease, health care providers should be aware of other reportable tick-borne diseases of public health significance that may be transmitted by black-legged ticks in Ontario: 

• Anaplasmosis 
• Babesiosis 
• Powassan virus infection 

Health care providers should consider these infections in patients with compatible signs and symptoms and a history of possible tick exposure, particularly during periods of increased tick activity. Testing is generally not recommended for asymptomatic patients. 

Actions for Health Care Providers and Pharmacists 

• Review Ontario Health’s Guidance for Managing Tick Bites and Investigating and Treating Early Localized Lyme Disease and Public Health Ontaroio’s Assessment and Prescribing Algorithm for Pharmacists 
• Maintain a high index of suspicion for Lyme disease in patients presenting with compatible signs and symptoms, particularly if they have had possible exposure to black-legged ticks 
• Assess patients with tick bites based on clinical presentation and exposure history, including determining whether antibiotic prophylaxis for the prevention of Lyme disease is warranted  
• Initiate treatment for early localized Lyme disease without waiting for laboratory confirmation when a patient presents with a rash consistent with erythema migrans greater than five centimetres in diameter and a history of exposure in a risk area 
• Report suspected and confirmed cases of reportable tick-borne diseases to Niagara Region Public Health 

 More Information 

For consultation or more information please contact the Environmental Health Duty Officer: Monday to Friday, 8:30 a.m. to 4:30 p.m.:  

• Phone number: 905-688-8248 ext. 7590 (toll-free: 1-888-505-6074) 
• Email: inspect@niagararegion.ca 
• Lyme Disease and Tick Information for Health Care Professionals