Assessing the Risk of Lyme Disease

Lyme disease continues to be the most frequently reported vector-borne disease in Canada, and cases are on the rise in Ontario. From 2013 to 2022, the number of confirmed cases has jumped from 309 to 1490. This trend is likely to continue, as public health experts estimate that case numbers will continue to increase due to climate change. As the number of cases climb in Ontario, pharmacists may be experiencing an increase in the number of questions regarding ticks, and many may not feel comfortable assessing a patient’s risk for Lyme disease. 

While the typical manifestation of Lyme disease is mild, progression to more severe neurologic and cardiac complications can occur. A pharmacist’s involvement in risk assessment is critical for patients, as prompt identification and removal of ticks, early identification of symptoms and counselling on preventative measures can have significant impacts on patient outcomes. The following is meant to provide some guidance on Lyme disease.

Chinese doctor talking with female patient in doctors office.

The probability of acquiring Lyme disease depends on the type of tick, the geographic location where the tick was acquired, and the duration of attachment. In Ontario, the tick of concern is the blacklegged deer tick, Ixodes scapularis. Nymphs (immature ticks) and adult ticks can transmit the bacterium, B. burgdorferi. Nymphs are about the size of a poppy seed, and adults are closer in size to a sesame seed. In Canada, the highest risk of acquiring Lyme disease will be in areas where ticks carrying the bacterium have been identified; endemic areas are present now in eight provinces, the exceptions being Alberta and Saskatchewan. See this updated 2024 map to identify the specific areas in Ontario where the risk is greatest.

The most difficult part about assessing the risk for Lyme disease may surround the timing of tick attachment. A tick should be removed quickly. Tick attachment under 24 hours will usually not cause Lyme disease, as a tick must be attached for at least 36 hours before the bacterium can be transmitted. However, even with these time periods, the bacterium is still not usually transmitted within the first 48 – 72 hours of being attached. Thus, there is an increased risk if a tick has been attached for at least 72 hours. How much the tick is engorged can be used to estimate how long the tick may have been attached. Images can be seen in the Infectious Diseases Society of America (IDSA) guideline.

When to Refer

After a tick bite, a small red bump similar to a mosquito bite is common, but this is not a sign of Lyme disease and will usually disappear within 1-2 days. The difficulty surrounds symptoms of Lyme disease, which can vary depending on the stage of infection (Table 1). If fever, facial paralysis, rash, or arthritis are present and occur after a tick bite, or after a patient has been to an area where Lyme disease has been identified, the patient should seek medical attention. Illness within several weeks after removing a tick bite should also be assessed.

It is important to be aware that 1) an erythema migrans (EM) rash may not occur in all patients with Lyme disease, and 2) if an EM does occur, it may not necessarily have the typical “bull’s-eye” appearance. Examples of how EM may present in Lyme disease can be seen here.

Table 1. Signs and symptoms of different stages of Lyme disease.*

Time PeriodSigns & SymptomsComments
Early localized Lyme disease (< 30 days)Headache, fever, myalgia, arthralgia and single, local skin lesion called erythema migrans (EM) If the bacterium was transmitted, most patients present with EM within 7 days of a tick bite, although incubation can vary from 3-30 days. Appearance of EM: greater than 5cm, slowly increases size and is not usually itchy or painful. Sometimes the EM will be clear in the centre (creating a bull’s-eye), or may look like a bruise in dark-skinned patients. An EM suggestive of Lyme disease can be: blistering, solid, crusted, blue-purple, or a bulls-eye appearance.
Early disseminated Lyme disease (< 3 months) Fatigue, general weakness, skin reactions (e.g. multiple EMs), cardiac symptoms, neurological symptoms, and rare symptoms (uveitis, keratitis, conjunctivitis, mild hepatitis, splenomegaly) Untreated, the bacteria can travel to other sites of the body and damage tissue.
Late Lyme disease (> 3 months)Musculoskeletal (e.g. Baker’s cyst, chronic arthritis) and neurological (e.g. memory, concentration issues) Untreated, late Lyme disease can last months-years.
Post-treatment symptomsEven when treated, some patients may continue to have symptoms months-years after.

*Information compiled from: Government of Canada. For health professionals: Lyme disease. Updated 28 Feb 2022. Accessed 26 April 2022 from


General prevention includes using an insect repellant with 10-20% icaridin for those patients > 6 months of age for seven to eight hours of protection; or 10% DEET for ages 6 months – 12 years for approximately two to four hours of protection; or 20-30% DEET for patients > 12 years old for four to eight hours of protection. Frequency of DEET and icaridin application depends on age and patients should be counselled on the safe and appropriate use of their preferred product. Patients wishing to use natural products such as oil of lemon eucalyptus should be cautioned that additional studies are needed to determine their efficacy against ticks. Further general information on safe insect repellant use can be found on the government of Canada website. 

Alternatively, clothing that has been treated with the insecticide permethrin is available to protect against tick bites for patients 16 years of age and older. 

Avid hikers or outdoor enthusiasts may benefit from this additional layer of protection. However, protection from permethrin-treated clothing is incomplete, and patients should be advised to still apply bug spray with DEET or icaridin to protect exposed skin. 

Patients should also wear a long-sleeved shirt, pants, socks and boots all tucked in when in risk areas. Skin should also be checked after possible exposure and patients should shower within two hours. If a tick is found, it should be carefully removed as quickly as possible. For information on tick removal, see these CDC instructions. 

Overall, if Lyme disease is suspected, timely treatment with antibiotics in the early stages can enable quick recovery. Therefore, after a tick bite, patients should be monitored for symptoms of Lyme disease up to 30 days after being bitten.

As of October 1st, 2023, Ontario pharmacists have the scope of practice to assess patients and, if necessary, prescribe medications for 19 minor ailments. Pharmacist’s expanded scope of practice now includes the ability to assess a patient’s risk of Lyme disease following a high-risk tick bite and, if appropriate, prescribe antibiotics for Lyme disease post-exposure prophylaxis.

For additional information on pharmacist-led minor ailment assessments, access our member-exclusive webpage. Additionally, the Assessment and Prescribing Algorithm for Pharmacists, a resource developed by Public Health Ontario in collaboration with Ontario Health, can help support appropriate antibiotic prescribing by community pharmacists for Lyme disease prophylaxis to individuals following a tick bite.

Written by:

Chelsea Geen, BScH, MES, PharmD, RPh

Chelsea Geen, BScH, MES, PharmD, RPh

Chelsea has been a pharmacist since 2018 and currently practices in a busy independent community pharmacy. She enjoys being involved with research/medical writing and patient education - you can find her on Instagram @pharmacistchelsea!

Updated July 2021 by:

Joanne Deshpande, BSc Phm, RPh

Joanne Deshpande, BSc Phm, RPh

Joanne has diversified her pharmacy background by working in industry, hospital, retail and drug information. She currently divides her time between doing medical writing for the Ontario Pharmacists Association and working at an independent clinic pharmacy in Toronto.

Updated April 2022, May 2023 and May 2024 by:

Arthur Catapano

Arthur Catapano

Arthur has been a pharmacist since 2020, and throughout his professional career, has developed a passion for medical writing and education. He currently works as the Pharmacy Practice Advisor at OPA and continues to practice as a relief pharmacist all over Ontario.

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