Increased Incidence of Anaplasmosis in Ontario, 2025

To: Ottawa Physicians and Nurse Practitioners
Date: September 16, 2025
From: Dr. Emil Prikryl, Associate Medical Officer of Health
Subject: Increased Incidence of Anaplasmosis in Ontario, 2025

Dear Colleagues,

A recent report of a death in an Ottawa resident caused by anaplasmosis serves as a reminder that we remain very much in the season for tick-borne diseases such as anaplasmosis, Lyme disease, babesiosis, and Powassan virus, as well as mosquito-borne diseases such as West Nile virus. There have been 34 Ottawa residents with confirmed or probable anaplasmosis in the Ottawa region so far this year, already exceeding last year. One in three reported possible tick exposure in Ottawa, while over 70% reported possible tick exposure in cottaging and camping regions popular in Southeastern Ontario. This is consistent with provincial data indicating a particularly high incidence of anaplasmosis in the Southeastern region, which includes Perth, Murphy’s Point Provincial Park, Kingston, Belleville, Prince Edward County, and surrounding areas.

Anaplasmosis is caused by the bacterium Anaplasma phagocytophilum, transmitted to humans by the black-legged tick (Ixodes scapularis), the same vector responsible for Lyme disease. Although historically rare in Ontario, incidence has been increasing, and cases are now being reported across multiple regions.

A recent Public Health Alert discussed the new Public Health Ontario Laboratory (PHOL) algorithm for anaplasmosis testing using PCR. While this entails a simpler approach to testing, clinical assessment and diagnosis remains essential to ensure timely treatment for your patients if clinical suspicion is high for Lyme disease or anaplasmosis.

To report tick- and mosquito-borne diseases to Ottawa Public Health: Call 613-580-2424, extension 24224 and leave a detailed, confidential message including your contact information; or fax 613-580-9640.