Anaplasmosis is caused by Anaplasma phagocytophilum. In Ontario, transmission occurs through the bite of infected blacklegged ticks called Ixodes scapularis or deer ticks.
The overall risk of acquiring anaplasmosis in Toronto is low but is increased if participating in activities in wooded and brushy areas.
For general information about tick-borne diseases including epidemiology and prevention, visit TPH’s Tick-Borne Diseases of Public Health Significance (TBDoPHS) webpage.
Symptoms usually occur one to two weeks after a tick bite but can begin as early as five days to as long as 21 days after a tick bite.
Symptoms include:
Respiratory, central nervous symptoms, and rash are infrequently reported.
Infections usually last one to two weeks if untreated, with persistent symptoms lasting up to 60 days infrequently seen in subacute cases. Rarely, if treatment is delayed, anaplasmosis can lead to severe illness including respiratory failure, bleeding problems, organ failure, and/or death.
Risk factors for severe illness include:
Refer to Public Health Ontario’s summary table for distinguishing clinical symptoms between tick-borne diseases of public health significance.
Anaplasma phagocytophilum is mostly spread to humans by the bite of an infected tick. The tick usually needs to be attached and feeding on a person’s blood for at least 12 hours to transmit the bacteria.
In rare cases, the bacteria can spread through blood transfusions, solid organ transplantation, direct contact with infected blood (human or animal), or inhalation of aerosolized infected carcass while butchering an infected animal.
Testing is indicated for individuals with compatible clinical symptoms and a relevant exposure history (e.g., outdoor activity in an endemic area, tick bite(s), if known).
As of July 2, 2025, polymerase chain reaction (PCR) testing will replace serology at the Public Health Ontario Laboratory (PHOL). The sample should be collected within two weeks of symptom onset. If a subsequent (convalescent) specimen is received two to 12 weeks after the initial (acute) specimen, the acute and convalescent serum samples will be tested for serology in parallel to compare serological titres. A second serum sample for paired serology is not advised if the acute sample was PCR positive.
Public Health Ontario Laboratory has information on Anaplasma PCR and Serology.
Doxycycline is the most recommended oral antibiotic for symptomatic adult and pediatric patients suspected of having anaplasmosis. Rifampin is an alternative treatment.