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Reporting Obligations

Confirmed and suspected cases shall be reported to the local Health Unit.

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Aetiologic Agent

Anaplasmosis (also known as human granulocytic anaplasmosis) is a tick-borne disease caused by the intraleukocytic bacterium Anaplasma phagocytophilum.

Clinical Presentation

Symptoms of anaplasmosis typically begin to show within 1-2 weeks (up to 21 days) from a bite of an infected tick (Ixodes scapularis in eastern North America, I. pacificus in western North America, and I. ricinus in Europe).

Symptoms can include fever, chills, severe headache, myalgia, abdominal pain, nausea, vomiting, diarrhea, and/or loss of appetite. Respiratory, central nervous symptoms, and rash are infrequently reported. Infections usually last 1-2 weeks if untreated, with persistent symptoms up to 60 days infrequently seen in subacute cases.

Rarely, if treatment is delayed or other medical conditions are present, anaplasmosis can lead to severe illness. Symptoms of severe illness can include respiratory failure, bleeding problems, organ failure, and/or death.

Risk factors for severe illness include:

  • Coinfection with other tick-borne diseases (e.g., Borrelia burgdorferi)
  • Delayed treatment
  • Advanced age
  • Weakened immune system (due to cancer, AIDS, transplantation, or certain medications)

Modes of Transmission

A bite by infected tick carrying A. phagocytophilum bacterium that has been attached for at least 12 hours. In Ontario, the bacteria is carried by the blacklegged tick (Ixodes scapularis). In Western Canada, the bacteria is carried by Ixodes pacificus.

Less commonly, A. phagocytophilum can spread through blood transfusions, solid organ transplantation, direct contact with infected blood (human or animal), or inhalation of aerosolized infected carcass while butchering infected hosts (e.g., deer carcass). There has been rare reports of perinatal acquisition of anaplasmosis but the mechanism of perinatal transmission is yet to be established.

Incubation Period

Signs and symptoms of anaplasmosis begin to typically appear from 5-21 days after exposure, with an average of 7-14 days.

Period of Communicability

There is no evidence of person to person spread.

In rare cases, A. phagocytophilum has been spread by blood transfusion or solid organ transplantation.

Risk Factors/Susceptibility

Persons with history of tick bites in an area where ticks carry the A. phagocytophilum bacteria.

Occupations/activities in tall grass or wooded areas where ticks reside.

Please refer to PHO’s Infectious Disease Trends in Ontario reporting tool and other reports for the most up-to-date information on infectious disease trends in Ontario.

Diagnosis and Laboratory Testing

Diagnosis is based on laboratory confirmation or supportive laboratory evidence of infection with clinically compatible signs and symptoms of infection. 

Laboratory Confirmation

  • Serological demonstration of a four-fold or greater increase in Anaplasma phagocytophilum IgG-specific antibody titres by indirect immunofluorescence assay (IFA) between acute and convalescent sera taken 2-4 weeks apart;


  • Detection of A. phagocytophilum nucleic acid by molecular methods from an appropriate clinical specimen (e.g., whole blood, buffy coat, cerebrospinal fluid [CSF], or bone marrow/tissue biopsy);


  • Detection of A. phagocytophilum antigen by immunohistochemistry (IHC) from an appropriate clinical specimen;
  • Isolation of A. phagocytophilum in cell culture from an appropriate clinical specimen followed by molecular confirmation;

Supportive Laboratory Evidence of Infection

  • Serological demonstration of elevated A. phagocytophilum IgG antibody titres by IFA or by enzyme-linked immunosorbent assay (ELISA);


  • Identification of typical morulae (microcolonies of A. phagocytophilum) in the cytoplasm of granulocytes by microscopic examination from an appropriate specimen.

Clinical evidence

Anaplasmosis is characterized by an acute onset of fever with one or more of the following non-specific symptoms: chills, malaise, headache, myalgia, arthralgia, leukopenia, thrombocytopenia or elevated hepatic transaminases.

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Treatment and Case Management

Treatment is under the direction of the attending health care provider.

Patient Information

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Infectious diseases protocol 2023

Appendix 1 Case definitions and disease-specific Information: Anaplasmosis

Public Health Ontario: Anaplasmosis

Centers of Disease Control and Prevention: Anaplasmosis