National case definition: Anaplasmosis

Date of last revision/review: January 2024

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National notification

Confirmed and probable cases of disease should be notified to the Public Health Agency of Canada.

Type of surveillance

Routine case-by-case notification to the federal level.

Case classification

Confirmed case

A case that meets confirmatory laboratory results with or without clinical evidence criteria (can include transfusion transmission).

Probable case

A case that meets supportive laboratory results and:

Laboratory criteria

Confirmatory laboratory tests include:

Supportive laboratory tests include:

Clinical evidence

Clinical description:

Asymptomatic infections of A. phagocytophilum do occur and may even be more common than symptomatic infections.Footnote 2

Symptoms of anaplasmosis typically begin within 5–21 days after the bite of an infected tick, and commonly manifest as an acute non-specific flu-like illness (e.g. fever, chills, headache, myalgia, arthralgia, malaise, fatigue).Footnote 1,Footnote 2,Footnote 3

Less commonly noted manifestations include gastrointestinal manifestations, respiratory symptoms, and neurological issues.Footnote 1,Footnote 2,Footnote 3 Skin rash may be present, but could also indicate co-infection with Borrelia spp.Footnote 1 or other tick-borne diseases.

Laboratory abnormalities are common in the early phase and can include leukopenia, thrombocytopenia, elevated aminotransferase levels, and anemia.Footnote 1,Footnote 2

Patients with comorbidities, who are elderly, immunocompromised, or for whom treatment is delayed are at greater risk for more severe illness, and in rare cases, death.Footnote 1,Footnote 3,Footnote 4

Severe illness can include renal failure, respiratory distress, hemorrhage, meningitis, encephalitis, and sepsis.Footnote 2,Footnote 4

Clinical criteria:

Clinical evidence of infection includes fever and at least one of the following: headache, malaise/asthenia, arthralgia/myalgia, mild anemia, thrombocytopenia, leukopenia, elevated hepatic transaminase concentrations, or elevated numbers of immature neutrophils.Footnote 1,Footnote 2,Footnote 3


Anaplasmosis is a tick-borne illness caused by the intracellular bacterium A. phagocytophilum. The main transmission route for A. phagocytophilum is blacklegged ticks (Ixodes scapularis and Ixodes pacificus).Footnote 5,Footnote 6

Although cases of tick-borne illness can occur during any month of the year, most cases occur when ticks are most active, in the spring, summer, and fall. Consideration should be given to patients who have recently spent time in potential blacklegged tick habitats, or who have a history of tick bite (although as many patients have no recollection of a tick bite, lack of a tick bite should not preclude consideration of anaplasmosis).

Evidence suggests transmission of A. phagocytophilum from an infected tick may occur more quickly when compared to Borrelia burgdorferi for Lyme disease and may occur within the first 24 hours of attachment.Footnote 11

The spatial distribution of A. phagocytophilum in Canada is similar, but more restricted, to the geographical distribution of established blacklegged tick populations that correspond to Lyme disease risk areas. However, with the expansion of suitable tick habitats, there may be a risk for transmission outside of these pre-defined areas.

Updated information regarding the distribution of Lyme disease risk areas

A. phagocytophilum can survive for prolonged periods in blood products, and cases of transfusion-transmitted anaplasmosis have been reported in the United States.Footnote 7,Footnote 8,Footnote 9,Footnote 10 Currently, no Health Canada or United States of America Food and Drug Administration licensed test exists for the screening of A. phagocytophilum in blood donors.

For the purposes of surveillance, epidemiologic linkage between a transfusion recipient and a blood donor is demonstrated if all of the following criteria are met:

  1. Laboratory evidence of A. phagocytophilum infection in the recipient and donor; and
  2. Transfusion recipient received one or more red blood cell or platelet unit(s) within one year before the collection date of the recipient's positive specimen; and
  3. Transfused unit(s) was/were plausibly infectious based on assessment of donor infectivity at time of donation of implicated unit(s); and
  4. Transfusion-associated infection in the recipient is considered at least as plausible as tick-borne transmission.

ICD code(s)

ICD-10-CA code(s)

ICD-9 code(s)



Footnote 1

Dumler JS, Choi K-S, Garcia-Garcia JC, et al. Human granulocytic anaplasmosis and Anaplasma phagocytophilum. Emerg Infect Dis. 2005;11(12):1828-1834. doi:10.3201/eid1112.050898.

Return to footnote 1 referrer

Footnote 2

Bakken JS, Dumler JS. Human granulocytic anaplasmosis. Infect Dis Clin North Am. 2015;29(2):341-355. doi:10.1016/j.idc.2015.02.007.

Return to footnote 2 referrer

Footnote 3

Biggs HM, Behravesh CB, Bradley KK, et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever, Ehrlichioses, and Anaplasmosis --- United States. MMWR Recomm Reports 2016. 2016;65(2):1-44.

Return to footnote 3 referrer

Footnote 4

Dahlgren, FS, Heitman, KN, Drexler, NA, Massung, RF, Behravesh, CB. Human granulocytic anaplasmosis in the United States from 2008 to 2012: A summary of national surveillance data. American Journal of Tropical Medicine and Hygiene. 2015; 93(1), 66–72. doi:10.4269/ajtmh.15-0122.

Return to footnote 4 referrer

Footnote 5

Krakowetz CN, Dibernardo A, Lindsay LR, Chilton NB. Two Anaplasma phagocytophilum strains in Ixodes scapularis ticks, Canada. Emerg Infect Dis. 2014;20(12):2064-2067. doi:10.3201/eid2012.140172.

Return to footnote 5 referrer

Footnote 6

Eshoo MW, Carolan HE, Massire C, et al. Survey of Ixodes pacificus Ticks in California Reveals a Diversity of Microorganisms and a Novel and Widespread Anaplasmataceae Species. PLoS One. 2015;10(9):e0135828. doi:10.1371/journal.pone.0135828.

Return to footnote 6 referrer

Footnote 7

Goel R, Westblade LF, Kessler DA, et al. Death from Transfusion-Transmitted Anaplasmosis, New York, USA, 2017. Emerg Infect Dis. 2018;24(8):1548-1550. doi:

Return to footnote 7 referrer

Footnote 8

Fine AB, Sweeney JD, Nixon CP, Knoll BM. Transfusion-transmitted anaplasmosis from a leukoreduced platelet pool. Transfusion. 2016;56(3):699-704. doi:

Return to footnote 8 referrer

Footnote 9

Alhumaidan H, Westley B, Esteva C, Berardi V, Young C, Sweeney J. Transfusion-transmitted anaplasmosis from leukoreduced red blood cells. Transfusion. 2013;53(1):181-186. doi:10.1111/j.1537-2995.2012.03685.

Return to footnote 9 referrer

Footnote 10

Centers for Disease Control and Prevention (CDC). Anaplasma phagocytophilum transmitted through blood transfusion--Minnesota, 2007. MMWR Morb Mortal Wkly Rep. 2008;57(42):1145–1148.

Return to footnote 10 referrer

Footnote 11

Eisen L. Pathogen transmission in relation to duration of attachment by Ixodes scapularis ticks. Ticks Tick Borne Dis. 2018 Mar;9(3):535-542. doi: 10.1016/j.ttbdis.2018.01.002.

Return to footnote 11 referrer

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