National case definition: Babesiosis

Date of last revision/review: January 2024

On this page

• National notification
• Type of surveillance
• Case classification
• Laboratory criteria
• Clinical evidence
• Exposure
• ICD code(s)
• Comments

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 has confirmatory laboratory results with or without clinical evidence criteria (can include transfusion transmission)

Probable case

A case that has supportive laboratory results and:

• meets clinical evidence criteria; or
• is in a blood donor or recipient epidemiologically linked (see Exposure) to a confirmed or probable babesiosis case.

Laboratory criteria

Confirmatory laboratory tests include:

• detection of Babesia species (e.g. Babesia microti, Babesia duncani or Babesia divergens) DNA in a whole blood specimen by amplification of a specific target nucleic acid amplification test (NAAT).

Supportive laboratory tests include:

• serological evidence of elevated IgG antibodies to B. microti in a single sample by indirect immunofluorescence assay (IFA) where the endpoint titre is equal to or greater than 1:64; or
• identification of intraerythrocytic Babesia organisms by light microscopy in a Giemsa, Wright, or Wright-Giemsa–stained blood smear; or
• demonstration of a positive B. microti IgG immunoblot result by Centers for Disease Control and Prevention (CDC); or
• demonstration of a B. divergens total immunoglobulin (Ig) or IgG antibody titre equal to or greater than 1:256 in an IFA; or
• demonstration of a B. duncani total immunoglobulin (Ig) or IgG antibody titre equal to or greater than 1:512 in an IFA.

Clinical evidence

Clinical description:

Babesiosis infections range in severity from asymptomatic to severe (occasionally fatal) depending on host and parasite factors. Most symptomatic infections caused by B. microti are mild and self-limiting, developing 1 to 4 weeks after the tick bite and 1 to 9 weeks after contamination of blood products.^{Footnote 1} The salient features are fever and non-specific flu-like illness (malaise, fatigue, chills, sweats, and headache).

Laboratory findings can include hemolytic anemia, thrombocytopenia. Patients who are asplenic, immunocompromised, elderly, or co-infected with other pathogens are at risk for severe disease.^{Footnote 1},^{Footnote 2},^{Footnote 3}

Severe babesiosis is associated with a parasitemia of 10% or greater; hemolytic anemia; pulmonary, renal, and hepatic complications; and death.^{Footnote 4}

Clinical criteria:

Clinical criteria include fever and at least one of fatigue, chills, sweats, headache, anorexia, hemolytic anemia, or thrombocytopenia.^{Footnote 5}

Exposure

Babesia is an intraerythrocytic protozoan parasite genus, several species of which can cause disease in humans. Most human cases of babesiosis in North America are caused by B. microti; sporadic cases caused by B. duncani and B. divergens-like organisms have also been reported.^{Footnote 1} In Europe B. divergens is the main species infecting humans, but affects only immunocompromised individuals.^{Footnote 6} In Asia B. venatorum and B. crassa-like organisms are a described cause of babesiosis.^{Footnote 5},^{Footnote 6},^{Footnote 7}

The main route of transmission of B. microti is the tick vector, Ixodes scapularis.^{Footnote 1} 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 I. scapularis 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 babesiosis). I. scapularis is also the vector for the agent of Lyme disease, so Lyme disease risk areas may approximate risk areas for babesiosis. 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

Transmission can occur via blood transfusion, and rarely, via transplacental, perinatal, and solid organ transplantation.^{Footnote 2};^{Footnote 8},^{Footnote 9},^{Footnote 10},^{Footnote 11},^{Footnote 12},^{Footnote 13},^{Footnote 14} Babesia-infected individuals can remain parasitemic for long periods following infection, and Babesia parasites can survive in blood products.^{Footnote 14} Babesiosis is the most commonly reported transfusion-transmitted tick-borne infection in the United States, and there has been one documented case in Canada.^{Footnote 14}

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:

• laboratory evidence of Babesia infection in the recipient and donor; and
• 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
• transfused unit(s) was/were plausibly infectious based on assessment of donor infectivity at time of donation of implicated unit(s); and
• transfusion-associated infection is considered at least as plausible as tick-borne transmission.

ICD code(s)

ICD-10-CA code(s)

• B60.0 Babesiosis (includes Piroplasmosis)

ICD-9-CA code(s)

• 088.8 Other Arthropod-borne diseases

Comments

• These are definitions for surveillance and epidemiologic purposes only and should not be used for clinical diagnostic purposes.
• Diagnostic testing should be performed by provincial public health laboratories and/or appropriate reference diagnostic centres (e.g., National Microbiology Laboratory for molecular testing, National Reference Centre for Parasitology for B. microti IFA).
• Some forms of Babesia can be difficult to distinguish from Plasmodium on blood smears. Confirmation by a reference laboratory may be required if a patient's travel history and area of residence indicate exposure to Babesia is unlikely.
• In persons who are immunosuppressed or who have asymptomatic Babesia infections, active infections can be associated with lower antibody titers; titres may also be low early in the course of infection.
• Due to the persistence of elevated antibody titres in some patients, a single elevated titre may indicate either a recent or remote infection. Demonstration of an increase in titres or seroconversion between paired samples is therefore necessary for confirmation.
• Validated commercial IFAs and/or immunoblots specific for B. divergens and B. duncani are not currently available but samples may be submitted to reference centres such as the CDC who have validated assays for these rare pathogens.