Test Catalog

Interpretive Handbook

Test 62847 :
Babesia species, Molecular Detection, PCR, Blood

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Babesiosis is an emergent zoonosis caused by an intraerythrocytic protozoan in the genus Babesia. Babesia microti is responsible for the vast majority of human cases in the United States, with "hot spots" of disease along the Northeast Coast (eg, Martha's Vineyard, Long Island, and Nantucket) and the upper Midwestern states, although the distribution of disease is spreading. In addition, a small number of cases of Babesia duncani and Babesia duncani-like human infection (WA and CA strains) have been reported along Pacific Coast states from Washington to northern California, and Babesia divergens/Babesia divergens-like strains have been isolated from humans in Missouri (MO-1 strain), Kentucky, and Washington. At this time, only Babesia microti is a nationally notifiable disease.


Babesia microti shares a tick vector with Borrelia burgdorferi and Anaplasma phagocytophilum, the causative agents of Lyme disease and human granulocytic anaplasmosis (HGA), respectively. Recent studies suggest that exposure to Babesia microti is quite common in areas endemic for Lyme disease and anaplasmosis, so it is prudent to consider testing for all 3 diseases concurrently. Less commonly, babesiosis may be acquired through blood transfusion, and therefore donor units are tested for this parasite in some endemic areas.


Most patients with babesiosis have a mild illness or are asymptomatic, but some develop a severe illness that may result in death. Patient symptoms may include fever, chills, extreme fatigue, and severe anemia. The most severe cases occur in asplenic individuals and those over 50 years of age. Rare cases of chronic parasitemia, usually in immunocompromised patients, have been described.


The definitive laboratory diagnosis of babesiosis rests on the demonstration of Babesia species characteristic intraerythrocytic parasites in Giemsa-stained thick and thin blood films. This method is capable of detecting (but not differentiating) human-infective Babesia species.


Babesia may closely resemble those of Plasmodium falciparum. The Mayo Clinic real-time PCR assay provides a rapid and sensitive alternative to blood film examination and enables the detection and differentiation of Babesia microti, Babesia duncani/Babesia duncani-like and Babesia divergens/Babesia divergens-like parasites. It does not cross-react with malaria parasites. Finally, antibody testing may be used and is useful for detection of babesiosis, but may be negative in the early phase of illness and cannot distinguish active from past infection.

Useful For Suggests clinical disorders or settings where the test may be helpful

An initial screening or confirmatory testing method for suspected babesiosis during the acute febrile stage of infection in patients from endemic areas, especially when Giemsa-stained peripheral blood smears do not reveal any organisms or the organism morphology is inconclusive.

Interpretation Provides information to assist in interpretation of the test results

A positive result indicates the presence of Babesia species DNA and is consistent with active or recent infection. While positive results are highly specific indicators of disease, they should be correlated with blood smear microscopy, serological results and clinical findings.


A negative result indicates absence of detectable DNA from Babesia species in the specimen, but does not always rule out ongoing babesiosis in a seropositive person, since the parasitemia may be present at a very low level or may be sporadic.


Other tests to consider in the evaluation of a patient presenting with an acute febrile illness following tick exposure include serologic tests for Lyme disease (Borrelia burgdorferi), and molecular detection (PCR) for ehrlichiosis/anaplasmosis. For patients who are past the acute stage of infection, serologic tests for these organisms should be ordered prior to PCR testing.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

While this assay is designed to detect symptomatic infection with Babesia microti, Babesia duncani and Babesia divergens/MO-1, it may detect low-grade asymptomatic parasitemia in individuals in babesiosis-endemic areas. Thus, it should only be used for testing patients with a clinical history and symptoms consistent with babesiosis.


Inhibitory substances may cause false-negative results.


Inadequate specimen collection or improper storage may invalidate test results.


This is a qualitative assay and the results are reported either as negative or positive for targeted Babesia species DNA.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Anderson JF, Mintz ED, Gadbaw JJ, et al: Babesia microti, human babesiosis and Borrelia burgdorferi in Connecticut. J Clin Microbiol 1991;29(12):2779-2783

2. Herwaldt BL, de Bruyn G, Pieniazek NJ, et al: Babesia divergens-like infection, Washington State. Emerg Infect Dis 2004;10(4):622-629

3. Herwaldt B, Persing DH, Precigout EA, et al: A fatal case of babesiosis in Missouri: identification of another piroplasm that infects humans. Ann Intern Med 1996;124(7):643-650

4. Homer MJ, Aguilar-Delfin I, Telford SR, et al: Babesiosis. Clin Microbiol Rev 2000;13(3):451-469

5. Thompson C, Spielman A, Krause PJ: Coinfecting deer-associated zoonoses: Lyme disease, babesiosis, and ehrlichiosis. Clin Infect Dis 2001 Sept 1;33(5):676-685

6. Persing DH, Herwaldt BL, Glaser C, et al: Infection with a Babesia-like organism in northern California. N Engl J Med 1995;332(5):298-303

7. Quick RE, Herwaldt BL, Thomford JW, et al: Babesiosis in Washington State: a new species of Babesia? Ann Intern Med 1993;119(4):284-290

8. Vannier E and Krause PJ: Human Babesiosis. N Engl J Med 2012 Jun 21;366(25):2397-2407

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