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Test ID: LBAB    
Babesia species, Molecular Detection, PCR, Blood

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.

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

Babesiosis is a tick-transmitted zoonosis caused by intraerythrocytic protozoa in the genus Babesia. Babesia microti is responsible for the vast majority of human cases in the United States, with most cases occurring along the Northeast Coast and the upper Midwestern states. A small number of cases of B duncani human infection have also been reported along Pacific Coast states from Washington to northern California, and B divergens/B divergens-like strains have been detected in humans in Missouri (MO-1 strain), Kentucky, and Washington. In Europe, B divergens and B venatorum are the primary causes of human babesiosis.

 

Humans most commonly acquire infection through the bite of an infected tick. The most common tick vectors in the United States are Ixodes scapularis and Ixodes pacificus, while Ixodes ricinus and other ticks transmit the parasite in Europe and Asia. Less commonly, babesiosis may be acquired through blood transfusion and across the placenta from the mother to the fetus.

 

Most patients with babesiosis are asymptomatic or have only a self-limited mild flu-like illness, 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.

 

Babesiosis is conventionally diagnosed through microscopic examination of Giemsa-stained thick and thin peripheral blood films looking for characteristic intraerythrocytic Babesia parasites. This method is relatively rapid, widely available, and capable of detecting (but not differentiating) human-infective Babesia species. It is also necessary for calculating the percentage of parasitemia which is used to predict prognosis, guide patient management, and monitor response to treatment. However, microscopic examination requires skilled microscopists and may be challenging in the setting of low parasitemia or prior drug therapy. Also, Babesia species may closely resemble those of Plasmodium falciparum.

 

The Mayo Clinic real-time PCR assay provides a rapid and more sensitive alternative to blood film examination for detection and differentiation of B microti, B duncani, and B divergens/B divergens-like parasites. It does not cross-react with malaria parasites.

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.

Negative

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, B duncani, and B 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.

Supportive Data

The following validation data supports the use of this assay for clinical testing.

 

Accuracy/Diagnostic Sensitivity and Specificity:

Ninety-six whole blood specimens were tested by this real-time PCR assay and another real-time PCR assay. Concordance was 99%.

 

Analytical Sensitivity/Limit of Detection (LoD). The LoD established using whole organism spiked into specimen matrix (whole blood) is as follows:

-Babesia microti, ATCC PRA 99 -                        2,670 target copies/mL

-B duncani ATCC PRA 302         -           1,540 target copies/mL

-B MO-1 positive patient DNA -  10,700 target copies/mL

-B divergens positive patient DNA -        5,270 target copies/mL

 

Serial 10-fold dilutions of microscopy-positive specimens were also tested in a blinded fashion using conventional thick and thin blood films and the Mayo Babesia species PCR. The PCR was able to consistently detect 2 10-fold dilutions lower than using microscopy.

 

Analytical Specificity:

No cross-reactivity was noted using a panel of 34 bacteria, viruses, parasites and fungi were detected by the Babesia species PCR.

 

Precision:

Interassay and intra-assay precision was 100% precision.

 

Reference Range:

The reference range is negative. This was confirmed by testing 93 blood specimens from asymptomatic individuals for the presence of Babesia species by the Babesia species PCR assay. All 93 specimens were negative.

 

Reportable Range:

This test is a qualitative assay, and results are reported as positive or negative for Babesia species (B microti, B duncani, B divergens, and Babesia MO-1).

Clinical Reference Recommendations for 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. 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

5. 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

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

7. Burgess MJ, Rosenbaum ER, Pritt BS, et al. Possible Transfusion-Transmitted Babesia divergens-like/MO-1 in an Arkansas Patient. Clin Infect Dis 2017