From the Guidelines
The diagnostic approach for babesiosis involves a combination of clinical evaluation and laboratory testing, with a focus on microscopic examination of Giemsa-stained thin blood smears and PCR testing of blood. Diagnosis begins with a thorough history focusing on potential tick exposures, travel to endemic areas, and symptoms such as fever, fatigue, and hemolytic anemia. Laboratory diagnosis primarily relies on microscopic examination of Giemsa-stained thin blood smears to identify Babesia parasites within red blood cells, which may appear as ring forms or tetrads ("Maltese cross" formations) 1.
Some key points to consider in the diagnostic approach include:
- The diagnosis of babesiosis is based on epidemiologic, clinical, and laboratory information, and only occurs in patients who live in or travel to areas of endemicity or who have received a blood transfusion containing the parasite within the previous 9 weeks 1.
- Specific diagnosis of babesiosis is made by microscopic identification of the organism on Giemsa stains of thin blood smears 1.
- PCR testing of blood is more sensitive than microscopy and can detect low-level parasitemia, making it particularly valuable in early infection or when microscopy is inconclusive.
- Serologic testing using indirect immunofluorescence antibody (IFA) assays can detect antibodies against Babesia, though a four-fold rise in titer between acute and convalescent samples provides stronger evidence of recent infection.
- Complete blood count typically shows hemolytic anemia, thrombocytopenia, and elevated liver enzymes.
- In cases with suspected co-infection, testing for Lyme disease, anaplasmosis, and other tick-borne illnesses should be performed, as these frequently occur together and may complicate the clinical picture 1.
It is essential to note that the diagnosis of active babesial infection should include the presence of viral infection–like symptoms and identification of babesial parasites in blood by smear evaluation or by PCR amplification of babesial DNA 1. Symptomatic patients whose serum contains antibody to Babesia but whose blood lacks identifiable babesial parasites on smear or babesial DNA by PCR should not receive treatment 1. Treatment is also not recommended for asymptomatic individuals, regardless of the results of serologic examination, blood smears, or PCR 1.
From the Research
Diagnostic Approach for Babesiosis
The diagnostic approach for babesiosis involves several steps, including:
- Screening tests: A complete blood count (CBC) is a useful screening test, as anemia and thrombocytopenia are commonly observed in patients with babesiosis 2.
- Microscopic examination: Conclusive diagnosis of babesiosis generally depends upon microscopic examination of thin blood smears, although parasites may be overlooked due to sparse parasitemia 2.
- Polymerase chain reaction (PCR): Identification of amplifiable babesial DNA by PCR has comparable sensitivity and specificity to microscopic analysis of thin blood smear for detection of babesia in blood 2.
- Serologic testing: Serologic testing provides useful supplementary evidence of infection, as a robust antibody response characterizes human babesial infection, even at the time that parasitemia first becomes detectable 2.
Key Considerations
When diagnosing babesiosis, it is essential to consider the following:
- Clinical presentation: Babesiosis can present with a range of symptoms, from subclinical illness to fulminant disease resulting in death 3, 2.
- Risk factors: Patients with advanced age, asplenia, or other immune compromise are at risk for severe babesiosis and may require prolonged treatment to eradicate parasitemia 3, 4.
- Transmission: Babesiosis can be transmitted through tick bites or blood transfusion, and incidence of transfusion-transmitted babesiosis has increased over the past decade 4.
Laboratory Tests
Laboratory tests used to diagnose babesiosis include: