Blood Smear Analysis: Babesiosis

Babesiosis represents an emerging zoonotic tick-borne disease caused by intraerythrocytic protozoan parasites of the genus Babesia, which are transmitted by hard-bodied (Ixodes) ticks. Several different species are known causes of disease in humans, most notably Babesia microti, Babesia divergens and Babesia duncani.

Babesia infection may be completely asymptomatic or may present with an illness with a severity range from mild to fulminant, sometimes even resulting in death. Thus a complete descriptive history that includes clinical manifestations, travel history to endemic areas, tick bite or exposure, splenectomy, as well as a recent blood transfusion should be conducted.

As the symptoms and signs of the disease can be relatively non-specific,

The aforementioned ring forms that are seen within red blood cells can vary significantly and can be easily misinterpreted as Plasmodium falciparum (i.e. a malaria parasite), although the absence of the hemozoin pigment should point to Babesia parasites. And indeed, there are cases described in the literature when the patient was erroneously diagnosed with malaria, which may result in misguided treatment and pose a serious risk to the

The need to differentiate the nuances of babesial morphology and likely low parasitaemias may trigger inaccurate diagnoses, which is why new approaches to diagnostics are constantly being refined.

Serologic Methods

The indirect immunofluorescence assay (IFA) is the most frequent serologic test used in diagnosing human babesiosis, predominantly due to its sensitivity and specificity. The cut-off titer for determining a positive result varies between different laboratories, albeit higher titers (1:128 to 1:256) are linked to improved diagnostic specificity.

Antibodies are most often detectable when patients are diagnosed with Babesia microti infection for the first time; conversely, Babesia divergens infections are usually too serious or severe to allow serologic diagnostic approach, as antibodies are not detectable in serum until ten days after the emergence of hemoglobinuria.

Also, a potential drawback to serologic testing is a possible cross-reactivity with other protozoal parasites, generating in turn false-positive results. Such false-positivity may also arise in patients with rheumatoid arthritis or systemic lupus erythematosus, whereas in immunosuppressed patients the test could show false-negative