Molecular diagnosis
In some infections with intraerythrocytic parasites, the morphologic characteristics observed on microscopic examination of blood smears do not allow an unambiguous differentiation between Babesia and Plasmodium.  Moreover, potential blood donors may have subclinical symptoms and very low parasitemia, undetectable in blood smears.  In such cases, the diagnosis can be derived from molecular techniques, such as PCR using the appropriate primers and single-step, or the more sensitive nested PCR technique.  In addition, molecular approaches are very valuable in investigations of new Babesia variants (or species) observed in recent human infections in the United States and in Europe.

A

A: Agarose gel (2%) analysis of a PCR diagnostic test for detection of Babesia microti DNA.  PCR was performed using a nested protocol with primers BAB1 and BAB4¹ (first round) and BAB2 and BAB3¹ (second round).

• Lane S: Molecular base pair standard (50-bp ladder).  Black arrows show the size of standard bands.
• Lane 1: First step amplification with primers BAB1 and BAB4¹ of the nested PCR protocol for detection of B. microti in DNA extracted from whole blood.  The specimen, serologically positive for B. microti, was submitted to CDC by the American Red Cross.  The red arrow shows the single-step PCR diagnostic band for B. microti (size: 238 bp).
• Lane 2: Nested PCR with primers BAB2 and BAB3¹ using as template the product of the first step amplification.  The blue arrow shows the nested PCR diagnostic band for B. microti (size: 154 bp).  Please note the enhanced sensitivity of B. microti DNA detection with the nested reaction.

Reference:

Persing DH, Mathiesen D, Marshall WF, Telford SR, Spielman A, Thomford JW, Conrad PA. Detection of Babesia microti by polymerase chain reaction. J Clin Microbiol 1992;30:2097-103.