Screening Blood Donors at Risk for Malaria: Reply to Hänscheid et al.

To the Editor: The letter to editor by Hänscheid et al. addresses our suggestion that polymerase chain reaction (PCR) could serve as a reference test for screening blood donations. At present, PCR is the most sensitive and specific method for parasite detection in malaria-endemic areas. However, additional measures should be taken into account, such as serologic testing, refining donor history, defining at-risk locations, and delimiting malaria-endemic areas. Therefore, we do not suggest that only PCR should be used as a reference method to exclude blood donors at risk, but it could help shorten the deferral period for blood donor (currently 3 years after an asymptomatic person leaves the malaria-endemic area). PCR should be accompanied by serologic tests and the elimination of actual or possible plasmodial infection in the blood donor. In our laboratory, we use the indirect fluorescent antibody test (IFAT) for antigens of the four plasmodia species , in addition to PCR screening. At present, we have analyzed a total of 531 blood samples (406 more than the 125 described in our previous letter to the editor) from possible donors at risk for malaria, and only the five described in the letter were malaria positive. Moreover, 40% (50 of 125) of these sera were negative by IFAT (unpub. data), a fact that indicates the importance of having a complete donor history and being certain of the patient's origin in the context of malaria endemicity (i.e., several geographic areas without malaria transmission in some Central and South American countries could be excluded as malaria-risk areas; these areas coincide with sera negative by IFAT). On the other hand, with a standard 450-mL blood donation, parasitemias <90 could test negative by PCR; but, as previously described, this technique should be accompanied by careful questioning, serologic testing, and eliminating parasites from the recipient during blood processing and storage. We take for granted that, theoretically , any method would have to detect a single parasite per unit of blood to be safe and that little is known about the frequency of low parasitemias. In nature, and in accordance with the parasitologic definition of equilibrium between parasite and host (defined over thousands or millions of years according to different phylogenetic theories), one of the main strategies for parasite survival is sustained malaria transmission, which allows low parasitemias to be ingested by the anopheline vector (the amount of blood ingested by the female anopheline varies from …