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The extent of cryptic leishmaniasis in blood donors from a Spanish endemic area, (Eivissa Island) was studied using various immunological and parasitological methods. Sera from 656 blood donors were analysed: 16 (2.4%) were positive by ELISA and 50 (7.6%) by Western blot. Peripheral blood mononuclear cells (PBMC) and buffy coat (BC) samples, were analyzed by culture and nested-PCR. DNA of L. infantum was amplified in 27 (22.1%) of 122 PBMC. Parasites were isolated in 3 (4.5%) of 67 BC cultures and the strains were identified as L. infantum zymodeme MON-28. No parasites were isolated in PBMC culture. After 12 months, a second blood sample was obtained from 18 blood donors who were positive by nested-PCR in the first extraction; nine of them remained positive. Delayed type hypersensitivity (DTH) tests on 15/67 donors (22.3%) were positive. Comparison of results obtained by ELISA, WB and DTH; ELISA, WB and nested-PCR and nested-PCR and BC culture showed a significant association (Pearson test, P < 0.05). L. infantum zyodeme MON-28 was identified in three strains isolated from asymptomatic donors, which suggests a low virulence capacity of these strains. The detection of Leishmania DNA in a high number of asymptomatic subjects supports the need to monitor it in blood donors endemic areas.

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Cryptic Leishmania infection is highly prevalent in blood donors from the Balearic Islands. DTH and L. infantum nested PCR appear to be more sensitive to detect asymptomatic infection than the serology. The use of leukodepletion filters appears to remove parasites from RBC units efficiently.