Rapid identification of Leishmania spp. in formalin-fixed, paraffin-embedded tissue samples by fluorescence in situ hybridization.

OBJECTIVE

To describe and validate fluorescence in situ hybridization (FISH), a new method of Leishmania spp. identification. FISH allows for a rapid detection of target organisms by specific binding of fluorescently labelled oligonucleotide probes to ribosomal RNA.

METHODS

Two genus-specific, fluorescently labelled Leishmania spp. FISH probes were designed and evaluated with a panel of 18 Leishmania spp. and six Trypanosoma spp. including well-defined strains and clinical isolates. In addition, the FISH probes were tested in comparison with Giemsa staining in formalin-fixed, paraffin-embedded tissues of five mice that had been artificially infected with Leishmania major strains, leading to concordant results. Finally, 11 tissue samples of patients with cutaneous leishmaniasis, four tissue samples of patients with visceral leishmaniasis, and one native bone marrow sample of a patient with visceral leishmaniasis were analysed with FISH and Giemsa staining.

RESULTS

Concordant results were achieved by FISH and Giemsa staining in 15/16 specimens.

CONCLUSION

This analysis provides proof of principle that FISH is a suitable method for the rapid and easy detection of Leishmania spp. in formalin-fixed, paraffin-embedded tissue samples. Because of the good contrast of Leishmania spp. in tissue, FISH facilitates the identification of these organisms in tissue samples even by less experienced investigators.