Immunohistochemistry to identify Leishmania parasites in fixed tissues

The definitive diagnosis of leishmaniasis currently depends on the identification of characteristic amastigote morphology in tissue, or isolation of promastigotes by culture. Histopathological identification can be difficult, and is variably sensitive; culture is considered 'the gold standard', but is not uniformly diagnostic or available. In this study, we compared light microscopic immunohistochemistry (IHC) using a monoclonal anti-Leishmania antibody (G2D10) to standard hematoxylin and eosin (H+E) stain in the diagnosis of Leishmania on skin. Sixty-one archived specimens from patients suspected of being infected with Leishmania were used; 41 of these had leishmaniasis confirmed by culture. Although not statistically significant, both sensitivity and specificity were higher for IHC compared to H+E: 51% (95% CI: 35-67%) compared to 42% (CI: 26-58%; 2p = 0.29) for sensitivity, and 100% (CI: 83-100%) compared to 85% (CI: 62-97%, 2p = 0.25) for specificity, respectively. Furthermore, because organisms could be diagnosed by IHC at low power (x 20-40), this assay was more rapid than H+E, in which parasite morphology could best be identified at oil immersion power. The G2D10 antibody has broad Leishmania species recognition, and offers promise as a simple, rapid diagnostic screen for leishmaniasis. Further study is underway to better characterize this antibody.