Higher sensitivity of immunohistochemistry for bona fide diagnosis of dog Leishmania (Viannia) braziliensis-driven American tegumentary leishmaniasis: description of an optimized immunohistochemistry method

Background: The in situ detection of parasite antigens in tissue sections by immunohistochemistry (IHC) is a diagnostic alternative for human American tegumentary leishmaniasis (ATL), but has not been used for the diagnosis of cutaneous lesions in dogs with ATL. This study describes the results of IHC for the detection of amastigote forms and other Leishmania sp. antigen-positive cells and compares the results of IHC, histopathology and cytopathology for the diagnosis of canine ATL. In addition, possible cross-reactivity with sporotrichosis is analyzed. Methods: Forty paraffin-embedded biopsies and 40 smears of cutaneous lesions from dogs with ATL, confirmed by isolation and characterization of Leishmania (Viannia) braziliensis, and 40 paraffin-embedded biopsies of cutaneous lesions from dogs with sporotrichosis, confirmed by isolation of Sporothrix schenckii in culture (control group), were studied. Results: Immunohistochemistry was more sensitive in detecting amastigote forms than cytopathology and histopathology, with a positivity rate of 70% (n=28) versus 37.5% and 22.5% for histopathology and cytopathology, respectively. Cytoplasmic staining of mononuclear and endothelial cells was detected by IHC, which was highly specific since no cytoplasmic staining of these cells or staining of fungal structures was observed in sporotrichosis fragments. Conclusions: In view of the higher sensitivity of IHC in detecting Leishmania sp. antigen and patterns of positivity for Leishmania sp. antigen compared to histopathology or cytopathology and the absence of cross-reactions with sporotrichosis, we recommend this technique for the diagnosis of canine tegumentary leishmaniasis.