Sensitivity and specificity of in situ hybridization for diagnosis of cutaneous infection by Leishmania infantum in dogs.

An accurate diagnosis of infection by Leishmania infantum in dogs is fundamental for the control of zoonotic visceral leishmaniasis (VL). Histopathology (HP) and immunohistochemistry (IHC) are frequently used for the histological diagnosis of L. infantum in dogs but have shown limited accuracy. To improve the sensitivity and specificity of the histological diagnosis of VL, we evaluated automated in situ hybridization (ISH) using a generic probe for Leishmania and a specific probe for L. infantum in surgical skin biopsy specimens of dogs. The ISH results were compared with those of HP and IHC, using parasitological culture as the reference standard. Skin samples from 51 dogs with cutaneous L. infantum infection and 51 noninfected dogs were randomly selected from samples of dogs from various cities in Brazil where canine VL is endemic. These samples were processed for parasitological culture, HP, IHC, and ISH using both probes. The sensitivities of ISH using the specific probe, ISH using the generic probe, IHC, and HP were, respectively, 74.5%, 70.6%, 69.5%, and 57.6%. The specificity of both ISH probes tested was 100%, and there was no cross-hybridization of the generic and specific probes with selected pathogenic fungi and protozoa. The specific probe discriminated L. infantum from the other species of Leishmania that infect dogs in the New World. ISH is highly sensitive and specific for the diagnosis of L. infantum in histologic samples of skin from infected dogs and can be used on routine biopsy material to make a diagnosis of leishmaniasis.