Vaginal canine transmissible venereal tumour associated with intra-tumoural Leishmania spp. amastigotes in an asymptomatic female dog.

A 2-year-old female boxer dog was presented with a vaginal serosanguineous discharge not associated with oestrus. There was a friable mass occupying the upper caudal part of the vagina. Cytological and histological examination revealed a monomorphic population of neoplastic round cells consistent with canine transmissible venereal tumour (TVT). In addition, Leishmania spp. amastigotes were found within the neoplastic tissue. In order to characterize whether the amastigotes were present inside macrophages and/or neoplastic cells, a co-localization study using cell- and pathogen-specific markers was performed. To detect Leishmania spp. a 5.8S ribosomal RNA (rRNA) parasite-specific sequence was used for in-situ hybridization and Mac387 was used as a macrophage marker for immunohistochemistry. Leishmania spp. rRNA was detected inside Mac387(+) macrophages and within the cytoplasm of some neoplastic cells. DNA isolation and polymerase chain reaction using specific primers and sequencing analysis identified the organism as Leishmania infantum (syn. Leishmania chagasi). This is the first report describing infection of tumour cells by L. infantum in a genital TVT from an asymptomatic bitch. Transplantation of Leishmania-laden neoplastic cells could represent an alternative route of venereal transmission of leishmaniasis among dogs.