Molecular and parasitological evidence of Leishmania (Mundinia) martiniquensis infection in a horse from Brazil.

Leishmania (Mundinia) martiniquensis is an emerging human pathogen with increasing reports of infection in domestic animals. This study describes a naturally infected mare from Brazil with no history of international travel, presenting with persistent nodular cutaneous lesions and cervical lymph node enlargement, without evidence of systemic involvement. Considering the endemicity of cutaneous and visceral leishmaniasis in the study area, as well as previous reports of equine leishmaniasis, infection by Leishmania (Leishmania) infantum was initially suspected. Anti-L. (L.) infantum antibodies (titer 320) were detected by indirect immunofluorescence assay, and histopathological analysis of the lymph node revealed amastigote forms compatible with Leishmania spp. Therefore, while the etiological agent was still unknown, xenodiagnosis using Lutzomyia (Lutzomyia) longipalpis was performed during the diagnostic investigation based on the initial suspicion of L. (L.) infantum infection. Limited blood feeding was observed, and no evidence of parasite transmission was detected. In addition, flagellated parasites were isolated in vitro from a fine-needle aspiration biopsy of the cervical lymph node. Molecular characterization of clinical samples and culture isolate was performed by amplification of Leishmania spp. kinetoplast DNA (kDNA) and the internal transcribed spacer 1 (ITS1) region of Trypanosomatidae ribosomal DNA, followed by Sanger sequencing, which revealed the presence of L. (M.) martiniquensis. These findings provide documented evidence of natural infection by L. (M.) martiniquensis in a horse in Brazil and highlight the circulation of this emerging pathogen in areas endemic for cutaneous and visceral leishmaniasis. Furthermore, they reinforce the need for additional studies to better elucidate its epidemiological cycle and vector-host interactions.