First molecular detection of Leishmania infantum in a domestic cat from Costa Rica.

CASE SUMMARY: A 4-year-old, neutered male domestic cat was presented with an indolent, non-ulcerated and painless subcutaneous nodule on the left hindlimb. Abdominal ultrasonography revealed generalized lymphadenomegaly and splenomegaly with a honeycomb pattern. The cat tested negative for feline leukemia virus and feline immunodeficiency virus. Fine-needle aspiration of the lesion showed mixed inflammatory cells, including eosinophils and macrophages containing small intracytoplasmic basophilic inclusions considered suspicious for Leishmania-like organisms. The mass was surgically excised for histopathological and molecular evaluation. Histopathology demonstrated eosinophilic granulomatous inflammation with secondary furunculosis, without unequivocal visualization of amastigotes. Quantitative RT-PCR was positive for Leishmania species, and conventional PCR targeting the ITS-1 gene, followed by sequencing, showed 99.62% identity with Leishmania infantum. No anti-Leishmania treatment was administered because the lesion was completely excised, the cat remained clinically well and specific anti-Leishmania drugs are not readily accessible in Costa Rica. At the 7-month follow-up, no recurrence of the nodule was observed.

RELEVANCE AND NOVEL INFORMATION: This report describes the first molecular detection of L infantum in a Costa Rican domestic cat and the first record from the country's Central Valley. The case highlights the diagnostic challenges of feline Leishmania infection and supports Leishmania infection among the differential diagnoses for feline cutaneous nodules in Central America. It also underlines the need for further studies on the epidemiological role of cats in a One Health context.