Histopathological findings and staining performance in cutaneous nodules from a cat with Leishmania amazonensis...

Cutaneous leishmaniasis (CL) is a zoonotic disease with wide geographic distribution and significant public health impact. In Brazil, the main etiological agents are Leishmania braziliensis and Leishmania amazonensis. In animals, the disease usually presents as a chronic condition characterized by poorly healing skin lesions, oral and ocular involvement, and cutaneous nodules, most commonly affecting the head and neck regions. Diagnosis may be achieved using molecular techniques, immunohistochemistry, cytology, histopathology, and culture. Despite the endemic nature of CL in several regions, histopathological descriptions of the disease in felines remain scarce. This study aimed to describe the histopathological features of cutaneous nodular tissue parasitized by amastigote forms of Leishmania amazonensis in a domestic cat, using different histological staining protocols to compare the performance of different histological staining protocols in this case. A fragment of cutaneous nodular tissue was subjected to routine histological processing and stained with hematoxylin and eosin (H&E), periodic acid-Schiff (PAS), fast green, Fontana-Masson, and Mallory's trichrome. Histological evaluation was performed using photomicrographs obtained from five microscopic fields. Among the evaluated staining techniques, hematoxylin and eosin appeared to provide the best visualization and differentiation of amastigote forms from surrounding tissue structures in the evaluated tissue. The evaluated sections showed moderate lymphoplasmacytic dermal infiltrates and numerous macrophages with cytoplasm filled with amastigotes. Special stains yielded variable contrast, with fast green and Mallory's trichrome allowing reasonable differentiation, while Fontana-Masson showed limited diagnostic utility.