Fatal Canine Distemper Virus Infections in Free-Ranging Black-Tufted Marmosets (Callithrix penicillata) in Central Brazil.

Canine distemper virus (CDV), a morbillivirus with a broad host range, has increasingly been reported in wildlife, including nonhuman primates. However, data on CDV infection in free-ranging Neotropical primates remain limited. Herein, we describe the pathologic, immunohistochemical, and molecular findings associated with CDV infection in three free-ranging black-tufted marmosets (Callithrix penicillata) from periurban areas of Palmas, Tocantins state, Brazil Between February and March 2023, residents reported sick or dead marmosets with facial cutaneous lesions. Postmortem examination revealed mucocutaneous lesions and pulmonary changes. Histologically, all animals exhibited moderate-to-severe interstitial pneumonia characterized by mononuclear inflammation, marked type II pneumocyte hyperplasia, necrotizing bronchiolitis, and multinucleated syncytial cells. Additional findings included epithelial degeneration and ulceration, viral inclusions in the skin and esophagus, and lymphoid depletion in the spleen. Eosinophilic intranuclear and intracytoplasmic inclusion bodies were observed in epithelial cells and macrophages. Immunohistochemistry demonstrated multifocal CDV antigen labeling in pulmonary and esophageal tissues, whereas tests for yellow fever virus, human alphaherpesvirus, and Toxoplasma gondii were negative. Molecular analysis confirmed CDV infection by amplification of short fragments of the conserved L gene, which showed ≥98% nucleotide identity with Brazilian strains. However, further sequencing was not possible due to nucleic acid degradation. These findings expand current knowledge of CDV infection in Neotropical primates and highlight the importance of integrated wildlife surveillance at the human-domestic animal-wildlife interface.