Mycobacterial infections in cats and a dog: A case series from Southern Brazil and one health implications.

Infections by M. avium and M. tuberculosis in companion animals are little reported. This case series describes four instances of mycobacterial infections in companion animals (three cats and one dog) in southern Brazil. We detail the diagnostic challenges and emphasize their epidemiological relevance in a One Health context. Histopathology, acid-fast bacilli staining, mycobacterial culture and PCR were used to confirm the infections. Clinical presentations, diagnostic workups, and therapeutic outcomes were reviewed. One case involved disseminated infection by M. avium in a cat with partial therapeutic success, representing the first such case reported in Rio Grande do Sul. Two cats were diagnosed with disseminated M. tuberculosis var bovis infection, all with a fatal outcome. A final case of M. tuberculosis var tuberculosis in a dog showed multisystemic dissemination and was linked to an owner previously treated for TB. These findings highlight the underrecognized role of companion animals in the epidemiology of mycobacterial infections in Brazil. Increased awareness and surveillance are needed, particularly in rural settings. A One Health approach is crucial for mitigating risks to both animal and human health.