Mycobacterium tuberculosis complex species-induced infections in dogs: a narrative review of five cases reported in Brazil (1990-2024).

Canine tuberculosis (TB) is rarely or sporadically reported, although it comprises a zoonotic issue. In Brazil, a lack of comprehensive studies has been described, and the disease is restricted to case reports. Considering this scenario, we retrospectively studied cases of canine Mycobacterium tuberculosis complex (MTBC) infections in Brazil over 35-year period (1990–2024), and only five cases were described. Four MTBC species were initially identified (two M. tuberculosis and two M. bovis isolates) via microbiological culture/phenotypic methods and confirmed by molecular techniques (PCR-PRA, spoligotyping, and/or MIRU-VNTR). Dogs with TB-related M. tuberculosis infections had a prolonged history of contact with TB-positive owners, ingestion of leftover food from family members, or owners’ habit of spitting on the floor of households, indicating probable spillover of M. tuberculosis from owners-to-dogs. Dogs with TB-related M. bovis infections had a history of contact with bovines or buffaloes, milk ingestion, or contact with carcasses in farm environments, representing a probable transmission route of M. bovis from bovines or buffaloes-to-dogs. Clinical signs were observed in three (60%) dogs, represented mainly by progressive weight loss (100%), sarcopenia/cachexia (100%), melena (100%), and dyspnea/respiratory distress (66%). No specific antimicrobial therapy was carried out. Among the five dogs enrolled, two (40%) died, and three were euthanized (60%). Our results contribute to the understanding of the etioepidemiological aspects of canine TB (with emphasis on the probable transmission routes of the pathogen from livestock or humans-to-dogs infections), clinical findings, the need for a combination of methods to confirm the diagnosis, and better knowledge of veterinarians regarding canine TB due to nonspecific clinical signs and zoonotic risks. Despite the rarity of cases, we emphasize the challenging diagnosis of canine mycobacterial infections, the need for legal requirement to notify Brazilian public health agencies of confirmed canine TB cases, in addition to multiprofessional approaches in a One Health perspective in households with dogs infected, and the adoption of control/preventive measures against mycobacterial infections in dogs due to the risk of transmission of the pathogen to humans and other animals.