Unveiling mycobacterial infections in Brazilian swine: Insights from epidemiological and diagnostic studies

Stringent sanitary standards are imperative for swine production, ensuring high biosecurity and safe meat. However, granulomatous lesions, often detected as "lymphadenitis" in slaughterhouses, lack routine laboratory examination, potentially overlooking tuberculosis among other etiologies. This study aimed to: (i) explore epidemiological variables linked to swine carcasses condemned due to "tuberculosis" or "lymphadenitis" in Rio Grande do Sul, southern Brazil in a retrospective survey; and (ii) evaluate the frequency of Mycobacterium tuberculosis in granulomatous lymphadenitis lesions. Epidemiological data from the public surveillance system including farm origin, slaughter location, season, producer type and the inspection scope, were evaluated by their association with the occurrence of animal transport guides (ATG) with at least one animal condemned due to lymphadenitis or tuberculosis. For the prospective study, tissue samples from 118 animals with granulomatous lymphadenitis lesions were examined through histopathology and bacterial isolation. The frequency of ATG with at least one carcass condemned due to lymphadenitis or tuberculosis was 2.27 % and 0.027 % respectively. The factors associated with lymphadenitis were slaughter location, origin, producer type, and inspection scope (state or municipal). However, no significant risk factors emerged for tuberculosis in multivariable analysis. Histopathology confirmed granulomatous lymphadenitis in 44.92 % of lymph nodes, and M. tuberculosis var. bovis was isolated in 2.54 % of cases. Although the tuberculosis frequency (0.002 %) was low, it surpassed federal inspection data (<0.001 %), evidencing that laboratory diagnosis should be considered in such lesions. This study underscores the need for improved diagnostic routine in slaughterhouses to enhance biosecurity and public health protection in the swine industry.