Tuberculous lesions in pig lymph nodes caused by kaolin fed as a supplement

An increased incidence of tuberculous lesions in head and mesenteric lymph nodes from slaughtered pigs weighing about 115 kg was recorded in a herd of pigs kept in two farms A and B in the CzechRepublic. Tuberculous lesions were more frequently (P < 0.01) diagnosed in pigs from Farm A (10.4%) than from Farm B (1.1%). The follow-up investigation of potential sources of infection on Farm A revealed that the piglets were fed kaolin from a nearby mine as a supplement. Among 20 samples from the pigs' environment, atypical conditionally pathogenic mycobacteria (ACPM) were detected in four samples as follows: dust (n = 2), pig faeces (n = 1) and kaolin fed as a supplement (n = 1). Mycobacterium avium subsp. hominissuis of genotype IS901- and IS1245+ and serotype 8 was isolated from kaolin and pig lymph nodes, M. fortuitum from stable dust and pig faeces and other ACPM from stable dust. When kaolin feeding to piglets ceased, the incidence of tuberculous lesions in these pigs at slaughter 5-6 months later decreased from 16.1% to 3.4%. No ACPM was detected on Farm B in 27 samples from the environment. An investigation of surface kaolin mines did not detect mycobacteria in non-extracted kaolin. However, surface water (three isolates among 13 samples) from the pond used for kaolin levigation and 23 batches of the final product of kaolin (10 samples from each batch, i.e. a total of 230 samples were examined) were contaminated with ACPM. Among the latter, ACPM were isolated from three samples originating from three different batches. ACPM were likely to survive during transport of the kaolin, as a suspension through the pipeline, and during its further processing to the final product (sedimentation, addition of colloid substances, drying and other procedures).