Isolation of Rhodococcus equi and atypical mycobacteria from lymph nodes of pigs and cattle in herds with the occurrence of tuberculoid gross changes in the Czech Republic over the period of 1996-1998

The prevalence of Rhodococcus equi and atypical mycobacteria in the lymph nodes of pigs (n = 1 382) and cattle (n = 231) without clinical signs was studied in the Czech Republic over the period 1996-1998. R. equi alone was isolated from 7.4% of pigs, and in a mixed infection with atypical mycobacteria in another 2.3% of pigs and 1.7% of cattle. The frequency of R. equi was higher (p = 0.01) in pigs than in cattle. Atypical mycobacteria alone were more frequently isolated from pigs - 37.2% positive findings than from cattle - 28.2% positive findings (p = 0.01). Of the total of 546 mycobacterial strains isolated from pigs, 96.2% belonged to the Mycobacterium avium complex, and 3.8% (21 strains) belonged to other species(5 strains M. chelonae, 6 strains M. terrae, 2 strains M. phlei, 6 strains M. forruitum and 2 strains not identified). A total of 65 mycobacterial strains belonging only to M. avium complex were identified in cattle. Of 492 pigs, R. equi alone was isolated from submaxillary lymph nodes at frequency of 19.5%, atypical mycobacteria were isolated at 30.1% and mixed infection at 4.9%. On the other hand, of the total of 639 pigs, R. equi alone was isolated from mesenteric lymph nodes in 0.5% of animals; atypical mycobacteria in 42.6% and mixed infection in 0.8% of pigs. The isolation of R, equi from submaxillary lymph nodes was more frequent (p = 0.01) than isolation from mesenteric lymph nodes. Examinations of lymph nodes from 218 pigs without tuberculoid nodules (group S1) resulted in isolation of R. equi in 2.8% of animals compared with significantly higher (p = 0.01) isolation from 703 pigs with caseated tuberculoid nodules (group S2) which was 13.7%. No R. equi was isolated in the 461 animals with calcified tuberculoid nodules (group S3). The detection rate of atypical mycobacteria increased in these groups S1, S2 and S3, the values being 19.3, 373 and 45.6%, respectively, and those of R. equi and/or atypical bacteria from pigs were 23.4, 45.8 and 54.9%, respectively. The difference between the groups was highly significant (p = 0.01). The differences between the groups were highly significant (p = 0.01). Of a total of 765 pig and cattle farms R. equi was isolated from 93 farms. Contact of swine on these farms with horses or their faeces was confirmed only in 19 (20.4%) cases.