Granulomatous lesions in lymph nodes of slaughter pigs bacteriologically negative for Mycobacterium avium subsp. avium and positive for Rhodococcus equi

Abstract

The prevalence of granulomatous lesions in lymph nodes of pigs was studied. From January till August 2004 in two slaughterhouses in The Netherlands 2,116,536 pigs were examined for the presence of granulomatous lesions in the submaxillary lymph nodes. In 15,900 (0.75%) of these pigs, lesions could be detected. Nine farms with the highest incidence of lesions were selected for a more detailed pathological and bacteriological examination. On these farms, the prevalence of lesions in sub-maxillary lymph nodes ranged from 2.3 to 5.7% with a mean of 3.0%. From 1276 pigs that were sampled, 98 (7.7%) displayed granulomatous lesions in the sub-maxillary lymph nodes and one (0.1%) pig showed lesions in its mesenteric lymph node. Mycobacterium avium subsp. avium (MAA) could not be isolated from the lymph nodes of the 99 pigs with lesions and from a selection of lymph nodes (n = 61) of pigs without lesions. Rhodococcus equi was isolated from 44 out of 98 (44.9%) of the sub-maxillary lymph nodes with granulomatous lesions and from two mesenteric lymph nodes without lesions. A comparison of former studies and the current results indicate that the prevalence of MAA infections in slaughter pigs has strongly decreased over the last decade, whereas R. equi is highly prevalent. The high incidence of granulomatous lesions associated with the bacteriological presence of R. equi could be considered as a serious cause of misdiagnosis of MAA infections in cases where meat inspection is carried out by inspection for granulomatous changes of lymph nodes only. #

Intermediately virulent Rhodococcus equi isolates from pigs in Slovenia: discovery of new plasmid types and assessment of genetic diversity by pulsed-field gel electrophoresis

“…The studies on this topic report conflicting results: some authors recovered R. equi from the lymph nodes of healthy pigs (Takai et al, 1996;Madarame et al, 1998;Dvorska et al, 1999;Makrai et al, 2005) while others reported the isolation of R. equi almost exclusively from lymph nodes with granulomatous lesions, identifying it as the causative agent of lymphadenitis in pigs (Komijn et al, 2007). In the scope of one study, R. equi was found in pigs with and without caseous lymphadenitis, but the isolation rate was reported to be five times higher in the lymph nodes with lesions (Katsumi et al, 1991).…”

“…Although there seems to be a increasing trend for isolation of R. equi from swine lymph nodes (Shitaye et al, 2006;Komijn et al, 2007), either due to a true increase of infections or as a consequence of improved diagnostics in terms of awareness of this pathogen, relatively little research has been carried out with respect to characterization of its virulence plasmid types. It has been demonstrated that R. equi strains from pigs may express VapA or VapB, which are characteristic for strains from AIDS patients (Takai et al, 1996;Makrai et al, 2002;Takai et al, 2002).…”

“…Infection can also occur in a wide variety of other mammals, usually due to immunosuppression (Prescott, 1991). R. equi is frequently isolated from the lymph nodes of pigs (Barton and Hughes, 1980;Katsumi et al, 1991;Prescott, 1991;Takai et al, 1996;Pate et al, 2004;Makrai et al, 2005;Shitaye et al, 2006;Komijn et al, 2007); it also seems to be gaining importance in human health (Jones et al, 1989;Kedlaya et al, 2001;Weinstock and Brown, 2002;Torres-Tortosa et al, 2003;Ulivieri and Oliveri, 2006). Increased numbers of human R. equi infections might be a consequence of the AIDS epidemic but may also reflect the increasing awareness of this opportunistic pathogen (Prescott, 1991).…”

An Invertron-Like Linear Plasmid Mediates Intracellular Survival and Virulence in Bovine Isolates of Rhodococcus equi

“…While best known as an equine pathogen, R. equi also infects other animal species (1,(6)(7)(8). In abattoir surveys, R. equi is frequently recovered from porcine submaxillary lymph nodes with granulomatous lesions as well as from apparently healthy pigs (9)(10)(11). In cattle, it is typically isolated from caseating abscesses in respiratory lymph nodes resembling bovine tuberculosis (TB) lesions (12).…”

Usability of a gamma interferon release assay in the diagnosis of naturally infected pigs with Mycobacterium avium subspecies hominissuis

“…This approach is, however, nonspecific for mycobacteria because other bacteria species such as Rhodococcus equi have been isolated from granulomatous lesions in pigs. 7,12 Thus, bacteriological cultivation or molecular biological approaches are required for a confirmation of mycobacterial infection.…”