Abstract
Abstract
Background:
Mycobacterium avium
subsp.
hominissuis
(MAH) is an opportunistic environmental pathogen affecting pigs, humans, and occasionally other animal species. Although molecular typing has improved the understanding of MAH epidemiology, information on the genetic diversity and dissemination of MAH in pig populations remains limited. This study investigated the genetic diversity and distribution of MAH in slaughtered fattening pigs in Switzerland using variable-number tandem repeat (VNTR) typing combined with complete
hsp65
gene sequencing.
Results:
A total of 490 tissue samples from 120 pigs with granulomatous lesions collected between 2015 and 2022 were examined. Among 342 MAH isolates recovered from 117 pigs, 84 distinct strain genotypes were identified. MAH was detected in tissues with and without granulomatous lesions, including five macroscopically unremarkable muscle samples obtained from pigs in which MAH was also detected in other organs. Eight strain genotypes accounted for 203 of 342 isolates (59.4%), whereas 52 of 84 strain genotypes were represented by a single isolate. Mixed infections were common, with 56 of 117 pigs (47.9%) harbouring two or more strain genotypes and up to six detected within a single animal. Dominant strain genotypes occurred across multiple farms, cantons, and sampling years, while epidemiological clusters showed no significant geographic clustering. Comparison with previously published data identified closely related strain genotypes among isolates from pigs, cattle, and humans from several countries.
Conclusions:
The MAH population was characterized by a high genetic diversity, frequent mixed infections, and the coexistence of a small number of geographically widespread strain genotypes alongside numerous rare variants. The observed population structure is consistent with repeated environmental exposure as the principal driver of MAH epidemiology in pigs. The occurrence of closely related strain genotypes across animal species and humans further supports the relevance of MAH from a One Health perspective.