Brachyspira murdochii-associated colitis in grower pigs: Guilt by association or innocent bystander?
Josepha DeLay, Clint Lichty
Animal Health Laboratory, University of Guelph, Guelph, ON (DeLay), South West Vets, Stratford, ON (Lichty)
AHL Newsletter 2024;28(4):13.
Grower pigs from a 1200 sow multi-site farrow-to-finish operation were examined due to persistent diarrhea involving 20% of the group. Nursery and grower pigs from the herd were housed in the same continuous-flow barn. Occasional diarrhea was noted in the nursery group, but became a more significant issue at the grower stage. Although some fading pigs were present, pigs with diarrhea were often in good body condition. Mortality was not increased.
Enteritis due to Lawsonia intracellularis was identified in nursery pigs and was considered the likely cause of ongoing diarrhea in growers as well. However, lack of response to treatment in the grower pigs prompted additional diagnostic testing. On-farm necropsy of euthanized pigs with clinical signs identified gross lesions of ulcerative colitis. Histologic lesions confirmed erosive to ulcerative colitis, and L. intracellularis was detected in feces or colon from multiple pigs by PCR (Ct 27-37); however, typical lesions of proliferative enteritis were not present. Salmonella spp. was not isolated from colon of multiple pigs, and Trichuris vulpis (whipworm) eggs were not detected in feces by fecal flotation.
Brachyspira hampsonii (Ct 37) was detected by PCR in the colon from 1 of 3 pigs examined, but the organism was not identified in other animals subsequently tested. PCR identified Brachyspira murdochii (Ct 22-29) in the colon from 3 of 4 additional pigs.
Erosive to ulcerative colitis was confirmed as a common lesion in affected grower pigs in this herd, but the definitive cause remains elusive. Contribution of Brachyspira spp., especially B. murdochii, to diarrhea in these pigs is suspected. Rather than simple and direct disease causation by this organism, diarrhea in this case is likely due to colonic dysbacteriosis (disruption and imbalance in the normal microbiota), potentially influenced by a number of factors. Importantly, infection of swine with any species of Brachyspira spp. does not necessarily cause disease, and the composition of the colonic microbial community influences disease expression in the form of diarrhea. In this case, pathogen build-up in the grower rooms is a suspected factor in the persistence of clinical diarrhea and was likely influenced by continuous flow and limited washing of grower rooms, and direct conection of nursery and grower rooms in the same barn. Subclinical infection with L. intracellularis may also be contributing to disruption of the normal colonic microbial community. Diet and the Brachyspira spp. profile in colon in other age groups in the herd, mainly sows, may have also influenced the grower situation. The pathogenic species B. hampsonii was confirmed in feces from only 1 pig and with a low pathogen load, suggesting that this finding may also be a manifestation of colonic dysbacteriosis in the group.
B.murdochii is considered an opportunistic pathogen in the colon of pigs. A report from Western Canada has identified a recent increase in the proportion of B. murdochii-positive clinical cases, suggesting that the organism may have an increasing role in swine colitis. Other investigations have also indicated that in some circumstances, B. murdochii is of low pathogenicity and can cause colitis in pigs. In the current case, B. murdochii was the only potential pathogen identified in multiple pigs with colitis. The organism may have contributed to colitis in these animals, but a more accurate interpretation may be that this finding demonstrates a detrimental shift in colonic flora.
References
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