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Investigations into the possible causes of colitis and typhlocolitis were carried out on 85 pig units in the United Kingdom between 1992 and 1996. Serpulina pilosicoli was identified most commonly, occurring as the suggested primary agent on 21 (25 per cent) of the units but forming part of mixed infections on another 23 (27 per cent) of the units, the main co-infections being Yersinia pseudotuberculosis (eight units), proliferative enteropathy (six units), Salmonella species (four units) or Serpulina hyodysenteriae (two units). 'Atypical' Serpulina species, S hyodysenteriae, Salmonella typhimurium, Y pseudotuberculosis and Lawsonia intracellularis (proliferative enteropathy) were the suggested primary agents on seven, six, four, four and three units, respectively. Various combinations of mixed infections involving the latter organisms and other possibly incidental agents were recorded on another 10 units. Investigations on a further six units failed to detect any recognised pathogens. On units where S pilosicoli was the suggested primary agent, pigs ranging between 20 to 40 kg (eight to 16 weeks of age), but occasionally up to 50 kg, had diarrhoea and grew poorly over a period of two to three weeks. The prevalence was estimated to be between 5 and 15 per cent in affected batches, with a mortality of approximately 1 per cent. The clinical signs usually developed seven to 14 days after the moving and mixing of pigs. At postmortem examination, affected pigs had liquid contents in their colon, which contained accumulations of mucus in some chronic cases. Gross and histological lesions of colitis were prominent in the mid-spiral region of the colon. In mixed infections with Y pseudotuberculosis, Salmonella typhimurium or S hyodysenteriae, lesions were more extensive and affected the caecum as well as the colon. In the colon, lesions of proliferative enteropathy were usually confined to the proximal half of the ascending spiral but mixed infection with S pilosicoli caused more extensive colitis. Mixed infections were reported to prolong the time taken for pigs to recover naturally and to have a more detrimental effect on growth rates than S pilosicoli infection alone. Despite the successful treatment of batches of pigs with tiamulin or lincomycin, S pilosicoli infection persisted as a chronic problem on many units, with diarrhoea and colitis in successive batches of pigs unless prophylactic medication was used.

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HighlightsDisease and non-disease associated isolates had different resistance profiles.Antimicrobial resistance increased over time among clinical isolates.Prevalence of isolates with resistance to multiple antimicrobials is increasing.Combination of different approaches enhances the information obtained from the data.

To characterize the immune response associated with Lawsonia intracellularis infection, twenty-eight, 7-week-old pigs were dosed orally with a pure culture of L. intracellularis. Animals were killed 3, 7, 14, 21, 28, 35, and 42 days postinfection. Light microscopic studies were undertaken to immunophenotype the immunologic response using specific antibodies to T-cell subsets (CD3, CD4, and CD8), B cells, major histocompatibility complex class II, cadherin, and macrophages over the course of time. The results indicate that there is a direct association between the presence of L. intracellularis and reduced T-cell and B-cell numbers. For the first time, this provides evidence of the presence of an immunosuppressive mechanism operating in this disease. Furthermore, macrophage marker studies indicated that macrophages may play a more complex and significant role in the disease process than has been previously reported, with activated macrophages accumulating in infected hyperplastic crypts.