Pathogenicity of three strains of Serpulina pilosicoli in pigs with a naturally acquired intestinal flora

Abstract

Serpulina pilosicoli is an anaerobic spirochete which has been isolated from the colons of pigs with enteric disease. The clinical and pathologic features of experimental infections of conventional pigs (born by normal farrowing with a naturally acquired intestinal flora) with three strains of S. pilosicoli were determined in order to confirm the enteropathogenicity of this species. Strains were derived from the colons of British pigs with colitis and passaged 8 to 10 times during expansion and purification in vitro. Eighteen ten-week-old Large White-Landrace cross pigs were each inoculated once orally with 0.7 ؋ 10 9 to 1.6 ؋ 10 9 of one of three strains of S. pilosicoli. Six pigs were challenged with each strain. Control pigs were dosed with uninfected broth medium or with 1.8 ؋ 10 7 cells of the nonpathogenic Serpulina innocens. Eight pigs (two to four per S. pilosicoli challenge group) developed soft or diarrheic feces (fecal dry matter < 24%) between 3 and 8 days after challenge, which persisted for 7 to 8 days or until necropsy at 14 days after challenge. Average weight gains in two of the three groups challenged with S. pilosicoli were significantly less than controls. The feed conversion ratios of all the groups challenged with S. pilosicoli were impaired compared to controls. The mean values for daily liveweight gain (and feed conversion ratio) for the three groups challenged with S. pilosicoli were 0.799 (2.13), 0.783 (2.05), and 0.844 kg (2.10), respectively, while that of the uninoculated controls was 0.944 kg (1.70). Gross lesions with slight mucosal thickening, congestion, and multifocal erosions were evident in seven of eight diarrheic pigs. The relative weights of the large intestines of pigs challenged with S. pilosicoli were significantly less than controls. Histologic lesions with an increase in mucosal height, infiltration of the lamina propria with mononuclear cells, mucosal erosion with mixed inflammatory cell infiltration, and goblet cell hyperplasia in colonic glands were evident in 15 of the 18 challenged pigs. S. pilosicoli was recovered on bacterial culture of the colon from all except one of the pigs with these histologic lesions. Serpulina sp. was clearly visible within the colonic glands of these affected pigs in silver-stained sections of the gut. Clinical and pathologic findings in control pigs were unremarkable, with no diarrhea or colonic lesions evident. The results provide further evidence that S. pilosicoli is a specific enteric pathogen for conventional pigs. It is capable of colonizing the large intestine and causing mucosal damage, which although mild is sufficient to result in significant adverse effects on growth.

Scanning Electron Microscopy and Fluorescent In Situ Hybridization of Experimental Brachyspira (Serpulina) pilosicoli Infection in Growing Pigs

“…14,20,34,35 The gross lesions in pigs with B. pilosicoli infection are relatively mild compared with those occurring in swine dysentery, although diphtheritic lesions, multifocal erosions, and mucoid colitis have been described in previous experimental studies. 35,37,39 Even though significant morphologic changes were present microscopically, the most serious gross lesions in this study were hyperemia of the mucosa. Similarly, absence of significant gross lesions has been reported in field cases indicating that histologic examination of colons from pigs with diarrhea is relevant in cases that lack gross lesions.…”

“…The spirochetes were observed invading the crypt epithelium, particularly the goblet cells, causing cell degeneration, necrosis, and inflammation and initiating regenerative epithelial hyperplasia resulting in crypt elongation similar to mucosal and cryptal changes described for experimental swine dysentery. 1,14,20 Evidence of spirochetal invasion of the crypt epithelium has been observed in experimental B. pilosicoli infection 37 in pigs, but not as commonly as it has been reported in natural infections. 17,18,32 In previous challenge studies, B. pilosicoli-associated colitis has histologically been observed in 25 (4/12) and 83% (15/ 18 and 5/6) of the pigs.…”

“…7,11,29,36,41 Results of this study demonstrate that oral inoculation of growing pigs with a Danish isolate of B. pilosicoli can induce clinical signs and macroscopic changes similar to those observed in naturally occurring infection and further confirm the pathogenicity of B. pilosicoli as shown in a few previous experimental studies from the UK, Australia, and the USA. 7,35,36,37,39 Thus, detection of the spirochete in situ or by culture from cases of naturally occurring porcine colitis is likely to be significant, particularly in the absence of other intestinal pathogens.…”

“…The incubation period of between 9 and 24 days in the clinically affected animals was longer than that reported previously (3-9 days). 7,35,37 Challenging 5week-old pigs with an Australian isolate of porcine B. pilosicoli, Trott et al 41 observed diarrhea developing on the second postinoculation day in two of 12 animals followed by diarrhea in another two animals on postinoculation days 8 and 10. When necropsied on postinoculation day 11, moderate microscopic changes were observed only in the four pigs that developed diarrhea.…”

“…4,12 The genus Serpulina (S. hyodysenteriae, S. pilosicoli, and S. innocens) has recently been unified with the genus Brachyspira. 30 Experimentally, spirochetal infection with colitis and diarrhea has hitherto only been induced in pigs after oral inoculation of B. pilosicoli 35,37,39 and a WBHIS classified as Brachyspira (formerly Serpulina) innocens. 3 Microscopically, the infection is characterized by a variable increase in the number of mononuclear cells and neutrocytes in the colonic mucosa followed by slight edema.…”