0
The present study evaluated the susceptibility of growing pigs to the new potentially virulent Brachyspira species (“B hampsonii”) compared with B murdochii and B hyodysenteriae infection in order to establish an experimental infection model for testing prospective methods to prevent and control the disease.
Twenty 5-week-old pigs were obtained from a herd without history of brachyspiral colitis. The animals were randomly divided into five groups (n = 4/group): negative control; B murdochii; “B hampsonii” clade I; “B hampsonii” clade II and B. hyodysenteriae. Feces were individually collected directly from the rectum for bacterial isolation. The pigs were maintained for acclimatization prior to experimental inoculation for one week and were fed during the study with oat-based, non-medicated, age- balanced diet. Each animal was intragastrically infected during three consecutive days with 100 ml/day of blood-agar plates or broth containing approximately 109 Brachyspira species according to their respective groups and the control group with sterile plates and broth. The animals were monitored daily during the study regarding attitude, appetite and evidence of mucous and/or bloody diarrhea based on the fecal consistency. All animals were weighed on day -7, 0, 7, 14 and 21 post-infection (PI) to evaluate the average of daily gain. On these days fecal samples were collected individually for mi crobial culture. One animal from each group was necropsied on days 7 and 14 and two animals on day 21 PI. The animals were macroscopically evaluated for the presence of lesions compatible with brachyspiral colitis. Samples of jejunum, ileum, cecum and colon were collected and processed for histopathology and immunohistochemistry evaluation. Fresh samples of cecum and colon were also collected for bacterial isolation.
Prior the experimental inoculation, weakly hemolytic colonies genetically identified as B murdochii were isolated from three groups (B. murdochii; “B hampsonii” clade I; “B hampsonii” clade II), but it were not associated with clinical diarrhea. All the experimental groups had a B murdochii isolate from at least one time point during the study. Based on the nox gene sequences, these B murdochii isolates were genetically different from the isolate used in the study. These results confirmed the lack of cross-contamination among the experimental groups. Intermittent watery and/or mucous diarrhea was first observed in the “B hampsonii” clade I group from day 5 PI and it was followed by the B murdochii and “B hampsonii” clade II groups until day 14 PI. Bloody diarrhea was not detected in any experimental group. Macroscopic lesions characterized by mild hyperemia were observed in the colonic mucosa of pigs infected with B murdochii on days 7 and 14 PI. On the same days PI, severe hyperemia and marked presence of mucous contents in the colonic mucosa associated with variable degrees of mucosal thickening were observed in pigs infected with “B hampsonii” (clades I and II). Histological lesions compatible with brachyspiral colitis characterized by multifocal mixed inflammatory infiltration (lymphoplasmacytic and neutrophilic) and sporadic multifocal hemorrhage in the lamina propria were observed in all infected groups (B murdochii; “B hampsonii” clade I; “B hampsonii” clade II and B. hyodysenteriae). Marked presence of Brachypira sp. organisms identified by immunohistochemistry within the histological changes confirmed the presence of the etiologic agent in the lesions. On days 7, 14 and 21 PI strongly hemolytic colonies genetically characterized as “B hampsonii” clade I, II and B hyodysenteriae were exclusively isolated from their respective group. The B murdochii strain used in the study was isolated on days 14 and 21 PI. This strain was designated as “B.MUR” in order to differentiate from the strain commonly isolated in all experimental groups.
The present study successfully demonstrated the experimental reproduction of the brachyspiral colitis caused by “B hampsonii” clade I and II with peak of the infection approximately 14 days PI. This experimental model may be valuable for evaluating the efficacy of different interventions to prevent and control this emerging pathogen.
Fabio A. Vannucci, Albert Rovira, Aschalew Z. Bekele, Brianna Larson, Connie J. Gebhart. Experimental reproduction of brachyspiral colitis in pigs infected with Brachyspira hampsonii. 44th Annual Meeting Proceedings, AASV, 2013.