Publications – Swine in Minnesota

A roadmap to Food Animal Careers at the UMN CVM

Today we are sharing a publication in the Journal of Veterinary Medical Education from Dr. Perle Boyer (Zhitnitskiy) presenting a new online tool for students enrolled at the University of Minnesota, College of Veterinary Medicine to choose selective course tailored to their career path.

Swine conjunctivitis outbreaks associated with Mycoplasma hyorhinis

New PhD-graduate Talita Resende described in this open-access publication from the Journal of Veterinary Diagnostic Investigation conjunctivitis cases in 3 wean-to-finish barns. After extensive investigation, Mycoplasma hyorhinis was identified as a causative agent.

Can Streptococcus suis genotype predict its pathogenicity?

PhD candidate April Estrada, working with Drs. Gebhart and Marthaler published an open-access article on Streptococcus suis in the Journal of Clinical Microbiology. Streptococcus suis is an older pathogen but its prevalence as well as its virulence have been rising lately. This study investigates if categorizing isolates into serotypes and genotypes could help predict the severity of the disease on the farm.

Exposing gilts to Mycoplasma hyopneumoniae using a herd-specific lung homogenate

The last issue of the Journal of Swine Health and Production featured a practice tip written by Dr. Rebecca Robbins from Seaboard Foods, in collaboration with Dr. Maria Pieters and the MycoLab. This publication has for objective to share a safe, reliable and herd-specific technique to expose gilts to Mycoplasma hyopneumoniae.

Subclinical colitis associated with moderately hemolytic Brachyspira strains

Our latest addition to the swine group at the University of Minnesota College of Veterinary Medicine is Dr. Matheus Costa whose research interests are in pathogen virulence mechanisms and more specifically swine dysentery and streptococcal meningitis.

In this latest publication in the Journal of Swine Health and Production, Dr. Costa and his former collaborators from the University of Saskatchewan introduced less-known Brachyspira strains and what their consequences are on the clinical level for the pig.

Summary

Objective: Microbiological and virulence characterization of 2 moderately hemolytic Brachyspira strains.

Materials and methods: Clinical isolates were obtained from diarrheic (3603-F2) and healthy (G79) pigs. Phenotypic characterization included assessment of hemolytic activity on blood agar and biochemical profiling. Genotyping was performed by sequencing the nicotinamide adenine dinucleotide oxidase (nox) gene, whole genome sequencing, and comparison to relevant Brachyspira. Pig inoculation included 4 treatment groups in 2 challenge experiments: negative control (sterile broth media; n = 12), positive control (Brachyspira hampsonii genomovar 2 strain 30446; n = 18), and 3603-F2 (n = 12) or G79 (n = 12). Fecal scoring and rectal swabbing for culture were performed daily. Animals were euthanized following onset of mucohemorrhagic diarrhea or between 21 and 28 days post inoculation (dpi). Gross and microscopic pathology were assessed. Terminal colon samples were used to characterize post-infection mucosal ion secretion.

Hematoxylin and eosin (HE; bar = 200 µm) and Warthin-Faulkner (WF; bar = 20 µm) stained porcine colon from the challenge experiments. A) Negative control pig with normal colon, HE stain. B) Negative control pig with no spirochetes, WF stain. C) Positive control (30446) pig with moderate to severe muconecrotic colitis, HE stain. D) Positive control (30446) pig with many spirochetes in glands (arrows), WF stain. E) Strain 3046-F2 inoculated pig with moderately increased mucus, minimal necrosis and mild colitis, HE stain. F) Strain 3046-F2 inoculated pig with small numbers of spirochetes in glands (arrows), WF stain. G) Strain G79 inoculated pig with a mild mucus increase and minimal colitis, HE stain. H) Strain G79 inoculated pig with occasional glands containing many spirochetes (arrows), WF stain.

Results: Both strains were moderately hemolytic. Whole genome and nox sequencing identified 3603-F2 as Brachyspira murdochii and G79 as a novel strain. Both challenge trials revealed intestinal colonization, but no mucohemorrhagic diarrhea. Sporadic watery diarrhea was induced by 3603-F2 associated with a pattern of microscopic lesions similar to pigs with swine dysentery (positive controls). No diarrhea was observed in G79 inoculated pigs, but microscopic lesions were more severe than in controls. Both strains induced greater colonic anion secretory potential than negative controls 21 dpi.

Implications: Allegedly avirulent Brachyspira species most closely related to B murdochii can be associated with subclinical colitis and may be a concern for grow-finish pigs.