title: Assessing virulence of vaccine strains of Mycobacterium avium subspecies paratuberculosis in a calf model.
abstract: The purpose of this investigation was to characterise the virulence of two Mycobacterium avium subspecies paratuberculosis (M.a. paratuberculosis) vaccine strains and compare them with a recent virulent isolate in new born calves over a time course of 8 months post-inoculation. Paratuberculosis-free new born calves were inoculated orally with either a vaccine strain (2e or 316F) or a wild type strain (F13) of M.a. paratuberculosis. Blood and faecal samples were collected throughout the experiment to analyse immune responses to infection and assess faecal shedding of M.a. paratuberculosis. Tissue samples were taken at post-mortem for histological examination and bacteriological culture. Cell-mediated immune responses were measured using a Bovigam (CSL) interferon-gamma assay. At 20 weeks post-inoculation there was a significant increase in the cell-mediated immune responses in calves infected with the wild type strain relative to the two vaccine strains. Acid fast bacteria were detected in the faeces of calves in all three groups between 4 and 8 weeks post-inoculation. Histopathology was unrewarding in all three groups. M.a. paratuberculosis was recovered only from tissues of calves inoculated with the wild type strain. Therefore, it appeared that the vaccine strains used in this study had reduced virulence. Identifying the genes responsible for pathogenesis observed in the wild type isolate and reduced or inactive in these vaccine isolates may offer a valuable resource for improving our knowledge of pathogenesis and permit the development of improved diagnostic reagents and vaccines for the control of M.a. paratuberculosis in livestock.
authors.affiliation: Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Midlothian EH26 0PZ, UK. Craig.Watkins@moredun.ac.uk
authors.forename: Craig
authors.initials: C
authors.lastname: Watkins
authors.forename: Alex
authors.initials: A
authors.lastname: Schock
authors.forename: Linda
authors.initials: L
authors.lastname: May
authors.forename: Susan
authors.initials: S
authors.lastname: Denham
authors.forename: Jill
authors.initials: J
authors.lastname: Sales
authors.forename: Louise
authors.initials: L
authors.lastname: Welch
authors.forename: J Michael
authors.initials: JM
authors.lastname: Sharp
authors.forename: Karen
authors.initials: K
authors.lastname: Stevenson
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology; D001428:Bacterial Vaccines / Q000276:immunology*; D002417:Cattle; D002418:Cattle Diseases / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control*; D005243:Feces / Q000382:microbiology; D007111:Immunity, Cellular / Q000276:immunology; D007371:Interferon-gamma / Q000097:blood; D016927:Mycobacterium avium subsp. paratuberculosis / Q000276:immunology* / Q000472:pathogenicity; D010283:Paratuberculosis / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D014774:Virulence / Q000276:immunology
chemical_list: D000907:Antibodies, Bacterial; D001428:Bacterial Vaccines; D007371:Interferon-gamma