title: Evaluation of the non-temperature-sensitive field clonal isolates of the Mycoplasma synoviae vaccine strain MS-H.
abstract: The live attenuated temperature-sensitive (ts+) Mycoplasma synovia (MS) strain, MS-H, is used as a vaccine in a number of countries to control virulent MS infection in commercial chicken flocks. Nine out of 50 isolates made from flocks vaccinated with MS-H were found to have lost the ts+ phenotype of the original vaccine strain. In order to examine the influence of the ts- phenotype on virulence of the isolates, four of the ts- isolates, the MS-H vaccine, and the vaccine parent strain 86079/7NS were administered by aerosol in conjunction with infectious bronchitis virus to 3-wk-old specific-pathogen-free chickens. The four ts- clones induced only minimal air sac lesions that were not different in severity from those caused by MS-H vaccine; however, the vaccine parent strain 86079/7NS caused air sac lesions that were significantly greater than those of MS-H and all ts- clones. The vaccine parent strain 86079/7NS and two of the ts- clones were recovered from the air sacs of the respectively infected chickens whereas the MS-H vaccine and two other ts- clones were not. Three of the ts- isolates caused increased tracheal mucosal thicknesses that were significantly greater than those from birds inoculated with MS-H, and one caused increased tracheal mucosal thicknesses that were significantly less than those from birds inoculated with 86079/7NS. In conclusion, unlike the MS-H vaccine, the MS-H ts- clones were associated with minor changes in tracheal mucosa; however, unlike the vaccine parent strain, they did not induce lesions in the air sacs. These results suggest that factors other than ts+ phenotype are involved in the attenuation of the MS-H vaccine.
authors.affiliation: School of Veterinary Science, The University of Melbourne, Werribee, Victoria, 3030, Australia.
authors.forename: Amir H
authors.initials: AH
authors.lastname: Noormohammadi
authors.forename: Jillian F
authors.initials: JF
authors.lastname: Jones
authors.forename: Karl E
authors.initials: KE
authors.lastname: Harrigan
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Whithear
mesh_terms: D000400:Air Sacs / Q000382:microbiology / Q000473:pathology; D000818:Animals; D001428:Bacterial Vaccines / Q000235:genetics*; D002645:Chickens / Q000276:immunology / Q000382:microbiology*; D009092:Mucous Membrane / Q000382:microbiology / Q000473:pathology; D009154:Mutation; D009174:Mycoplasma / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity*; D010641:Phenotype; D013047:Specific Pathogen-Free Organisms; D013696:Temperature; D014132:Trachea / Q000382:microbiology / Q000473:pathology; D014613:Vaccines, Attenuated / Q000235:genetics*; D014774:Virulence
chemical_list: D001428:Bacterial Vaccines; D014613:Vaccines, Attenuated