title: Identification of the 1B vaccine strain of Chlamydia abortus in aborted placentas during the investigation of toxaemic and systemic disease in sheep.
abstract: METHODS
  One hundred and forty Cheviot and 100 Suffolk cross Mule primiparous 1-2-year-old ewes, from a flock of about 700 ewes, were vaccinated with an attenuated live 1B strain Chlamydia abortus vaccine about 4 weeks before ram introduction (September 2011). Between 08 March and 01 April 2012, 50 2-year-old ewes aborted and 29 of these died, despite antimicrobial and anti-inflammatory treatment and supportive care.
  
  
  RESULTS
  Seven fetuses and three placentae from five 2-year-old ewes were submitted for pathological investigation. The aborted fetuses showed stages of autolysis ranging from being moderately fresh to putrefaction. Unusual, large multifocal regions of thickened membranes, with a dull red granular surface and moderate amounts of grey-white surface exudate were seen on each of the placentae. Intracellular, magenta-staining, acid fast inclusions were identified in Ziehl Neelsen-stained placental smears. Immunohistochemistry for Chlamydia-specific lipopolysaccharide showed extensive positive labelling of the placental epithelia.
  
  
  RESULTS
  Molecular analyses of the aborted placentae demonstrated the presence of the 1B vaccine-type strain of C. abortus and absence of any wild-type field strain. The vaccine strain bacterial load of the placental tissue samples was consistent with there being an association between vaccination and abortion.
  
  
  METHODS
  Initial laboratory investigations resulted in a diagnosis of chlamydial abortion. Further investigations led to the identification of the 1B vaccine strain of C. abortus in material from all three of the submitted aborted placentae.
  
  
  CONCLUSIONS
  Timely knowledge and understanding of any potential problems caused by vaccination against C. abortus are prerequisites for sustainable control of chlamydial abortion. This report describes the investigation of an atypical abortion storm in sheep, and describes the identification of the 1B vaccine strain of C. abortus in products of abortion. The significance of this novel putative association between the vaccine strain of C. abortus and severe clinical disease is unknown. Aspects of the approach that is described are relevant to the investigation of all outbreaks of ovine abortion, irrespective of the diagnosis. Awareness of the changing role of C. abortus as a major global cause of abortion ought to reinforce the importance of monitoring of adequate biosecurity in those countries which are currently free from chlamydial abortion.
authors.affiliation: a Easter Bush Veterinary Centre , University of Edinburgh, Royal (Dick) School of Veterinary Studies , Roslin, Midlothian , EH25 9RG , UK.
authors.forename: N D
authors.initials: ND
authors.lastname: Sargison
authors.forename: I G R
authors.initials: IG
authors.lastname: Truyers
authors.forename: F E
authors.initials: FE
authors.lastname: Howie
authors.forename: J R
authors.initials: JR
authors.lastname: Thomson
authors.forename: A L
authors.initials: AL
authors.lastname: Cox
authors.forename: M
authors.initials: M
authors.lastname: Livingstone
authors.forename: D
authors.initials: D
authors.lastname: Longbottom
mesh_terms: D000034:Abortion, Veterinary / Q000382:microbiology*; D000818:Animals; D001428:Bacterial Vaccines / Q000276:immunology* / Q000382:microbiology; D002689:Chlamydia / Q000145:classification*; D002690:Chlamydia Infections / Q000517:prevention & control / Q000662:veterinary*; D005260:Female; D010920:Placenta / Q000382:microbiology*; D011247:Pregnancy; D012756:Sheep; D012757:Sheep Diseases / Q000382:microbiology; D014115:Toxemia / Q000382:microbiology / Q000662:veterinary*
chemical_list: D001428:Bacterial Vaccines
keywords: Chlamydia abortus; Sheep; abortion; vaccine