Abortion storm induced by the live C. abortus vaccine 1B strain in a vaccinated sheep flock, mimicking a natural wild-type infection

Vet Microbiol. 2018 Nov;225:31-33. doi: 10.1016/j.vetmic.2018.09.012. Epub 2018 Sep 18.


Chlamydia abortus is responsible for enzootic abortion (known as ovine enzootic abortion (OEA) and enzootic abortion of ewes (EAE)) in both sheep and goats and has major economic implications for the farming industry worldwide. A virulence-attenuated mutant strain of C. abortus (strain 1B) is currently commercially available as a live attenuated vaccine for immunization of sheep and goats in several European countries. Following an abortion storm in a French flock of 200 ewes that occurred two years after vaccination of 36 replacement ewes with the commercial 1B vaccine strain, the vaginal swabs of 3 vaccinated and 7 unvaccinated aborted ewes and 12 of the 13 dead fetuses were found to be positive for C. abortus by real-time PCR. Genotyping of the samples, using vaccine-specific SNP markers, identified all as positive for the vaccine-type strain. The recent vaccination of this flock with the attenuated commercial vaccine strain, the large number of abortion cases observed in ewes irrespective of vaccination status, the high C. abortus load detected in vaginal swabs or abortion tissues and the identification of specific vaccine-type markers in these samples strongly suggest that the 1B strain has been transmitted from vaccinated to naïve animals, thus mimicking a natural wild-type infection.

Keywords: Abortion; Chlamydiosis; Sheep; Vaccine.

MeSH terms

  • Aborted Fetus / microbiology*
  • Abortion, Veterinary / epidemiology*
  • Abortion, Veterinary / microbiology
  • Abortion, Veterinary / prevention & control
  • Animals
  • Bacterial Vaccines / administration & dosage
  • Bacterial Vaccines / adverse effects*
  • Chlamydophila / genetics
  • Chlamydophila Infections / microbiology
  • Chlamydophila Infections / mortality
  • Chlamydophila Infections / prevention & control
  • Chlamydophila Infections / veterinary*
  • Female
  • France / epidemiology
  • Mutation
  • Polymerase Chain Reaction
  • Pregnancy
  • Real-Time Polymerase Chain Reaction
  • Sheep / immunology
  • Sheep Diseases / immunology
  • Sheep Diseases / prevention & control
  • Vaccination / adverse effects*
  • Vaccines, Attenuated / administration & dosage
  • Vaccines, Attenuated / adverse effects
  • Vaccines, Attenuated / immunology
  • Vagina / microbiology
  • Whole Genome Sequencing


  • Bacterial Vaccines
  • Vaccines, Attenuated