Caspe, S.G., Palarea Albaladejo, J., Underwood, C., Livingstone, M., Wattegedera, S., Milne, E., Sargison, N.D., Chianini, F. and Longbottom, D.
||Chlamydia abortus infects livestock species worldwide and is the cause of enzootic abortion
of ewes (EAE). In Europe, control of the disease is achieved using a live vaccine based on C. abortus 1B
strain. Although the vaccine has been useful for controlling disease outbreaks, abortion events due to
the vaccine have been reported. Recently, placental pathology resulting from a vaccine type strain (vt)
infection has been reported and shown to be similar to that resulting from a natural wild-type (wt)
infection. The aim of this study was to extend these observations by comparing the distribution and
severity of the lesions, the composition of the predominating cell infiltrate, the amount of bacteria
present and the role of the blood supply in infection. A novel system for grading the histological and
pathological features present was developed and the resulting multi-parameter data were statistically
transformed for exploration and visualisation through a tailored principal component analysis
(PCA) to evaluate the difference between them. The analysis provided no evidence of meaningful
differences between vt and wt strains in terms of the measured pathological parameters. The study
also contributes a novel methodology for analysing the progression of infection in the placenta for
other abortifacient pathogens.