Efficacy of Two Chlamydia abortus Subcellular Vaccines in a Pregnant Ewe Challenge Model for Ovine Enzootic Abortion.

Morag Livingstone,Cecilia Corbett,Sean Ranjan Wattegedera,David Longbottom,Kevin Aitchison,Gary Entrican,Javier Palarea-Albaladejo,Mara Silvia Rocchi,Nicholas Wheelhouse,Kim Wilson,Michelle Sait,Francesca Chianini

doi:10.3390/vaccines9080898

Morag Livingstone, Cecilia Corbett + Show 10 more

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https://doi.org/10.3390/vaccines9080898

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Abstract

Chlamydia abortus, the aetiological agent of enzootic abortion of ewes, is a major cause of reproductive loss in small ruminants worldwide, accounting for significant economic losses to the farming industry. Disease can be managed through the use of commercial inactivated or live whole organism-based vaccines, although both have limitations particularly in terms of efficacy, safety and disease-associated outbreaks. Here we report a comparison of two experimental vaccines (chlamydial outer membrane complex (COMC) and octyl glucoside (OG)-COMC) based on detergent extracted outer membrane preparations of C. abortus and delivered as prime-boost immunisations, with the commercial live vaccine Cevac® Chlamydia in a pregnant sheep challenge model. No abortions occurred in either experimental vaccine group, while a single abortion occurred in the commercial vaccine group. Bacterial shedding, as a measure of potential risk of transmission of infection to naïve animals, was lowest in the COMC vaccinated group, with reductions of 87.5%, 86.4% and 74% observed for the COMC, OG-COMC and live commercial vaccine groups, respectively, compared to the unvaccinated challenge control group. The results show that the COMC vaccine performed the best and is a safer efficacious alternative to the commercial vaccines. However, to improve commercial viability, future studies should optimise the antigen dose and number of inoculations required.

Highlights

Introduction conditions of the Creative CommonsEnzootic abortion of ewes (EAE), known as ovine enzootic abortion (OEA) or ovine chlamydial abortion, is caused by the obligate intracellular, Gram-negative bacteriumChlamydia abortus
The aim of this study was to investigate the efficacy of two subcellular vaccines based on detergent-extracted whole organism C. abortus outer membrane preparations in pregnant ewes experimentally challenged with C. abortus, with a view to developing a safer and more stable alternative to the commercial live vaccines
Abortions were judged to be due to C. abortus if chlamydial organisms and/or DNA could be detected by modified Ziehl–Neelsen (mZN), quantitative real-time polymerase chain reaction (qPCR) or following pathological investigations

Summary

Introduction

Introduction conditions of the Creative CommonsEnzootic abortion of ewes (EAE), known as ovine enzootic abortion (OEA) or ovine chlamydial abortion, is caused by the obligate intracellular, Gram-negative bacteriumChlamydia abortus. New Zealand and Australia, and is one of the most common infectious causes of abortion worldwide [6]. C. abortus is a zoonotic pathogen and as well as leading to abortion or still-birth of the unborn child, it has the potential to cause serious pathology in pregnant women and is a potential significant health risk for those in contact with sheep, especially at lambing [8,9,10,11,12]. Animals can shed high loads of C. abortus in products of abortion, vaginal excretions and on the coats of live and dead lambs, all of which act as the main sources of transmission to naïve sheep [4,13]

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