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

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.

Recent advances and public health implications for environmental exposure to Chlamydia abortus: from enzootic to zoonotic disease

“…However, none of these vaccines have yet yielded satisfactory results, lacking effectiveness in protection greater or equal to the live attenuated vaccines currently used [ 68 ]. Conversely, vaccine preparations based on C. abortus outer membrane complexes (COMC) have shown more promise in several animal models [ 69 – 72 ] as well as in the natural sheep host [ 73 ] probably due to the preservation of the native conformation of the different components.…”

Inactivated Flagellin-Containing Vaccine Efficacy against Ovine Enzootic Abortion

“…Some countries use commercially available live attenuated vaccines (Enzovax, MSD Animal Health; Cevac Chlamydia, Ceva Animal Health) or inactivated vaccines (e.g., Mydiavac, Benchmark Animal Health). Vaccines of neither type can fully guarantee safety, as chlamydia shedding with birth has been detected, and there is no certainty that the protective immunity duration is estimated correctly [ 12 , 29 , 30 , 31 ].…”

Coxiella burnetii and Co-Infections with Other Major Pathogens Causing Abortion in Small Ruminant Flocks in the Iberian Peninsula

“…In addition to routine hygiene and disinfection of housing facilities, aborted ewes and those giving birth to dead full-term lambs should be isolated immediately, and aborted material and infected bedding removed and destroyed [ 4 ]. In Europe, vaccination against enzootic abortion has been achieved using inactivated whole organism-based vaccines or live attenuated vaccines, based on the 1B strain of C. abortus (Cevac Chlamydia ® , Ceva Animal Health, Barcelona, Spain; Enzovax ® , MSD Animal Health, Salamanca, Spain; Inmeva ® ; Laboratorios Hipra S.A., Amer, Spain) [ 88 ]. An inactivated vaccine, combining S. enterica and C. abortus (Inmeva ® Laboratorios Hipra S.A., Amer, Spain), has been shown to provide a 75% reduction in enzootic abortion rate and 55% reduction in the shedding of C. abortus [ 89 ].…”