Evaluation of the Efficacy of a New Commercially Available Inactivated Vaccine Against Ovine Enzootic Abortion

Abstract

Ovine enzootic abortion (OEA), caused by Chlamydia abortus , is an economically important disease in many countries. Inactivated vaccines have been used for many years as they induce immunity in sheep, although outbreaks of abortions have been described in vaccinated flocks. In addition, there is a commercially available live attenuated vaccine that provides good protective results. Recently however, reports question the attenuation of this vaccine and associate it with the appearance of outbreaks of OEA in vaccinated flocks. In the present study, a recently commercialized inactivated vaccine (INMEVA®; Laboratorios Hipra S.A., Amer, Spain) has been evaluated using mouse and sheep experimental models. In the mouse models (non-pregnant and pregnant models), the efficacy of INMEVA vaccine has been compared to an unvaccinated control group and to an experimental inactivated vaccine considered as a positive protection control (UMU vaccine). In the non- pregnant model, the UMU vaccine was more effective than the INMEVA vaccine regarding the impact on body weight or the presence of C. abortus in the liver, but both vaccinated groups (UMU and INMEVA) had significantly lower C. abortus in the liver compared to the control group. In the pregnant model in terms of reproductive failures, pups per mouse or the presence of C. abortus in the liver or uterus, no significant differences were found between both vaccines, inducing protection compared to the control group. In the ovine pregnant model, where INMEVA vaccine was compared only to an unvaccinated group, the results indicate that this new commercial vaccine is safe and provides a suitable level of protection against an experimental challenge with C. abortus . A 75% reduction in reproductive disorders, 55% reduction in animals with C. abortus shedding on day of parturition/abortion, and a significant reduction of the average amount of chlamydial shedding from parturition/abortion over the next 21 days was observed, in relation to the infected control group. The results suggest that this vaccine is adequate for the control and prevention of OEA; however, future studies are necessary to elucidate the type of protective immune response that it induces.

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

“…Specifically, two live attenuated vaccines are marketed throughout Europe: Enzovax® (MSD Animal Health) and Cevac Chlamydia® (Ceva Animal Health Ltd). In addition, Mydiavac® (Benchmarks Vaccines Ltd. UK) and INMEVA® (Laboratorios Hipra S.A.) [ 57 ], both killed vaccines, consisting of inactivated EBs or of their sub-constituents, are also available in the UK and mainland Europe. The live attenuated vaccines are both based on a live attenuated strain, called 1B, which was obtained by chemical mutagenesis of the wild-type strain AB7, making 1B temperature-sensitive and unable to grow at the temperature of 39.5 °C, which is the normal body temperature of sheep [ 58 ].…”

“…Despite the vaccines conferring a great protection against C. abortus and reducing the incidence of abortion, they have some drawbacks: production is expensive, operator infection after accidental injection during administration has been reported, conflicting evidences are outlined on reduction of shedding from ewes and, in some animals, presence of an infection indistinguishable from that seen with the wild-type microorganism, causing the development of placental lesions and abortion in the vaccinated flock [ 41 , 59 – 64 ]. On the other side, inactivated vaccines are able to reduce the incidence of abortions and the shedding of C. abortus at parturition, but they do not prevent shedding completely [ 57 ].…”

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

“…A recent study evaluating two recombinant antigens, macrophage infectivity potentiator (MIP) and chlamydial protease-like activity factor (CPAF), in pregnant sheep found that the separate administration of these antigens did not confer any protection following challenge, while a combination of both antigens resulted in a 50% reduction in abortion rate when compared to the unvaccinated challenge control group [27], suggesting that other antigens are required for protective efficacy. Another study evaluated a new commercial inactivated vaccine (INMEVA ® , Hipra UK and Ireland Ltd., Nottingham, UK) which achieved a 75% reduction in abortion rate and a 55% reduction in the shedding of organisms when compared to the challenge control group [14]. However, in this latter study there was no comparison to show how the vaccine compared to the current live commercial vaccines.…”

“…Management of the disease in sheep in Europe has been achieved through the use of inactivated whole organism-based vaccines [14][15][16][17] or live attenuated vaccines based on the 1B strain of C. abortus (Cevac ® Chlamydia, Ceva Animal Health; Enzovax ® , MSD Animal Health) [18,19]. However, both types of vaccines have limitations principally in terms of safety, stability, shedding of infectious organisms at parturition or in the duration of the protective immune response [1,20].…”

“…Research into developing new EAE vaccines has focussed on evaluating alternate inactivated formulations [14][15][16][17]26], on virulence-associated recombinant antigens [27][28][29] and on the major outer membrane protein (MOMP) [30,31], which is also the major immunodominant antigen of C. abortus, with mixed results. In general, experimental chlamydial vaccines based on denatured or non-native recombinant MOMP preparations have yielded inconsistent results and only partial protection [20,32,33], suggesting that protein conformation may be important.…”