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.
Highlights
Ovine enzootic abortion (OEA), caused by Chlamydia abortus, an obligate intracellular Gram-negative bacterium belonging to the Chlamydiaceae family, is an economically important disease in many countries
Reproductive Incidences Related to C. abortus and Shedding After Challenge Thirteen days after challenge, a vaccinated animal suffered a traumatic abortion, as this animal was accidentally caught at the trough for several hours
The present study has shown that INMEVA, a recently commercialized inactivated vaccine developed against OEA, is effective in promoting a significant decrease in the number of reproductive failures and minimizing chlamydial shedding at delivery
Summary
Ovine enzootic abortion (OEA), caused by Chlamydia abortus, an obligate intracellular Gram-negative bacterium belonging to the Chlamydiaceae family, is an economically important disease in many countries. The disease spreads in infected flocks, at lambing time when ewes shed large amounts of C. abortus via vaginal discharges at abortion or parturition (placenta and fetuses). This infection will provide an effective immune response in OEA-affected ewes, protecting from future C. abortus-induced abortions. They could, shed the bacteria in subsequent estrus or parturition, maintaining the risk of infection in the flock [5]. After an infection of a naïve ewe it is believed that C. abortus may remains in a latent state in lymphoid tissue, controlled by cytokines like IFN-γ [7], and may not show clinical signs until the last weeks of the gestation, leading to potential reproductive failure. The reproductive failure rate in an endemically infected flock is around 10%, whereas in a newly infected naïve flock it is around 30%, up to 60% in goat herds [4]
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