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

Protective Efficacy of Decreasing Antigen Doses of a Chlamydia abortus Subcellular Vaccine Against Ovine Enzootic Abortion in a Pregnant Sheep Challenge Model

BACKGROUND/OBJECTIVE

Chlamydia abortus, the cause of ovine enzootic abortion, is a zoonotic bacterial pathogen and one of the most infectious causes of foetal death in sheep worldwide. Although the disease can be controlled using commercial inactivated and live whole-organism vaccines, there are issues with both, particularly concerning efficacy and safety. Recently, we have described the development of a new COMC (chlamydial outer membrane complex) vaccine based on a detergent-extracted outer membrane protein preparation of the pathogen, which can be delivered in a single inoculation and is both efficacious and safe.

METHODS

In this study, we have evaluated the COMC vaccine further in a dose-response titration of the chlamydial antigen content of the vaccine (from 20 to 2.5 µg in seven experimental groups) using an established pregnant sheep challenge model.

RESULTS

No obvious dose-response relationship was observed across the groups, with a single abortion event occurring in four of the groups and three in the lowest dose group (2.5 µg). No abortions occurred in the 15 and 10 µg groups. The abortion rates (0-14%) were significantly below that of the challenge control group (33%). A similar reduction in bacterial shedding of infectious organisms following parturition was observed in the vaccinated groups compared to the challenge control group, which is important in terms of reducing potential transmission to naive animals.

CONCLUSIONS

The results show that a dose of 10 µg antigen in the vaccine will be optimal in terms of maximising efficacy, reducing shedding at parturition, and ensuring it is cost-effective to produce for commercial manufacture.

EAVLD 2024 - 7th Congress of the European Association of Veterinary Laboratory Diagnosticians

This abstract book contains the abstracts presented at the 7th Congress of the European Association of Veterinary Laboratory Diagnosticians.

Chlamydiosis in Animals

The Chlamydiaceae family consists of Gram-negative, obligate intracellular bacteria that replicate within the cells of a diverse range of hosts. These hosts include domesticated animals such as cats, dogs, and livestock, as well as wildlife like koalas and birds, exotic species such as reptiles and amphibians, and humans. Chlamydial infection can result in various clinical signs, including respiratory diseases, reproductive failures, ocular pathologies, and enteritis, though the infected organism may remain asymptomatic. In recent years, chlamydial nomenclature has undergone several revisions due to the wide range of hosts, the frequent discovery of novel strains, and the reclassification of existing ones. Given this and the clinical significance of these infections, ranging from asymptomatic to fatal, an updated review is essential. This article outlines key characteristics of Chlamydia species and provides an updated overview of their nomenclature, offering a concise reference for future research on chlamydial diseases.

Evaluation of the Protective Efficacy of Different Doses of a Chlamydia abortus Subcellular Vaccine in a Pregnant Sheep Challenge Model for Ovine Enzootic Abortion

Chlamydia abortus causes the disease ovine enzootic abortion, which is one of the most infectious causes of foetal death in small ruminants worldwide. While the disease can be controlled using live and inactivated commercial vaccines, there is scope for improvements in safety for both sheep and human handlers of the vaccines. We have previously reported the development of a new prototype vaccine based on a detergent-extracted outer membrane protein preparation of C. abortus that was determined to be more efficacious and safer than the commercial vaccines when administered in two inoculations three weeks apart. In this new study, we have developed this vaccine further by comparing its efficacy when delivered in one or two (1 × 20 µg and 2 × 10 µg) doses, as well as also comparing the effect of reducing the antigen content of the vaccine by 50% (2 × 5 µg and 1 × 10 µg). All vaccine formulations performed well in comparison to the unvaccinated challenge control group, with no significant differences observed between vaccine groups, demonstrating that the vaccine can be administered as a single inoculation and at a lower dose without compromising efficacy. Future studies should focus on further defining the optimal antigen dose to increase the commercial viability of the vaccine.

Surface Display of Cholera Toxin B Subunit Recombinant Escherichia coli Ghosts Further Enhances Resistance to Chlamydia abortus Infection in Mice

Chlamydia abortus (C. abortus) is an important zoonotic pathogen that seriously endangers the development of animal husbandry. Vaccination is the most effective approach to preventing C. abortus infection. We previously reported a recombinant Escherichia coli ghost (rECG)-based C. abortus vaccine that demonstrated outstanding protective efficacy. In this study, we further attempted to fuse the cholera toxin B subunit (CTB), a widely studied potent mucosal immune adjuvant, with macrophage infectivity potentiator (MIP), a candidate antigen of C. abortus, on the surface of the rECG and explore its protective effect against C. abortus infection. The MIP fusion protein was highly expressed in the rECGs, and the CTB-modified rECGs significantly induced the activation of mouse bone marrow-derived dendritic cells in vitro. Intranasal immunization with rECGs induced a Th1-biased cellular immune response. Compared to the rECGs without CTB, the CTB-modified rECGs induced higher concentrations of IgA in the serum and vaginal wash solution. Moreover, in a mouse infection model, the CTB-modified rECGs significantly improved the clearance efficiency of C. abortus and reduced the pathological damage to the uterus. This study demonstrates that incorporating CTB into rECGs significantly enhances the immunogenic potential of the rECG vaccine and can significantly enhance its protective efficacy against a C. abortus challenge.

Design and characterization of a multi-epitope vaccine targeting Chlamydia abortus using immunoinformatics approach

Chlamydiosis is a widespread ailment affecting humans, livestock, and wildlife, caused by C. abortus, a member of the Chlamydia genus. This disease leads to reproductive disorders in bovines and poses a zoonotic risk, resulting in adverse outcomes such as abortion, stillbirths, weak offspring, endometritis, repeat breeding, and perinatal mortality. However, current chlamydiosis vaccines have limitations in terms of safety, efficacy, and stability, necessitating the development of effective and safe alternatives. In this study, our objective was to design a multi-epitope vaccine (MEV) targeting all strains of C. abortus using bioinformatics and immunoinformatics approaches. We identified highly antigenic and non-allergic proteins (yidC, yajC, secY, CAB503, and CAB746) using VaxiJen and AlgPred tools. Physicochemical analyses and secondary structure predictions confirmed protein stability through ProtParam and SOPMA methods. Furthermore, we employed IEDB-AR, NETMHCpan, and ToxinPred2 tools to predict cytotoxic T lymphocyte (CTL), helper T lymphocyte (HTL), and B-cell epitopes, resulting in the identification of conserved epitopes for further analysis. The MEV construct, consisting of 545 amino acids, incorporated the adjuvant Beta defensin-3, along with 9 CTL epitopes and 21 HTL epitopes linked by EAAAK, KK, and AAY linkers. We assessed the safety and immunogenicity of the vaccine through comprehensive evaluations of antigenicity, toxicity, allergenicity, and physicochemical properties. Structural stability and quality were examined using 3D modeling via the ab initio approach with the Robetta platform. Molecular docking analysis explored the compatibility of the MEV with Toll-like receptor 9 (TLR9) using ClusPro, while molecular dynamics simulation with the DESMOND Maestro software predicted the stability and flexibility of the docked complex. Despite promising in silico findings, further wet lab investigations are crucial to validate the safety and efficacy of the MEV. Successful development and validation of this MEV hold significant potential in combatting chlamydiosis in both animal and human populations.Communicated by Ramaswamy H. Sarma.

Inactivated Flagellin-Containing Vaccine Efficacy against Ovine Enzootic Abortion

Chlamydia abortus is the etiological agent of abortion and fetal loss in sheep, goats and bovine cattle in many countries. Even though commercially available vaccines can reduce the incidence in sheep, the development of new, safe, and effective vaccines remains high on the agenda. In this study, an evaluation was made of the efficacy of a vaccine candidate, an inactivated antigen based on the extract of outer membrane proteins of a C. abortus strain known as Chlamydia VNITIBP-21, in combination with recombinant flagellin as an adjuvant. Pregnant sheep (n = 43) were divided into three groups: an experimental vaccinated group, a control infected group and a control non-infected group. The sheep were vaccinated twice, with an interval of 3 weeks, then infected with the homologous virulent strain of Chlamydia abortus on pregnancy day 75. The vaccine candidate reduced C. abortus shedding in vaginal swabs considerably, in comparison with the control group. In addition, ewes in the experimental group experienced no abortions, while those in the control group experienced instances of abortion, as well as births of weak and nonviable lambs. The findings show that the vaccine candidate proved itself to be promising in combatting the agent of ovine abortion and fetal loss.

Seroprevalence and Risk Factors Associated with Chlamydia abortus Infection in Sheep and Goats in North-Western Italy

Chlamydia abortus, although poorly recognized as a human pathogen, is a zoonotic microorganism that can cause many different symptoms in humans, including subclinical infection and fatal illnesses in pregnant women. C. abortus is one of the most common causes of ovine and caprine infectious abortion worldwide, known as the causative agent of the enzootic abortion of ewes (EAE) or ovine enzootic abortion (OEA). To estimate C. abortus seroprevalence and the risk factors related to C. abortus in small ruminants, the sera from 3045 animals (both sheep and goat) belonging to 202 herds were tested and a questionnaire investigating flock management was administered. At the herd level, the true seroprevalence was 56.6% (CI95%: 46.9-66.3%), at sheep-farm and goat-farm level, the true seroprevalence was 71.4% (CI95%: 54.6-88.3%) and 44.8% (CI95%: 41.3-57.0%), respectively. The true seroprevalence was significantly higher among the sheep than the goats. The logistic regression model identified four factors associated with Chlamydia seropositivity: flock size (i.e., farms with >50 heads), contact with cattle, introduction of animals, and Coxiella seropositivity. The study evidenced a high seroprevalence of Chlamydia abortus in small ruminant farms in the Piedmont region. Considering its zoonotic potential and the health consequences in humans, communication to farmers on the importance of vaccination, as well as the sensibilization of farm vets, seem to be strategical.

A novel cold-chain free VCG-based subunit vaccine protects against Chlamydia abortus-induced neonatal mortality in a pregnant mouse model

Chlamydia abortus (Cab) causes spontaneous abortion and neonatal mortality in infected ruminants and pregnant women. Most Cab infections are asymptomatic, although they can be treated with antibiotics, signifying that control of these infections may require alternative strategies, including the use of effective vaccines. However, the limitations imposed by live attenuated and inactivated vaccines further suggest that employment of subunit vaccines may need to be considered. The efficacy of a newly generated Vibrio cholerae ghost (rVCG)-based subunit vaccine harboring the N-terminal portion of the Cab Pmp18D protein (rVCG-Pmp18.3) in preventing Cab-induced abortion or neonatal mortality was evaluated in pregnant mice. Mice were intranasally (IN) immunized and boosted twice, 2 weeks apart with the vaccine, and immunized and unimmunized mice were caged with males 4 weeks postimmunization. The mice were then infected either IN or transcervically (TC) 10 days after pregnancy, and the fertility rate was determined 7 days postpartum. Eight days after delivery, the mice were sacrificed, and Cab infectivity in the lungs and spleens was evaluated by culturing tissue homogenates in tissue culture. Our results demonstrated that the vaccine induced immune effectors that mediated complete clearance of infection in the lungs and significantly reduced Cab infectivity in the spleen following IN immunization. Vaccine immunization also afforded protection against Cab-induced upper genital tract pathology (uterine dilation). Furthermore, while there was no incidence of abortion in both immunized and unimmunized mice, immunized mice were completely protected against neonatal mortality compared to unimmunized infected controls, which lost a significant percentage of their litter 7 days postpartum. Our results establish the capability of the rVCG-Pmp18.3 vaccine to prevent infection in the lungs (mucosal) and spleen (systemic) and protect mice from Cab-induced tubal pathologies and neonatal mortality, a hallmark of Cab infection in ruminants. To advance the commercial potential of this vaccine, future studies will optimize the antigen dose and the number of vaccine doses required for protection of ruminants.

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

Coxiella burnetii is an intracellular bacterium causing human Q fever and reproductive disorders in domestic ruminants. We analyzed the occurrence of C. burnetii and co-infections with six other major pathogens causing abortion in sheep (1242 cases) and goat (371 cases) flocks from Spain and Portugal. After real-time PCR detection, co-infections were established by principal component and cluster analysis that grouped cases based on the joint presence/absence of several microorganisms. C. burnetii and Chlamydia abortus were the most common abortifacient agents with approximately 75% of cases from both hosts testing positive, followed by Toxoplasma gondii, Campylobacter sp., Salmonella enterica, border disease virus and Neospora caninum. C. burnetii was significantly more common than C. abortus in goat abortions (p < 0.001). Co-infections with at least two pathogens were found in more than 66% cases of ovine abortions and 36% cases of caprine abortions testing positive for C. burnetii, mostly including mixed infections with only C. abortus. These findings indicate that both pathogens are the most significant ones to be readily prevented by vaccination in this geographical area. Biosecurity and biocontainment measures are also steadfastly recommended to prevent both the economic losses and public health risks associated with most of these abortifacient agents.

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

Environmental transmission of Chlamydia abortus as a result of enzootic disease or disease outbreaks and the threats posed by this pathogen has been previously reported, however a state-of-the-science review of these reports and the identification of future research priorities in this area is still lacking. This study provides an overview of the current knowledge of host–pathogen–environment interactions, addressing public health risks and identifying critical questions and research gaps. We performed a systematic PubMed and Web of Science search for publications related to Chlamydia abortus in the past four decades, and we reviewed and combined the evidence critically discussing and commenting the results. A total of 182 studies, 5 chapters of specific books and the “OIE terrestrial manual” were included in this review. There were substantial variations between the studies in topic addressed and experimental design. Overall, the literature largely supports the crucial role played by environmental exposure on the acquisition of zoonotic disease caused by Chlamydia abortus. We also identify the paucity of information related to interspecies transmission and pathogen adaptation in relation to environmental dissemination and zoonotic risk. This analysis further highlights the need for additional research given that environmental transmission represents a serious risk not only to susceptible patients (pregnant women and immunocompromised individuals), but also for other species including wildlife.