Evaluation of the Diagnostic Potential of Recombinant Coxiella burnetii Com1 in an ELISA for the Diagnosis of Q Fever in Sheep, Goats and Cattle

Development of a single-dose Q fever vaccine with an injectable nanoparticle-loaded hydrogel: effect of sustained co-delivery of antigen and adjuvant

Q fever is a zoonotic infectious disease caused by Coxiella burnetii, and there is currently no FDA-approved vaccine for human use. The whole-cell inactivated vaccine Q-VAX, which is only licensed in Australia, has a risk of causing severe adverse reactions, making subunit vaccines a good alternative. However, most subunit antigens are weak immunogens and require two or more immunizations to elicit an adequate level of immunity. We hypothesized that by combining a nanoparticle to co-deliver both a protein antigen and an adjuvant, together with a hydrogel depot for sustained-release kinetics, a single-administration of a nanoparticle-loaded hydrogel vaccine could elicit a strong and durable immune response. We synthesized and characterized a protein nanoparticle (CBU-CpG-E2) that co-delivered the immunodominant protein antigen CBU1910 (CBU) from C. burnetii and the adjuvant CpG1826 (CpG). For sustained release, we examined different mixtures of PLGA-PEG-PLGA (PPP) polymers and identified a PPP solution that was injectable at room temperature, formed a hydrogel at physiological temperature, and continuously released protein for 8 weeks in vivo. Single-dose vaccine formulations were administered to mice, and IgG, IgG1, and IgG2c levels were determined over time. The vaccine combining both the CBU-CpG-E2 nanoparticles and the PPP hydrogel elicited a stronger and more durable humoral immune response than the soluble bolus nanoparticle vaccines (without hydrogel) and the free antigen and free adjuvant-loaded hydrogel vaccines (without nanoparticles), and it yielded a balanced IgG2c/IgG1 response. This study demonstrates the potential advantages of using this modular PPP hydrogel/nanoparticle system to elicit improved immune responses against infectious pathogens.

Harmonisation of the diagnostic performances of serological ELISA tests for C. burnetii in ruminants in the absence of a gold standard: Optimal cut-offs and performances reassessment

None of the three ELISA tests currently available in Europe for the serological diagnosis of Coxiella burnetii (C. burnetii) infections in ruminants can be considered as a gold standard. The difference in their diagnostic performances (e.g., from 39 % to 87 % for sensitivity in sheep - Lurier et al. 2021) affects the agreement between the test results obtained in different veterinary laboratories and limits the comparability of prevalence estimates for surveillance. In order to harmonise these tests, we tried to adjust their cut-offs so that there is a maximum of agreement between them. Using the results of the three ELISAs applied to 1258 cattle, 1474 goat and 1432 sheep serum samples collected in France, we identified the cut-offs that maximised Hubert's kappa, an agreement coefficient applicable to more than two tests, using a differential evolution algorithm for optimisation. We then evaluated the effect of changing the cut-offs. In particular, we estimated the sensitivities and specificities of each test at the optimal cut-offs using a latent class model. While the manufacturer's cut-offs of the three tests were 30, 40 and 40 respectively, regardless of the species, the cut-offs that maximise the agreement are 44.7, 30.8 and 84.3 for cattle, 6.6, 18.8 and 49.8 for goats, and 26.2, 50.9 and 88.6 for sheep. By using these cut-offs instead of those provided by the manufacturers, the observed proportion of disagreement between the tests is reduced by approximately half, and the diagnostic performances and apparent prevalence are more consistent from one test to another. The use of these species-specific cut-offs allows for better harmonisation of the tests. However, before implementing these new cut-offs, it is essential to assess the measurement uncertainty around them to ensure that the analytical performances of the tests are maintained.

Innovative antigens for more accurate diagnosis of Q fever

Coxiella burnetii, the causative agent of Q fever, poses a significant public health concern worldwide. Diagnosis primarily relies on serological tests. Traditional antigen production methods, typically involving embryonated hen eggs, are labor-intensive, costly, and require biosafety level 3 facilities. In this study, we tested inactivated whole-cell antigens (SAP9 and NMII/AP9) from C. burnetii strains grown in axenic media, offering a safer and more efficient alternative to egg-based production. These antigens were validated using an in-house ELISA method against human patient sera, demonstrating high sensitivity and specificity comparable to ELISA and to the Gold Standard, IFA commercial kits. Notably SAP9 and NMII/AP9 antigens showed no cross-reactivity with intracellular pathogens that cause illness with similar symptoms. This approach represents significant advancement in diagnostic antigen production for Q fever, facilitating cost-effective epidemiological studies and enhancing laboratory safety.

Diagnostic serology test comparison for Q fever and Rift Valley fever in humans and livestock from pastoral communities

Q fever (QF) and Rift Valley fever (RVF) are endemic zoonotic diseases in African countries, causing significant health and economic burdens. Accurate prevalence estimates, crucial for disease control, rely on robust diagnostic tests. While enzyme-linked immunosorbent assays (ELISA) are not the gold standard, they offer rapid, cost-effective, and practical alternatives. However, varying results from different tests and laboratories can complicate comparing epidemiological studies. This study aimed to assess the agreement of test results for QF and RVF in humans and livestock across different laboratory conditions and, for humans, different types of diagnostic tests. We measured inter-laboratory agreement using concordance, Cohen's kappa, and prevalence and bias-adjusted kappa (PABAK) on 91 human and 102 livestock samples collected from rural regions in Chad. The serum aliquots were tested using ELISA in Chad, and indirect immunofluorescence assay (IFA) (for human QF and RVF) and ELISA (for livestock QF and RVF) in Switzerland and Germany. Additionally, we examined demographic factors influencing test agreement, including district, setting (village vs. camp), sex, age, and livestock species of the sampled individuals. The inter-laboratory agreement ranged from fair to moderate. For humans, QF concordance was 62.5%, Cohen's kappa was 0.31, RVF concordance was 81.1%, and Cohen's kappa was 0.52. For livestock, QF concordance was 92.3%, Cohen's kappa was 0.59, RVF concordance was 94.0%, and Cohen's kappa was 0.59. Multivariable analysis revealed that QF test agreement is significantly higher in younger humans and people living in villages compared to camps and tends to be higher in livestock from Danamadji compared to Yao, and in small ruminants compared to cattle. Additionally, RVF agreement was found to be higher in younger humans. Our findings emphasize the need to consider sample conditions, test performance, and influencing factors when conducting and interpreting epidemiological seroprevalence studies.

Efficiency of recombinant Ybgf in a double antigen-ELISA for the detection of Coxiella antibodies in ruminants

Q fever is a zoonosis whose main reservoirs are domestic ruminants. Surveillance in these species is carried out mainly with serological tests, which, however, have limited diagnostic performance, and their manufacturing requires laboratories equipped with high biosafety requirements for antigen production. Recombinant ELISAs do not depend on these requirements and, being based on a single antigen, can reduce potential false positivity by identifying antibodies specific to a phase of infection. The aim of this study was to apply a new technology (dual antigen test) to a recombinant protein (Ybgf), an antigen produced in recombinant form and already used in previous studies for the design of an indirect ELISA. The successfully produced recombinant antigen was used to coat 96-well plates and, at the same time, another antigen aliquot was conjugated with HRP to obtain an HRP-conjugated Ybgf. After setting the test conditions, the results obtained with the recombinant double antigen test were compared with those obtained with a commercial assay (considered as reference assay) testing a total of 514 ruminant samples (280 goats and 234 cattle). A concordance of 86.2 and a Cohen's Kappa value of 0.72 were obtained, with no significant difference between the two species tested. Notably, the test proved to be highly specific, having correctly identified 250 out of 253 animals. This research represents an additional effort to use recombinant antigens to enhance serological methods in veterinary medicine. In a "one-health scenario", improving the performance of serological tests used in veterinary practice also means improving the surveillance of this infection.

Coxiella burnetii seroprevalence in domestic goat does in the United States: Prevalence, distribution, and associated risk factors

Infection with the bacterium Coxiella burnetii can cause coxiellosis in animals and Q fever in humans. Coxiellosis a consistently underreported infectious disease. The infection can result in reproductive consequences for humans and animals. Ruminants are a reservoir for infection and humans are generally infected via aerosolized secretions, making it a public health concern. Studies of ruminant seroprevalence are generally limited in size and scope. This study determined seroprevalence in a large-scale U.S. population of female goats using serum samples from 7736 does from 24 states. This study identified C. burnetii seroprevalence in the United States domestic goat population. Overall, 14.5 % (SE = 2.3) of does were seropositive and 21.0 % (SE = 2.4) of operations had at least 1 seropositive doe. Further, operation demographics and herd management practices associated with seropositivity were as follows: the suspected or confirmed presence of caprine arthritis encephalitis (CAE), caseous lymphadenitis (CL), Johne's disease, or sore mouth in the herd in the previous 3 years, not cleaning or disinfecting the kidding areas or removing aborting does from other does, allowing visitors to access the kidding areas, and a lower percentage of adult goat inventory that were adult bucks or wethers. Furthermore, goat breed was associated with seropositivity. These data show C. burnetii seroprevalence in the United States and identify operation and animal characteristics and management practices associated with C. burnetii seropositivity. Together, this information can be used to help limit animal transmission, inform public health measures, and help educate and protect individuals working with goats.

Detection of Coxiella antibodies in ruminants using a SucB recombinant antigen

The detection of Coxiella burnetii in ruminants remains challenging despite the use of new technology and the accumulation of novel knowledge. Serology tools, the primary methods of infection surveillance in veterinary medicine, have limitations. We used recombinant antigen production to develop an ELISA based on the SucB protein, one of the major immunodominant antigens described in humans and laboratory animals. We produced the antigen successfully in an Escherichia coli heterologous system, confirmed by sequencing and mass spectrometry, and seen as a band of ~50 kDa in SDS-PAGE and on western blot analysis. We compared the performance of the recombinant ELISA with a commercial ELISA. We observed agreement of 83.5% and a substantial Cohen κ value of 0.67 in our pilot study.

Genome-wide epitope mapping across multiple host species reveals significant diversity in antibody responses to Coxiella burnetii vaccination and infection

Coxiella burnetii is an important zoonotic bacterial pathogen of global importance, causing the disease Q fever in a wide range of animal hosts. Ruminant livestock, in particular sheep and goats, are considered the main reservoir of human infection. Vaccination is a key control measure, and two commercial vaccines based on formalin-inactivated C. burnetii bacterins are currently available for use in livestock and humans. However, their deployment is limited due to significant reactogenicity in individuals previously sensitized to C. burnetii antigens. Furthermore, these vaccines interfere with available serodiagnostic tests which are also based on C. burnetii bacterin antigens. Defined subunit antigen vaccines offer significant advantages, as they can be engineered to reduce reactogenicity and co-designed with serodiagnostic tests to allow discrimination between vaccinated and infected individuals. This study aimed to investigate the diversity of antibody responses to C. burnetii vaccination and/or infection in cattle, goats, humans, and sheep through genome-wide linear epitope mapping to identify candidate vaccine and diagnostic antigens within the predicted bacterial proteome. Using high-density peptide microarrays, we analyzed the seroreactivity in 156 serum samples from vaccinated and infected individuals to peptides derived from 2,092 open-reading frames in the C. burnetii genome. We found significant diversity in the antibody responses within and between species and across different types of C. burnetii exposure. Through the implementation of three different vaccine candidate selection methods, we identified 493 candidate protein antigens for protein subunit vaccine design or serodiagnostic evaluation, of which 65 have been previously described. This is the first study to investigate multi-species seroreactivity against the entire C. burnetii proteome presented as overlapping linear peptides and provides the basis for the selection of antigen targets for next-generation Q fever vaccines and diagnostic tests.

Engineering Protein Nanoparticles Functionalized with an Immunodominant Coxiella burnetii Antigen to Generate a Q Fever Vaccine

Coxiella burnetii is the causative agent of Q fever, for which there is yet to be an FDA-approved vaccine. This bacterial pathogen has both extra- and intracellular stages in its life cycle, and therefore both a cell-mediated (i.e., T lymphocyte) and humoral (i.e., antibody) immune response are necessary for effective eradication of this pathogen. However, most proposed vaccines elicit strong responses to only one mechanism of adaptive immunity, and some can either cause reactogenicity or lack sufficient immunogenicity. In this work, we aim to apply a nanoparticle-based platform toward producing both antibody and T cell immune responses against C. burnetii. We investigated three approaches for conjugation of the immunodominant outer membrane protein antigen (CBU1910) to the E2 nanoparticle to obtain a consistent antigen orientation: direct genetic fusion, high affinity tris-NTA-Ni conjugation to polyhistidine-tagged CBU1910, and the SpyTag/SpyCatcher (ST/SC) system. Overall, we found that the ST/SC approach yielded nanoparticles loaded with the highest number of antigens while maintaining stability, enabling formulations that could simultaneously co-deliver the protein antigen (CBU1910) and adjuvant (CpG1826) on one nanoparticle (CBU1910-CpG-E2). Using protein microarray analyses, we found that after immunization, antigen-bound nanoparticle formulations elicited significantly higher antigen-specific IgG responses than soluble CBU1910 alone and produced more balanced IgG1/IgG2c ratios. Although T cell recall assays from these protein antigen formulations did not show significant increases in antigen-specific IFN-γ production compared to soluble CBU1910 alone, nanoparticles conjugated with a CD4 peptide epitope from CBU1910 generated elevated T cell responses in mice to both the CBU1910 peptide epitope and whole CBU1910 protein. These investigations highlight the feasibility of conjugating antigens to nanoparticles for tuning and improving both humoral- and cell-mediated adaptive immunity against C. burnetii.

Seropositivity for Coxiella burnetii in Wild Boar (Sus scrofa) and Red Deer (Cervus elaphus) in Portugal

Q fever is caused by the pathogen Coxiella burnetii and is a zoonosis that naturally infects goats, sheep, and cats, but can also infect humans, birds, reptiles, or arthropods. A survey was conducted for the detection of antibodies against C. burnetii in a sample of 617 free-ranging wild ruminants, 358 wild boar (Sus scrofa) and 259 red deer (Cervus elaphus), in east-central Portugal during the 2016-2022 hunting seasons. Only adult animals were sampled in this study. Antibodies specific to C. burnetii were detected using a commercial enzyme-linked immunosorbent assay (ELISA; IDVet®, Montpellier, France) according to the manufacturer's instructions. The seroprevalence of C. burnetii infection was 1.5% (n = 9; 95% confidence interval [CI]: 0.7-2.8%). Antibodies against C. burnetii were detected in 4/358 wild boar (1.1%; 95% CI: CI: 0.3-2.8%) and 5/259 red deer (1.9%; 0.6-4.5%). Results of the present study indicate that antibodies against C. burnetii were present in wild boar and red deer in Portugal. These findings can help local health authorities to focus on the problem of C. burnetii in wildlife and facilitate the application of a One Health approach to its prevention and control.

Characterization of recombinant Ybgf protein for the detection of Coxiella antibodies in ruminants

Q fever remains a One Health problem, posing a zoonotic threat and causing significant economic losses to the livestock industry. The advancement of detection tools is critical to the effective control of infection. In humans, laboratory investigations depend largely on the immunofluorescence assay, considered the gold standard. In contrast, serologic tools routinely used for veterinary screening have several gaps, resulting in interpretations that are frequently misleading. We investigated the potential application of recombinant Ybgf antigen (r-Ybgf), a periplasmic protein described as one of the most immunodominant antigens in humans, in an indirect ELISA. Following successful expression in the prokaryotic system and the preliminary evaluation of immunoreactivity in western blot, we used r-Ybgf to develop an in-house ELISA using serum samples from sheep, goats, and cattle, which were tested in parallel with an Idexx ELISA kit. The results obtained with the 2 tests were compared, and r-Ybgf performed favorably, with 81.8% sensitivity and 90.1% specificity and substantial agreement, as revealed by receiver operating characteristic analysis. Moreover, we evaluated the serologic response against phase I (PhI) and phase II (PhII) antigens, and r-Ybgf antigen induced by vaccination, using phase-specific ELISAs. The dynamics of antibody response showed a significant increase in reactivity against PhI and PhII, but not against r-Ybgf, antigens. This property may be very useful given the absence of a protocol for the differentiation of infected from vaccinated animals.

Development of High-Throughput Multiplex Serology to Detect Serum Antibodies against Coxiella burnetii

The causative agent of Q fever, the bacterium Coxiella burnetii (C. burnetii), has gained increasing interest due to outbreak events and reports about it being a potential risk factor for the development of lymphomas. In order to conduct large-scale studies for population monitoring and to investigate possible associations more closely, accurate and cost-effective high-throughput assays are highly desired. To address this need, nine C. burnetii proteins were expressed as recombinant antigens for multiplex serology. This technique enables the quantitative high-throughput detection of antibodies to multiple antigens simultaneously in a single reaction. Based on a reference group of 76 seropositive and 91 seronegative sera, three antigens were able to detect C. burnetii infections. Com1, GroEL, and DnaK achieved specificities of 93%, 69%, and 77% and sensitivities of 64%, 72%, and 47%, respectively. Double positivity to Com1 and GroEL led to a combined specificity of 90% and a sensitivity of 71%. In a subgroup of seropositives with an increased risk for chronic Q fever, the double positivity to these markers reached a specificity of 90% and a sensitivity of 86%. Multiplex serology enables the detection of antibodies against C. burnetii and appears well-suited to investigate associations between C. burnetii infections and the clinical manifestations in large-scale studies.

Seroepidemiological study on Coxiella burnetii and associated risk factors in ruminants at Kurdistan Province, west of Iran

Q fever is zoonotic disease caused by Coxiella burnetii. Ruminants are the main reservoir of this pathogen, which is often asymptomatic but lead to abortion. This study aims to survey the seroprevalence and risk factors of this zoonose among ruminants in Kurdistan province, the west of Iran. 480 blood samples were collected from ruminants including sheep, goats and cows, each 160 samples, in the age groups of <1, ≥1-3, >3-5 year with and without the history of abortion in two groups border and non-border cities in Kurdistan province. Serums were tested by use of indirect ELISA to determine specific antibodies against C. burnetii. The results indicate the seroprevalence of 46.6 % for Q fever. Seroprevalence in sheep, goats and cows were 28.58 % (n = 64), 45.53 % (n = 102) and 25.89 % (n = 58), respectively. Seroprevalence is significantly higher in animals with abortion than in those without such history (P < 0.05). The seroprevalence in the border cities has been significantly higher than other geographical areas (P < 0.05). Seroprevalence had no significant correlation with animal age (P> 0.05). This study is the first seroepidemiological study done on Q fever in ruminants of Kurdistan province, Iran. The results indicate the high seroprevalence of Coxiella burnetii in the area under the study. Therefore, doing an epidemiologically study aimed at isolating C. brunetii in the human population of Kurdistan province is recommended, so that the epidemiological aspect of this pathogen in the people of Kurdistan province be clarified and subsequently disease control and prevention programs be applied.

Evaluation using latent class models of the diagnostic performances of three ELISA tests commercialized for the serological diagnosis of Coxiella burnetii infection in domestic ruminants

ELISA methods are the diagnostic tools recommended for the serological diagnosis of Coxiella burnetii infection in ruminants but their respective diagnostic performances are difficult to assess because of the absence of a gold standard. This study focused on three commercial ELISA tests with the following objectives (1) assess their sensitivity and specificity in sheep, goats and cattle, (2) assess the between- and within-herd seroprevalence distribution in these species, accounting for diagnostic errors, and (3) estimate optimal sample sizes considering sensitivity and specificity at herd level. We comparatively tested 1413 cattle, 1474 goat and 1432 sheep serum samples collected in France. We analyzed the cross-classified test results with a hierarchical zero-inflated beta-binomial latent class model considering each herd as a population and conditional dependence as a fixed effect. Potential biases and coverage probabilities of the model were assessed by simulation. Conditional dependence for truly seropositive animals was high in all species for two of the three ELISA methods. Specificity estimates were high, ranging from 94.8% [92.1; 97.8] to 99.2% [98.5; 99.7], whereas sensitivity estimates were generally low, ranging from 39.3 [30.7; 47.0] to 90.5% [83.3; 93.8]. Between- and within-herd seroprevalence estimates varied greatly among geographic areas and herds. Overall, goats showed higher within-herd seroprevalence levels than sheep and cattle. The optimal sample size maximizing both herd sensitivity and herd specificity varied from 3 to at least 20 animals depending on the test and ruminant species. This study provides better interpretation of three widely used commercial ELISA tests and will make it possible to optimize their implementation in future studies. The methodology developed may likewise be applied to other human or animal diseases.

Validation of a Novel Commercial ELISA Test for the Detection of Antibodies against Coxiella burnetii

Q fever is a zoonosis caused by Coxiella burnetii, a Gram-negative pathogen with a complex life cycle and a high impact on public and animal health all over the world. The symptoms are indistinguishable from those belonging to other diseases, and the disease could be symptomless. For these reasons, reliable laboratory tests are essential for an accurate diagnosis. The aim of this study was to validate a novel enzyme-linked immunosorbent assay (ELISA) test, named the Chorus Q Fever Phase II IgG and IgM Kit (DIESSE, Diagnostica Senese S.p.A), which is performed by an instrument named Chorus, a new device in medical diagnostics. This diagnostic test is employed for the detection of antibodies against C. burnetii Phase II antigens in acute disease. Our validation protocol was performed according to the Italian Accreditation Body (ACCREDIA) (Regulation UNI CEI EN ISO/IEC 17025:2018 and 17043:2010), OIE (World Organization for Animal Health), and Statement for Reporting Studies of Diagnostic Accuracy (STARD). Operator performance was evaluated along with the analytical specificity and sensitivity (ASp and ASe) and diagnostic accuracy of the kit, with parameters such as diagnostic specificity and sensitivity (DSp and DSe) and positive and negative predictive values (PPV and NPV), in addition to the repeatability. According to the evaluated parameters, the diagnostic ELISA test was shown to be suitable for validation and commercialization as a screening method in human sera and a valid support for clinical diagnostics.