A minor role of CD4+ T lymphocytes in the control of a primary infection of cattle with Mycoplasma mycoides subsp. mycoides

Temperature impacts the bovine ex vivo immune response towards Mycoplasmopsis bovis

Although cattle are the mammalian species with most global biomass associated with a huge impact on our planet, their immune system remains poorly understood. Notably, the bovine immune system has peculiarities such as an overrepresentation of γδ T cells that requires particular attention, specifically in an infectious context. In line of 3R principles, we developed an ex vivo platform to dissect host-pathogen interactions. The experimental design was based on two independent complementary readouts: firstly, a novel 12-14 color multiparameter flow cytometry assay measuring maturation (modulation of cell surface marker expression) and activation (intracellular cytokine detection) of monocytes, conventional and plasmacytoid dendritic cells, natural killer cells, γδ T cells, B and T cells; secondly, a multiplex immunoassay monitoring bovine chemokine and cytokine secretion levels. The experiments were conducted on fresh primary bovine blood cells exposed to Mycoplasmopsis bovis (M. bovis), a major bovine respiratory pathogen. Besides reaffirming the tight cooperation of the different primary blood cells, we also identified novel key players such as strong IFN-γ secreting NK cells, whose role was so far largely overlooked. Additionally, we compared the host-pathogen interactions at different temperatures, including commonly used 37 °C, ruminant body temperature (38-38.5 °C) and fever (≥ 39.5 °C). Strikingly, working under ruminant physiological temperature influenced the capacity of most immune cell subsets to respond to M. bovis compared to 37 °C. Under fever-like temperature conditions the immune response was impaired compared to physiological temperature. Our experimental approach, phenotypically delineating the bovine immune system provided a thorough vision of the immune response towards M. bovis and the influence of temperature towards that immune response.

Mycoplasmas as Host Pantropic and Specific Pathogens: Clinical Implications, Gene Transfer, Virulence Factors, and Future Perspectives

Mycoplasmas as economically important and pantropic pathogens can cause similar clinical diseases in different hosts by eluding host defense and establishing their niches despite their limited metabolic capacities. Besides, enormous undiscovered virulence has a fundamental role in the pathogenesis of pathogenic mycoplasmas. On the other hand, they are host-specific pathogens with some highly pathogenic members that can colonize a vast number of habitats. Reshuffling mycoplasmas genetic information and evolving rapidly is a way to avoid their host's immune system. However, currently, only a few control measures exist against some mycoplasmosis which are far from satisfaction. This review aimed to provide an updated insight into the state of mycoplasmas as pathogens by summarizing and analyzing the comprehensive progress, current challenge, and future perspectives of mycoplasmas. It covers clinical implications of mycoplasmas in humans and domestic and wild animals, virulence-related factors, the process of gene transfer and its crucial prospects, the current application and future perspectives of nanotechnology for diagnosing and curing mycoplasmosis, Mycoplasma vaccination, and protective immunity. Several questions remain unanswered and are recommended to pay close attention to. The findings would be helpful to develop new strategies for basic and applied research on mycoplasmas and facilitate the control of mycoplasmosis for humans and various species of animals.

Depletion of CD8+ T cells from vaccinated goats does not affect protection from challenge with wild-type peste des petits ruminants virus

Peste des petits ruminants (PPR) is a severe disease of goats and sheep that is widespread in Africa, the Middle East and Asia. The disease is caused by peste des petits ruminants virus (PPRV); cell culture-attenuated strains of PPRV have been shown, both experimentally and by extensive use in the field, to be effective vaccines and are widely used. We have previously demonstrated that these vaccines elicit both serological (PPRV-specific antibody) and cell-based (PPRV-specific CD4⁺ and CD8⁺ T cells) immune responses. However, it is not known which of these responses are required for protection from PPRV, information that would be useful in the evaluation of new vaccines that are being developed to provide the capability to differentiate infected and vaccinated animals (DIVA capability). To begin to address this issue, we have used a complement-fixing monoclonal antibody recognizing caprine CD8 to deplete >99.9% of circulating CD8⁺ T cells from vaccinated goats. Animals were then infected with wild-type PPRV. Despite the absence of the CD8⁺ T-cell component of the vaccine-induced immune response, the vaccinated animals were almost fully protected, showing no pyrexia or viraemia, and almost no clinical signs. These data suggest that a virus-specific CD8⁺ T-cell response is not critical for protection against PPRV and that virus-specific antibody and/or CD4⁺ T cells are the main mediators of protection. We have also shown that the leucopenia caused by infection with wild-type PPRV affects all major classes of circulating leucocytes.

Reproduction of contagious bovine pleuropneumonia via aerosol-based challenge with Mycoplasma mycoides subsp. mycoides

Contagious bovine pleuropneumonia (CBPP) is a respiratory disease caused by Mycoplasma mycoides subsp. mycoides. Infection occurs via Mycoplasma-containing droplets and therefore requires close contact between animals. The current infection models are suboptimal and based on intratracheal installation of mycoplasmas or in-contact infection. This work tested the infection of adult cattle via aerosols containing live mycoplasmas mimicking the infection of cattle in the field. Therefore, we infected six cattle with aerosolized Mycoplasma mycoides subsp. mycoides strain Afadé over seven consecutive days with altogether 10⁹ colony forming units. All animals seroconverted between 11–24 days post infection and five out of six animals showed typical CBPP lesions. One animal did not show any lung lesions at necropsy, while another animal had to be euthanized at 25 days post infection because it reached endpoint criteria. Seroconversion confirmed successful infection and the spectrum of clinical and lesions observed mirrors epidemiological models and the field situation, in which only a fraction of animals suffers from acute clinical disease post infection.

Contagious Bovine Pleuropneumonia: Challenges and Prospects Regarding Diagnosis and Control Strategies in Africa

Contagious bovine pleuropneumonia (CBPP) is an infectious and contagious respiratory disease of cattle, caused by Mycoplasma mycoides subsp. mycoides (Mmm). In this review, basic epidemiological features of CBPP, complicated by existing different strains of Mycoplasmas with similar biochemical characteristics, with preference to Sub-Saharan Africa are discussed. Many sub-Saharan African countries are challenged by variable gaps that include diagnostic tools and control strategies. Science-based issues on diagnostic procedures, vaccination, treatment, and other control strategies are discussed. Participatory epidemiology (PE), a diagnostic technique used in the identification and solving of animal health problems in rural communities, was also discussed. PE application, in conjunction with conventional diagnostic tools, will improve CBPP identification in pastoral rural communities and promote control of the disease in Africa. Furthermore, adequate CBPP control can be achieved through stronger political commitments from governments by prioritizing the disease among major diseases of high economic importance to the livestock industry for surveillance and control. Investment in CBPP control in endemic African countries will assure food security, livelihoods and the general well-being of people, and international trade.

Contagious Bovine and Caprine Pleuropneumonia: a research community's recommendations for the development of better vaccines

Contagious bovine pleuropneumonia (CBPP) and contagious caprine pleuropneumonia (CCPP) are major infectious diseases of ruminants caused by mycoplasmas in Africa and Asia. In contrast with the limited pathology in the respiratory tract of humans infected with mycoplasmas, CBPP and CCPP are devastating diseases associated with high morbidity and mortality. Beyond their obvious impact on animal health, CBPP and CCPP negatively impact the livelihood and wellbeing of a substantial proportion of livestock-dependent people affecting their culture, economy, trade and nutrition. The causative agents of CBPP and CCPP are Mycoplasma mycoides subspecies mycoides and Mycoplasma capricolum subspecies capripneumoniae, respectively, which have been eradicated in most of the developed world. The current vaccines used for disease control consist of a live attenuated CBPP vaccine and a bacterin vaccine for CCPP, which were developed in the 1960s and 1980s, respectively. Both of these vaccines have many limitations, so better vaccines are urgently needed to improve disease control. In this article the research community prioritized biomedical research needs related to challenge models, rational vaccine design and protective immune responses. Therefore, we scrutinized the current vaccines as well as the challenge-, pathogenicity- and immunity models. We highlight research gaps and provide recommendations towards developing safer and more efficacious vaccines against CBPP and CCPP.

Baseline analysis of Mycoplasma mycoides subsp. mycoides antigens as targets for a DIVA assay for use with a subunit vaccine for contagious bovine pleuropneumonia

BACKGROUND

Mycoplasma mycoides subsp. mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia in cattle. A prototype subunit vaccine is being developed, however, there is currently no diagnostic test that can differentiate between infected cattle and those vaccinated with the prototype subunit vaccine. This study characterized Mmm proteins to identify potential antigens for use in differentiating infected from vaccinated animals.

RESULTS

Ten Mmm antigens expressed as recombinant proteins were tested in an indirect ELISA using experimental sera from control groups, infected, and vaccinated animals. Data were imported into R software for analysis and drawing of the box and scatter plots while Cohen's Kappa assessed the level of agreement between the Mmm antigens. Two vaccine antigens (MSC_0499 and MSC_0776) were superior in detecting antibodies in sera of animals vaccinated with the subunit vaccines while two non-vaccine antigens (MSC_0636 and LppB) detected antibodies in sera of infected animals showing all clinical stages of the disease. Sensitivity and specificity of above 87.5% were achieved when the MSC_0499 and MSC_0636 antigens were tested on sera from vaccinated and infected animals.

CONCLUSIONS

The MSC_0499 and MSC_0776 antigens were the most promising for detecting vaccinated animals, while MSC_0636 and LppB were the best targets to identify infected animals. Further testing of sera from vaccinated and infected animals collected at different time intervals in the field should help establish how useful a diagnostic test based on a cocktail of these proteins would be.

Removal of a Subset of Non-essential Genes Fully Attenuates a Highly Virulent Mycoplasma Strain

Mycoplasmas are the smallest free-living organisms and cause a number of economically important diseases affecting humans, animals, insects, and plants. Here, we demonstrate that highly virulent Mycoplasma mycoides subspecies capri (Mmc) can be fully attenuated via targeted deletion of non-essential genes encoding, among others, potential virulence traits. Five genomic regions, representing approximately 10% of the original Mmc genome, were successively deleted using Saccharomyces cerevisiae as an engineering platform. Specifically, a total of 68 genes out of the 432 genes verified to be individually non-essential in the JCVI-Syn3.0 minimal cell, were excised from the genome. In vitro characterization showed that this mutant was similar to its parental strain in terms of its doubling time, even though 10% of the genome content were removed. A novel in vivo challenge model in goats revealed that the wild-type parental strain caused marked necrotizing inflammation at the site of inoculation, septicemia and all animals reached endpoint criteria within 6 days after experimental infection. This is in contrast to the mutant strain, which caused no clinical signs nor pathomorphological lesions. These results highlight, for the first time, the rational design, construction and complete attenuation of a Mycoplasma strain via synthetic genomics tools. Trait addition using the yeast-based genome engineering platform and subsequent in vitro or in vivo trials employing the Mycoplasma chassis will allow us to dissect the role of individual candidate Mycoplasma virulence factors and lead the way for the development of an attenuated designer vaccine.

Reproduction of contagious caprine pleuropneumonia reveals the ability of convalescent sera to reduce hydrogen peroxide production in vitro

Contagious caprine pleuropneumonia (CCPP), caused by Mycoplasma capricolum subsp. capripneumoniae is a severe disease widespread in Africa and Asia. Limited knowledge is available on the pathogenesis of this organism, mainly due to the lack of a robust in vivo challenge model and the means to do site-directed mutagenesis. This work describes the establishment of a novel caprine challenge model for CCPP that resulted in 100% morbidity using a combination of repeated intranasal spray infection followed by a single transtracheal infection employing the recent Kenyan outbreak strain ILRI181. Diseased animals displayed CCPP-related pathology and the bacteria could subsequently be isolated from pleural exudates and lung tissues in concentrations of up to 10⁹ bacteria per mL as well as in the trachea using immunohistochemistry. Reannotation of the genome sequence of ILRI181 and F38^T revealed the existence of genes encoding the complete glycerol uptake and metabolic pathways involved in hydrogen peroxide (H₂O₂) production in the phylogenetically related pathogen M. mycoides subsp. mycoides. Furthermore, the expression of L-α-glycerophosphate oxidase (GlpO) in vivo was confirmed. In addition, the function of the glycerol metabolism was verified by measurement of production of H₂O₂ in medium containing physiological serum concentrations of glycerol. Peroxide production could be inhibited with serum from convalescent animals. These results will pave the way for a better understanding of host-pathogen interactions during CCPP and subsequent vaccine development.

Capsular polysaccharide from Mycoplasma mycoides subsp. mycoides shows potential for protection against contagious bovine pleuropneumonia

Contagious Bovine Pleuropneumonia (CBPP) is a severe respiratory disease caused by Mycoplasma mycoides subsp. mycoides (Mmm) which is widespread in Africa. The capsule polysaccharide (CPS) of Mmm is one of the few identified virulence determinants. In a previous study, immunization of mice against CPS generated antibodies, but they were not able to prevent multiplication of Mmm in this model animal. However, mice cannot be considered as a suitable animal model, as Mmm does not induce pathology in this species. Our aim was to induce antibody responses to CPS in cattle, and challenge them when they had specific CPS antibody titres similar or higher than those from cattle vaccinated with the live vaccine. The CPS was linked to the carrier protein ovalbumin via a carbodiimide-mediated condensation with 1-ethyl-3(3-imethylaminopropyl) carbodiimide (EDC). Ten animals were immunized twice and challenged three weeks after the booster inoculation, and compared to a group of challenged non-immunized cattle. When administered subcutaneously to adult cattle, the vaccine elicited CPS-specific antibody responses with the same or a higher titre than animals vaccinated with the live vaccine. Pathology in the group of immunized animals was significantly reduced (57%) after challenge with Mmm strain Afadé compared to the non-immunized group, a figure in the range of the protection provided by the live vaccine.

Development of a Novel Cocktail Enzyme-Linked Immunosorbent Assay and a Field-Applicable Lateral-Flow Rapid Test for Diagnosis of Contagious Bovine Pleuropneumonia

Contagious bovine pleuropneumonia (CBPP) is a severe respiratory disease that is widespread in sub-Saharan Africa. It is caused by Mycoplasma mycoides subsp. mycoides, a bacterium belonging to the Mycoplasma mycoides cluster. In the absence of an efficient CBPP vaccine, improved and easy-to-use diagnostic assays for recurrent testing combined with isolation and treatment of positive animals represent an option for CBPP control in Africa. Here we describe the comprehensive screening of 17 immunogenic Mycoplasma mycoides subsp. mycoides proteins using well-characterized bovine sera for the development of a novel cocktail enzyme-linked immunosorbent assay (ELISA) for laboratory use. Two recombinant Mycoplasma immunogens, MSC_0136 and MSC_0636, were used to set up a standardized cocktail ELISA protocol. According to the results from more than 100 serum samples tested, the sensitivity and specificity of the novel cocktail ELISA were 85.6% and 96.4%, respectively, with an overall diagnostic accuracy comparable to that of the Office International des Epizooties (OIE)-prescribed serological assays. In addition, we provide a proof of principle for a field-applicable, easy-to-use commercially produced prototype lateral-flow test for rapid (<30-min) diagnosis of CBPP.

Morphological characterization and immunohistochemical detection of the proinflammatory cytokines IL-1β, IL-17A, and TNF-α in lung lesions associated with contagious bovine pleuropneumonia

Contagious bovine pleuropneumonia (CBPP), a severe respiratory disease, is characterized by massive inflammation of the lung especially during the acute clinical stage of infection. Tissue samples from cattle, experimentally infected with Mycoplasma mycoides subsp. mycoides Afadé, were subjected to histopathological and immunohistochemical examination in order to provide insight into innate immune pathways that shape inflammatory host responses. Lung lesions were characterized by vasculitis, necrosis, and increased presence of macrophages and neutrophils, relative to uninfected animals. The presence of three cytokines associated with innate inflammatory immune responses, namely, IL-1β, IL-17A, and TNF-α, were qualitatively investigated in situ. Higher cytokine levels were detected in lung tissue samples from CBPP-affected cattle compared to samples derived from an uninfected control group. We therefore conclude that the cytokines TNF-α and IL-1β, which are prevalent in the acute phase of infections, play a role in the inflammatory response seen in the lung tissue in CBPP. IL-17A gets released by activated macrophages and attracts granulocytes that modulate the acute phase of the CBPP lesions.

High quality draft genomes of the Mycoplasma mycoides subsp. mycoides challenge strains Afadé and B237

Members of the Mycoplasma mycoides cluster' represent important livestock pathogens worldwide. Mycoplasma mycoides subsp. mycoides is the etiologic agent of contagious bovine pleuropneumonia (CBPP), which is still endemic in many parts of Africa. We report the genome sequences and annotation of two frequently used challenge strains of Mycoplasma mycoides subsp. mycoides, Afadé and B237. The information provided will enable downstream 'omics' applications such as proteomics, transcriptomics and reverse vaccinology approaches. Despite the absence of Mycoplasma pneumoniae like cyto-adhesion encoding genes, the two strains showed the presence of protrusions. This phenotype is likely encoded by another set of genes.

Whole Blood Transcriptome Analysis of Mycoplasma mycoides Subsp. mycoides-Infected Cattle Confirms Immunosuppression but Does Not Reflect Local Inflammation

Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides (Mmm), is a severe respiratory disease of cattle responsible for major economic losses in sub-Saharan Africa. Disease control relies mainly on the use of empirically attenuated vaccines that provide limited protection. Thus, understanding the virulence mechanisms used by Mmm as well as the role of the host immune system in disease development, persistence, and control is a prerequisite for the development of new, rationally designed control strategies. The aim of this study was to assess the use of whole blood transcriptome analysis to study cattle-Mmm interactions, starting by the characterization of the bovine response to Mmm infection during the acute form of the disease. For that purpose, we compared the transcriptome profile of whole blood from six cattle, before challenge by contact with Mmm-infected animals and at the appearance of first clinical signs, using a bovine microarray. Functional analysis revealed that 680 annotated genes were differentially expressed, with an overwhelming majority of down-regulated genes characterizing an immunosuppression. The main bio-functions affected were "organismal survival", "cellular development, morphology and functions" and "cell-to cell signaling and interactions". These affected functions were consistent with the results of previous in vitro immunological studies. However, microarray and qPCR validation results did not highlight pro-inflammatory molecules (such as TNFα, TLR2, IL-12B and IL-6), whereas inflammation is one of the most characteristic traits of acute CBPP. This global gene expression pattern may be considered as the result, in blood, of the local pulmonary response and the systemic events occurring during acute CBPP. Nevertheless, to understand the immune events occurring during disease, detailed analyses on the different immune cell subpopulations, either in vivo, at the local site, or in vitro, will be required. Whole blood transcriptome analysis remains an interesting approach for the identification of bio-signatures correlating to recovery and protection, which should facilitate the evaluation and validation of novel vaccine formulations.

Field-Applicable Recombinase Polymerase Amplification Assay for Rapid Detection of Mycoplasma capricolum subsp. capripneumoniae

Contagious caprine pleuropneumonia (CCPP) is a highly contagious disease caused by Mycoplasma capricolum subsp. capripneumoniae that affects goats in Africa and Asia. Current available methods for the diagnosis of Mycoplasma infection, including cultivation, serological assays, and PCR, are time-consuming and require fully equipped stationary laboratories, which make them incompatible with testing in the resource-poor settings that are most relevant to this disease. We report a rapid, specific, and sensitive assay employing isothermal DNA amplification using recombinase polymerase amplification (RPA) for the detection of M. capricolum subsp. capripneumoniae. We developed the assay using a specific target sequence in M. capricolum subsp. capripneumoniae, as found in the genome sequence of the field strain ILRI181 and the type strain F38 and that was further evidenced in 10 field strains from different geographical regions. Detection limits corresponding to 5 × 10³ and 5 × 10⁴ cells/ml were obtained using genomic DNA and bacterial culture from M. capricolum subsp. capripneumoniae strain ILRI181, while no amplification was obtained from 71 related Mycoplasma isolates or from the Acholeplasma or the Pasteurella isolates, demonstrating a high degree of specificity. The assay produces a fluorescent signal within 15 to 20 min and worked well using pleural fluid obtained directly from CCPP-positive animals without prior DNA extraction. We demonstrate that the diagnosis of CCPP can be achieved, with a short sample preparation time and a simple read-out device that can be powered by a car battery, in <45 min in a simulated field setting.

Development of an improved vaccine for contagious bovine pleuropneumonia: an African perspective on challenges and proposed actions

Contagious bovine pleuropneumonia (CBPP) caused by Mycoplasma mycoides subsp. mycoides (Mmm) is an economically very important cattle disease in sub-Saharan Africa. CBPP impacts animal health and poverty of livestock-dependent people through decreased animal productivity, reduced food supply, and the cost of control measures. CBPP is a barrier to trade in many African countries and this reduces the value of livestock and the income of many value chain stakeholders. The presence of CBPP also poses a constant threat to CBPP-free countries and creates costs in terms of the measures necessary to ensure the exclusion of disease. This opinion focuses on the biomedical research needed to foster the development of better control measures for CBPP. We suggest that different vaccine development approaches are followed in parallel. Basic immunology studies and systematic OMICs studies will be necessary in order to identify the protective arms of immunity and to shed more light on the pathogenicity mechanisms in CBPP. Moreover a robust challenge model and a close collaboration with African research units will be crucial to foster and implement a new vaccine for the progressive control of this cattle plague.

Characterization of the in vitro core surface proteome of Mycoplasma mycoides subsp. mycoides, the causative agent of contagious bovine pleuropneumonia

Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides (Mmm) is a severe cattle disease, present in many countries in sub-Saharan Africa. The development of improved diagnostic tests and vaccines for CBPP control remains a research priority. Polyacrylamide gel electrophoresis and mass spectrometry were used to characterize the Triton X-114 soluble proteome of nine Mmm strains isolated from Europe or Africa. Of a total of 250 proteins detected, 67 were present in all strains investigated. Of these, 44 were predicted to be lipoproteins or cytoplasmic membrane-associated proteins and are thus likely to be members of the core in vitro surface membrane-associated proteome of Mmm. Moreover, the presence of all identified proteins in other ruminant Mycoplasma pathogens were investigated. Two proteins of the core proteome were identified only in other cattle pathogens of the genus Mycoplasma pointing towards a role in host-pathogen interactions. The data generated will facilitate the identification and prioritization of candidate Mycoplasma antigens for improved control measures, as it is likely that surface-exposed membrane proteins will include those that are involved in host-pathogen interactions.

Plasma levels of TNF-α, IFN-γ, IL-4 and IL-10 during a course of experimental contagious bovine pleuropneumonia

Background

Contagious Bovine Pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides, is widespread in sub-Saharan Africa. The current live vaccine T1/44 has limited efficacy and occasionally leads to severe side effects in the animals. A better understanding of the immune responses triggered by Mycoplasma mycoides subsp. mycoides and their role in disease progression will help to facilitate the design of a rational vaccine. Currently, knowledge of cytokines involved in immunity and immunopathology in CBPP is rather limited. The aim of this study was to characterize the in vivo plasma concentrations of the cytokines TNF-α, IFN-γ, IL-4, IL-10 and the overall role of CD4⁺ T cells in the development of cytokine levels during a primary infection. Plasma cytokine concentrations in two groups of cattle (CD4⁺ T cell-depleted and non-depleted cattle) experimentally infected with Mycoplasma mycoides subsp. mycoides were measured and their relationship to the clinical outcomes was investigated.

Results

Plasma cytokine concentrations varied between animals in each group. Depletion of CD4⁺ T cells did not induce significant changes in plasma levels of TNF-α, IL-4, and IL-10, suggesting a minor role of CD4⁺ T cells in regulation or production of the three cytokines during the time window of depletion (1-2 weeks post depletion). Unexpectedly, the IFN-γ concentrations were slightly, but statistically significantly higher in the depleted group (p < 0.05) between week three and four post infection. Three CD4⁺ T cell-depleted animals that experienced severe disease, had high levels of TNF-α and IFN-γ. Only one severely diseased non-depleted animal showed a high serum concentration of IL-4 post infection.

Conclusions

Comparison of most severely diseased animals, which had to be euthanized prior to the expected date, versus less severe diseased animals, irrespective of the depletion status, suggested that high TNF-α levels are correlated with more severe pathology in concomitance with high IFN-γ levels.

Serological testing of cattle experimentally infected with Mycoplasma mycoides subsp. mycoides Small Colony using four different tests reveals a variety of seroconversion patterns

BACKGROUND

To study the specific antibody response to infection with Mycoplasma mycoides subsp. mycoides Small Colony (MmmSC), the agent of Contagious Bovine Pleuropneumonia (CBPP), we examined three panels of sera collected during three experimental infection trials in African cattle. The methods used included an in-house complement fixation test (CFT), a commercially available CFT, a competitive antibody ELISA (cELISA) and the immunoblotting test (IBT). In addition, lung tissue samples were examined by culture.

RESULTS

A total of 89% (51/59) of all experimentally infected animals tested positive on at least one of the serological tests throughout the trial. The specific antibody titres to the MmmSC infection became positive first by CFT (6 to 9 days post infection [dpi]), followed by IBT (9 to 13 dpi) and cELISA (13 to 16 dpi). Individual animals were found to display remarkably distinct seroconversion patterns, which allowed their classification into i) early high responders, ii) late high responders, and iii) low responders. In accordance with other studies, none of the present serological tests was capable of detecting all CBPP infected animals.

CONCLUSION

Comparison of the assays' performance in terms of sensitivity and specificity raises serious questions as to their reliability for identification of infected individuals in the field. In view of these limitations, a combination of CFT and cELISA can markedly improve CBPP diagnosis at single-animal level.

Assessment of a novel multiplex real-time PCR assay for the detection of the CBPP agent Mycoplasma mycoides subsp. mycoides SC through experimental infection in cattle

Background

Mycoplasma mycoides subsp. mycoides SC is the pathogenic agent of contagious bovine pleuropneumonia (CBPP), the most important disease of cattle in Africa causing significant economic losses. The re-emergence of CBPP in Europe in the 1980s and 1990s illustrates that it is still a threat also to countries that have successfully eradicated the disease in the past. Nowadays, probe-based real-time PCR techniques are among the most advanced tools for a reliable identification and a sensitive detection of many pathogens, but only few protocols have been published so far for CBPP diagnosis. Therefore we developed a novel TaqMan^®-based real-time PCR assay comprising the amplification of two independent targets (MSC_0136 and MSC_1046) and an internal exogenous amplification control in a multiplex reaction and evaluated its diagnostic performance with clinical samples.

Results

The assays detected 49 MmmSC strains from diverse temporal and geographical origin, but did not amplify DNA from 82 isolates of 20 non-target species confirming a specificity of 100%. The detection limit was determined to be 10 fg DNA per reaction for the MSC_0136 assay and 100 fg per reaction for the MSC_1046 assay corresponding to 8 and 80 genome equivalents, respectively. The diagnostic performance of the assay was evaluated with clinical samples from 19 experimentally infected cattle and from 20 cattle without CBPP and compared to those of cultivation and a conventional PCR protocol. The two rt-PCR tests proved to be the most sensitive methods and identified all 19 infected animals. The different sample types used were not equally suitable for MmmSC detection. While 94.7% of lung samples from the infected cohort were positively tested in the MSC_0136 assay, only 81% of pulmonal lymph nodes, 31% of mediastinal lymph nodes and 25% of pleural fluid samples gave a positive result.

Conclusions

The developed multiplex rt-PCR assay is recommended as an efficient tool for rapid confirmation of a presumptive CBPP diagnosis in a well-equipped laboratory environment.