Identification and Analysis of Immunodominant Antigens for ELISA-Based Detection of Theileria annulata

Prediction, Synthesis and Evaluation of a Synthetic Peptide as an Enzyme-Linked Immunosorbent Assay (ELISA) Candidate for Screening of Bovine Antibodies against Theileria annulata

Tick-borne diseases (TBDs) of livestock are endemic across various parts of tropical countries. Theileriosis is one such economically important TBD, caused by the Theileriidae family of organisms, which is transmitted by ticks. Theileria annulata, the causative agent of tropical theileriosis, contributes a significant loss to the dairy sector by causing anorexia, high fever, anemia, inflammatory changes in vital organs and icterus, thus, a loss in milk yield. Though vaccines are available, their protective efficacy is not absolute, and treatment is limited to early diagnosis of the causative agent. Routinely, microscopic identification of piroplasms in the erythrocytes (Giemsa-stained) of infected animals or schizonts in lymph node biopsies are practiced for diagnosis. PCR-based techniques (multiplex, uniplex, nested and real-time) have been reported to perform well in diagnosing active infection. Several attempts have been made using serological assays like Dot blot, ELISA and ICT, but the results were of variable sensitivity and specificity. Recombinant proteins like the Theileria annulata merozoite surface antigen (Tams1) and Theileria annulata surface protein (TaSP) have been explored as antigenic candidates for these assays. In the present study, we predicted an immunogenic peptide, i.e., TaSP-34, from the TaSP using various computational tools. The predicted peptide was custom synthesized. The diagnostic potential of the peptide was assessed by indirect plate ELISA to detect the bovine-IgM against Theileria annulata. Alongside, a recombinant truncated TaSP (rTaSP(tr)) was expressed and purified, which was used to compare the performance of the peptide as a diagnostic candidate. The IgM-based peptide ELISA was 100% sensitive and 92.77% specific as compared to PCR (Tams1 targeting), while 98.04% sensitivity and 97.44% specificity were observed in comparison with rTaSP(tr) ELISA. Almost perfect agreement between peptide ELISA and Tams1 PCR was observed with a Cohen's kappa coefficient (κ-value) of 0.901 and agreement of 95.31%. Further, the κ-value between the peptide ELISA and rTaSP(tr) ELISA was found to be 0.95, and the agreement was 97.65%, which shows a good correlation between the two tests. The findings suggest that the TaSP-34 peptide can be an efficient and new-generation diagnostic candidate for the diagnosis of T. annulata. Furthermore, the peptide can be synthesized commercially at a larger scale and can be a cost-effective alternative for the protein-based diagnostic candidates for T. annulata.

Cattle co-infection patterns by hemopathogens and their phylogenetic analysis during the tick season in Constantine and Mila, Northeast Algeria

Tropical theileriosis, babesiosis, and anaplasmosis are the most dominant tick-borne infections in North Africa where they cause significant economic losses in ruminants' industry. The aim of the present work was to study infections and co-infection patterns in 66 cattle with clinical signs of piroplasmosis and/or anaplasmosis in two localities, Beni Hamidene and Grarem Gouga, districts of Constantine and Mila (Northeast of Algeria), respectively. This study was conducted between early May and late September during four years 2017, 2018, 2020, and 2021. PCR showed that the most frequent pathogen in cattle with clinical signs of piroplasmosis and/or anaplasmosis was Theileria annulata (66/66; 100%) followed by Babesia bovis (21/66; 31.8%), Anaplasma marginale (15/66; 22.7%), and Babesia bigemina (3/66; 4.5%) (p < 0.001). Giemsa-stained blood smears examinations revealed that 66.7% (44/66); 10.6% (7/66); and 9.1% (6/66) of cattle were infected by T. annulata, Babesia spp., and A. marginale, respectively (p < 0.001). PCR revealed seven co-infection patterns: T. annulata/A. marginale (15/66; 22.7%), T. annulata/B. bovis (21/66; 31.8%), T. annulata/B. bigemina (3/66; 4.5%), T. annulata/A. marginale/B. bovis (7/66; 10.6%), T. annulata/B. bovis/B. bigemina (2/66; 3%), T. annulata/A. marginale/B. bigemina (1/66; 1.5%), and T. annulata/A. marginale/B. bigemina/B. bovis (1/66; 1.5%). Phylogenetic analyses showed that T. annulata Tams1 and B. bigemina gp45 sequences were identical to isolates from Mauritania and South Africa, respectively. The three A. marginale amplicons obtained herein had 99.63 to 99.88% similarity between them. This study provides data that can be used to improve control programs targeting these cattle hemopathogens.

Genetic Resistance of Bovines to Theileriosis

Diseases caused by ticks have a high impact on the health, welfare, and productivity of livestock species. They are also an important cause of economic losses in farms worldwide. An example of such diseases is theileriosis, which can be controlled by drugs or vaccines, although these are not fully efficient. Therefore, there is a need to develop alternative and more sustainable and efficient complementary strategies. These may involve the identification and selection of animals more resistant to the disease. Several previous studies have identified significant differences in resistance between different breeds, with resistant breeds typically identified as those native to the region where they are being studied, and susceptible as those from exotic breeds. These studies have indicated that resistance traits are intrinsically related to the modulation of the immune response to infection. This review aims to systematize the general knowledge about theileriosis, emphasize resistance to this disease as a sustainable control strategy, and identify which traits of resistance to the disease are already known in cattle.

Molecular identification of Theileria spp. in ruminants and ticks from southern littoral of Caspian Sea, Iran

The present study aimed at evaluating the presence of tick-borne apicomplexan parasites including Theileria ovis, Theileria lestoquardi, Theileria annulata, and Theileria orientalis in 92 cattle and 105 sheep from 6 different districts of Guilan and Mazandaran Provinces, in the southern littoral of Caspian Sea. Furthermore, ixodid ticks were collected from the same animals. Stained blood smears were microscopically evaluated for the presence of blood parasites, and a specific PCR was applied for the detection of Theileria species. Besides, ticks were subsequently examined by species-specific PCR. Microscopic examination of blood smears demonstrated no evidence of intraerythrocytic piroplasms. Species-specific diagnostic PCRs demonstrated that 52.17% of sheep blood samples were positive for T. ovis. In addition, 31.03% and 24.13% of cattle blood samples were positive for T. annulata and T. orientalis, respectively. Moreover, 3 species of the ixodid ticks, namely, Rhipicephalus annulatus (58.47%), Ixodes ricinus (29.82%), and Haemaphysalis inermis (11.69%), were identified in Guilan Province, while Hyalomma detritum (73.03%) and Rhipicephalus sanguineus (26.92%) were found in Mazandaran Province. Additionally, by obtaining the data with respect to tick-borne apicomplexan parasites in 122 infected ticks, 35.24%, 22.95%, and 2.45% of tick samples were positive for T. annulata, T. orientalis, and T. ovis, respectively. Species-specific PCR revealed that H. inermis and R. annulatus were positive for T. orientalis. In addition, T. annulata was found in R. annulatus, H. inermis, and H. detritum. Besides, T. ovis was the only species of Theileria found in R. sanguineus. In conclusion, the results revealed that T. annulata infection was prevalent among cattle and ovine theileriosis caused by T. ovis was the only Theileria species found in sheep in the studied areas of the southern littoral of Caspian Sea. R. annulatus, H. inermis, and H. detritum were the main vectors for T. annulata, followed by H. inermis and R. annulatus for T. orientalis, and R. sanguineus for T. ovis.

Systematic Determination of TCR–Antigen and Peptide–MHC Binding Kinetics among Field Variants of a Theileria parva Polymorphic CTL Epitope

Positions 1–3 in the Tp9 CTL epitope are required for binding to BoLA-1*023:01.

Positions 5–8 in the Tp9 epitope are required for TCR recognition in diverse CTLs.

Tp9-specific CTLs from Muguga-immunized animals can cross-react with variants 4 and 7.

CTLs are known to contribute to immunity toward Theileria parva, the causative agent of East Coast fever. The Tp9_67–75 CTL epitope from the Muguga strain of T. parva is polymorphic in other parasite strains. Identifying the amino acids important for MHC class I binding, as well as TCR recognition of epitopes, can allow the strategic selection of Ags to induce cellular immunity toward T. parva. In this study, we characterized the amino acids important for MHC class I binding and TCR recognition in the Tp9_67–75 epitope using alanine scanning and a series of variant peptide sequences to probe these interactions. In a peptide–MHC class I binding assay, we found that the amino acids at positions 1, 2, and 3 were critical for binding to its restricting MHC class I molecule BoLA-1*023:01. With IFN-γ ELISPOT and peptide–MHC class I Tet staining assays on two parasite-specific bovine CTL lines, we showed that amino acids at positions 5–8 in the epitope were required for TCR recognition. Only two of eight naturally occurring polymorphic Tp9 epitopes were recognized by both CTLs. Finally, using a TCR avidity assay, we found that a higher TCR avidity was associated with a stronger functional response toward one of two variants recognized by the CTL. These data add to the growing knowledge on the cross-reactivity of epitope-specific CTLs and specificities that may be required in the selection of Ags in the design of a wide-spectrum vaccine for East Coast fever.

Susceptibility to disease (tropical theileriosis) is associated with differential expression of host genes that possess motifs recognised by a pathogen DNA binding protein

Background

Knowledge of factors that influence the outcome of infection are crucial for determining the risk of severe disease and requires the characterisation of pathogen-host interactions that have evolved to confer variable susceptibility to infection. Cattle infected by Theileria annulata show a wide range in disease severity. Native (Bos indicus) Sahiwal cattle are tolerant to infection, whereas exotic (Bos taurus) Holstein cattle are susceptible to acute disease.

Methodology/Principal findings

We used RNA-seq to assess whether Theileria infected cell lines from Sahiwal cattle display a different transcriptome profile compared to Holstein and screened for altered expression of parasite factors that could generate differences in host cell gene expression.

Significant differences (<0.1 FDR) in the expression level of a large number (2211) of bovine genes were identified, with enrichment of genes associated with Type I IFN, cholesterol biosynthesis, oncogenesis and parasite infection. A screen for parasite factors found limited evidence for differential expression. However, the number and location of DNA motifs bound by the TashAT2 factor (TA20095) were found to differ between the genomes of B. indicus vs. B. taurus, and divergent motif patterns were identified in infection-associated genes differentially expressed between Sahiwal and Holstein infected cells.

Conclusions/Significance

We conclude that divergent pathogen-host molecular interactions that influence chromatin architecture of the infected cell are a major determinant in the generation of gene expression differences linked to disease susceptibility.

Cross-sectional survey of cattle haemopathogens in Constantine, Northeast Algeria

This aim of the present study was to estimate the prevalence of haemopathogens in cattle in Beni Hamidene locality, district of Constantine (Νortheastern Algeria). Between June and October 2014, 169 bovines from 25 farms were included in this survey, 32 (18.9%) among them were suspected of piroplasmosis and/or anaplasmosis. Infection prevalences were estimated by microscopic examination of Giemsa‐stained blood smears and blood samples from all included cattle (n = 169). Animals were infected by Theileria annulata (65/169; 38.46%), Anaplasma marginale (22/169; 13%) and Babesia bovis (5/169; 3%). Two co‐infection patterns were found: Theileria annulata/Anaplasma marginale (7.69%) and Theileria annulata/Babesia bovis (1.18%). Only one farm had no cattle infected by any of the haemopathogens. There was a signification difference of T. annulata infection prevalence according to age category (p =.04). These results emphasised mainly the presence of bovine tropical theileriosis in northeastern, Beni Hamidene locality, province of Constantine, Algeria.

Evaluation of sporozoite and macroschizont antigen (Spm2) of Theileria annulata for its diagnostic potential

Theileria are tick-borne apicomplexan parasites, which mainly infect ruminants in tropical and subtropical regions of the world. The present study was directed to investigate the serological methods for the diagnosis of theileriosis in crossbred cattle. Blood samples (n = 176) were collected from the regional cattle populations of Bihar state situated at the Gangetic plains of India. Microscopic examination of blood smears from the cattle revealed the presence of tick-borne infectious organisms (Theileria and Anaplasma) in the region. PCR-based detection of Tams1 (Theileria annulata merozoite surface antigen) gene and the sequencing of 18S rRNA amplicon from the blood samples confirmed T. annulata as the primary causative agent of theileriosis in cattle of the Bihar region. Similarly, the amplification of the msp5 gene confirmed Anaplasma marginale infection. For the large-scale epidemiological investigation, sporozoite and macroschizont (spm2) partial gene from T. annulata was cloned in pET-28a (+) vector and overexpressed in E. coli BL21 cells. Overexpressed recombinant-Spm2 (43 kDa) was purified by Ni-NTA affinity chromatography and was used for immunodetection of theileriosis in cattle serum samples. Sequence analysis of the cloned partial spm2 gene in this study showed multiple SNPs (single nucleotide polymorphisms) in T. annulata. Recombinant-Spm2 antigen was explicitly recognised by the immunoglobulins (IgG) of the cattle naturally infected with Theileria. Further, an indirect enzyme-linked immunosorbent assay (ELISA) was developed using partial r-Spm2 antigen that exhibited high sensitivity (100 %) and specificity (90.9 %). Thus, this study suggests that partial r-Spm2 can be used as a diagnostic antigen for seroepidemiological studies of T. annulata infection in crossbred cattle.

Bovine piroplasmosis-anaplasmosis and clinical signs of tropical theileriosis in the plains of Djurdjura (north Algeria)

The study was conducted during tick activity season over a period of 5 years in the Djurdjura Plains, Algeria. A total of 299 cattle (Holstein, Montbeliard, Fleckvieh and crossbred animals) with clinical signs were included in this study. A total of 171 animals were found positive for at least one pathogen by Giemsa-stained blood smears examination Theileria annulata (136/299, 45.5%), Babesia bovis (14/299, 4.7%), B. bigemina (3/299, 1.0%) and Anaplasma marginale (12/299, 4.0%) were identified. Six animals were co-infected by T. annulata and A. marginale. Although no ticks were collected from diseased animals, clinical signs in cattle were hyperthermia (120/136, 88.3%), gluttony followed by anorexia (113/136, 83.1%), lymph node enlargement (99/136, 72.8%), anaemia (82/136, 60.3%), icterus (58/136, 42.6%) and haemoglobinuria (36/136, 26.5%). Gluttony followed by anorexia was considered highly suggestive of an incubation of tropical theileriosis as shown by a higher receptivity index (IR = 0.89-1). This clinical sign is evident in young Montbeliard and young Holstein males with anaemia (IR = 1) and icterus (IR = 0.78-0.81) which is earlier than haemoglobinuria (IR = 0.51-0.54). The incidence of T. annulata was maximum in July (n = 57), as well as B. bovis (n = 6) and A. marginale (n = 13). These results highlight the preponderance of tropical theileriosis in north-central Algeria, where gluttony followed by anorexia is probably a prodromal symptom during the incubation period of the disease.

Streptococcus halichoeri: Comparative Genomics of an Emerging Pathogen

Streptococcus halichoeri is an emerging pathogen with a variety of host species and zoonotic potential. It has been isolated from grey seals and other marine mammals as well as from human infections. Beginning in 2010, two concurrent epidemics were identified in Finland, in fur animals and domestic dogs, respectively. The fur animals suffered from a new disease fur animal epidemic necrotic pyoderma (FENP) and the dogs presented with ear infections with poor treatment response. S. halichoeri was isolated in both studies, albeit among other pathogens, indicating a possible role in the disease etiologies. The aim was to find a possible common origin of the fur animal and dog isolates and study the virulence factors to assess pathogenic potential. Isolates from seal, human, dogs, and fur animals were obtained for comparison. The whole genomes were sequenced from 20 different strains using the Illumina MiSeq platform and annotated using an automatic annotation pipeline RAST. The core and pangenomes were formed by comparing the genomes against each other in an all-against-all comparison. A phylogenetic tree was constructed using the genes of the core genome. Virulence factors were assessed using the Virulence Factor Database (VFDB) concentrating on the previously confirmed streptococcal factors. A core genome was formed which encompassed approximately half of the genes in Streptococcus halichoeri. The resulting core was nearly saturated and would not change significantly by adding more genomes. The remaining genes formed the pangenome which was highly variable and would still evolve after additional genomes. The results highlight the great adaptability of this bacterium possibly explaining the ease at which it switches hosts and environments. Virulence factors were also analyzed and were found primarily in the core genome. They represented many classes and functions, but the largest single category was adhesins which again supports the marine origin of this species.

Microbial Proteomics and Their Importance in Medical Microbiology

Microbial infection is a leading cause of death around the world. Most of the infectious diseases are caused by drug-resistant microbes; this may lead to a delay in the administration of microbiologically effective therapy (Chen et al., 2017; Del Chierico et al., 2014). Therefore, exhaustive understanding of microbial physiologies, infection and defense systems, and survival strategies is of great interest in order to actively defeat microbial infection. Microbial proteomics provides complete information of microbial physiology and expression and function of the proteins that are involved in infection and also gives a clue in clinical diagnosis and antimicrobial therapy (Pérez-Llarena and Bou, 2016; Vranakis et al., 2014). Microbial proteomics helps to identify the proteins associated with microbial activity, microbial host-pathogen interactions, and antimicrobial resistant mechanism. Microbial activity of pathogens can be confirmed by using the 2-D gel-based and gel-free method with the combination of MALDI-TOF-LC-MS/MS. Proteomic analysis of microbial host-pathogen interaction reveals valuable information about the virulence of the pathogen and its resistance; it helps in better understanding of the infection and for developing strategies against microbial infections (Cheng et al., 2016). Fig. 3.1 schematically illustrates the proteomic analysis of the bacterial samples.

Immuno-informatics Analysis to Identify Novel Vaccine Candidates and Design of a Multi-Epitope Based Vaccine Candidate Against Theileria parasites

Theileriosis poses a serious threat to ruminants in tropical and subtropical countries. It is a tick-borne disease, caused by an apicomplexan parasite, Theileria. The high disease burden in animals causes huge economic losses to marginal farmers. Further, with increasing cases of resistance to commonly used drugs, it is highly desirable to develop better and cost-effective vaccines against theileriosis. The only available vaccine, live attenuated parasite vaccine, has many drawbacks and hence is unsuitable for controlling this disease. Immuno-informatics has emerged as a useful tool in down selection of potential molecules for vaccine development. In this study, we have used an immuno-informatics driven genome-wide screening strategy to identify potential vaccine targets containing important and effective dominant immunogens against Theileria. The proteome of Theileria annulata was screened for proteins with probability of plasma membrane localization or GPI anchor. The proteins non-homologous to the host (bovine) were selected and their antigenicity was analyzed. The B-cell epitopes were identified in the selected proteins and mapped in the modeled structure of the proteins. A total of 19 linear epitopes in 12 proteins, exposed in the extracellular space and having the potential to induce protective antibodies were obtained. Additionally, CTL epitopes which are peptides with 9-mer core sequence, were also identified, modeled and docked with bovine MHC-I structures. The CTL epitopes showing high binding energy with the bovine MHC-I were further engineered in silico to design a putative multi-epitope vaccine candidate against Theileria parasites. The docking studies and molecular dynamics studies with the predicted multi-epitope vaccine candidate and modeled bovine TLR4 exhibited strong binding energy, suggesting that the complex is stable and the putative multi-epitope vaccine candidate can be a potentially good candidate for vaccine development.

Transcriptomics reveal potential vaccine antigens and a drastic increase of upregulated genes during Theileria parva development from arthropod to bovine infective stages

Theileria parva is a protozoan parasite transmitted by the brown ear tick Rhipicephalus appendiculatus that causes East Coast fever (ECF) in cattle, resulting in substantial economic losses in the regions of southern, eastern and central Africa. The schizont form of the parasite transforms the bovine host lymphocytes into actively proliferating cancer-like cells. However, how T. parva causes bovine host cells to proliferate and maintain a cancerous phenotype following infection is still poorly understood. On the other hand, current efforts to develop improved vaccines have identified only a few candidate antigens. In the present paper, we report the first comparative transcriptomic analysis throughout the course of T. parva infection. We observed that the development of sporoblast into sporozoite and then the establishment in the host cells as schizont is accompanied by a drastic increase of upregulated genes in the schizont stage of the parasite. In contrast, the ten highest gene expression values occurred in the arthropod vector stages. A comparative analysis showed that 2845 genes were upregulated in both sporozoite and schizont stages compared to the sporoblast. In addition, 647 were upregulated only in the sporozoite whereas 310 were only upregulated in the schizont. We detected low p67 expression in the schizont stage, an unexpected finding considering that p67 has been reported as a sporozoite stage-specific gene. In contrast, we found that transcription of p67 was 20 times higher in the sporoblast than in the sporozoite. Using the expression profiles of recently identified candidate vaccine antigens as a benchmark for selection for novel potential vaccine candidates, we identified three genes with expression similar to p67 and several other genes similar to Tp1-Tp10 schizont vaccine antigens. We propose that the antigenicity or chemotherapeutic potential of this panel of new candidate antigens be further investigated. Structural comparisons of the transcripts generated here with the existing gene models for the respective loci revealed indels. Our findings can be used to improve the structural annotation of the T. parva genome, and the identification of alternatively spliced transcripts.

The secreted Theileria annulata Ta9 protein contributes to activation of the AP-1 transcription factor

Theileria annulata is an obligate intracellular protozoan parasite of the phylum Apicomplexa. Theileria sporozoites invade bovine leukocytes and develop into a multinucleate syncytial macroschizont that causes uncontrolled proliferation and dissemination of infected and transformed leukocytes. Activator protein 1 (AP-1) is a transcription factor driving expression of genes involved in proliferation and dissemination and is therefore a key player in Theileria-induced leukocytes transformation. Ta9 possesses a signal peptide allowing it to be secreted into the infected leukocyte cytosol and be presented to CD8 T cells in the context of MHC class I. First, we confirmed that Ta9 is secreted into the infected leukocyte cytosol, and then we generated truncated versions of GFP-tagged Ta9 and tested their ability to activate AP-1 in non-infected HEK293T human kidney embryo cells. The ability to activate AP-1-driven transcription was found to reside in the C-terminal 100 amino acids of Ta9 distant to the N-terminally located epitopes recognised by CD8+ T cells. Secreted Ta9 has therefore, not only the ability to stimulate CD8+ T cells, but also the potential to activate AP-1-driven transcription and contribute to T. annulata-induced leukocyte transformation.