Molecular characterization of a novel 32-kDa merozoite antigen of Babesia gibsoni with a better diagnostic performance by enzyme-linked immunosorbent assay

Molecular detection and characterization of Anaplasma marginale and Babesia canis vogeli infecting dogs in Luxor, Egypt

Tick-borne diseases in animals are increasing rapidly worldwide, but there is insufficient information about tick-borne diseases infecting dogs in southern Egypt. Thus, in the current study, we detected the presence of Anaplasma marginale (A. marginale) and Babesia canis vogeli (B. canis vogeli) in the blood of dogs. The results revealed that 4/100 (4%) were positive, and a higher infection rate was found in males (75%), than females (25%). The phylogenetic analysis for the major surface protein 4 (msp4) gene in this study was compared with amplicons separate from other reported isolates with alignment by identity 100% with cattle and camels from Egypt, and the phylogenetic analysis for the B. canis vogeli small subunit ribosomal RNA (SSU rRNA) gene in this study identified identity by 99.89% with dogs from Egypt. This report is considered the first report in southern Egypt about A. marginale in dogs based on the sequence analysis of the msp4 gene, providing new data for the classification and identification of A. marginale in dogs compared to A. marginale isolated from other animals in southern Egypt.

A novel promising diagnostic candidate selected by screening the transcriptome of Babesia gibsoni (Wuhan isolate) asexual stages in infected beagles

BACKGROUND

Babesia gibsoni is one of the causative agents of canine babesiosis worldwide. Some dogs infected with B. gibsoni show severe clinical signs with progressive anemia, hemoglobinuria and splenomegaly. However, most infected dogs present a state of chronic infection and thereby may be a persistent pathogen carrier, increasing the risk of pathogen spreading. To date, little is known about this pathogen, with genomic and transcriptomic data in particular generally unavailable. This lack of knowledge extensively limits the development of effective diagnostic strategies and vaccines.

METHODS

High-throughput RNA sequencing of total RNA of B. gibsoni asexual stages collected from infected beagles was performed. The unigenes were annotated in seven databases. The genes were sorted according to their fragments per kilobase per million (FPKM) value, which was used as an indicator for expression level. The gene with the highest FPKM value was cloned from the genome of B. gibsoni and further tested for immunogenicity, cellular localization and efficacy as a potential diagnostic candidate for detecting B. gibsoni in sera collected from beagles.

RESULTS

A total of 62,580,653 clean reads were screened from the 64,336,475 raw reads, and the corresponding 70,134 transcripts and 36,587 unigenes were obtained. The gene with the highest FPKM value was screened from the unigenes; its full length was 1276 bp, and it was named BgP30. The BgP30 gene comprised three exons and two introns, with a 786-bp open reading frame, and encoded 261 amino acids with a predicted molecular weight of 30 kDa. The cellular localization assay confirmed the existence of P30 protein in B. gibsoni parasites. Moreover, P30 was detected in the serum of experimentally B. gibsoni-infected beagles, from 15 days up to 422 days post-infection, suggesting its usefulness as a diagnostic candidate for both acute and chronic infections.

CONCLUSIONS

We sequenced the transcriptome of B. gibsoni asexual stages for the first time. The BgP30 gene was highly expressed in the transcriptome screening experiments, with further studies demonstrating that it could induce immune response in B. gibsoni-infected dogs. These results lead us to suggest that bgP30 may be a good diagnostic candidate marker to detect both acute and chronic B. gibsoni infections.

Evaluation of recombinant BgSA3 protein based indirect-ELISA for sero-diagnosis and sero-surveillance of Babesia gibsoni in dogs

Canine babesiosis, a tick-borne haemoprotozoan disease of dogs, is of significance globally due to its rapid spread. A precise confirmatory diagnosis is required to curtail the rapid spread of infection. Our study described the evaluation of recombinant BgSA3 protein based indirect ELISA for sero-diagnosis and sero-surveillance of Babesia gibsoni infection in dogs. A partial BgSA3 gene segment (1921 bp) of B. gibsoni, encoding for recombinant truncated BgSA3 (75 kDa) protein devoid of predicted signal peptide (23 aa) at N-terminus and transmembrane region (20 aa) at C-terminus, was expressed in E. coli using a pET28a(+) vector. The rBgSA3 protein purified under native conditions using Ni-NTA superflow cartridge was confirmed by SDS-PAGE and Western blotting using sera from dogs infected/uninfected with B. gibsoni, and erythrocyte lysate/ plasma from infected/uninfected dogs. The rBgSA3 protein was specific only to B. gibsoni antibodies but did not react with uninfected sera. Further, rBgSA3 protein was evaluated for sero-diagnosis/sero-surveillance using Indirect-ELISA format. There was no cross reactivity to B. vogeli, E. canis, H. canis and D. repens infected dogs serum samples. The diagnostic sensitivity and specificity of rBgSA3 based I-ELISA was found to be 86.4 and 93.1 % respectively, in comparison with cytb based PCR assay. Additionally, rBgSA3-ELISA evaluated using survey serum samples (n = 287), detected 11.85 % samples as positive. In conclusion, B. gibsoni infection, an emerging disease is prevalent in the present study area and the standardized rBgSA3 protein based indirect-ELISA was found to be a specific and sensitive test for large scale sero-diagnosis and sero-surveillance of B. gibsoni infection in dogs.

Detection of Babesia gibsoni in dogs by combining recombinase polymerase amplification (RPA) with lateral flow (LF) dipstick

Babesia gibsoni is a protozoan parasite responsible for the majority of reported cases of canine babesiosis in China. Currently, microscopic examination of the Giemsa-stained thin blood smears is the main diagnosis method in clinic. Here, we report the recombinase polymerase amplification-lateral flow (LF-RPA) dipstick detection method for targeting B. gibsoni cytochrome c oxidase subunit I (cox I) gene. The reaction takes only 20-30 min under isothermal temperatures between 30 and 45 °C. Specificity was evaluated using DNA from related apicomplexan parasites and their host, while the sensitivity was calculated based on the DNA from the experimental B. gibsoni-infected dogs. Results indicated that the LF-RPA method is 20 times more sensitive than the conventional PCR based on 18S rRNA and has no cross reaction with any other test DNAs. The applicability of the LF-RPA method was further evaluated using 15 samples collected from clinic. Thirteen of the 15 samples (86.67%) were detected as positive by LF-RPA, while 10 of them (66.67%) were found positive by conventional PCR. Overall, the novel LF-RPA assay is effective for the detection of B. gobsini and has considerable advantages over the conventional PCR in sensitivity, specificity, simplicity in operation, less time consumption, and visual detection. The LF-RPA method may facilitate the surveillance and early detection of B. gibsoni infection in dogs.

Development of recombinant BgP12 based enzyme linked immunosorbent assays for serodiagnosis of Babesia gibsoni infection in dogs

Indirect ELISA and dot-ELISA using recombinant BgP12 (rBgP12) were developed for the diagnosis of Babesia gibsoni infected dogs. The complete open reading frame of BgP12 gene (378bp) was cloned in pET-32a(+) expression vector and expressed in Escherichia coli as a soluble thioredoxin (Trx) fusion protein. The purified rBgP12 was used for production of anti-rBgP12 rabbit serum, which recognized a native 12-kDa protein in B. gibsoni infected erythrocyte by Western blot analysis. To evaluate the potential of rBgP12 for the serodiagnosis of B. gibsoni, a panel of serum/plasma samples from dogs infected with B. gibsoni (n=13), uninfected sera (n=13) and sera from dogs infected with other haemoparasites viz., Babesia canis vogeli (n=3), Ehrlichia canis (n=3), Hepatozoon canis (n=1) and Dirofilaria immitis (n=1) were used in ELISA formats. In addition, the performance of rBgP12 based indirect ELISA and dot-ELISA were evaluated using 75 serum/plasma samples collected from suspected dogs, in respect to the nested PCR as reference test. The diagnostic sensitivities of indirect ELISA and dot-ELISA were 94.59% and 89.18%, respectively, while their specificities were 84.21% and 81.57%, respectively. Moreover, both the assays using rBgP12 showed no cross reaction with sera from dogs infected with other common haemoparasites indicating their high specificity. High kappa values of indirect ELISA and dot-ELISA indicated the potentials of these assays with substantial agreement at 95% confidence level. It is concluded that indirect ELISA and dot ELISA using rBgP12 might be used in large scale epidemiological surveys and clinical diagnosis of B. gibsoni infection in dogs.

Identification and characterization of a novel 34 kDa merozoite protein in Babesia orientalis

A novel Babesia orientalis 34 kDa protein (designated BoP34) was obtained by immunoscreening of a cDNA expression library using B. orientalis infected water buffalo serum. The complete nucleotide sequence of the BoP34 was 1088 bp, which contained one open reading frame (ORF), two untranslated regions (UTRs) and a poly (A) tail. The length of ORF was 933 bp, encoding a polypeptide of 310 aa with a predicted size of 34 kDa. BLAST analysis showed that the nucleotide sequence of BoP34 had 71% similarity with that of the Babesia bovis gene XM_001611335, which encodes a nuclear movement family protein. This suggested that BoP34 is a homologous of the movement family protein. Structural analysis of the BoP34 protein indicated a CS domain which may interact with the ATPase domain of the heat shock protein 90. A truncated version of BoP34 was cloned into the expression vector pET-32a and subsequently expressed and purified from the Escherichia coli Rosetta™ (DE3) pLysS stain as a Trx-fusion (designated rBoP34-T). Antibodies in the serum of a B. orientalis-infected water buffalo were able to recognize this protein in immune-bloting analysis. Rabbit antibodies raised against rBoP34-T could detecte native BoP34 (34 kDa) in B. orientalis-infected water buffalo erythrocytes. These results suggested that BoP34 might be a good diagnostic antigen for the specific detection of anti-B. orientalis antibody in water buffalo. Further research is required to explore the biological function and diagnostic potential of this molecule.

New Molecules in Babesia gibsoni and their application for diagnosis, vaccine development, and drug discovery

Babesia gibsoni is an intraerythrocytic apicomplexan parasite that causes piroplasmosis in dogs. B. gibsoni infection is characterized clinically by fever, regenerative anemia, splenomegaly, and sometimes death. Since no vaccine is available, rapid and accurate diagnosis and prompt treatment of infected animals are required to control this disease. Over the past decade, several candidate molecules have been identified using biomolecular techniques in the authors' laboratory for the development of a serodiagnostic method, vaccine, and drug for B. gibsoni. This review article describes newly identified candidate molecules and their applications for diagnosis, vaccine production, and drug development of B. gibsoni.

Four promising antigens, BgP32, BgP45, BgP47, and BgP50, for serodiagnosis of Babesia gibsoni infection were classified as B. gibsoni merozoite surface protein family

We determined the molecular characteristics of four proteins, BgP32, BgP45, BgP47, and BgP50, of Babesia gibsoni. Localization by subcellular fractionations followed by Western blotting revealed that the corresponding native proteins belong to merozoite surface protein family of B. gibsoni (BgMSP). Moreover, antisera against either rBgP45 or rBgP47 cross-reacted with all the proteins of the BgMSP family on ELISA and IFAT analyses. Of the four candidate antigens, ELISA with rBgP45 yielded high sensitivity, and ELISA with rBgP32 resulted in high specificity and in concordance with IFAT results.

Expression of truncated Babesia gibsoni thrombospondin-related adhesive proteins in Escherichia coli and evaluation of their diagnostic potential by enzyme-linked immunosorbent assay

Among the previously established enzyme-linked immunosorbent assays (ELISAs), an ELISA using the full length of a recombinant thrombospondin-related adhesive protein of Babesia gibsoni (rBgTRAPf) is considered as the most sensitive diagnostic method for the detection of an antibody to B. gibsoni in dogs. However, the expression of rBgTRAPf in high concentration is poor and, thus, limits its usefulness as a diagnostic antigen. To improve its expression level, we have truncated BgTRAPf into two fragments having either an N- or a C-terminus (BgTRAPn or BgTRAPc, respectively). The expression of BgTRAPc protein in Escherichia coli yielded adequate recombinant protein. The specificity and sensitivity of ELISAs with the truncated proteins were determined using dog sera experimentally infected with B. gibsoni and specific pathogen-free (SPF) dog sera. A total of 254 field dog sera were examined by the ELISA with rBgTRAPn, rBgTRAPc, and rBgTRAPf as well as by an indirect fluorescent antibody test (IFAT). The specificity of rBgTRAPc was the highest (97.15%), and its kappa value was more (0.8003) than rBgTRAPn (0.7083). With a sufficient level of expression as well as higher specificity and reliable sensitivity, rBgTRAPc appears to be a potential candidate antigen for the serodiagnosis of B. gibsoni infection in dogs.

Clinical management of canine babesiosis

OBJECTIVE

To review and summarize current information regarding epidemiology, pathogenesis, and pathophysiology leading to the various clinical syndromes associated with canine babesiosis. Diagnosis, treatment, preventative strategies, and zoonotic implications are discussed.

ETIOLOGY

Babesiosis is caused by hemoprotozoa of the genus Babesia. Numerous species of Babesia exist worldwide. An increased incidence of babesiosis is described, especially in North America. The babesial organism spends the majority of its life cycle within the erythrocyte of the definitive host, resulting in hemolysis, with or without systemic complications.

DIAGNOSIS

Definitive diagnosis depends on direct visualization of the organism on blood smear or polymerase chain reaction. A positive serologic antibody test indicates exposure with or without active infection.

THERAPY

Antiprotozoal drugs, antimicrobials, and supportive care are the mainstays of babesiosis therapy.

PROGNOSIS

Prognosis depends on the severity of disease, which in turn depends on both organism and host factors. Clinical syndromes associated with a poorer prognosis include red biliary syndrome, acute renal failure, acute respiratory distress syndrome, neurologic dysfunction, acute pancreatitis, cardiac dysfunction, and hypoglycemia.

Canine babesiosis: from molecular taxonomy to control

Canine babesiosis is a clinically significant emerging vector-borne disease caused by protozoan haemoparasites. This review article considers recent literature pertaining to the taxonomic classification of Babesia and Theileria species affecting dogs and the geographical distribution of these parasites. The diagnosis of canine babesiosis by traditional, molecular and serological methods is reviewed, together with recent advances in our understanding of the pathophysiology of piroplasmosis, and of the treatment and prevention of this disease.

Cloning, expression, and characterization of Babesia gibsoni dihydrofolate reductase-thymidylate synthase: inhibitory effect of antifolates on its catalytic activity and parasite proliferation

Dihydrofolate reductase-thymidylate synthase (DHFR-TS) is a well-validated antifolate drug target in certain pathogenic apicomplexans, but not in the genus Babesia, including Babesia gibsoni. Therefore, we isolated, cloned, and expressed the wild-type B. gibsoni dhfr-ts gene in Escherichia coli and evaluated the inhibitory effect of antifolates on its enzyme activity, as well as on in vitro parasite growth. The full-length gene consists of a 1,548-bp open reading frame encoding a 58.8-kDa translated peptide containing DHFR and TS domains linked together in a single polypeptide chain. Each domain contained active-site amino acid residues responsible for the enzymatic activity. The expressed soluble recombinant DHFR-TS protein was approximately 57 kDa after glutathione S-transferase (GST) cleavage, similar to an approximately 58-kDa native enzyme identified from the parasite merozoite. The non-GST fusion recombinant DHFR enzyme revealed K(m) values of 4.70 +/- 0.059 (mean +/- standard error of the mean) and 9.75 +/- 1.64 microM for dihydrofolic acid (DHF) and NADPH, respectively. Methotrexate was a more-potent inhibitor of the enzymatic activity (50% inhibition concentration [IC(50)] = 68.6 +/- 5.20 nM) than pyrimethamine (IC(50) = 55.0 +/- 2.08 microM) and trimethoprim (IC(50) = 50 +/- 12.5 microM). Moreover, the antifolates' inhibitory effects on DHFR enzyme activity paralleled their inhibition of the parasite growth in vitro, indicating that the B. gibsoni DHFR could be a model for studying antifolate compounds as potential drug candidates. Therefore, the B. gibsoni DHFR-TS is a molecular antifolate drug target.