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

Evaluation of recombinant Babesia gibsoni thrombospondin-related adhesive protein (BgTRAP) for the sero-diagnosis of canine babesiosis

Canine babesiosis, caused by Babesia gibsoni is one of the most significant tick-borne illnesses across the world. Light microscopy as well as polymerase chain reaction may fail in the diagnosis of disease when the level of parasitaemia is very low during subclinical and chronic cases. The serological techniques using a recombinant protein will be useful for the accurate and sensitive surveillance of the disease, especially in chronic cases. The present study describes the evaluation of recombinant N-terminal B. gibsoni Thrombospondin-related adhesive protein (BgTRAP) based indirect ELISA for the sero-diagnosis of B. gibsoni infection in dogs. A partial N-terminal BgTRAP gene (870 bp) of B. gibsoni, was expressed in Escherichia coli using a pET32a (+) vector. The recombinant BgTRAP based indirect ELISA was compared with the PCR targeting the same gene. A sensitivity and a specificity of 84% and 73.33% were observed in the indirect ELISA. The accuracy, positive predictive value and negative predictive value were 78.18%, 72.30%, 84.60% respectively. The rBgTRAP antigen did not show any cross-reactivity with sera from dogs infected with common helminth parasites viz. Ancylostoma caninum, Dirofilaria immitis, D. repens, Spirometra spp., Toxocara canis and haemoparasites like Trypanosoma evansi, Babesia vogeli, Hepatozoon canis and Ehrlichia canis.

Babesia gibsoni Whole-Genome Sequencing, Assembling, Annotation, and Comparative Analysis

The intracellular protozoan parasite Babesia gibsoni infects canine erythrocytes and causes babesiosis. The hazards to animal health have increased due to the rise of B. gibsoni infections and medication resistance. However, the lack of high-quality full-genome sequencing sets has expanded the obstacles to the development of pathogeneses, drugs, and vaccines. In this study, the whole genome of B. gibsoni was sequenced, assembled, and annotated. The genomic size of B. gibsoni was 7.94 Mbp in total. Four chromosomes with the size of 0.69 Mb, 2.10 Mb, 2.77 Mb, and 2.38 Mb, respectively, 1 apicoplast (28.4 Kb), and 1 mitochondrion (5.9 Kb) were confirmed. KEGG analysis revealed 2,641 putative proteins enriched on 316 pathways, and GO analysis showed 7,571 annotations of the nuclear genome in total. Synteny analysis showed a high correlation between B. gibsoni and B. bovis. A new divergent point of B. gibsoni occurred around 297.7 million years ago, which was earlier than that of B. bovis, B. ovata, and B. bigemina. Orthology analysis revealed 22 and 32 unique genes compared to several Babesia spp. and apicomplexan species. The metabolic pathways of B.gibsoni were characterized, pointing to a minimal size of the genome. A species-specific secretory protein SA1 and 19 homologous genes were identified. Selected specific proteins, including apetala 2 (AP2) factor, invasion-related proteins BgAMA-1 and BgRON2, and rhoptry function proteins BgWH_04g00700 were predicted, visualized, and modeled. Overall, whole-genome sequencing provided molecular-level support for the diagnosis, prevention, clinical treatment, and further research of B. gibsoni. IMPORTANCE The whole genome of B. gibsoni was first sequenced, annotated, and disclosed. The key part of genome composition, four chromosomes, was comparatively analyzed for the first time. A full-scale phylogeny evolution analysis based on the whole-genome-wide data of B. gibsoni was performed, and a new divergent point on the evolutionary path was revealed. In previous reports, molecular studies were often limited by incomplete genomic data, especially in key areas like life cycle regulation, metabolism, and host-pathogen interaction. With the whole-genome sequencing of B. gibsoni, we provide useful genetic data to encourage the exploration of new terrain and make it feasible to resolve the theoretical and practical problems of babesiosis.

Identification of three members of the multidomain adhesion CCp family in Babesia gibsoni

Babesia gibsoni is an intraerythrocytic apicomplexan parasite transmitted by Haemaphysalis longicornis and causes canine babesiosis. Within the tick, the Babesia parasite undergoes sexual conjugation and the sporogony process of its life cycle. To control B. gibsoni infection, prompt and effective treatment of acute infections and curing chronic carriers are urgently needed. Gene disruption of Plasmodium CCps resulted in blocking the transition of sporozoites from the mosquito midgut to the salivary glands, showing that these proteins are potential targets for the development of a transmission-blocking vaccine. In this study, we described the identification and characterization of three members of the CCp family in B. gibsoni, named CCp1, CCp2, and CCp3. The B. gibsoni sexual stages were induced in vitro by exposing parasites to xanthurenic acid (XA), dithiothreitol (DTT), and tris (2-carboxyethyl) phosphine (TCEP) at serial concentrations. Among them, 100 µM XA-exposed and cultured at 27 °C without CO₂B. gibsoni presented diverse morphologies, including parasites with long projections, gradually increased free merozoites, and aggregated and round forms, indicative of sexual stage induction. Then, the expression of CCp proteins of induced parasites was confirmed by real-time reverse transcription PCR, immunofluorescence, and western blot. The results showed that BgCCp genes were highly significantly increased at 24 h post-sexual stage induction (p < 0.01). The induced parasites were recognized by anti-CCp mouse antisera and anti-CCp 1, 2, and 3 antibodies weakly reacted with sexual stage proteins of expected molecular weights of 179.4, 169.8, and 140.0 KDa, respectively. Our observations on morphological changes and confirmation of sexual stage protein expression will advance elemental biological research and lay the foundation for the development of transmission-blocking vaccines against canine babesiosis.

Phylogenetic analysis of Babesia gibsoni isolates of south India using apical membrane antigen, 50 kDa surface antigen, and 70 kDa heat shock protein genes

The prevalence of canine babesiosis due to Babesia gibsoni has increased throughout the world including in southern India. The polymerase chain reaction (PCR) based molecular characterization of B. gibsoni in dogs of Kerala, south India, targeting three specific genes viz., apical membrane antigen (AMA1), 50 kDa surface antigen (P50), and heat shock protein (HSP70) was undertaken in this study. Out of 297 blood samples collected from clinically suspected animals, microscopy detected piroplasms of B. gibsoni in 60 (20.20 per cent), while the PCR targeting the BgP50 gene detected 85 (28.61 per cent). Polymerase chain reaction targeting the BgAMA1 and BgHSP70 detected a lesser number of samples (60 and 65 respectively) as positive. The phylogenetic analysis of BgHSP70 gene sequences did not reveal genetic heterogeneity among the B. gibsoni isolates of South India and from other countries, while the BgP50 gene differentiated the Indian isolates from Japanese isolates. When BgAMA1 was used for phylogenetic analysis, genetic variation was not observed among Indian and Taiwanese isolates, however, differentiated them from the Japanese isolates.

Establishment and Application of an Indirect Enzyme-Linked Immunosorbent Assay for Measuring GPI-Anchored Protein 52 (P52) Antibodies in Babesia gibsoni-Infected Dogs

Babesia gibsoni is a malaria-like protozoan that parasitizes the red blood cells of canids to cause babesiosis. Due to its high expression and essential function in the survival of parasites, the Glycosylphosphatidylinositol (GPI) anchor protein family is considered an excellent immunodiagnostic marker. Herein, we identified a novel GPI-anchored protein named as BgGPI52-WH with a size of 52 kDa; the recombinant BgGPI52-WH with high antigenicity and immunogenicity was used as a diagnostic antigen to establish a new iELISA method. The iELISA had a sensitivity of 1:400, and no cross-reaction with other apicomplexan parasites occurred. We further demonstrated that the degree of variation was less than 10% using the same samples from the same or different batches of an enzyme-labeled strip. It was found that the method was able to detect early infection (6 days after infection) in the sera of the B. gibsoni-infected experimental dogs in which antibody response to rBgGPI52-WH was evaluated. Clinical sera from pet hospitals were further tested, and the average positive rate was about 11.41% (17/149). The results indicate that BgGPI52-WH is a reliable diagnostic antigen, and the new iELISA could be used as a practical method for the early diagnosis of B. gibsoni.

Molecular survey and phylogenetic analysis of Babesia vogeli in dogs

Canine babesiosis is a life-threatening haemoparasitic disease in dogs that is prevalent worldwide. In this study, the prevalence of Babesia vogeli (B. vogeli) was investigated in dogs from Egypt by using Polymerase Chain Reaction (PCR) assay, and associated risk factors were evaluated. In addition, phylogenetic position of B. vogeli Egyptian isolate was determined by sequencing. A total of 275 blood samples were taken from dogs located in four governorates belonging to the north of Egypt. Samples were examined by PCR targeting the B. vogeli 18S rRNA gene and this species was also confirmed by sequencing. Overall, the prevalence of B. vogeli was 5.1% among the studied dogs and the highest prevalence rate was found in the Giza governorate. Univariate logistic regression was used to evaluate each variable individually. The results revealed a significant association between the prevalence of B. vogeli infection and whether or not dogs were infested with ticks and the type of floor used in dog shelters. Additionally, tick infestation (OR 6.1, 95% CI 1.2-31.4), and living in shelters with soil floors (OR 3.8, 95% CI 0.8-17.8) were identified as potential risk factors for B. vogeli infection. Phylogenetic analysis was performed using B. vogeli 18S rRNA partial sequences with the hypervariable V4 region from GenBank. The Egyptian isolate was assigned to second sub-cluster with B. vogeli isolates from Japan, Venezuela and Paraguay within the B. vogeli/B. canis cluster. The present data will be useful to improve the understanding of canine babesiosis epidemiology and ways to control the disease in companion dogs.

THE INFECTION AND SPECIES IDENTIFICATION OF CANINE BABESIA SPP. IN PARTS OF SHAANXI PROVINCE

Canine babesiosis is a serious disease among tick-borne haemoprotozoan diseases that threaten dog health. To find out the prevalence of canine babesiosis and its main pathogenic species in Shaanxi Province, the study was centered on the infection of babesiosis in dogs in different regions of the Province. First, a total of 367 blood samples were collected in Shaanxi Province, and 53 Babesia nucleic-acid-positive samples were found by polymerase chain reaction (PCR) identification, with a positive rate of 14.44%, and Babesia gibsoni was found by sequencing analysis. Further analysis showed that the prevalence of canine babesiosis was significantly different in 5 regions. There was no significant difference in infection rates between age groups, with the lowest prevalence in young dogs (10.81%) and the highest in adult dogs (17.29%). The infection rate in male dogs was higher than in female dogs. The morbidity of canine Babesia spp. was significantly different between different seasons, with the highest infection rate in autumn (27.78%) and the lowest in winter (6.10%). In conclusion, the epidemicity of canine Babesia spp. in dogs was mainly affected by region and season, and B. gibsoni was the most common canine Babesia spp. within Shaanxi Province in our study. These results provide basic data for the prevention and control of canine babesiosis in this region.

In vitro screening of novel anti-Babesia gibsoni drugs from natural products

Babesia gibsoni is a tick-transmitted intraerythrocytic apicomplexan parasite that causes babesiosis in dogs. Due to the strong side effects and lack of efficacy of current drugs, novel drugs against B. gibsoni are urgently needed. Natural products as a source for new drugs is a good choice for screening drugs against B. gibsoni. The current study focuses on identifying novel potential drugs from natural products against B. gibsoniin vitro. Parasite inhibition was verified using a SYBR green I-based fluorescence assay. A total of 502 natural product compounds were screened for anti-B. gibsoni activity in vitro. Twenty-four compounds showed high growth inhibition (>80%) on B. gibsoni and 5 plant-derived compounds were selected for further study. The half-maximal inhibitory concentration (IC₅₀) values of lycorine (LY), vincristine sulfate (VS), emetine·2HCl (EME), harringtonine (HT) and cephaeline·HBr (CEP) were 784.4 ± 3.3, 643.0 ± 2.8, 253.1 ± 1.4, 23.4 ± 1.2, and 108.1 ± 4.3 nM, respectively. The Madin-Darby canine kidney (MDCK) cell line was used to assess cytotoxicity of hit compounds. All compounds showed minimal toxicity to the MDCK cells. The effects of hit compounds combined with diminazene aceturate (DA) on B. gibsoni were further evaluated in vitro. VS, EME, HT or CEP combined with DA showed synergistic effects against B. gibsoni, whereas LY combined with DA showed an antagonistic effect against B. gibsoni. The results obtained in this study indicate that LY, VS, EME, HT and CEP are promising compounds for B. gibsoni treatment.

Survey and Molecular Study of Babesia gibsoni in Dogs of Baghdad Province, Iraq

This study aimed to detect Babesia gibsoni (B. gibsoni) in dogs of different ages, sex and breeds in Baghdad province by microscopic and molecular investigations using polymerase chain reaction (PCR), sequencing, and phylogenetic analyses. The present study was investigated B. gibsoni in 310 blood samples of dogs for the period from December 2018 to September 2019 in Baghdad province, Iraq. The molecular study was carried out by using universal primers of Babesia spp. (PIRO-A and PIRO-B) and specific primers of B. gibsoni (BAGIF and BAGIR) products size of 410 bp and 488 bp fragments of 18S rRNA gene respectively. The clinical signs revealed higher percentage and specific clinical signs of B. gibsoni as depression, anorexia, fever, pale mucus membrane, and ticks infestation, however icterus, and dead were low in which only occurred in two dogs out of infected dogs. The PCR assay and microscopic diagnosis revealed the infection rate of B. gibsoni 9 out of 310 (2.9%) in dogs. The sequence data analyses of nine DNA products were 98-100% similar to sequences of 18S rRNA gene of B. gibsoni data available in Gene bank. According to breed, age, and sex, the results revealed a significantly high-risk factor of infection in Husky dogs; B. gibsoni detected in females which was increased non-significantly than males; while the highest occurrence of disease was in young dogs aged three years or less in addition to the above, the infection rate of B. gibsoni was high in spring season. In conclusion, this study was considered the first molecular record of B. gibsoni in Baghdad, Iraq documented no differences in diagnosis by blood smear and conventional PCR to amplify of 18S rRNA gene and partial sequencing of B. gibsoni with low-cost method and easily done.

Babesia canis spp. in dogs in Baghdad Province, Iraq: First molecular identification and clinical and epidemiological study

AIMS

The aim of this study was to investigate babesiosis in dogs of different breeds and ages and of both sexes in Baghdad Province by molecular detection of Babesia canis using conventional polymerase chain reaction (PCR) and sequencing followed by phylogenetic analyses.

MATERIALS AND METHODS

Blood samples were collected from 310 dogs of different ages and breeds, and of both sexes in different areas of Baghdad Province from December 2018 to September 2019; during clinical examinations, body temperature, pulse, respiratory rate, and signs of diseases were recorded. PCR was used to amplify a specific 450-bp fragment of the 18S rRNA gene of B. canis. PCR products were sequenced, and MEGA 6.0 software was used for analysis. Chi-square and odds ratio tests were used to investigate the prevalence and risk factors of babesiosis.

RESULTS

Clinical signs of babesiosis included paleness or icterus of the mucus membranes, tick infestation, and febrile illness during the acute and subacute phase. The prevalence of infection with B. canis was 5.1%, with the higher prevalence in male dogs and in dogs <3 years of age. Huskies were more likely to be infected than other dogs. Infection prevalence was highest in April and June and was higher in spring and summer than in winter. Using sequence data, 14 isolates of Babesia canis canis and one isolate of each Babesia canis rossi and Babesia canis vogeli were identified. Phylogenetic analyses of B. canis canis revealed that three shared clades and several isolated lineages were similar to other isolates (97-99% similarity), whereas B. canis vogeli and B. canis rossi showed similarities of 98% and 99% with isolates from other geographical regions.

CONCLUSION

This study provides the first molecular record and phylogenic analysis of B. canis in dogs in Iraq, and it will be valuable for confirming clinical signs and studying epidemiological risk factors of babesiosis in dogs.

Closing the empty anti-Babesia gibsoni drug pipeline in vitro using fluorescence-based high throughput screening assay

In the current study, we evaluated the usefulness of a SYBR Green I (SG I) fluorescence assay for evaluation of the inhibitory effects of antibabesial drugs against the in vitro growth of Babesia gibsoni. Linearity and high-throughput screening (HTS) assays exhibited the validity of the SG I fluorescence assay for B. gibsoni parasite when performed at low hematocrits (HCTs) (2.5% and 5%) without daily changing of the medium. Interestingly, 5% HCT showed the highest value of the signal/noise ratio. Of note, there were no significant differences (P > .05) in the IC₅₀s of the commonly used antibabesial drugs (diminazene aceturate and/or imidocarb dipropionate) that calculated by either the SG I fluorescence assay with and without daily medium changing or by the fluorescence and microscopy methods at 2.5% and 5% HCTs. Such results confirmed that both HCTs are valid for mass drug screening against the in vitro growth of B. gibsoni. While the results of the HTS assay add merit to the assay when performed at 5% HCT especially when incubating the plates for 2 h in a dark after adding lysis buffer with SG I stain. Next, nine different drugs were screened to confirm the assay's usefulness. MMV396693, pyronaridine tetraphosphate and nerolidol drugs exhibited the highest effectiveness against the in vitro growth of B. gibsoni, next to diminazene aceturate. In summary, SG I fluorescence assay with 5% HCT without daily changing of the medium for B. gibsoni offers a novel approach for the large-scale screening of huge chemical libraries in in vitro cultures.

Evaluation of Babesia gibsoni GPI-anchored Protein 47 (BgGPI47-WH) as a Potential Diagnostic Antigen by Enzyme-Linked Immunosorbent Assay

Babesia gibsoni is one of the important pathogens causing severe incurable canine babesiosis, suggesting the necessity to develop a sensitive, specific, and highly automated diagnostic method for clinical application. Surface proteins are ideal candidates for diagnostic targets because they are the primary targets for host immune responses during host-parasite interactions. Glycosylphosphatidylinositol (GPI)-anchored proteins are abundant on the surface of parasites and play an important role in parasite diagnosis. In this study, a GPI-anchored protein named BgGPI47-WH was obtained and mouse anti-rBgGPI47-WH polyclonal antibody was produced by immunizing mice with the purified protein and Freund's adjuvant. Western blot was used to identify the native form and immunogenicity of BgGPI47-WH. An ELISA method was established by using recombinant BgGPI47-WH protein to evaluate its potential as a diagnostic antigen and the established method exhibited high specificity. The antibody response was evaluated by using the B. gibsoni-infected sera collected from different experimental dogs and the established ELISA could recognize antibodies at day 6 until day 101 post infection, indicating the potential use of BgGPI47-WH for early stage diagnosis. The specificity of the established ELISA was further evaluated by using 147 clinical samples collected from animal hospitals and 17.0% (25/147) of the samples were tested positive, with an overall proportion agreement of 86.39% between the results from BgGPI47-WH and BgSA1. Our results indicated that BgGPI47-WH could be used as a reliable diagnostic antigen and this study has proposed a practical method for early diagnosis of B. gibsoni.

Two Imported Cases of Babesiosis with Complication or Co-Infection with Lyme Disease in Republic of Korea

Babesiosis, caused by Babesia microti and B. divergens, is transmitted by Ixodid ticks. Symptoms of babesiosis vary from a mild flu-like illness to acute, severe, and sometimes fatal and fulminant disease. In Korea, 7 imported babesiosis cases and 1 endemic case have been reported. We report 2 cases of severe babesiosis initially mistaken as malaria. The first patient was complicated by shock and splenic infarction, the other co-infected with Lyme disease. As the population traveling abroad increases every year, physicians should be aware of babesiosis which mimics malaria, co-infection with other diseases, and its complications.

Babesia gibsoni endemic to Wuhan, China: mitochondrial genome sequencing, annotation, and comparison with apicomplexan parasites

Babesia gibsoni (B. gibsoni), an intracellular apicomplexan protozoan, poses great threat to canine health. Currently, little information is available about the B. gibsoni (WH58) endemic to Wuhan, China. Here, the mitochondrial (mt) genome of B. gibsoni (WH58) was amplified by five pairs of primers and sequenced and annotated by alignment with the reported mt genome sequences of Babesia canis (B. canis, KC207822), Babesia orientalis (KF218819), Babesia bovis (AB499088), and Theileria equi (AB499091). The evolutionary relationships were analyzed with the amino acid sequences of cytochrome c oxidase I (cox1) and cytochrome b (cob) genes in apicomplexan parasite species. Additionally, the mt genomes of Babesia, Theileria, and Plasmodium spp. were compared in size, host infection, form, distribution, and direction of the protein-coding genes. The full size of the mt genome of B. gibsoni (WH58) was 5865 bp with a linear form, containing terminal-inverted repeats on both ends, six large subunit ribosomal RNA fragments, and three protein-coding genes: cox1, cob, and cytochrome c oxidase III (cox3). Babesia, Theileria, and Plasmodium spp. had a similar mt genome size of about 6000 bp. The mt genomes of parasites that cause canine babesiosis showed a slightly smaller size than the other species. Moreover, Babesia microti (R1 strain) was about 11,100 bp in size, which was twice larger than that of the other species. The mt form was linear for Babesia and Theileria spp. but circular for Plasmodium falciparum and Plasmodium knowlesi. Additionally, all the species contained the three protein-coding genes of cox1, cox3, and cob except Toxoplasma gondii (RH strain) which only contained the cox1 and cob genes. The phylogenetic analysis indicated that B. gibsoni (WH58) was more identical to B. gibsoni (AB499087), B. canis (KC207822), and Babesia rossi (KC207823) and most divergent from Babesia conradae in Babesia spp. Despite the highest similarity to B. gibsoni (AB499087) reported in Japan, B. gibsoni (WH58) showed notable differences in the sequence of nucleotides and amino acids and the property in virulence to host and in vitro cultivation. This study compared the mt genomes of the two B. gibsoni isolates and other parasites in the phylum Apicomplexa and provided new insights into their differences and evolutionary relationships.

Establishment of a stable transfection system for genetic manipulation of Babesia gibsoni

Background

Genetic manipulation techniques, such as transfection, have been previously reported in many protozoan parasites. In Babesia, stable transfection systems have only been established for bovine Babesia parasites. We recently reported a transient transfection system and the selection of promoter candidates for Babesia gibsoni. The establishment of a stable transfection system for B. gibsoni is considered to be urgent to improve our understanding of the basic biology of canine Babesia parasites for a better control of babesiosis.

Results

GFP-expressing parasites were observed by fluorescence microscopy as early as two weeks after drug selection, and consistently expressed GFP for more than 3 months without drug pressure. Genome integration was confirmed by PCR, sequencing and Southern blot analysis.

Conclusions

We present the first successful establishment of a stable transfection system for B. gibsoni. This finding will facilitate functional analysis of Babesia genomes using genetic manipulation and will serve as a foundation for the development of tick-Babesia and host-Babesia infection models.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2853-1) contains supplementary material, which is available to authorized users.

Identification and characterization of interchangeable cross-species functional promoters between Babesia gibsoni and Babesia bovis

The development of transgenic techniques has been reported in many protozoan parasites over the past few years. We recently established a successful transient transfection system for Babesia gibsoni based on Bg 5'-ef-1α promoter. This study investigated 6 homologous and 6 heterologous promoters for B. gibsoni and B. bovis and identified novel interchangeable cross-species functional promoters between B. gibsoni and B. bovis. Ten out of twelve promoters had heterologous promoter function. In particular, Bg 5'-ef-1α and Bg 5'-actin heterologous promoters resulted in a significantly higher luciferase activity than Bb 5'-ef-1α homologous promoter in B. bovis. The present study showed that Bg 5'-actin promoted the highest luciferase activity in both B. gibsoni and B. bovis. The study further indicates that heterologous promoter function widely exists between B. gibsoni and B. bovis. This finding is an important step for future stable transfection construct design and for the production of vaccines based on transfected B. gibsoni and B. bovis parasites.

Transient transfection of intraerythrocytic Babesia gibsoni using elongation factor-1 alpha promoter

The development of gene manipulation techniques has been reported in many protozoan parasites over the past few years. However, these techniques have not yet been established for Babesia gibsoni. Here, we report for the first time, the successful transient transfection of B. gibsoni. The plasmid containing the firefly luciferase reporter gene (pBS-ELA) was transfected into B. gibsoni by an AMAXA 4D Nucleofector™ device. Transfection using program FA113 and Lonza buffer SF showed the highest luciferase expression. Twenty micrograms of plasmid produced the highest relative transfection efficiency. The fluorescent protein-expressing parasites were determined by GFP-containing plasmid (pBS-EGA) at 48 and 72h post transfection. This finding is the first step towards a stable transfection method for B. gibsoni, which may contribute to a better understanding of the biology of the parasite.