Merozoite proteins from Babesia sp. BQ1 (Lintan) as potential antigens for serodiagnosis by ELISA

A universal ELISA assay for detecting six strains of ovine Babesia species in China

Ovine babesiosis, caused by genus of Babesia, is a zoonotic disease and mainly transmitted by hard ticks. It has led to enormous economic losses to the sheep industry in China. In the present study, an ELISA assay for simultaneous detection six strains of Babesia spp., including B. motasi Lintan, B. motasi Tianzhu, B. motasi Hebei, B. motasi Ningxian, Babesia sp. Xinjiang and Babesia sp. Dunhuang, was developed using Apical Membrane Antigen 1 (AMA1) as candidate diagnostic antigen. The sensitivity and specificity of the established ELISA were 97.4 % and 98.0 %, respectively. Relatively high level of specific antibodies could be detected from 12th day to 126th day after sheep experimentally infected with Babesia spp.. A small scale of field sera was investigated using the developed ELISA assay, and the average positive rate was 51.98 %. This study provides an easy to operate, cost effective and time saving approach, which is suitable for both field and experimental samples, thus it could be a useful tool in epidemiological investigations and diagnoses of ovine babesiosis.

Molecular cloning, characterization and antigenicity ofBabesiasp. BQ1 (Lintan) (Babesiacf.motasi) apical membrane antigen-1 (AMA-1)

Apical membrane antigen-1 (AMA-1) has been described as a potential vaccine candidate in apicomplexan parasites. Here we characterize theama-1gene. The full-lengthama-1gene ofBabesiasp. BQ1 (Lintan) (BLTAMA-1) is 1785 bp, which contains an open reading frame (ORF) encoding a 65-kDa protein of 594 amino acid residues; by definition, the 5′ UTR precedes the first methionine of the ORF. Phylogenetic analysis based on AMA-1 amino acid sequences clearly separated Piroplasmida from other Apicomplexa parasites. TheBabesiasp. BQ1 (Lintan) AMA-1 sequence is most closely associated with that ofB. ovataandB. bigemina, with high bootstrap value. A recombinant protein encoding a conserved region and containing ectodomains I and II of BLTAMA-1 was constructed. BLTrAMA-1-DI/DII proteins were tested for reactivity with sera from sheep infected byBabesiasp. BQ1 (Lintan). In Western-blot analysis, nativeBabesiasp. BQ1 (Lintan) AMA-1 proteins were recognized by antibodies raised in rabbits against BLTrAMA-1in vitro. The results of this study are discussed in terms of gene characterization, taxonomy and antigenicity.

Evaluating an indirect rMPSP enzyme-linked immunosorbent assay for the detection of bovine Theileria infection in China

Bovine theileriosis, a tick-borne protozoan disease caused by Theileria annulata, Theileria orientalis and Theileria sinensis, is widespread in China and is a serious economic problem for the Chinese livestock industry. In this study, recombinant major piroplasma surface proteins (MPSP) of T. annulata, T. orientalis and T. sinensis based on MPSP genes were expressed in Escherichia coli BL21(DE3). The immunogenicity and specificity of the three purified recombinant MPSP proteins were evaluated with the reference positive sera of T. annulata, T. orientalis, T. sinensis, Babesia bovis, B abesia bigemina, Babesia major, Babesia motasi, Theileria luwenshuni, Theileria uilenbergi and Anaplasma ovis using an enzyme-linked immunosorbent assay (ELISA) or western blotting. The results showed that all three of the rMPSP proteins had a strong reaction with the sera from cattle infected with T. annulata, T. orientalis and T. sinensis via western blotting but not with other piroplasma and Anaplasma species. Then, the rMPSP protein of T. sinensis was used to develop an iELISA for detecting the three Theileria species infections. The specificity and sensitivity were 95.7 and 95.5 %, respectively, with a threshold of 28.8 % of the specific mean antibody rate (AbR). Finally, 2473 field-collected bovine sera, from 42 prefectures of 17 provinces in China, were tested using the ELISA to evaluate the prevalence of bovine theileriosis, and the average positive rate was 43.6 %. The developed iELISA could be a suitable tool to detect the three bovine Theileria species, and the data also provided important information regarding the current prevalence of bovine theileriosis in China.

Seroprevalence of bovine theileriosis in northern China

Background

Bovine theileriosis is a common disease transmitted by ticks, and can cause loss of beef and dairy cattle worldwide. Here, an indirect enzyme-linked immunosorbent assay (iELISA) based on Theileria luwenshuni surface protein (TlSP) was developed and used to carry out a seroepidemiological survey of bovine theileriosis in northern China.

Methods

We used the BugBuster Ni-NTA His•Bind Purification Kit to purify recombinant TlSP (rTlSP), which was subsequently analyzed by Western Blotting to evaluate cross-reactivity with other pathogen-positive sera. The iELISA method based on rTlSP was successfully developed. Sera from 2005 blood samples were tested with the rTlSP-iELISA method, and blood smears from these samples were observed by microscopy.

Results

The specificity of iELISA was 98.9%, the sensitivity was 98.5%, and the cut-off was selected as 24.6%. Western Blot analysis of rTlSP confirmed that there were cross-reactions with Theileria luwenshuni, Theileria uilenbergi, Theileria ovis, Theileria annulata, Theileria orientalis and Theileria sinensis. The epidemiological survey showed that the highest positive rate of bovine theileriosis was 98.3%, the lowest rate was 84.1%, and the average positive rate was 95.4% by iELISA. With microscopy, the highest positive rate was 38.9%, the lowest rate was 5.1%, and the relative average positive rate was 13.7%.

Conclusions

An rTlSP-iELISA was developed to detect circulating antibodies against bovine Theileria in northern China. This is the first report on the seroprevalence of bovine theileriosis in northern China, and it also provides seroepidemiological data on bovine theileriosis in China.

Mitochondrial genomes of two Babesia taxa from sheep in China as a foundation for population genetic and epidemiological investigations

Here, we sequenced, assembled and annotated the mitochondrial (mt) genomes of two operational taxonomic units of Babesia from sheep from China using a deep sequencing-coupled approach. Then, we defined and compared the gene order of these mt genomes (~5.8 to 6.2kb in size), assessed sequence differences in mt genes among Babesia taxa and evaluated genetic relationships among these taxa and related apicomplexans (Theileria) for which mt genomic data sets were available. We also identified mt genetic regions that might be useful as markers for future population genetic and molecular epidemiological studies of Babesia from small ruminants. We propose that the sequencing-bioinformatic approach used here should be applicable to a wide range of protists of veterinary importance.

Expression analysis and biological characterization of Babesia sp. BQ1 (Lintan) (Babesia motasi-like) rhoptry-associated protein 1 and its potential use in serodiagnosis via ELISA

Background

In China, ovine babesiosis is one of the most important tick-borne haemoparasitic diseases of small ruminants. It has a significant economic impact, and several Babesia motasi-like isolates have been recently shown to be responsible for ovine babesiosis in this country.

Methods

Full-length and C-terminal-truncated forms of the rap-1a61-1 gene of Babesia sp. BQ1 (Lintan) were cloned into the pET-30a plasmid and subsequently expressed as His-fusion proteins. The resulting recombinant RAP-1a proteins (rRAP-1a61-1 and rRAP-1a61-1/CT) were purified and evaluated as diagnostic antigens using Western blot analysis and ELISA. The native Babesia sp. BQ1 (Lintan) RAP-1 protein was recognized using Western blots and IFAT by antibodies that were raised in rabbits against rRAP-1a61-1/CT. The specificity, sensitivity and positive threshold values for rRAP-1a61-1/CT in ELISA were evaluated.

Results

Cross-reactivity was observed between rRAP-1a61-1/CT and positive sera for Babesia sp. BQ1 (Lintan), Babesia sp. BQ1 (Ningxian) and Babesia sp. Tianzhu isolates obtained from infected sheep. At one week post-inoculation, a significant increase was observed in the amount of antibodies produced against RAP-1a, and high levels of antibodies against RAP-1a were observed for 3 months (at 84 days p.i.). A total of 3198 serum samples were collected from small ruminants in 54 different regions in 23 provinces of China. These samples were tested using ELISA based on the rRAP-1a61-1/CT protein. The results indicated that the average positive rate was 36.02 %.

Conclusions

The present study suggests that rRAP-1a61-1/CT might be a potential diagnostic antigen for detecting several isolates of B. motasi-like parasites infection.

Genetic diversity and molecular characterization of Babesia motasi-like in small ruminants and ixodid ticks from China

Ovine babesioses, an important tick-borne disease of sheep and goats in China, is caused by the reproduction of intraerythrocytic protozoa of the Babesia genus. Babesia motasi-like is a Babesia parasite that infects small ruminant in China, and two sub-groups of B. motasi-like can be subdivided based on differences in the rhoptry-associated-protein-1 gene. This study aimed to characterize the distribution, epidemiology and genetics of B. motasi-like in animals and ticks. A molecular investigation was carried out from 2009 to 2015 in 16 provinces in China. In total, 1081 blood samples were collected from sheep and goats originating from 27 different regions, and 778 ixodid tick samples were collected from 8 regions; the samples were tested for the presence of B. motasi-like using a specific nested PCR assay based on the rap-1b gene. The results indicated that 139 (12.9%), 91 (8.4%), 48 (4.4%) and 6 (0.7%) of the blood samples were positive for general B. motasi-like, Babesia sp. BQ1 (Lintan and Ningxian), Babesia sp. Tianzhu and Babesia sp. Hebei sub-groups, mixed infections, respectively. Among the collected 778 ixodid ticks (including Haemaphysalis longicornis, Haemaphysalis qinghaiensis, Dermacentor silvarum, Ixodes persulcatus, Rhipicephalus sanguineus and Rhipicephalus (Boophilus) microplus), the most frequently infected with Babesia were D. silvarum and I. persulcatus (35.7%), followed by H. longicornis (26.8%), H. qinghaiensis (24.8%) and R. sanguineus (9.3%). The PCR results were confirmed by DNA sequencing. The positive rates of B. motasi-like infection in ticks were found to be higher in China, compared with previous studies in other countries. B. motasi-like infections have not previously been reported in D. silvarum, I. persulcatus or R. sanguineus. The findings obtained in this study could be used for planning effective control strategies against babesiosis in China.

A member of the HSP90 family from ovine Babesia in China: molecular characterization, phylogenetic analysis and antigenicity

Heat shock protein 90 (HSP90) is a key component of the molecular chaperone complex essential for activating many signalling proteins involved in the development and progression of pathogenic cellular transformation. A Hsp90 gene (BQHsp90) was cloned and characterized from Babesia sp. BQ1 (Lintan), an ovine Babesia isolate belonging to Babesia motasi-like group, by screening a cDNA expression library and performing rapid amplification of cDNA ends. The full-length cDNA of BQHsp90 is 2399 bp with an open reading frame of 2154 bp encoding a predicted 83 kDa polypeptide with 717 amino acid residues. It shows significant homology and similar structural characteristics to Hsp90 of other apicomplex organisms. Phylogenetic analysis, based on the HSP90 amino acid sequences, showed that the Babesia genus is clearly separated from other apicomplexa genera. Five Chinese ovine Babesia isolates were divided into 2 phylogenetic clusters, namely Babesia sp. Xinjiang (previously designated a new species) cluster and B. motasi-like cluster which could be further divided into 2 subclusters (Babesia sp. BQ1 (Lintan)/Babesia sp. Tianzhu and Babesia sp. BQ1 (Ningxian)/Babesia sp. Hebei). Finally, the antigenicity of rBQHSP90 protein from prokaryotic expression was also evaluated using western blot and enzyme-linked immunosorbent assay (ELISA).

Identification and expression of Babesia ovis secreted antigen 1 and evaluation of its diagnostic potential in an enzyme-linked immunosorbent assay

In order to identify immunoreactive proteins that are usable for the immunological diagnosis of Babesia ovis infections, a phage lambda cDNA expression library was constructed and screened using parasite-specific immune serum. Immunoscreening resulted in the identification of a full-length cDNA clone encoding a secreted protein designated Babesia ovis secreted antigen 1 (BoSA1). The full-length BoSA1 cDNA contained a 1,137-bp open reading frame that encoded a protein of 378 amino acids, with a signal peptide and 2 internal repeat domains. The theoretical molecular mass of the mature protein was 42.5 kDa. Recombinant BoSA1 (rBoSA1) protein was expressed in Escherichia coli strain DH5α cells as a glutathione S-transferase (GST) fusion protein and was purified by affinity chromatography. Purified rBoSA1 was tested for reactivity with sera from animals experimentally or naturally infected with B. ovis, in an indirect enzyme-linked immunosorbent assay (ELISA). The results showed that specific antibodies against rBoSA1 were detectable on days 7 and 8 of the experimental infection and were maintained during the sampling period. Additionally, 38 field sera taken from sheep naturally infected with B. ovis gave strong positive reactions in the ELISA between day 20 and day 30 of treatment. As a result, the identified recombinant BoSA1 protein seems to be a promising diagnostic antigen that is usable for the development of serological assays for the diagnosis of ovine babesiosis. This is the first report on the molecular cloning, expression, and potential use of a recombinant antigen for the diagnosis of ovine babesiosis.

Determination of immunoreactive proteins of Babesia ovis

Babesia ovis, an intraerythrocytic protozoan parasite transmitted by ticks, causes severe infections in sheep in tropical and subtropical regions of the world. Parasite-specific immunoreactive proteins have been used as antigen in the serological diagnosis of babesiosis. There is no study about determination of B. ovis-specific proteins in sheep. This study was planned to determine the immunoreactive proteins of B. ovis. In this study, two splenectomized lambs, and twelve seropositive sheep and five seronegative lambs for anti-B. ovis antibodies were used as materials. Infected blood samples at 5% of parasitemia from the two splenectomized lambs experimentally infected with a virulent B. ovis field strain were analyzed for B. ovis-specific proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting (WB). B. ovis-specific five major proteins were recognized by anti-B. ovis serum but not by healthy sheep serum. They were of approximate molecular weights 154, 109, 77, 58, and 38 kDa. As the control samples, protein profiles of the blood extracts of two lambs before splenectomy operation were also blotted with the immune sera, but none of the five proteins was detected. These proteins were also immunoblotted with heterologous positive and negative sheep sera. All of twelve positive sera recognized the 109 kDa protein with 100 percent sensitivity. The 77 kDa protein reacted in 11 of 12 sera (91.6%). The sensitivities of the other 3 proteins ranged between 83.3% and 25%. The five protein bands immunoblotted with sera of the 5 negative lambs did not give any positive reaction. The results of this study revealed the presence of proteins recognized by the serum antibodies of experimentally and naturally infected sheep with B. ovis. Additional studies on the purification of these proteins and on subsequently their utilization in a serodiagnostic method are required to improve the serological diagnosis of ovine babesiosis.

A sero-epidemiological survey of Chinese Babesia motasi for small ruminants in China

Babesia motasi BQ1 (Lintan) was first isolated from Haemaphysalis qinghaiensis collected in Gannan Tibet Autonomous Region, Gansu province in April 2000. In this study, a total of 3,204 serum samples from small ruminants in 22 provinces located in different districts of China were tested for antibodies against merozoite antigens from cultured B. motasi BQ1 (Lintan) by enzyme-linked immunosorbent assay. This method can survey the prevalence of low-pathogenic Chinese B. motasi. The results of this survey indicated that the average positive rate was 43.5 %, and the positive rates of investigated provinces were significantly different from 6.1 to 91.0 %, and the infections had been found in all provinces investigated. Our data provide large important information regarding the current sero-prevalence of B. motasi in China.

A recently identified ovine Babesia in China: serology and sero-epidemiology

Babesia sp. in Xinjiang, transmitted by Hyalomma, is a large Babesia that is infective for small ruminants, but it has almost no pathogenicity in healthy sheep. On the basis of the sequences of the 18S rRNA and internal transcribed spacer (ITS) genes, morphological characteristics, vector tick species and pathogenicity it was identified recently as a novel Babesia species. In the present study, an enzyme-linked immunosorbent assay (ELISA) was developed using soluble merozoite antigens of Babesia sp. in Xinjiang (BXJMA) derived from in vitro culture. When the positive threshold was chosen as 24.65% of the specific mean antibody rate, the specificity and sensitivity were both 97.3%. There was no cross-reaction between BXJMA and positive sera from sheep infected with other Chinese ovine piroplasms or Anaplasma ovis in the ELISA and western blotting. Specific antibodies against Babesia sp. in Xinjiang could be detected 2 weeks post infection and a high level of antibodies persisted for more than 12 weeks in experimentally infected sheep. The ELISA was tested on 3857 sera collected from small ruminants in 50 prefectures of 22 provinces to evaluate the sero-epidemiology of Babesia sp. in Xinjiang infection, and the average positive rate was 31.66%. These data provide that the developed ELISA is a powerful tool for the sero-diagnosis of Babesia sp. in Xinjiang and confirm that it is a novel species.

BQP35 is a novel member of the intrinsically unstructured protein (IUP) family which is a potential antigen for the sero-diagnosis of Babesia sp. BQ1 (Lintan) infection

A new gene of Babesia sp. BQ1 (Lintan) (BQP35) was cloned by screening a merozoite cDNA expression library with infected sheep serum and using rapid amplification of cDNA ends (RACE). The nucleotide sequence of the cDNA was 1140bp with an open reading frame (ORF) of 936bp encoding a 35-kDa predicted polypeptide with 311 amino acid residues. Comparison of BQP35 cDNA and genomic DNA sequences showed that BQP35 does not possess an intron. Recombinant BQP35 (rBQP35), expressed in a prokaryotic expression system, showed abnormally slow migration on SDS-PAGE. Gel shifting, amino acid sequence and in silico disorder region prediction indicated that BQP35 protein has characteristics of intrinsically unstructured proteins (IUPs). This is the first description of such proteins in the Babesia genus. BQP35 induced antibodies production as early as one week after Babesia sp. BQ1 (Lintan) infection in sheep. No cross-reaction was observed with sera from sheep infected with other ovine piroplasms dominant in China, except with Babesia sp. Tianzhu. The interest of BQP35 as a diagnostic antigen is discussed.