Studies on buffalo babesiosis in Hubei Province, China

Novel Strategy for In Vitro Validation of Babesia orientalis Heat Shock Proteins Chaperone Activity and Thermostability

BACKGROUND

Babesia orientalis is an intra-erythrocytic protozoan parasite that causes babesiosis in water buffalo. The genome of B. orientalis has been reported and various genes have been accurately annotated, including heat shock proteins (HSP). Three B. orientalis HSPs (HSP90, HSP70 and HSP20) have been previously identified as potential antigenic targets. Here, a new validation strategy for the chaperone activities and cell protection characteristics of the three HSPs was developed in vitro.

METHODS

BoHSP20, BoHSP70 and BoHSP90B were amplified from cDNA, followed by cloning them into the pEGFP-N1 vector and transfecting the vector plasmid separately into 293T and Hela mammalian cells. Their expression and localization were determined by fluorescence microscopy. The biological functions and protein stability were testified through an analysis of the fluorescence intensity duration. Their role in the protection of cell viability from heat-shock treatments was examined by MTT assay (cell proliferation assay based on thiazolyl blue tetrazolium bromide).

RESULTS

Fusion proteins pEGFP-N1-BoHSP20, pEGFP-N1-BoHSP70, and pEGFP-N1-BoHSP90B (pBoHSPs: pBoHSP20; pBoHSP70 and pBoHSP90B) were identified as 47 kDa/97 kDa/118 kDa with a 27 kDa GFP tag, respectively. Prolonged fluorescent protein half-time was observed specifically in pBoHSPs under heat shock treatment at 55 °C, and BoHSP20 showed relatively better thermotolerance than BoHSP70 and BoHSP90B. Significant difference was found between pBoHSPs and controls in the cell survival curve after 2 h of 45 °C heat shock.

CONCLUSION

Significant biological properties of heat stress-associated genes of B. orientalis were identified in eukaryote by a new strategy. Fusion proteins pBoHSP20, pBoHSP70 and pBoHSP90B showed good chaperone activity and thermo-stability in this study, implying that BoHSPs played a key role in protecting B. orientalis against heat-stress environment during parasite life cycle. In conclusion, the in vitro model explored in this study provides a new way to investigate the biological functions of B. orientalis proteins during the host-parasite interaction.

The Structural Basis of Babesia orientalis Lactate Dehydrogenase

Glycolytic enzymes play a crucial role in the anaerobic glycolysis of apicomplexan parasites for energy generation. Consequently, they are considered as potential targets for new drug development. Previous studies revealed that lactate dehydrogenase (LDH), a glycolytic enzyme, is a potential drug target in different parasites, such as Plasmodium, Toxoplasma, Cryptosporidium, and Piroplasma. Herein, in order to investigate the structural basis of LDH in Babesia spp., we determined the crystal structure of apo Babesia orientalis (Bo) LDH at 2.67-Å resolution in the space group P1. A five-peptide insertion appears in the active pocket loop of BoLDH to create a larger catalytic pocket, like other protozoa (except for Babesia microti LDH) and unlike its mammalian counterparts, and the absence of this extra insertion inactivates BoLDH. Without ligands, the apo BoLDH takes R-state (relaxed) with the active-site loop open. This feature is obviously different from that of allosteric LDHs in T-state (tense) with the active-site loop open. Compared with allosteric LDHs, the extra salt bridges and hydrogen bonds make the subunit interfaces of BoLDH more stable, and that results in the absence of T-state. Interestingly, BoLDH differs significantly from BmLDH, as it exhibits the ability to adapt quickly to the synthetic co-factor APAD⁺. In addition, the enzymatic activity of BoLDH was inhibited non-competitively by polyphenolic gossypol with a K_i value of 4.25 μM, indicating that BoLDH is sensitive to the inhibition of gossypol and possibly to its new derivative compounds. The current work provides the structural basis of BoLDH for the first time and suggests further investigation on the LDH structure of other Babesia spp. That knowledge would indeed facilitate the screening and designing of new LDH inhibitors to control the intracellular proliferation of Babesia spp.

Use of molecular markers can help to understand the genetic diversity of Babesia bovis

Cattle babesiosis is a tick-borne disease responsible for significant losses for the livestock industries in tropical areas of the world. These piroplasms are under constant control of the host immune system, which lead to a strong selective pressure for arising more virulent or attenuated phenotypes. Aiming to better understand the most critical genetic modifications in Babesia bovis genome, related to virulence, an in silico analysis was performed using DNA sequences from GenBank. Fourteen genes (sbp-2, sbp-4, trap, msa-1, msa-2b, msa-2c, Bv80 (or Bb-1), 18S rRNA, acs-1, ama-1, β-tub, cp-2, p0, rap-1a) related to parasite infection and immunogenicity and ITS region were selected for alignment and comparison of several isolates of Babesia bovis from different geographic regions around the world. Among the 15 genes selected for the study of diversity, only 7 genes (sbp-2, sbp-4, trap, msa-1, msa-2b, msa-2c, Bv80) and the ITS region presented sufficient genetic variation for the studies of phylogeny. Despite this genetic diversity observed into groups, there was not sufficient information available to associate molecular markers with virulence of isolates. However, some genetic groups no were correlated with geographic region what could indicate some typical evolutionary characteristics in the relation between parasite-host. Further studies using these genes in herds presenting diverse clinical conditions are required. The better understanding of evolutionary mechanisms of the parasite may contribute to improve prophylactic and therapeutic measures. In this way, we suggest that genes used in our study are potential markers of virulence and attenuation and have to be analyzed with the use of sequences from animals that present clinical signs of babesiosis and asymptomatic carriers.

Comparative Analysis of Erythrocyte Proteomes of Water Buffalo, Dairy Cattle, and Beef Cattle by Shotgun LC-MS/MS

A number of studies have demonstrated that Babesia orientalis (B. orientalis) can only infect water buffalo (Bubalus bubalis) and not dairy cattle (Bos taurus) or beef cattle (Bos taurus), even though all three belong to the tribe Bovini and have close evolutionary relationships. In addition, Babesia species are intracellular protozoans that obligately parasitize in erythrocytes. This may indicate that the infection specificity is due to differences in erythrocyte proteins. Totals of 491, 1,143, and 1,145 proteins were identified from water buffalo, beef cattle, and dairy cattle, respectively, by searching the Uniprot and NCBI databases. The number of proteins identified for water buffalo was far lower than for beef cattle and dairy cattle, particularly in the range from 15 to 25 kDa. Remarkably, 290 identified proteins were unique to water buffalo, of which putative gamma-globin and putative epsilon-globin had a significant possibility of being relevant to the survival of B. orientalis only in water buffalo. A total of 2,222 proteins were annotated in terms of molecular function, biological process, and cellular component according to GO annotation. The number of proteins of water buffalo in oxygen binding was far higher than for beef cattle and dairy cattle. This is the first time that the protein profiles of water buffalo, beef cattle, and dairy cattle have been comparatively analyzed. The uniquely expressed proteins in water buffalo obtained in this study may provide new insights into the mechanism of B. orientalis infection exclusivity in water buffalo and may be a benefit for the development of strategies against B. orientalis.

Identification of a novel thrombospondin-related anonymous protein (BoTRAP2) from Babesia orientalis

BACKGROUND

The thrombospondin-related anonymous protein (TRAP) was first discovered in the sporozoite of Plasmodium falciparum and TRAP family proteins are secreted by micronemes and transported to the parasite surface to participate in the invasion process. Various TRAP proteins have been identified in apicomplexan protozoans, but there have been few reports about TRAP proteins in Babesia orientalis.

METHODS

The functional domain of TRAP2 in B. orientalis was cloned, sequenced, characterized and compared to the TRAP sequences of related apicomplexan parasites. The functional domain of BoTRAP2 was truncated, named BoTRAP2-1, and then cloned into the pET-28a expression vector. Rabbit anti-rBoTRAP2-1 polyclonal antibody was produced by immunizing three rabbits. Western blot analysis was used to identify the native form and immunogenicity of BoTRAP2. The localization of BoTRAP2 was identified by indirect fluorescence assay (IFA).

RESULTS

The amplified genes of BoTRAP2 are 2817 bp in length, encoding a functional domain of about 938 aa with two vWFA domains, one TSP domain and one transmembrane domain. The amino acid sequence of BoTRAP2 has a high similarity with that of B. bovis and B. gibsoni. The predicted tertiary structure of truncated BoTRAP2-1 confirmed that BoTRAP2 contains two vWFA domains and a TSP domain, the main functional areas of the protein. The native BoTRAP2 was identified from B. orientalis lysate by using rabbit polyclonal anti-rBoTRAP2-1. A band corresponding to rBoTRAP2-1 was detected by reaction with serum from a B. orientalis-infected water buffalo, indicating that the protein has a high immunogenicity. IFA showed that BoTRAP2 is mainly localized on the apical end of parasites by rabbit anti-rBoTRAP2-1 polyclonal serum.

CONCLUSIONS

The rBoTRAP2 could differentiate serum from B. orientalis-infected water buffalo and normal water buffalo, implicating that BoTRAP2 has high immunogenicity and could serve as a candidate antigen for diagnosis of B. orientalis infection in buffalo.

Identification and molecular characterization of a novel Babesia orientalis thrombospondin-related anonymous protein (BoTRAP1)

Background

The thrombospondin-related anonymous protein (TRAP) family, a kind of transmembrane protein, is widely distributed with a conserved feature of structure in all apicomplexan parasites and plays a crucial role in the gliding motility and survival of parasites.

Methods

The Babesia orientalis TRAP1 gene (BoTRAP1) was truncated and cloned into a pET-42b expression vector and expressed as a GST-tag fusion protein with a TEV protease site. Rabbit anti-rBoTRAP1 antibody was produced and purified using a protein A chromatography column. Western blot analysis was performed to identify the native protein of BoTRAP1 and differentiate B. orientalis-infected positive from negative serum samples. The localization of BoTRAP1 on merozoites was identified by the indirect florescent antibody test (IFAT).

Results

The partial sequence of the TRAP1 gene was cloned from B. orientalis cDNA and identified to contain a von Willebrand factor A (vWFA) region and a thrombospondin type-1 (TSP-1) domain; it had a length of 762 bp, encoding a polypeptide of 254 amino acid residues with a predicted size of 28.2 kDa. The partial sequence was cloned into a pET-42b expression vector and expressed in E. coli as a GST fusion protein. Western blot indicated that rBoTRAP1 has a high immunogenicity and can differentiate B. orientalis-infected positive and negative serum samples collected from water buffaloes. IFAT showed that BoTRAP1 is mainly localized on the apical end of intracellular parasites by using polyclonal antibodies (PcAb) against rBoTRAP1. Meanwhile, the PcAb test also identified the native BoTRAP1 as a ~65 kDa band from B. orientalis lysates. The predicted 3D structure of BoTRAP1 contains a metalion-dependent adhesion site (MIDAS), which could be important for interaction with ligand on the surface of the host cells.

Conclusions

Like all known protozoa, B. orientalis has a TRAP family, comprising TRAP1, TRAP2, TRAP3 and TRAP4. The newly identified and characterized BoTRAP1 may play a key role in the invasion of B. orientalis into water buffalo erythrocytes.

Characterization of a novel secretory spherical body protein in Babesia orientalis and Babesia orientalis-infected erythrocytes

Background

The spherical body, a membrane bound organelle localized in the apical organelle complex, is unique to Babesia and Theileria spp. The spherical body proteins (SBPs) secreted by spherical bodies include SBP1, SBP2, SBP3 and SBP4. Up to now, only SBP3 has been characterized in Babesia orientalis.

Methods

The BoSBP4 gene was amplified from cDNA and gDNA and cloned into the pGEX-6P-1 vector by homologous recombination, sequenced and analyzed by bioinformatics tools. The amino acid (aa) sequence of BoSBP4 was compared with that of Babesia bovis and Babesia bigemina as well as SBP3 of B. orientalis. The immunoreactivity was evaluated by incubating recombinant BoSBP4 (rBoSBP4) with the serum of B. orientalis-infected water buffalo. The native form of BoSBP4 was identified by incubating lysate of B. orientalis-infected water buffalo erythrocytes with the anti-rBoSBP4 mouse serum. The cellular localization of BoSBP4 was determined by indirect immunofluorescence assay.

Results

The full length of the BoSBP4 gene was estimated to be 945 bp without introns, encoding a 314 aa polypeptide with a predicted molecular weight of 37 kDa. The truncated recombinant protein was expressed from 70 to 945 bp as a GST fusion protein with a practical molecular weight of 70 kDa. BoSBP4 shared a 40% and 30% identity with B. bovis and B. bigemina, respectively. Furthermore, it was 31% identical to SBP3 of B. orientalis. BoSBP4 was identified in the lysate of B. orientalis-infected water buffalo erythrocytes with a molecular weight of 37 kDa, corresponding to the expected molecular mass of BoSBP4. The result of rBoSBP4 with positive serum revealed that BoSBP4 can elicit an immune response to B. orientalis-infected water buffalo. The cellular localization of BoSBP4 was detected to be adjacent to the merozoite nucleus in the intracellular phase, followed by the diffusion of the fluorescence of BoSBP4 into the cytoplasm of B. orientalis-infected erythrocytes as puncta-like specks and a gradual increase of the fluorescence.

Conclusions

In this study, SBP4 in B. orientalis was characterized for the first time. It may play a key role in interaction with the host cell by being secreted into the cytoplasm of the B. orientalis-infected erythrocytes to facilitate parasite growth and reproduction.

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.

Molecular cloning and characterization of Babesia orientalis rhoptry-associated protein 1

The rhoptry-associated protein 1 (RAP-1) gene of Babesia orientalis was obtained from a cDNA expression library by immunoscreening with B. orientalis-infected water buffalo sera. The nucleotide sequence of the cDNA was 1732 bp with an open reading frame (ORF) of 1434 bp, encoding a polypeptide of 478 amino acid residues with a predicted size of 52.5 kDa. The ORF was cloned into a pGEX-KG plasmid and subsequently expressed as a GST-fusion protein. The recombinant RAP-1 of B. orientalis (rBoRAP-1) was purified and evaluated as an antigen using Western blotting. The native BoRAP-1 was recognized by the antibodies raised in rabbits against rBoRAP-1. Strong immunofluorescence signals were observed in erythrocytes infected with B. orientalis. Phylogentic analysis revealed that B. orientalis fell into a Babesia clade and most closely related to Babesia bovis and Babesia ovis, which was similar to the previous reported trees based on 18S rRNA and HSP70 genes. The present study suggests that the BoRAP-1 might be a potential diagnostic antigen, and the RAP-1 genes can aid in the classification of Babesia and Theileria species.

Identification of two novel HSP90 proteins in Babesia orientalis: molecular characterization, and computational analyses of their structure, function, antigenicity and inhibitor interaction

Background

HSP90 protects the cells from heat stress and facilitates protein maturation and stability. The full genome sequences of piroplasms contain two putative HSP90 proteins, which are yet uncharacterized. To this end, the two putative HSP90 proteins of Babesia orientalis were identified and characterized by molecular and in silico methods.

Methods

The two putative proteins in B. orientalis genome showing homology with putative HSP90 of other piroplasms were cloned and sequenced. A computational analysis was carried out to predict the antigenic determinants, structure and function of these proteins. The interactions of two HSP90 isoforms with respective inhibitors were also examined through docking analysis.

Results

The length of BoHSP90-A gene (amplified from gDNA) was 2706 bp with one intron from position 997 to 1299 bp. This gene amplified from cDNA corresponded to full length CDS with an open reading frame (ORF) of 2403 bp encoding a 800 amino acid (AA) polypeptide with a predicted size of 91.02 kDa. The HSP90-B gene was intronless with an ORF of 2349 bp, and predicted polypeptide comprised of 797 AA with a size of 90.59 kDa. The AA sequences of these two proteins of B. orientalis were the most identical to those of B. bovis. The BoHSP90-A and BoHSP90-B were recognized as 90 kDa in the parasite lysate by the rabbit antisera raised against the recombinant BoHSP90 proteins. The anti-B. orientalis buffalo serum reacted with the rBoHSP90s expressed in E. coli, indicating that these proteins might be secreted by the parasite before entry into host cells. The overall structure and functional analyses showed several domains involved in ATPase activity, client protein binding and HSP90 dimerization. Likewise, several HSP90 inhibitors showed binding to ATP binding pockets of BoHSP90-A and BoHSP90-B, as observed through protein structure-ligand interaction analysis.

Conclusions

The two putative HSP90 proteins in B. orientalis were recognized as 90 kDa. The rBoHSP90-A and rBoHSP90-B were reacted with the B. orientalis infected buffalo serum. The computational structure and functional analyses revealed that these two proteins may have chaperonic activity. The protein structure-ligand interaction analyses indicated that these two proteins had many drug target sites.

Detecção sorológica e molecular de Anaplasma marginale em búfalos na Ilha de Marajó, Pará

O objetivo do estudo foi testar a prevalência sorológica e molecular de Anaplasma marginale em búfalos do municipio de Soure, Ilha de Marajó, estado do Pará, Brasil. Para a pesquisa sorologica foram selecionados randomicamente 800 animais e para a pesquisa molecular 50 destes animais foram aleatoriamente escolhidos. Para quantificar a prevalência sorológica utilizou-se o ensaio de imunoadsorção enzimático indireto (iELISA) com antígeno total contendo proteínas de superfície externa e para quantificar a prevalência molecular utilizou-se a reação em cadeia da polimerase (PCR), envolvendo a amplificação de fragmento gênico da proteína de superfície maior 5 (MSP5). A prevalência de animais positivos no ELISA para A. marginale foi de 25% (200/800). Na PCR foi detectada a presença de A. marginale em 2% (1/50) dos animais. Embora apenas um animal tenha sido positivo na PCR, observou-se que o mesmo foi negativo no ELISA. A presença do agente, mesmo em baixa prevalência, mostra que os bubalinos podem funcionar como um importante reservatório desse patógeno para os rebanhos bovinos da região norte do Brasil.

Babesia: a world emerging

Babesia are tick-transmitted hemoprotozooans that infect mammals and birds, and which are acknowledged for their major impact on farm and pet animal health and associated economic costs worldwide. Additionally, Babesia infections of wildlife can be fatal if associated with stressful management practices; and human babesiosis, also transmitted by blood transfusion, is an increasing public-health concern. Due to the huge diversity of species reported to serve as Babesia hosts, all vertebrates might be potential carriers, as long as they are adequate hosts for Babesia-vector ticks. We here provide a comprehensive overview of the most relevant Babesia species, and a discussion of the classical taxonomic criteria. Babesia, Cytauxzoon and Theileria parasites are closely related and collectively referred to as piroplasmids. A possible scenario for the history of piroplasmids is presented in the context of recent findings, and its implications for future research avenues are outlined. Phylogenetic trees of all available 18S rRNA and hsp70 genes were generated, based on which we present a thoroughly revised molecular classification, comprising five monophyletic Babesia lineages, one Cytauxzoon clade, and one Theileria clade. Updated 18S rRNA and beta-tubulin gene trees of the B. microti isolates agree with those previously reported. To reconcile estimates of the origin of piroplasmids and ticks (~300 Ma, respectively), and mammalian radiation (60 Ma), we hypothesize that the dixenous piroplasmid life cycle evolved with the origin of ticks. Thus, the observed time gap between tick origin and mammalian radiation indicates the existence of hitherto unknown piroplasmid lineages and/or species in extant vertebrate taxa, including reptiles and possibly amphibians. The development and current status of the molecular taxonomy of Babesia, with emphasis on human-infecting species, is discussed. Finally, recent results from population genetic studies of Babesia parasites, and their implications for the development of pathogenicity, drug resistance and vaccines, are summarized.

Molecular and serological prevalence of Babesia bovis and Babesia bigemina in water buffaloes in the northeast region of Thailand

Bovine babesiosis is a tick-transmitted hemoprotozoan disease that is mainly caused by Babesia bovis and Babesia bigemina and is characterized by significant morbidity and mortality worldwide. The disease is widespread in the northeastern region of Thailand, where an increasingly large part of the livestock is composed of water buffaloes. The present study was therefore conducted to investigate the epidemiological distribution of B. bovis and B. bigemina in water buffaloes in the northeastern region of Thailand. A total of 305 buffalo blood samples were randomly collected from five provinces and simultaneously analyzed by the nested PCR (nPCR) assay, ELISA, and IFAT techniques. The overall prevalence of B. bovis and B. bigemina was 11.2% and 3.6% by nPCR, 14.7% and 5.9% by ELISA, and 16.8% and 5.6% by IFAT, respectively. The high concordance between the molecular and the serological detection tests revealed the specificity and sensitivity of the diagnostic assays used for the detection of infection as well as the endemic stability status of the parasites in the surveyed areas. Statistically significant differences in the prevalence of the two infections were observed on the basis of age and location but not gender. Our data provide valuable information regarding the epidemiology of B. bovis and B. bigemina infection in water buffaloes in the northeastern region of Thailand which will likely be very beneficial for management and control programs of this disease.

Molecular cloning and phylogenetic analysis of Babesia orientalis heat shock protein 70

The heat shock protein 70 (hsp70) gene of Babesia orientalis was obtained from a cDNA expression library by immunoscreening with B. orientalis infected buffalo sera. The nucleotide sequence of the cDNA was 2192bp with an open reading frame (ORF) of 1944bp encoding a polypeptide of 648 amino acid residues. Phylogenetic analysis of the 1944bp sequence together with 30 inter-erythrocytic protozoa hsp70 nucleotide sequences available from GenBank was performed. The results showed that B. orientalis was occurred within the Babesia clade, and most closely related to B. ovis and B. bovis. Similar topologies were obtained from trees based on apicomplexa parasite 18S rRNA sequence. Meanwhile, the BoHsp70 gene was cloned into pET-32a and subsequently expressed in Escherichia coli Rosetta strain as a Trx-fusion protein. The recombinant hsp70 of B. orientalis (rBoHsp70) was purified and evaluated as an antigen in the western blot. The serum from B. orientalis infected buffalo recognized the 92kDa rBoHsp70 expressed in E. coli Rosetta (DE3) by western blotting. The rabbit antiserum against rBoHsp70 recognized a specific 70kDa band in lysates of B. orientalis infected buffalo erythrocytes. These results suggested that hsp70 gene was well conserved among inter-erythrocytic protozoa and the BoHsp70 might be a diagnostic and candidate vaccine antigen.

Water Buffalos as carriers of Babesia bovis in Argentina

The tick-transmitted hemoprotozoan Babesia bovis is a major causative agent of bovine babesiosis, an often fatal disease of cattle. The disease is widespread in the northeastern region of Argentina, where an increasing part of the livestock is composed of water buffalos. Although clinical cases of buffalo babesiosis have not been reported so far, the pathogen-transmitting tick vector has been occasionally observed by us to be feeding on water buffalos. We therefore set out to examine whether buffalos may constitute a reservoir of the parasite. Competitive enzyme-linked immunosorbent assay (cELISA) detected B. bovis-specific antibodies in 20% of investigated buffalos (21/103), while direct detection of the pathogen by nested PCR was demonstrated in 34% of the animals (35/103). In one field, more than 60% of investigated animals (22/36) tested positive by nested PCR. These results are discussed in the context of buffalo babesiosis reported in other countries and in view of the currently effected control measures against bovine babesiosis in the region.

Semi-nested PCR detection of Babesia orientalis in its natural hosts Rhipicephalus haemaphysaloides and buffalo

Babesiosis has recently been recognized as an emerging infectious disease of buffalo in China. In order to investigate the epidemiology and enzootic potential of this parasite in Hubei province, we sought to develop a semi-nested PCR to detect Babesia orientalis in buffalo and the potential tick vector-Rhipicephalus haemaphysaloides by amplifying a specific 257bp fragment of B. orientalis 18S rRNA gene. The practical limit of detection showed that it had high sensitivity and an approximate parasitemia of 0.00000012% was detected by the PCR system. The blood samples of 121 asymptomatic buffaloes collected from four babesia endemic counties and that of 71 asymptomatic buffaloes collected from three babesia free counties in Hubei province of China were examined for the presence of B. orientalis using both Wright-Giemsa stained blood smear and semi-nested PCR. Microscopic examination revealed that 5/121 animals were positive, whereas 24/121 animals were positive by the semi-nested PCR assay. Of 378 ticks (R. haemaphysaloides) collected from buffaloes and examined by the semi-nested PCR, 35 were positive. The results showed that the semi-nested PCR was a useful method to investigate the epidemiology of buffalo babesiosis (B. orientalis), which is widely distributed in Hubei province, China.

Babesia--a historical overview

The history of the genus Babesia is briefly outlined. The classical differences with the main other genus of non-pigment-forming hemoparasites, Theileria, are the absence of extra-erythrocytic multiplication (schizogony) in Babesia and the cycle in the vector tick, which includes transovarial transmission in Babesia but only transstadial transmission in Theileria. Also, the multiplication in the red cell of Babesia, by budding, most often results in two daughter cells (merozoites), while that of Theileria gives four merozoites, often as a Maltese cross. In particular this means that what is still commonly called Babesia microti is not a Babesia and that it would be just as logical to speak of human theileriosis as of babesiosis. The small piroplasm of horses, long known as Babesia equi, is already commonly designated as Theileria equi. However, on molecular grounds, it may be necessary to create a new genus for these parasites. The Babesia species of domestic animals are briefly discussed and presented in a table.