Purification of the erythrocytic stages of Babesia bigemina from cultures

An ELISA for the early diagnosis of acute canine babesiosis detecting circulating antigen of large Babesia spp

Babesia canis is the predominant Babesia species in dogs in Europe and is responsible for a severe and fatal disease. An increase in global pet tourism and a widening of the geographic distribution of the tick vector has led to the emergence of infections in areas where previously only imported cases have been reported. Due to the potential for rapid and serious disease progression, direct parasite detection by stained blood smears and light microscopy or DNA-based methods have traditionally been used for the diagnosis of acute infections. This study describes the production of a murine monoclonal antibody ('mAb BcFIII 7/1/2') that reacts to a 65kDa corpuscular epitope present in B. canis-infected erythrocytes and can be used in an ELISA to detect circulating Babesia antigen during acute infections. The sensitivity of the ELISA was 100% (95%CI: 84.5-100) as determined using blood lysate samples from 27 dogs with acute B. canis infections. Sensitivity was reduced to 53.8% in 13 patent Babesia vogeli infections (95%CI: 26.1-79.6) based on the current test design using convalescent serum from a B. canis-infected dog. The specificity was determined to be 86.4% (95%CI: 64-96.4) using 22 samples from healthy canine blood donors. In the course of acute B. canis infections, the ELISA showed a positive result at the same time as a positive PCR result was recorded. This was 24-48h before parasites could be detected by light microscopy. Convalescent samples collected from 6 B. canis-infected dogs at least 14days post treatment resulted in negative ELISA reactions. The hyper-acute to acute phase of a B. canis infection represents an emergency situation with high mortality. To increase the chances of survival, a fast and accurate diagnosis and immediate treatment is required. The current study demonstrates the opportunity of an early and specific detection of acute infections by an AgELISA that is potentially translatable to a rapid diagnostic test design.

Genome-wide analysis of gene expression and protein secretion of Babesia canis during virulent infection identifies potential pathogenicity factors

Infections of dogs with virulent strains of Babesia canis are characterized by rapid onset and high mortality, comparable to complicated human malaria. As in other apicomplexan parasites, most Babesia virulence factors responsible for survival and pathogenicity are secreted to the host cell surface and beyond where they remodel and biochemically modify the infected cell interacting with host proteins in a very specific manner. Here, we investigated factors secreted by B. canis during acute infections in dogs and report on in silico predictions and experimental analysis of the parasite’s exportome. As a backdrop, we generated a fully annotated B. canis genome sequence of a virulent Hungarian field isolate (strain BcH-CHIPZ) underpinned by extensive genome-wide RNA-seq analysis. We find evidence for conserved factors in apicomplexan hemoparasites involved in immune-evasion (e.g. VESA-protein family), proteins secreted across the iRBC membrane into the host bloodstream (e.g. SA- and Bc28 protein families), potential moonlighting proteins (e.g. profilin and histones), and uncharacterized antigens present during acute crisis in dogs. The combined data provides a first predicted and partially validated set of potential virulence factors exported during fatal infections, which can be exploited for urgently needed innovative intervention strategies aimed at facilitating diagnosis and management of canine babesiosis.

The 18 kDa antigen of Theileria equi is a specific but less abundant protein also expressed by parasites cultured in vitro

A universally applicable test has not yet been developed for the reliable diagnosis of equine theileriosis, mainly because of the paucity of specific antigens and antigenic variation between different isolates. In this study, we used Theileria equi parasites cultured in vitro to identify potential diagnostic antigens. Using preparative isoelectric focusing to resolve the proteins in a lysate of infected erythrocytes, we identified an 18 kDa component of the parasite as a specific but poorly expressed antigen. This antigen also appears to have conserved epitope(s) between the isolates from the New and the Old World, as positive sera from both European and South American horses recognize it. The recombinant replica of this antigen might be a valuable tool for inclusion in the development strategy for a diagnostic test.

Purification of a 28 kDa Babesia (Theileria) equi antigen and a 29 kDa spurious erythrocyte antigen from in vitro culture through ion exchange chromatography

An extract of in vitro cultivated Babesia equi was fractionated using a MonoQ anion exchange column. Separation of a 28 kDa B. equi antigen from a 29 kDa spurious erythrocyte antigen, both of which were intensely immunoreactive, was achieved by chromatography of the infected erythrocyte proteins. Using tricine-SDS-PAGE, the 28 kDa antigen of B. equi showed multiple band resolution, while the 29 kDa antigen was consistently resolved as a single band. The 29 kDa antigen was identified in both infected and non-infected erythrocyte extracts. Moreover, B. equi antiserum recognised this antigen in the non-infected erythrocyte extract, and conversely serum from horses not infected with babesia detected the antigen in infected erythrocyte extract. This 29 kDa antigen could represent a horse erythrocyte isoantigen. The purified 28 kDa antigen is specifically recognised by B. equi antisera and therefore could be useful for the production of the recombinant replica and to employ these in further test systems.

Development of conventional subunit vaccines for anaplasmosis and babesiosis

Tick-borne hemoparasitic diseases of cattle continue to impact the beef industry throughout a large portion of the world. A substantial amount of research is currently focused on development of improved vaccines. The two main approaches being followed are: (1) use of conventional inactivated or native protein subunit vaccines, and (2) development of recombinant DNA technology for expression of selected immunogens. Recombinant or synthetic peptide based vaccines hold promise owing to the exquisitely defined nature of the product. However, the development is long-term, and will require extensive testing and risk assessment before field trials can be considered. Until then, more conventional subunit immunogens may offer an attractive alternative, and can be defined immunologically better than before. This paper reviews progress in the development of improved vaccines for anaplasmosis and babesiosis with an emphasis on the characterization of culture-derived babesial exoantigens. Both in vitro and in vivo information is presented.

Identification of antigens diagnostic for European isolates of Babesia equi by two-dimensional electrophoresis and western blotting

A lysate of Babesia equi-infected erythrocytes (USDA strain) was separated by two-dimensional electrophoresis and analysed by Western blotting. Nine major antigens or antigen groups with mol. wts. ranging from 43 to 19 kDa were recognized by sera from horses experimentally infected with the USDA strain. Four antigens or antigen groups were also recognized by some or all sera from horses infected with B. caballi or not infected with Babesia spp. Of the remaining five antigens, four were recognized by all sera from field-infected horses from Europe. Thus, four antigens with mol. wts. of 33, 31, 19 and 20 kDa were identified as diagnostic antigens for European isolates of B. equi. None of the antigens diagnostic for European isolates was recognized by sera from field-infected horses from Brazil.

A new method for isolation of the intraerythrocytic stages of Plasmodium and Babesia from their host cells

A new method for the isolation of intraerythrocytic stages of Plasmodium berghei and Babesia divergens from red blood cells is described. The technique is based on hydrodynamic forces occurring in a flow channel containing a turbulent liquid current, which are capable of rupturing infected erythrocytes and removing their plasma membrane from the parasites' surface. The temperature and the concentration of cells were revealed as factors influencing the hydrodynamic forces. About 90% of the intact and apparently infectious parasites of both species were isolated from the lysed erythrocytes.

Evaluation of a DNA-based probe for the detection of cattle experimentally infected with Babesia bigemina

A digoxigenin-labeled probe was used for hybridization to various preparations of Babesia bigemina-infected erythrocyte extracts. Dot blot hybridization and immunological detection of DNA hybrids revealed that the probe was specific for B. bigemina DNA because it did not hybridize to the DNA of B. bovis, a closely related species. Studies of sensitivity showed that the probe would bind to as little as 1 ng of B. bigemina DNA, but not to 1 microgram of the B. bovis DNA. The probe reacted with equal intensity against seven B. bigemina isolates from different geographic areas. The lowest percentage of B. bigemina-infected erythrocytes detected was 0.001%, a level of parasitemia not usually detected with the light microscope. Six intact, mixed-breed steers, approximately 3 years old, were inoculated with a blood stabilate containing B. bigemina-infected erythrocytes. Blood samples collected from day -1 to day 86 postinoculation (PI) and prepared for DNA extraction were analyzed in a dot blot hybridization assay using a nonradioactive DNA probe. Hybridization reaction (HR) signals were compared to results obtained by light microscopy (LM) examination of Giemsa-stained blood smears and to antibody titers of serum samples assayed with the complement fixation test (CFT) and indirect fluorescent antibody test (IFAT). Four of six inoculated steers became infected with B. bigemina as assessed by LM. The parasitemias were low (less than 0.01-0.05) at day 10 PI. Only three steers were serologically positive by CFT (titer 1:40-1:160) and IFAT (1:1280). All four infected steers had positive HR signals in the dot blot assay. The HR signals were observed from day 10 to day 77 PI and were usually correlated with the presence of parasites in blood as observed by LM. The HR signals varied in intensity for different blood samples from the experimental animals and with day of blood sample collection. Although the signal intensity did not correlate with the parasitemia level estimated by LM, the nucleic acid hybridization assay was more sensitive than LM, CFT, or IFAT for the detection of B. bigemina-infected cattle.

Screening of a Babesia bigemina cDNA library with monoclonal antibodies directed to surface antigens

A Babesia bigemina cDNA library prepared in lambda ZAP bacteriophage vector was immunoscreened to detect clones expressing surface-exposed epitopes of B. bigemina. A nonradioactive indirect plaque-lift immunoassay was used to detect the positive clones. The primary antibody consisted of a pooled sample of six monoclonal antibodies (mAb) specific for B. bigemina that recognizes various parasite surface antigens of different molecular mass. Screening of approximately 300,000 plaque-forming units from the lambda ZAP cDNA expression library resulted in the identification of five positive clones. The five recombinant clones were immunoscreened individually with each of the six mAb. All five independently obtained clones consisted of lambda ZAP recombinants expressing B. bigemina components recognized by mAb C2F3G3 and B1B3C4. Restriction enzyme digests of rescued recombinant phagemids showed that only four clones contained B. bigemina cDNA. One clone (lambda ZAP Bbi1) contained an insert of approximately 0.6 kBp whereas the other three clones (lambda ZAP Bbi2, lambda ZAP Bbi3, and lambda ZAP Bbi5) carried a cDNA insert of approximately 1.7 kBp. Immunoblotting of protein extracts from recombinants lambda ZAP Bbi2, lambda ZAP Bbi3, and lambda ZAP Bbi5 with mAb C2F3G3 and B1B3C4 demonstrated the expression of a recombinant B. bigemina polypeptide of 55 kDa in E. coli.

Growth of Babesia bigemina parasites in suspension cultures for vaccine production

An Australian Babesia bigemina vaccine strain was maintained in suspension culture for 40 days. Parasite growth was compared using two tissue-culture flask sizes (25 and 75 cm2), four gas mixes (2%, 2.5%, 3% and 3.5% O2; 5% CO2; and the balance N2) and four packed blood cell (PCV) volumes (7%, 9%, 13% and 18%). The best continuous parasite yields were obtained from suspension cultures in 75-cm2 flasks at a PCV of 13% and gas mixtures of 2%-3% O2, 5% CO2 and the balance N2. Parasite yields per millilitre of culture medium were 3 times those obtained in microaerophilous stationary-phase cultures. The method has thus far been used for 6 months to produce the Australian requirements for live B. bigemina vaccine.

Babesia ovata: isolation from erythrocytes and development of an enzyme-linked immunosorbent assay for detection of antibodies

A method of isolating Babesia ovata merozoites from infected erythrocytes and an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-B. ovata antibodies were developed. After B. ovata-infected erythrocytes had been lysed using the nitrogen cavitation method, the merozoites were separated from erythrocyte components by differential centrifugation and density-gradient centrifugation. The light microscopic examination showed that the purified merozoites were morphologically intact and contained few contaminants. Sodium dodecyl sulfate-polyacrylamide electrophoretic (SDS-PAGE) analysis revealed that the merozoite fraction contained very little contamination with erythrocyte components. The merozoites thus obtained were sonicated and treated with Triton X-100 and then used as an antigen to measure anti-B. ovata antibodies in ELISA. The ELISA was more sensitive in detecting anti-B. ovata antibodies than was either the indirect fluorescent antibody test or the complement fixation test on sera from cattle infected with B. ovata.