Antigenic variation in babesiosis:is there more than one ˈwhyˈ?

Malignant human thyroid neoplasms associated with blood parasitic (haemosporidian) infection

Investigation of archival cytological material obtained by cytologists during fine-needle aspiration biopsy in follicular, papillary, and medullary human thyroid cancers revealed haemosporidian (blood parasitic) infection. Haemosporidian infection was detected as exo- and intraerythrocytic stages of development in thyrocytes schizogony. The exoerythrocytic stage of development is represented as microschizonts in a thyroid needle biopsy specimen. Probably, blood parasitic infection is the common etiology for these pathologies. All biopsy material in medical laboratories was stained with RomanowskyGiemsa stain. To clarify the localization of nuclei (DNA) of thyrocytes and nuclei (DNA) of haemosporidian infection in cytological material following investigation of the entire set of smears, a selective series of original archival smears was stained (restained) with a Feulgen/Schiff reagent. Staining of smears with RomanowskyGiemsa stain is an adsorption method that enables re-use of the same smears for staining with a Feulgen/Schiff reagent where the fuchsin dye, after DNA hydrolysis by hydrochloric acid, is incorporated into DNA and stains it in redviolet (crimsonlilac) color. An intentionally unstained protoplasm of blood parasitic infection was present as a light band around erythrocyte nuclei. In follicular thyroid cancer, Feulgen staining of thyrocytes revealed nuclear DNA and parasitic DNA (haemosporidium nuclei) as point inclusions and rings and diffusely distributed in the thyrocyte cytoplasm. The thyrocyte cytoplasm and nuclei were vacuolated, with thyrocyte nuclei being deformed, flattened, and displaced to the cell periphery. The erythrocytes, which were initially stained with eosin (orange color), contained haemosporidian nuclei (DNA). In some cases, endoglobular inclusions in thyrocytes and erythrocytes were of the same size. In papillary thyroid cancer, we were able to localize the nuclear DNA of thyrocytes and the parasitic DNA as point inclusions and diffusely distributed in the thyrocyte cytoplasm. Two or more polymorphic nuclei may eccentrically occur in the hyperplastic cytoplasm. Haemosporidian microschizonts occurred circumnuclearly in thyrocytes and as an exoerythrocytic stage in the blood. The erythrocyte cytoplasm contained redviolet polymorphic haemosporidian nuclei (DNA). In medullary thyroid cancer, the hyperplastic cytoplasm of thyrocytes contained eccentrically located nuclei (DNA) of thyrocytes and small haemosporidian nuclei (DNA), which may occupy the whole thyrocyte. There were thyrocytes with vacuolated cytoplasm and pronounced nuclear polymorphism. The size of hyperplastic nuclei was several times larger than that of normal thyrocyte nuclei. The color of stained cytoplasmic and nuclear vacuoles of thyrocytes was less redviolet compared with that of surrounding tissues, which probably indicates the presence of parasitic DNA in them. The haemosporidian nuclear material in erythrocytes is represented by polymorphic nuclei, which may indicate the simultaneous presence of different pathogen species and/or generations in the blood. Intracellular parasitism of haemosporidian infection in thyrocytes (schizogony) associated with three thyroid cancers leads to pronounced cytoplasmic hyperplasia, cytoplasmic vacuolization, and nuclear vacuolization of the thyrocyte, followed by impaired secretory function. Multinucleated thyrocytes with incomplete cytokinesis appear. The absence of lytic death of the affected thyrocytes indicates that the contagium is able to control apoptosis and influence physiological functions of the cell. There is deformation of the nuclei, which leads to a decrease in their size, their flattening and displacement to the cell periphery, with high risk of DNA mutations and deletions in affected cells, reaching a neoplastic level.

Identification of a novel variant erythrocyte surface antigen-1 (VESA1) in Babesia orientalis

Babesia orientalis, belonging to the phylum Apicomplexa, is mainly accountable for water buffalo babesiosis, which adversely affected the livestock industry in China. Variant erythrocyte surface antigen-1 (VESA1), an antigen that helps infected erythrocytes to escape from host immune responses, was first reported in Babesia bovis. Various VESA1 proteins have also been characterized in other Babesia species. Nevertheless, there is no research on the identification and characterization of VESA1 proteins in Babesia orientalis. In this study, the BoVESA1 gene was amplified from both gDNA and cDNA. The results revealed that it is an intronless gene with a full length of 753 bp, encoding a protein of 250 amino acids with a predicted molecular weight of 28 kDa. The coding sequence (CDS) was cloned into the pGEX-6p-1 vector using a homologous recombination kit and expressed as a glutathione-S-transferase (GST)-fusion protein with a molecular weight of 53 kDa. The tertiary structure of BoVESA1 was predicted using the I-TASSER software. The recombinant protein was subjected to western blotting; the immunogenicity of recombinant BoVESA1 (rBoVESA1) was identified by incubating it with B. orientalis-positive serum. The native BoVESA1 was identified using the lysates of B. orientalis-infected water buffalo erythrocytes incubated with the anti-rBoVESA1 mouse serum. The results showed a band of ~ 28 kDa, which is similar to the predicted size. Immunofluorescence assay (IFA) using anti-rBoVESA1 serum probed indicated a strong signal in the infected RBCs, while the negative control showed no signal. In conclusion, the VESA1 protein was first identified in B. orientalis. This study facilitated further investigation of B. orientalis, and the results indicated that BoVESA1 may serve as a potential candidate antigen for diagnosis and detection of B. orientalis infection.

Cloning and characterization of histone deacetylase from Babesia bovis

The effect of inhibitors of histone deacetylase (HDAC) on Apicomplexa has been previously reported with the discovery of apicidin, a cyclic tetrapeptide having broad-spectrum antiparasitic activity. In the current study, we expressed Babesia bovis (B. bovis) recombinant-HDAC 3 (rBbHDAC3) as a GST-fusion protein in Escherichia coli (E. coli) and found that it was antigenic. An antiserum against the recombinant protein was generated in mice. The mice serum demonstrated the presence of HDAC in B. bovis by a Western blot assay. The murine anti-rBbHDAC3 reacted with B. bovis, Babesia bigemina (B. bigemina), Theileria equi (T. equi), and Babeisa caballi (B. caballi) merozoites in the indirect fluorescent antibody test (IFAT). Furthermore, the HDAC-enzymatic activity of the rBbHDAC3 protein was evaluated by a colorimetric assay. The enzymatic activity of rBbHDAC3 was inhibited by 100 ng/ml of apicidin, and the inhibitory effect of apicidin was dose-dependent. The inhibition of BbHDAC3 by apicidin was confirmed by Western blot, IFAT, and reverse transcription-polymerase chain reaction (RT-PCR). Finally, apicidin potentially inhibited the in vitro growth of Babesia parasites. The lower IC(50) values of apicidin against apicomplexan parasites than those of mammalian cells point to HDAC as an excellent drug target. The findings of the present study indicate that BbHDAC3 is a potential target for apicidin and might be a promising target for the development of novel anti-babesial drugs.

Molecular and immunological characterization of a novel 32-kDa secreted protein of Babesia microti

A cDNA encoding the Babesia microti 32-kDa protein was identified by serological immunoscreening of a cDNA expression library and designated as BmP32. The full length of BmP32 contains an open reading frame of 918 base pairs consisting of 306 amino acids having a significant homology with B. microti secreted antigen 1. Antiserum raised against recombinant protein (rBmP32) specifically reacted with a 32-kDa native protein of the parasite lysate using western blot analysis. The indirect immunofluorescent antibody test showed a preferable localization of BmP32 in the cytoplasm of the intra- and extracellular parasites. Moreover, BmP32 was secreted in the cytosol of infected erythrocytes, especially during the peak parasitemia and the recovery phase of the infection. Next, the antigenicity of rBmP32 was examined by an enzyme-linked immunosorbent assay (ELISA) and sera from mice experimentally infected with either B. microti or closely related parasites. ELISA was highly specific and sensitive when used for the detection of B. microti antibody in a mouse model. Furthermore, mice immunized with rBmP32 emulsified with Freund's adjuvant were not significantly protected against challenge infection with B. microt i. However, high antibody titer was detected just before the challenge infection. Our data suggest that rBmP32 may be a specific diagnostic antigen but not a subunit vaccine.

Comparison of polymerase chain reaction methods for the detection of Theileria equi infection using whole blood compared with pre-extracted DNA samples as PCR templates

Rapid, efficient, and reproducible procedures for isolating DNA before PCR gene amplification are essential for the diagnosis of piroplasms. In this study, we evaluated the ease and reliability of detecting Theileria equi by PCR using pre-extracted DNA samples (by QIAamp DNA Mini Kit and phenol-chloroform methods) compared with blood spotted on FTA cards as PCR templates. Although minimal variations in limit of detection were observed among the methods compared, overall, the use of pre-extracted DNA samples and blood spotted on FTA cards had comparable detection limits. These results indicate that T. equi infection can be efficiently detected directly from FTA cards by PCR without the need for pre-extraction of DNA from blood samples.

Attenuated vaccines for tropical theileriosis, babesiosis and heartwater: the continuing necessity

Overwhelming evidence has accumulated of the effectiveness of immunization with live attenuated vaccines to control tick-borne diseases of livestock. Despite several disadvantages, vaccination with live attenuated organisms against tropical theileriosis, babesiosis and possibly heartwater constitutes one of the most cost-effective intervention strategies. Although great advances have been made through genomics and proteomics research, this has not yet translated into effective non-living vaccines. As a result, there is a continuing necessity to use available live vaccines in tick and tick-borne disease-control strategies adapted to conditions prevailing in many parts of the world.

Babesiosis of cattle

Tick fever or cattle fever (babesiosis) is economically the most important arthropod-borne disease of cattle worldwide with vast areas of Australia, Africa, South and Central America and the United States continuously under threat. Tick fever was the first disease for which transmission by an arthropod to a mammal was implicated at the turn of the twentieth century and is the first disease to be eradicated from a continent (North America). This review describes the biology of Babesia spp. in the host and the tick, the scale of the problem to the cattle industry, the various components of control programmes, epidemiology, pathogenesis, immunity, vaccination and future research. The emphasis is on Babesia bovis and Babesia bigemina.

Antigenic variation as an exploitable weakness of babesial parasites

Babesia bovis and its bovine host interact in many ways, resulting in a range of disease and infection phenotypes. Host responses to the parasite elicit or select for a variety of responses on the part of the parasite, the full range of which is not yet known. One well-established phenomenon, thought to aid parasite survival by evasion of host adaptive immune responses, is the sequential expansion of antigenically variant populations during an infection, a phenomenon referred to as "antigenic variation". Antigenic variation in B. bovis, like that in the human malarial parasite, Plasmodium falciparum, is intimately linked to a second survival mechanism, cytoadhesion. In cytoadhesion, mature parasite-containing erythrocytes bind to the capillary and post-capillary venous endothelium through parasite-derived ligands. The reliance of these parasites on both functions, and on their linkage, may provide opportunities to develop anti-babesial and, perhaps, anti-malarial protection strategies. The development of inhibitors of DNA metabolism in B. bovis may be used to abrogate the process of antigenic variation, whereas small molecular mimics may provide the means to vaccinate against a wide range of variants or to prevent the surface export of variant antigen ligands. In this article, aspects of antigenic variation and cytoadhesion in bovine babesiosis are explored, with a discussion of opportunities for prophylactic or therapeutic intervention in these intertwined processes.

Growth-inhibitory effect of heparin on Babesia parasites

We examined the inhibitory effects of three heparins on the growth of Babesia parasites. The multiplication of Babesia bovis, B. bigemina, B. equi, and B. caballi in in vitro cultures and that of B. microti in vivo were significantly inhibited in the presence of heparins, as determined by light microscopy. Treatment with various concentrations of heparin showed complete clearance of the intracellular parasites. Interestingly, a higher percentage of abnormally multidividing B. bovis parasites was observed in the presence of low concentrations of heparin. Furthermore, fluorescein isothiocyanate-labeled heparin was preferably found on the surfaces of extracellular merozoites, as detected by confocal laser scanning microscopy. These findings indicate that the heparin covers the surfaces of babesial merozoites and inhibits their subsequent invasion of erythrocytes.