Identification and molecular cloning of the Neospora caninum SAG4 gene specifically expressed at bradyzoite stage

Immunisation with Neospora caninum subunits rsNcSAG4 and rsNcGRA1 (NcSAG4 and NcGRA1 epitopes construct) in BALB/c mice: the profile of the immune response and controlling the vertical transmission

Neospora caninum is an apicomplexan protozoan that causes neosporosis, which has a high economic impact on cattle herds with no available vaccine. During infection, the secretion of dense granules and the expression of surface antigens play an important role in hosting immunomodulation. However, some epitopes of those antigens are immunogenic, and using these fractions could improve the subunit antigens in vaccine design. This study evaluates the recombinant peptides rsNcGRA1 and rsNcSAG4 derived from NcGRA1 and NcSAG4 native antigens as vaccine candidates produced by a fermentative process in the yeast culture system of Komagataella phaffii strain Km71, confirmed by colony PCR, SDS-PAGE, and western blotting. The assay was conducted in BALB/c mice using the peptides at low (25 μg) and standard (50 μg) dosages in monovalent and combined administrations at three time points with saponin as an adjuvant assessing the immunogenicity by antibodies response and cytokine production. We challenge the females after pregnancy confirmation using 2 × 105 NC-1 tachyzoites previously propagated in Vero cells. We assessed the chronic infection in dams and vertical transmission in the offspring by PCR and histopathology. Mice, especially those immunised with combined peptides and monovalent rsNcGRA1 at a standard dose, controlling the chronic infection in dams with the absence of clinical manifestations, showed an immune response with induction of IgG1, a proper balance between Th1/Th2 cytokines and reduced vertical transmission in the pups. In contrast, dams inoculated with a placebo vaccine showed clinical signs, low-scored brain lesions, augmented chronic infection with 80% positivity, 31% mortality in pups, and 81% vertical transmission. These findings indicate that rsNcGRA1 peptides in monovalent and combined with rsNCSAG4 at standard dose are potential vaccine candidates and improve the protective immune response against neosporosis in mice.

Global seroprevalence of Neospora spp. in horses and donkeys: A systematic review and meta-analysis

Neospora infections due to Neospora caninum and N. hughesi are prevalent among equids of the world. The disease may affect reproductive and neurological consequences. The present systematic review and meta-analysis was performed to evaluate the global Neospora seroprevalence among horses and donkeys. A number of 57 out of 1575 total retrieved studies were included by searching the PubMed, Scopus, Science Direct, Web of Science and ProQuest. A total of 25,783 horses and 4377 donkeys were examined serologically, yielding a weighted seroprevalence of 13.46 % (95 % CI: 10.26 %-17.42 %) globally. Subgroup analysis revealed that there were statistically significant differences in the overall prevalence of Neospora spp. in the examined animals according to year, continent, WHO region, country, host, and diagnostic method. Age and sex in horses as well as sex in donkeys were significantly associated with the Neospora seroprevalence (P < 0.001). Our findings showed a relatively high exposure to Neospora spp. in horses and donkeys worldwide. Considering the possible economic impact, as well as the importance in animal health, more studies are needed to clarify the species causing equine neosporosis, correlate serological findings with clinical outcomes and assess the risk factors, in order to define adequate prevention and control strategies.

Neospora caninum: Differential Proteome of Multinucleated Complexes Induced by the Bumped Kinase Inhibitor BKI-1294

Background: the apicomplexan parasite Neospora caninum causes important reproductive problems in farm animals, most notably in cattle. After infection via oocysts or tissue cysts, rapidly dividing tachyzoites infect various tissues and organs, and in immunocompetent hosts, they differentiate into slowly dividing bradyzoites, which form tissue cysts and constitute a resting stage persisting within infected tissues. Bumped kinase inhibitors (BKIs) of calcium dependent protein kinase 1 are promising drug candidates for the treatment of Neospora infections. BKI-1294 exposure of cell cultures infected with N. caninum tachyzoites results in the formation of massive multinucleated complexes (MNCs) containing numerous newly formed zoites, which remain viable for extended periods of time under drug pressure in vitro. MNC and tachyzoites exhibit considerable antigenic and structural differences. Methods: Using shotgun mass spectrometry, we compared the proteomes of tachyzoites to BKI-1294 induced MNCs, and analyzed the mRNA expression levels of selected genes in both stages. Results: More than half of the identified proteins are downregulated in MNCs as compared to tachyzoites. Only 12 proteins are upregulated, the majority of them containing SAG1 related sequence (SRS) domains, and some also known to be expressed in bradyzoites Conclusions: MNCs exhibit a proteome different from tachyzoites, share some bradyzoite-like features, but may constitute a third stage, which remains viable and ensures survival under adverse conditions such as drug pressure. We propose the term “baryzoites” for this stage (from Greek βαρυσ = massive, bulky, heavy, inert).

Global selective sweep of a highly inbred genome of the cattle parasite Neospora caninum

Neospora caninum, a cyst-forming apicomplexan parasite, is a leading cause of neuromuscular diseases in dogs as well as fetal abortion in cattle worldwide. The importance of the domestic and sylvatic life cycles of Neospora, and the role of vertical transmission in the expansion and transmission of infection in cattle, is not sufficiently understood. To elucidate the population genomics of Neospora, we genotyped 50 isolates collected worldwide from a wide range of hosts using 19 linked and unlinked genetic markers. Phylogenetic analysis and genetic distance indices resolved a single genotype of N. caninum Whole-genome sequencing of 7 isolates from 2 different continents identified high linkage disequilibrium, significant structural variation, but only limited polymorphism genome-wide, with only 5,766 biallelic single nucleotide polymorphisms (SNPs) total. Greater than half of these SNPs (∼3,000) clustered into 6 distinct haploblocks and each block possessed limited allelic diversity (with only 4 to 6 haplotypes resolved at each cluster). Importantly, the alleles at each haploblock had independently segregated across the strains sequenced, supporting a unisexual expansion model that is mosaic at 6 genomic blocks. Integrating seroprevalence data from African cattle, our data support a global selective sweep of a highly inbred livestock pathogen that originated within European dairy stock and expanded transcontinentally via unisexual mating and vertical transmission very recently, likely the result of human activities, including recurrent migration, domestication, and breed development of bovid and canid hosts within similar proximities.

Gene Expression Profiling of Neospora caninum in Bovine Macrophages Reveals Differences Between Isolates Associated With Key Parasite Functions

Intraspecific differences in biological traits between Neospora caninum isolates have been widely described and associated with variations in virulence. However, the molecular basis underlying these differences has been poorly studied. We demonstrated previously that Nc-Spain7 and Nc-Spain1H, high- and low-virulence isolates, respectively, show different invasion, proliferation and survival capabilities in bovine macrophages (boMØs), a key cell in the immune response against Neospora, and modulate the cell immune response in different ways. Here, we demonstrate that these differences are related to specific tachyzoite gene expression profiles. Specifically, the low-virulence Nc-Spain1H isolate showed enhanced expression of genes encoding for surface antigens and genes related to the bradyzoite stage. Among the primary up-regulated genes in Nc-Spain7, genes involved in parasite growth and redox homeostasis are particularly noteworthy because of their correlation with the enhanced proliferation and survival rates of Nc-Spain7 in boMØs relative to Nc-Spain1H. Genes potentially implicated in induction of proinflammatory immune responses were found to be up-regulated in the low-virulence isolate, whereas the high-virulence isolate showed enhanced expression of genes that may be involved in immune evasion. These results represent a further step in understanding the parasite effector molecules that may be associated to virulence and thus to disease traits as abortion and transmission.

Neospora caninum antigens displaying virus-like particles as a bivalent vaccine candidate against neosporosis

Neospora caninum is a causative and transmissible agent of dog and bovine neosporosis. The resulting reproductive failures in infected cattle lead to significant economic losses worldwide. However, there is no satisfactory treatment or vaccine currently available to combat this pathogen. Thus, the development of appropriate vaccines to manage its infection and transmission is urgently needed. In this study, we expressed Rous sarcoma virus-like particles (RSV-LP) that displayed dual N. caninum antigens in silkworms. The antigen candidates are modified by adding a transmembrane domain of GP64 protein from Bombyx mori nucleopolyhedrovirus (BmNPV) to the C-terminus of surface antigen 1 (NcSAG1) and SAG1-related sequence 2 (NcSRS2). The NcSRS2 alone or the NcSAG1/NcSRS2 bivalent form displaying RSV-LPs were purified using sucrose density gradient centrifugation. These purified VLPs were then used for immunizations in gerbils, Meriones unguiculatus, to evaluate the anti-N. caninum effects in vivo. The results demonstrated that antigens displaying RSV-LPs in immunized gerbils produced the antigen-specific antibody, leading to a relatively lower parasite load after infections of N. caninum. To the best of our knowledge, this is the first study to present an RSV-LP vaccine displaying bivalent antigens from neosporosis. Taken together, our strategy suggests that silkworm-expressed virus-like particles (VLPs) are promising bivalent vaccine candidates against N. caninum infections.

Immune response to Neospora caninum live tachyzoites in prepubertal female calves

The aim of the present study was to characterize the specific immune response in prepubertal female calves inoculated with Neospora caninum. Forty-eight N. caninum-seronegative 6-month-old Angus female calves were randomly allocated into two groups: group A calves were inoculated subcutaneously (sc) with 1 × 10⁶ tachyzoites of the low virulence NC-Argentina LP1 isolate in sterile phosphate-buffered saline (PBS); group B calves were mock inoculated sc with sterile PBS. Calves from group A developed a specific immune response characterized by the production of IgG antibodies and the expression of IFN-γ and TNF-α cytokines. Animals did not present any febrile reaction or reactions at the site of inoculation. Although chronic N. caninum infection was developed in 50% of calves of group A after inoculation, according to the presence of antibodies against rNc-SAG4, antigen characteristic of bradyzoites, N. caninum antibodies dropped below the cut-off of ELISA from day 210 post-inoculation onwards. Future trials using the same group of inoculated animals will allow the characterization of the evolution of the immune response during pregnancy and to determine whether the immunization with the local isolate is able to prevent congenital transmission and to protect against heterologous challenges.

The soluble fraction of Neospora caninum treated with PI-PLC is dominated by NcSRS29B and NcSRS29C

Neospora caninum is an obligate intracellular parasite related to cases of abortion and fertility impairment in cattle. The control of the parasite still lacks an effective protective strategy and the understanding of key mechanisms for host infection might be crucial for identification of specific targets. There are many proteins related to important mechanisms in the host cell infection cycle such as adhesion, invasion, proliferation and immune evasion. The surface proteins, especially SRS (Surface Antigen Glycoprotein - Related Sequences), have been demonstrated to have a pivotal role in the adhesion and invasion processes, making them potential anti-parasite targets. However, several predicted surface proteins were not described concerning their function and importance in the parasite life cycle. As such, a novel SRS protein, NcSRS57, was described. NcSRS57 antiserum was used to detect SRS proteins by immunofluorescence in parasites treated or not with phosphatidylinositol-specific phospholipase C (PI-PLC). The treatment with PI-PLC also allowed the identification of NcSRS29B and NcSRS29C, which were the most abundant SRS proteins in the soluble fraction. Our data indicated that SRS proteins in N. caninum shared a high level of sequence similarity and were susceptible to PI-PLC. In addition, the description of the SRS members, regarding abundance, function and immunogenicity will be useful in guiding specific methods to control the mechanism of adhesion and invasion mediated by these surface proteins.

Integrative transcriptome and proteome analyses define marked differences between Neospora caninum isolates throughout the tachyzoite lytic cycle

Neospora caninum is one of the main causes of transmissible abortion in cattle. Intraspecific variations in virulence have been widely shown among N. caninum isolates. However, the molecular basis governing such variability have not been elucidated to date. In this study label free LC-MS/MS was used to investigate proteome differences between the high virulence isolate Nc-Spain7 and the low virulence isolate Nc-Spain1H throughout the tachyzoite lytic cycle. The results showed greater differences in the abundance of proteins at invasion and egress with 77 and 62 proteins, respectively. During parasite replication, only 19 proteins were differentially abundant between isolates. The microneme protein repertoire involved in parasite invasion and egress was more abundant in the Nc-Spain1H isolate, which displays a lower invasion rate. Rhoptry and dense granule proteins, proteins related to metabolism and stress responses also showed differential abundances between isolates. Comparative RNA-Seq analyses during tachyzoite egress were also performed, revealing an expression profile of genes associated with the bradyzoite stage in the low virulence Nc-Spain1H isolate. The differences in proteome and RNA expression profiles between these two isolates reveal interesting insights into likely mechanisms involved in specific phenotypic traits and virulence in N. caninum.

SIGNIFICANCE

The molecular basis that governs biological variability in N. caninum and the pathogenesis of neosporosis has not been well-established yet. This is the first study in which high throughput technology of LC-MS/MS and RNA-Seq is used to investigate differences in the proteome and transcriptome between two well-characterized isolates. Both isolates displayed different proteomes throughout the lytic cycle and the transcriptomes also showed marked variations but were inconsistent with the proteome results. However, both datasets identified a pre-bradyzoite status of the low virulence isolate Nc-Spain1H. This study reveals interesting insights into likely mechanisms involved in virulence in N. caninum and shed light on a subset of proteins that are potentially involved in the pathogenesis of this parasite.

Importance of serological cross-reactivity among Toxoplasma gondii, Hammondia spp., Neospora spp., Sarcocystis spp. and Besnoitia besnoiti

Toxoplasma gondii, Neospora spp., Sarcocystis spp., Hammondia spp. and Besnoitia besnoiti are genetically related cyst-forming coccidia. Serology is frequently used for the identification of T. gondii, Neospora spp. and B. besnoiti-exposed individuals. Serologic cross-reactions occur in different tests among animals infected with T. gondii and H. hammondi, as well as among animals infected by T. gondii and N. caninum. Infections caused by N. caninum and N. hughesi are almost indistinguishable by serology. Neospora caninum, B. besnoiti and Sarcocystis spp. infections in cattle show some degree of serologic cross-reactivity. Antibody cross-reactivity between Neospora spp. and H. heydorni-infected animals is suspected, but not proven to occur. We review serologic cross-reactivity among animals and/or humans infected with T. gondii, Neospora spp., Sarcocystis spp., Hammondia spp. and B. besnoiti. Emphasis is laid upon antigens and serological methods for N. caninum diagnosis which were tested for cross-reactivity with related protozoa. Species-specific antigens, as well as stage-specific proteins have been identified in some of these parasites and have promising use for diagnosis and epidemiological surveys.

Constitutive expression and characterization of a surface SRS (NcSRS67) protein of Neospora caninum with no orthologue in Toxoplasma gondii

Neospora caninum is a parasite of the Apicomplexa phylum responsible for abortion and losses of fertility in cattle. As part of its intracellular cycle, the first interaction of the parasite with the target cell is performed with the surface proteins known as the SRS superfamily (Surface Antigen Glycoprotein - Related Sequences). SAG related or SRS proteins have been a target of intense research due to its immunodominant pattern, exhibiting potential as diagnostic and/or vaccine candidates. The aim of this study was the cloning, expression and characterization of the gene NcSRS67 of N. caninum using a novel designed plasmid. The coding sequence of NcSRS67 (without the signal peptide and the GPI anchor) was cloned and expressed constitutively instead of the ccdB system of pCR-Blunt II-TOPO. The protein was purified in a nickel sepharose column and identified by mass spectrometry (MS/MS). The constitutive expression did not affect the final bacterial growth, with a similar OD 600nm compared to the non-transformed strains. The recombinant NcSRS67 was over expressed and the native form was detected by the anti-rNcSRS67 serum on 1D western blot as a single band of approximately 38kDa as predicted. On an in vitro assay, the inhibitory effect of the polyclonal antiserum anti-rNcSRS67 was nearly 20% on adhesion/invasion of host cells. The NcSRS67 native protein was localised on part of the surface of N. caninum tachyzoite when compared to the nucleus by confocal immunofluorescence.

The tandemly repeated NTPase (NTPDase) from Neospora caninum is a canonical dense granule protein whose RNA expression, protein secretion and phosphorylation coincides with the tachyzoite egress

Background

NTPases (also NTPDases) are enzymes with apyrase activity. They are widely distributed among eukaryotes, and also among members of the family Sarcocystidae. In Toxoplasma gondii, the TgNTPase accumulates in the dense granules, and has been commonly associated with the strain virulence. In the closely related Neospora caninum, the NcNTPase lacks nucleoside diphosphate hydrolase activity and appears to be more abundant in virulent isolates, indicating that it may contribute to the pathogenicity of neosporosis. However, so far no additional information on NcNTPase has been provided.

Methods

Herein, the NcNTPase coding sequences were analysed by different in silico and de novo sequencing approaches. A comparative analysis of NcNTPase and NcGRA7 in terms of protein dynamics, secretion, phosphorylation, and mRNA expression profiles during the tachyzoite lytic cycle was also carried out. Moreover, NcNTPase immunolocalization was analysed by confocal microscopy techniques over a set number of time-points.

Results

We describe the presence of three different loci containing three copies of the NcNTPase within the Nc-Liv genome, and report the existence of up to four different NcNTPase alleles in Nc-Liv. We also provide evidence for the occurrence of diverse protein species of the NcNTPase by two-dimensional gel electrophoresis. Both NcNTPase and NcGRA7 were similarly up-regulated and secreted during the egress and/or early invasion phases, and were phosphorylated. However, its secretion was not affected by the addition of calcium modulators such as A23187 and ethanol. NcNTPase and NcGRA7 localized in dense granules and parasitophorous vacuole membrane throughout the lytic cycle, although differed in their inmunolocalization during early invasion and egress.

Conclusions

The present study reveals the complexity of the NcNTPase loci in N. caninum. We hypothesize that the expression of different isoforms of the NcNTPase protein could contribute to parasite virulence. Our findings showed regulation of expression, secretion and phosphorylation of NcNTPase suggesting a potential role for progression through the tachyzoites lytic cycle.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1620-4) contains supplementary material, which is available to authorized users.

Serology-Based Diagnostics for the Control of Bovine Neosporosis

The protozoan Neospora caninum is a primary infectious cause of abortion in cattle that causes significant economic losses worldwide. Because effective vaccines and licensed pharmacological treatments are currently unavailable, control measures rely on biosecurity and management practice. Serological diagnosis plays a crucial role in the identification of infected animals and several tests have been developed. However, owing to the particular dynamics of the host-parasite interaction and to the characteristics of the currently used diagnostic tools, a proportion of infected cattle may not be reliably identified, and can potentially undermine efforts towards the control of bovine neosporosis. Current diagnostic methods for N. caninum infection in cattle and the advances necessary to support effective control strategies are discussed.

Characterization of the Neospora caninum NcROP40 and NcROP2Fam-1 rhoptry proteins during the tachyzoite lytic cycle

Virulence factors from the ROP2-family have been extensively studied in Toxoplasma gondii, but in the closely related Neospora caninum only NcROP2Fam-1 has been partially characterized to date. NcROP40 is a member of this family and was found to be more abundantly expressed in virulent isolates. Both NcROP2Fam-1 and NcROP40 were evaluated as vaccine candidates and exerted a synergistic effect in terms of protection against vertical transmission in mouse models, which suggests that they may be relevant for parasite pathogenicity. NcROP40 is localized in the rhoptry bulbs of tachyzoites and bradyzoites, but in contrast to NcROP2Fam-1, the protein does not associate with the parasitophorous vacuole membrane due to the lack of arginine-rich amphipathic helix in its sequence. Similarly to NcROP2Fam-1, NcROP40 mRNA levels are highly increased during tachyzoite egress and invasion. However, NcROP40 up-regulation does not appear to be linked to the mechanisms triggering egress. In contrast to NcROP2Fam-1, phosphorylation of NcROP40 was not observed during egress. Besides, NcROP40 secretion into the host cell was not successfully detected by immunofluorescence techniques. These findings indicate that NcROP40 and NcROP2Fam-1 carry out different functions, and highlight the need to elucidate the role of NcROP40 within the lytic cycle and to explain its relative abundance in tachyzoites.

Buparvaquone is active against Neospora caninum in vitro and in experimentally infected mice

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Buparvaquone inhibits proliferation of Neospora caninum at nanomolar concentrations.

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In vitro, the drug acts mainly parasitostatic.

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Parasiticidal effects occur at µmolar concentrations after extended periods of time.

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Buparvaquone acts slowly as evidenced by transmission electron microscopy.

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Buparvaquone prevents clinical signs of acute neosporosis in mice.

The naphthoquinone buparvaquone is currently the only drug used against theileriosis. Here, the effects of buparvaquone were investigated in vitro and in an experimental mouse model for Neospora caninum infection. In 4-day proliferation assays, buparvaquone efficiently inhibited N. caninum tachyzoite replication (IC₅₀ = 4.9 nM; IC₁₀₀ = 100 nM). However, in the long term tachyzoites adapted and resumed proliferation in the presence of 100 nM buparvaquone after 20 days of cultivation. Parasiticidal activity was noted after 9 days of culture in 0.5 µM or 6 days in 1 µM buparvaquone. TEM of N. caninum infected fibroblasts treated with 1 µM buparvaquone showed that the drug acted rather slowly, and ultrastructural changes were evident only after 3–5 days of treatment, including severe alterations in the parasite cytoplasm, changes in the composition of the parasitophorous vacuole matrix and a diminished integrity of the vacuole membrane. Treatment of N. caninum infected mice with buparvaquone (100 mg/kg) either by intraperitoneal injection or gavage prevented neosporosis symptoms in 4 out of 6 mice in the intraperitoneally treated group, and in 6 out of 7 mice in the group receiving oral treatment. In the corresponding controls, all 6 mice injected intraperitoneally with corn oil alone died of acute neosporosis, and 4 out of 6 mice died in the orally treated control group. Assessment of infection intensities in the treatment groups showed that, compared to the drug treated groups, the controls showed a significantly higher parasite load in the lungs while cerebral parasite load was higher in the buparvaquone-treated groups. Thus, although buparvaquone did not eliminate the parasites infecting the CNS, the drug represents an interesting lead with the potential to eliminate, or at least diminish, fetal infection during pregnancy.

Vaccines against neosporosis: what can we learn from the past studies?

Neospora caninum is an intracellular apicomplexan parasite, which is a leading cause of abortion in cattle; thus neosporosis represents an important veterinary health problem and is of high economic significance. The parasite can infect cattle via trans-placental transmission from an infected cow to its fetus (vertical transmission), or through the oral route via ingestion of food or water contaminated with oocysts that were previously shed with the feces of a canid definitive host (horizontal transmission). Although vaccination was considered a rational strategy to prevent bovine neosporosis, the only commercialized vaccine (Neoguard®) produced ambiguous results with relatively low efficacy, and was recently removed from the market. Therefore, there is a need to develop an efficient vaccine capable of preventing both, the horizontal transmission through infected food or water to a naïve animal as well as the vertical transmission from infected but clinically asymptomatic dams to the fetus. Different vaccine strategies have been investigated, including the use of live attenuated vaccines, killed parasite lysates, total antigens or antigen fractions from killed parasites, and subunit vaccines. The vast majority of experimental studies were performed in mice, and to a certain extent in gerbils, but there is also a large number of investigations that were conducted in cattle and sheep. However, it is difficult to directly compare these studies due to the high variability of the parameters employed. In this review, we will summarize the recent advances made in vaccine development against N. caninum in cattle and in mice and highlight the most important factors, which are likely to influence the degree of protection mediated by vaccination.

Specific antibody responses against Neospora caninum recombinant rNcGRA7, rNcSAG4, rNcBSR4 and rNcSRS9 proteins are correlated with virulence in mice

The intraspecific diversity of Neospora caninum is a determinant for in vivo parasite virulence and in vitro parasite behaviour. The relationship between isolate virulence and specific antibody responses against key parasite proteins has not been well characterized. The response kinetics and the differences in specific anti-rNcGRA7, -rNcSAG4, -rNcBSR4 and -rNcSRS9 antibody levels were analysed by recombinant protein-based ELISA in groups of mice inoculated with 10 different N. caninum isolates that differ in their virulence. The majority of the virulence parameters analysed correlated with the specific antibody levels against the 4 recombinant proteins. The antibodies developed against the highly immunogenic protein NcGRA7 were significantly higher in mice inoculated with high virulence isolates than in those inoculated with low-to-moderate virulence isolates in both non-pregnant and pregnant mouse models. Moreover, these levels were correlated with the anti-N. caninum IgG1 and IgG2a responses and the in vitro tachyzoite yield at 56 h. The antibodies directed against the bradyzoite-specific proteins were not detected in a non-pregnant mouse model. However, some seropositive mice were found in groups inoculated with high virulence isolates in a pregnant mouse model. NcGRA7 and NcSAG4 are proteins clearly correlated with virulence, and to a lesser extent NcBSR4 and NcSRS9 proteins. Moreover, antibodies to bradyzoite-specific proteins appear to also be related to virulence in mice. Further analyses should be performed in order to verify the usefulness of these proteins as predictive markers for virulence in an experimental bovine model of neosporosis.

Gene cloning and characterization of the protein encoded by the Neospora caninum bradyzoite-specific antigen gene BAG1

Neospora caninum is an Apicomplexan parasite that causes repeated abortion and stillbirth in cattle. The aim of this study was to clone the gene encoding the N. caninum orthologue (NcBAG1) of the Toxoplasma gondii bradyzoite-specific protein TgBAG1 and characterize its expression pattern in the parasite. Isolation of the full-length 684-bp gene revealed that it shared 78.3% sequence similarity with TgBAG1. NcBAG1 encodes a predicted protein of 227 amino acids with 80.3% similarity to TgBAG1. A putative signal peptide sequence and an invariant GVL motif characteristic of small heat-shock proteins were identified in the predicted N. caninum amino acid sequence. We expressed the NcBAG1 gene as a recombinant glutathione S-transferase fusion protein (rNcBAG1) in Escherichia coli and used the purified 60 kDa protein to obtain a monoclonal antibody (Mab). rNcBAG1 reacted to Mabs specific for NcBAG1 and TgBAG1. No reaction between the NcBAG1 Mab and N. caninum tachyzoites was observed. Although the predicted molecular mass of NcBAG1 is 25 kDa, Western blot analysis of parasite lysates using the NcBAG1 Mab revealed a cross-reactive protein of approximately 30 kDa. Additionally, immunofluorescence assays using the tachyzoite-specific Mab for NcSAG1 and the bradyzoite-specific Mab for TgBAG1 or NcSAG4 revealed NcBAG1-specific expression in bradyzoites in cultures exposed to sodium nitroprusside, a reagent that increases the frequency of bradyzoites. Interestingly, the NcBAG1 protein was identified in the cytoplasm of the bradyzoite-stage parasites. This preliminary analysis of the NcBAG1 gene will assist investigations into the role of this protein in N. caninum .

Comparative study of protective activities of Neospora caninum bradyzoite antigens, NcBAG1, NcBSR4, NcMAG1, and NcSAG4, in a mouse model of acute parasitic infection

Neospora caninum is an obligate intracellular protozoan parasite that causes severe neuromuscular diseases, repeated abortion, stillbirth, and congenital infection in livestock and companion animals. The development of an effective vaccine against neosporosis in cattle is an important issue due to the significant worldwide economic impact of this disease. We evaluated the immunogenicity of four bradyzoite antigens, NcBAG1 (first described in this study), NcBSR4, NcMAG1, and NcSAG4, using an acute infection mouse model to determine synergistic effects with the tachyzoite antigen as a candidate for vaccine production. Mice were inoculated with the recombinant vaccines (r-)NcBAG1, rNcBSR4, rNcMAG1, rNcSAG4, or phosphate-buffered saline (PBS) (adjuvant control group) in an oil-in-water emulsion with bitter gourd extract, a Th1 immune stimulator, or PBS alone as the infection control group. Mice inoculated with each vaccine developed antigen-specific IgG1 and IgG2a antibodies and isolated splenocytes from mice produced high levels of interferon-γ when infected with the N. caninum tachyzoite. The mice inoculated with rNcBAG1, rNcMAG1, or rNcSAG4 developed slight to moderate clinical symptoms but did not succumb to infection. In contrast, rNcBSR4 and both control groups developed severe disease and some mice required euthanasia. The parasitic burden in the brain tissues of vaccinated mice was assessed by N. caninum-specific real-time PCR at 5 weeks after infection. The parasite load in rNcBAG1-, rNcMAG1-, and rNcSAG4-inoculated mice was significantly lower than that in adjuvant and infection control mice. Therefore, these antigens may be useful for the production of a N. caninum-specific vaccination protocol.

Low rates of Neospora caninum infection reactivation during gestation are observed in both chronically and congenitally infected mice

Endogenous transplacental transmission (EnTT) of Neospora caninum is the most common route of infection in cattle and occurs as a consequence of a reactivation of N. caninum infection that may lead to abortion or to the birth of congenitally infected calves. The reactivation of N. caninum infection was studied during the gestation of chronically infected dams and, for the first time, in their congenitally infected pups. BALB/c mice were infected with Nc-Spain 7 (Group 1) or Nc-Spain 3H (Group 2), high virulence isolates and low-to-moderate virulence isolates, respectively. The mice were mated after 90 days post-infection, and the morbidity, mortality, vertical transmission and humoral immune responses were recorded for 2 consecutive generations. In the first generation, higher morbidity and mortality rates were observed in G1 before mating than in G2 (P < 0·0001). In the second generation, low vertical transmission rates were observed in both inoculated groups (7·7% and 17·1% in G1 and G2, respectively) and were significantly diminished in the third generation (8·7% in G2 versus 0% in G1). Low rates of reactivation of N. caninum infection were induced in chronically infected mice and decreased in subsequent generations regardless of the isolate employed in the inoculations. Thus, further studies are needed to improve this reactivation mouse model.

A review of the infection, genetics, and evolution of Neospora caninum: from the past to the present

This paper is a review of current knowledge on Neospora caninum in the context of other apicomplexan parasites and with an emphasis on: life cycle, disease, epidemiology, immunity, control and treatment, evolution, genomes, and biological databases and web resources. N. caninum is an obligate, intracellular, coccidian, protozoan parasite of the phylum Apicomplexa. Infection can cause the clinical disease neosporosis, which most notably is associated with abortion in cattle. These abortions are a major root cause of economic loss to both the dairy and beef industries worldwide. N. caninum has been detected in every country in which a study has been specifically conducted to detect this parasite in cattle. The major mode of transmission in cattle is transplacental (or vertical) transmission and several elements of the N. caninum life cycle are yet to be studied in detail. The outcome of an infection is inextricably linked to the precise timing of the infection coupled with the status of the immune system of the dam and foetus. There is no community consensus as to whether it is the dam's pro-inflammatory cytotoxic response to tachyzoites that kills the foetus or the tachyzoites themselves. From economic analysis the most cost-effective approach to control neosporosis is a vaccine. The perfect vaccine would protect against both infection and the clinical disease, and this implies a vaccine is needed that can induce a non-foetopathic cell mediated immunity response. Researchers are beginning to capitalise on the vast potential of -omics data (e.g. genomes, transcriptomes, and proteomes) to further our understanding of pathogens but especially to identify vaccine and drug targets. The recent publication of a genome for N. caninum offers vast opportunities in these areas.

Sirtuins of parasitic protozoa: in search of function(s)

The SIR2 family of NAD⁺-dependent protein deacetylases, collectively called sirtuins, has been of central interest due to their proposed roles in life-span regulation and ageing. Sirtuins are one group of environment sensors of a cell interpreting external information and orchestrating internal responses at the sub-cellular level, through participation in gene regulation mechanisms. Remarkably conserved across all kingdoms of life SIR2 proteins in several protozoan parasites appear to have both conserved and intriguing unique functions. This review summarises our current knowledge of the members of the sirtuin families in Apicomplexa, including Plasmodium, and other protozoan parasites such as Trypanosoma and Leishmania. The wide diversity of processes regulated by SIR2 proteins makes them targets worthy of exploitation in anti-parasitic therapies.

The Neospora caninum-Spain 7 isolate induces placental damage, fetal death and abortion in cattle when inoculated in early gestation

The Nc-Spain 7 isolate of Neospora caninum, which was newly obtained from an asymptomatic congenitally infected calf, demonstrated a similar virulence as Nc-1 strain in mouse models. The aim of this study was to characterize the pathogenesis of Nc-Spain 7 isolate in cattle after experimental infection at 65 days of gestation. For this purpose, thirteen pregnant heifers were divided into three groups as follows: group A: 7 heifers inoculated with 1 × 10(8) tachyzoites of Nc-Spain 7 isolate; group B: 4 heifers inoculated with 1 × 10(8) tachyzoites of Nc 1 strain; and group C: 2 heifers received PBS. Serum samples were collected weekly and heparinized blood samples were collected three times (0, 28 and 42 days after inoculation) by jugular venipuncture. Placenta and fetal tissue samples were collected at time of necropsy. Specific antibody response in the dams was tested by IFAT, indirect ELISA, and rNcGRA7 and rNcSAG4 based-ELISA. Specific antibody response in fetal fluids was tested by IFAT. IFN-γ production was measured after in vitro culture of PBMC and the supernatant was assessed using a commercial kit (BOVIGAM). A significant increase in N. caninum antibody responses was detected in groups A and B by IFAT and by i-ELISA from day 14 after inoculation onwards. Besides, antibody response against rNCGra7 protein was also detected in all inoculated heifers by rNcGra7-based ELISA. Four fetuses from group A and one from group B were aborted between 3 and 5 weeks after infection. In the recovered fetuses, only 3 out of 4 fetal fluids from fetuses of group A and 1 out of 3 of group B were seropositive by IFAT, but all of them were positive by PCR. Transplacental transmission could be determined in all fetuses from groups A and B by PCR and/or IHC. Heifers of group C and their fetuses remained negative by all techniques. The results of this study demonstrate that the NC-Spain 7 isolate could be transmitted transplacentally, and produced fetal death and abortion in cattle.

Identification of a gene cluster for cell-surface genes of the SRS superfamily inNeospora caninumand characterization of the novelSRS9gene

Here we present the detection of a gene cluster forNeospora caninumsurface genes, similar to theToxoplasma gondiiSRS9 locus, and the cloning and characterization of the NcSRS9gene. PCR genome walking, using NcBSR4gene as a framework, allows the identification, upstream NcBSR4, of 2 sequences homologous to theSRS5and the Ubiquinol-cytochrome C reductase genes and, downstream NcBSR4, of an ORF of 1191 bp coding for a 396-amino acid polypeptide with 59% similarity to the TgSRS9 antigen. A putative 39-residue signal peptide was found at the NH2-terminus followed by a hydrophilic region, and a potential site for a glycosylphosphatidylinositol anchor at the COOH-terminus. A recombinant NcSRS9 protein was produced and was recognized on a Western blot by a low proportion of sera from a panel of naturally infected cows and calves. In addition, Western blot analysis using polyclonal anti-rNcSRS9 revealed stage-specific expression of NcSRS9 in bradyzoites but not in tachyzoites, and immunohistochemistry on brain from a congenitally infected calf showed NcSRS9 recognition in bradyzoites contained in tissue cysts. However, bradyzoite-specific expression of NcSRS9 could not be proven by immunofluorescence on bradyzoites obtainedin vitroand RT-PCR analysis showed no significant variations of NcSRS9transcripts duringin vitrotachyzoite-bradyzoite switch, probably due to incomplete maturity ofin vitrobradyzoites. Initial characterization of NcSRS9 in this study may lead to further studies for a better understanding ofN. caninumpersistence.

Genome walking in eukaryotes

Genome walking is a molecular procedure for the direct identification of nucleotide sequences from purified genomes. The only requirement is the availability of a known nucleotide sequence from which to start. Several genome walking methods have been developed in the last 20 years, with continuous improvements added to the first basic strategies, including the recent coupling with next generation sequencing technologies. This review focuses on the use of genome walking strategies in several aspects of the study of eukaryotic genomes. In a first part, the analysis of the numerous strategies available is reported. The technical aspects involved in genome walking are particularly intriguing, also because they represent the synthesis of the talent, the fantasy and the intelligence of several scientists. Applications in which genome walking can be employed are systematically examined in the second part of the review, showing the large potentiality of this technique, including not only the simple identification of nucleotide sequences but also the analysis of large collections of mutants obtained from the insertion of DNA of viral origin, transposons and transfer DNA (T-DNA) constructs. The enormous amount of data obtained indicates that genome walking, with its large range of applicability, multiplicity of strategies and recent developments, will continue to have much to offer for the rapid identification of unknown sequences in several fields of genomic research.

Comparative efficacy of immunization with inactivated whole tachyzoites versus a tachyzoite-bradyzoite mixture against neosporosis in mice

The worldwide economic impact ofNeospora caninuminfection has caused the development of effective vaccines to become one of the main goals in the field of neosporosis research. In this study, the protection conferred by antigens from inactivated whole tachyzoites (TZ) and a tachyzoite-bradyzoite mixture (TZ-BZ) ofN. caninum(Nc-Spain7 isolate) incorporated into a water-in-oil emulsion (W/O) and aluminium hydroxide-ginseng extract (Al/G) was evaluated in mouse models of congenital and cerebralN. caninuminfection. Immunization with TZ-BZ induced congenital and cerebral neosporosis exacerbation that was mainly characterized by reduced neonatal median survival time and increased parasite presence in adult mouse brains. The immune response of mice immunized with TZ-BZ was characterized by an increase in IFN-γexpression prior to challenge and an increase in IL-4 expression accompanied with significantly higher levels of antibodies against 2 recombinant bradyzoite-specific proteins (rNcSAG4 and rNcBSR4) after challenge. Immunization with TZ in W/O significantly reduced neonatal mortality, vertical transmission as well as parasite presence in adult mouse brains and induced a strong humoral immune response. The current study demonstrates the critical role of stage-specific antigens and adjuvants on the development of effective inactivated vaccines for the prevention ofN. caninuminfection.

The SnSAG merozoite surface antigens of Sarcocystis neurona are expressed differentially during the bradyzoite and sporozoite life cycle stages

Sarcocystis neurona is a two-host coccidian parasite whose complex life cycle progresses through multiple developmental stages differing at morphological and molecular levels. The S. neurona merozoite surface is covered by multiple, related glycosylphosphatidylinositol-linked proteins, which are orthologous to the surface antigen (SAG)/SAG1-related sequence (SRS) gene family of Toxoplasma gondii. Expression of the SAG/SRS proteins in T. gondii and another related parasite Neospora caninum is life-cycle stage specific and seems necessary for parasite transmission and persistence of infection. In the present study, the expression of S. neurona merozoite surface antigens (SnSAGs) was evaluated in the sporozoite and bradyzoite stages. Western blot analysis was used to compare SnSAG expression in merozoites versus sporozoites, while immunocytochemistry was performed to examine expression of the SnSAGs in merozoites versus bradyzoites. These analyses revealed that SnSAG2, SnSAG3 and SnSAG4 are expressed in sporozoites, while SnSAG5 was appeared to be downregulated in this life cycle stage. In S. neurona bradyzoites, it was found that SnSAG2, SnSAG3, SnSAG4 and SnSAG5 were either absent or expression was greatly reduced. As shown for T. gondii, stage-specific expression of the SnSAGs may be important for the parasite to progress through its developmental stages and complete its life cycle successfully. Thus, it is possible that the SAG switching mechanism by these parasites could be exploited as a point of intervention. As well, the alterations in surface antigen expression during different life cycle stages may need to be considered when designing prospective approaches for protective vaccination.

Genetic manipulation of Neospora caninum to express the bradyzoite-specific protein NcSAG4 in tachyzoites

Neospora caninum is an apicomplexan parasite and the aetiological agent of bovine neosporosis, one of the main causes of reproductive failure worldwide. We have generated 2 independent transgenic knock-in clones, Nc-1SAG4c1.1 and Nc-1SAG4c2.1, that express the bradyzoite stage-specific protein NcSAG4 in the tachyzoite stage. These clones have similar growth rates in vitro as the wild-type (WT) strain Nc-1. Studies in a cerebral mouse model of infection revealed a slightly lower rate of detection of the transgenic strains in brains during the chronic phase of infection. However, a pregnant mouse model of infection revealed a reduction in the virulence of the Nc-1SAG4c1.1 strain despite the same tachyzoite expression of NcSAG4 and a similar anti-NcSAG4 response displayed by mice inoculated with Nc-1 SAG4c1.1 or Nc-1 SAG4c2.1 parasites. This behaviour may be related to the reduced ability of the Nc-1SAG4c1.1 parasites to invade host cells, which was observed in in vitro assays. The apparent reduction in persistence and the high growth rate of the transgenic strains, together with their constitutive expression of the protein NcSAG4, may be useful features for future immunoprophylaxis trials based on a safe live attenuated vaccine.

Identification of Neospora caninum proteins regulated during the differentiation process from tachyzoite to bradyzoite stage by DIGE

Identification of differentially expressed proteins during Neospora caninum tachyzoite-bradyzoite conversion processes may lead to a better knowledge of the pathogenic mechanisms developed by this important parasite of cattle. In the present work, a differential expression proteomic study of tachyzoite and bradyzoite stages was accomplished for the first time by applying DIGE technology coupled with MS analysis. Up to 72 differentially expressed spots were visualized (1.5-fold in relative abundance, p<0.05, t-test). A total of 53 spots were more abundant in bradyzoites and 19 spots in tachyzoites. MS analysis identified 26 proteins; 20 of them overexpressed in the bradyzoite stage and 6 in the tachyzoite stage. Among the novel proteins, enolase and glyceraldehyde-3-phosphate dehydrogenase (involved in glycolysis), HSP70 and HSP90 (related to stress response) as well as the dense granule protein GRA9, which showed higher abundance in the bradyzoite stage, might be highlighted. On the other hand, isocitrate dehydrogenase 2, involved in the Krebs cycle, was found to be more abundant in tachyzoites extract. Biological functions from most novel proteins were correlated with previously reported processes during the differentiation process in Toxoplasma gondii. Thus, DIGE technology arises as a suitable tool to study mechanisms involved in the N. caninum tachyzoite to bradyzoite conversion.

Failure of a vaccine using immunogenic recombinant proteins rNcSAG4 and rNcGRA7 against neosporosis in mice

The development of an effective vaccine against Neospora caninum infection in cattle is an important issue due to the significant economic impact of this parasitic disease worldwide. In this work, the immune response, safety and efficacy of different vaccine formulations using the N. caninum recombinant proteins rNcSAG4 (the first bradyzoite-specific protein assayed as a vaccine) and rNcGRA7 were evaluated in mouse models. The survival curves of pups from all vaccinated groups showed a slight delay in time to death compared to control groups; this difference was statistically significant for rNcSAG4+adjuvant group. Immune response of mice vaccinated with rNcSAG4 was characterized by reduced specific IgG and cytokine levels with an equilibrated IFN-gamma/IL-10 balance. Regarding mice vaccinated with rNcGRA7, a very strong humoral and cellular immune response was generated characterized by a hyper-production of IFN-gamma. This response was not accompanied by significant protection. Vaccination with a mixture of both recombinant proteins reduced infection in lung and brain during acute and chronic infection, respectively, although it was not statistically significant. In summary, no significant protection was obtained with these vaccine formulations in the present mouse models. However, the study reveals some positive results on immune response and efficacy for both recombinant proteins; these results are being discussed in order to suggest new approaches with new chronic infection mouse models and adjuvants.

Pattern of recognition of Besnoitia besnoiti tachyzoite and bradyzoite antigens by naturally infected cattle

Bovine besnoitiosis is caused by the protozoan parasite Besnoitia besnoiti. Many recent cases have been described in different European countries, which may be indicative of expansion of the disease in the next few years. Many infected animals remain asymptomatic; therefore, serological tests are essential tools for diagnosis. The objective of the present work was to identify B. besnoiti tachyzoite and bradyzoite immunodominant antigens (IDAs). IDAs were recognised by SDS-PAGE under reducing conditions and Western blot analysis. Positive sera from symptomatic (n=18) and asymptomatic (n=18) cattle came from herds endemically infected by B. besnoiti and were confirmed positive by IFAT, whereas negative sera (n=4) came from besnoitiosis-free herds and were also confirmed negative by IFAT. Up to 28 tachyzoite antigens in the range of 8.5-190.8 kDa were recognised. Based on the frequency of recognition, six IDAs (14.2, 33, 37.1, 39.6, 46.3 and 190.8 kDa) were identified. The 37.1 kDa antigen was recognised by 100% of sera, usually as an intense band. On the other hand, 30 bradyzoite antigens in the range of 8.5-187.9kDa were detected. Seven bradyzoite IDAs (8.5, 15.1, 16.8, 19.0, 34.7, 38.6 and 124.4 kDa) were identified and two of them (15.1 and 16.8 kDa) were considered the most immunogenic ones. Additionally, sera from animals with clinical symptoms recognised a significantly higher number of bradyzoite antigens. Finally, significant cross-reactions with other closely related apicomplexan parasites were not detected. This is the first description of B. besnoiti bradyzoite antigens. In addition, the identification of tachyzoite and bradyzoite IDAs may be useful for the development of vaccines and diagnostic tools for differentiating between acute and chronic infections. Further proteomic studies are needed in order to identify stage-specific proteins.

Neospora caninum--how close are we to development of an efficacious vaccine that prevents abortion in cattle?

Neospora caninum is a protozoan parasite that causes abortion in cattle around the world. Although the clinical signs of disease in both dogs and cattle have now been recognised for over 20years, treatment and control options are still limited, despite the availability of a commercial vaccine in some countries of the world. The case for an efficacious vaccine has not been convincingly waged by farmers, veterinarians and other members of the agricultural and rural communities. In recent times, however, economic modelling has been used to estimate the industry losses due to Neospora-associated abortion, providing, in turn, the business case for forms of control for this parasite, including the development of vaccines. In this review, we document progress in all areas of the vaccine development pipeline, including live, killed and recombinant forms and the animal models available for vaccine evaluation. In addition, we summarise the main outcomes on the economics of Neospora control and suggest that the current boom in the global dairy industry increases the specific need for a vaccine against N. caninum-associated abortion.

Stage-specific expression of Nc SAG4 as a marker of chronic Neospora caninum infection in a mouse model

Neospora caninum infection persists throughout the life of its intermediate host due to the conversion of tachyzoites to slowly dividing bradyzoites that encyst in the brain. This event results in persistent N. caninum infection in bovine herds and partially explains the poor efficacy of many chemotherapeutic agents and vaccine formulations. Thus, there is a need for greater understanding of the tachyzoite-to-bradyzoite conversion mechanisms. Here we studied for the first time the transcription kinetics of the N. caninum bradyzoite-specific gene NcSAG4 in brain samples from chronically infected mice by means of real-time RT-PCR. NcSAG4-messenger RNA (mRNA) levels increased significantly during the chronic phase but followed 2 different expression patterns depending on the isolate used for murine inoculation. NcSAG4-mRNA levels in brains from Nc-1-inoculated mice peaked during late chronic infection (on day 64 post-infection, p.i.), whereas those from Nc-Liv-inoculated mice peaked earlier during the chronic infection (on day 32 p.i.). This difference could be a reflection of the different abilities of these isolates to replicate and form cysts in parasitized brains. These results are consistent with our observations of anti-rNcSAG4 antibody production; low levels were present at seroconversion and slowly increased during the chronic phase. In contrast, NcSAG1 transcription levels, which mark the tachyzoite stage, were maintained without variation in both groups of mice. This suggests the presence of a significant amount of tachyzoites or intermediate zoites expressing NcSAG1 in the brain, even during the late chronic infection.

The differentiation of transcription between tachyzoites and bradyzoites of in vitro cultured Neospora caninum

Interconversion between tachyzoites and bradyzoites of Neospora caninum plays a pivotal role in transmission of the parasite. Although significant efforts have been made toward understanding the mechanisms that trigger and control stage conversion of the parasite, little is known about this process. We used annealing control primer (ACP)-based polymerase chain reaction (PCR) technique to characterize the differences in transcription between tachyzoites and bradyzoites of N. caninum. The in vitro stage conversion of N. caninum-infected Vero cells was induced by treatment of infected cultures with 70 microM sodium nitroprusside. Subsequently, the gene expression profiles of the tachyzoites and bradyzoites were analyzed through comparison of the level of messenger RNA expression. ACP-based PCR revealed 85 amplicons that were consistently differentially expressed between tachyzoite and bradyzoite stages. Of the 85 differentially expressed transcripts identified, ten were cloned into Topo TA cloning vector, sequenced, and further analyzed by the Basic Local Alignment Search Tool. These differentially expressed transcripts include a combination of known genes and as yet unidentified genes. The present work provides candidate genes for further investigation on molecular basis of stage conversion from tachyzoites to bradyzoites of N. caninum.

The differential protein expression profiles and immunogenicity of tachyzoites and bradyzoites of in vitro cultured Neospora caninum

We report a study on the variations in the protein expression profiles of tachyzoites and bradyzoites of Neospora caninum. The in vitro stage conversion of N. caninum-infected Vero cells was induced by continuous treatment of infected cultures with 70 muM sodium nitroprusside (SNP) for up to 9 days. The stage conversion indicated by the expression of the bradyzoite-specific antigen BAG1 was analyzed by immunofluoresence assay. Morphological changes between tachyzoites and bradyzoites and localization of nuclei were demonstrated by transmission electron microscopy. Notably, we showed the differential protein expression profiles of tachyzoites and bradyzoites of N. caninum upon treatment with SNP. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated different protein patterns between tachyzoites and bradyzoites. Furthermore, Western blotting using rabbit polyclonal antibodies directed against tachyzoites revealed several reactive bands, one of which represented a tachyzoite-specific antigen of approximately 40 kDa remarkably expressed in the tachyzoite stage, but was absent from bradyzoites. Moreover, rabbit polyclonal serum raised against bradyzoites recognized a significant increased expression of an antigen with a MW of approximately 25 kDa in bradyzoites by Western blotting, suggesting that this protein is specifically expressed at the bradyzoite stage. Taken together, our data showed that differential protein expression profiling is a useful tool for discriminating between the two stages during tachyzoite-bradyzoite interconversion in N. caninum infections.

Neospora caninuminfection in birds: experimental infections in chicken and embryonated eggs

Neospora caninumcauses economical impact in cattle-raising farms since it is implicated as the major cause of bovine abortions. Although infection by the parasite has been widely described in mammals, the role of birds in its life-cycle is still obscure. Therefore, this work aimed to evaluate the infection byN. caninumin different chicken models. Experimental infections were conducted in 7-day-old chicks, laying hens and embryonated eggs, where samples were analysed for parasite burden, IgG antibodies and lesions promoted. Chickens demonstrated an asymptomatic infection, although with seroconversion and systemic replication of the parasite. In laying hens, no signs of vertical transmission were observed. However, embryonated eggs inoculated by the allantoic cavity route demonstrated susceptibility to infection, with mortality rates around 50% independent of the inoculum dose. Additionally, dogs became infected after ingestion of different amounts of inoculated eggs, producing either oocysts or specific IgG antibodies. The results herein presented demonstrate that chickens may be intermediate hosts ofN. caninumand that embryonated eggs could be a useful model to study the parasite's biology.

Molecular characterisation of BSR4, a novel bradyzoite-specific gene from Neospora caninum

Here we present the identification and cloning of the NcBSR4 gene, the putative Neospora caninum orthologue to the Toxoplasma gondii TgBSR4 gene. To isolate NcBSR4, genome walking PCR was performed on N. caninum genomic DNA using the expressed sequence tag NcEST3c28h02.y1 sequence, which shares a 44% identity with the TgBSR4 gene, as a framework. Nucleotide sequencing of amplified DNA fragments revealed a single uninterrupted 1227 bp open reading frame that encodes a protein of 408 amino acids with 66% similarity to the TgBSR4 antigen. A putative 39-residue signal peptide was found at the NH2-terminus, followed by a hydrophilic region. At the COOH-terminus, a potential site for a glycosylphosphatidylinositol anchor was identified at amino acid 379. A polyclonal serum against recombinant NcBSR4 protein was raised in rabbits, and immunolabelling demonstrated stage-specific expression of the NcBSR4 antigen in N. caninum bradyzoites produced in vitro and in vivo. Furthermore, RT-PCR analysis showed a slight increase of NcBSR4 transcripts in bradyzoites generated during in vitro tachyzoite-to-bradyzoite stage-conversion, suggesting that this gene is specifically expressed at the bradyzoite stage and that its transcription relies on the switch to this stage.

The NcGRA7 gene encodes the immunodominant 17 kDa antigen of Neospora caninum

A Neospora caninum 17-19 kDa antigenic protein fraction (p17) in one-dimensional polyacrylamide gel electrophoresis (SDS-PAGE) is the immunodominant antigen recognized by sera from bovines naturally infected by N. caninum. To identify the proteins making up the p17 fraction, we screened a new N. caninum tachyzoite cDNA library with an affinity-purified antibody against p17 (APA17). We isolated several cDNA clones with 100% sequence identity to the NcGRA7 gene. This previously described gene encodes a dense granule protein with an apparent molecular mass of 33 kDa. A second line of evidence emerged through a combined proteomic approach associating two-dimensional PAGE (2D-PAGE) to Western blotting and to mass spectrometry to characterize the p17 fraction. Two acidic immunodominant but minority protein spots were recognized by APA17 and by bovine sera. These antigens of 17 and 33 kDa are respectively composed of 4 and 2 isoforms. Furthermore, p17 isolation by 2D-PAGE and peptide sequencing by tandem mass spectrometry yielded a partial sequence of 17 amino acids, which allowed the putative amino terminal region of the NcGRA7 protein to be identified unambiguously. The NcGRA7 protein, without the putative signal peptide at the NH2-terminus, was cloned and expressed in Escherichia coli and when the purified recombinant protein (rNcGRA7) was analysed by SDS-PAGE and mass spectrometry, 2 bands of 24 and 33 kDa were resolved and identified as NcGRA7. These results demonstrate that the immunodominant 17 kDa antigen of N. caninum is encoded by the NcGRA7 gene.

Diagnosis of bovine neosporosis: Recent advances and perspectives

Neospora caninum is considered a major cause of abortion in cattle. Appropriate techniques for diagnosis of bovine neosporosis, both in vivo and in aborted foetuses, have been developed in the last ten years and some of them are commercially available. For diagnosis in live animals, detection of antibodies in serum or milk has been shown to be the best option both at the herd and the individual level. These techniques are excellent tools to examine N. caninum-associated abortion problems and to adopt some basic herd-control measures. Concerning foetal diagnosis, detection of compatible lesions by histological examination and parasites by PCR in brain (as well as heart and liver) are the best choices. Diagnostic criteria to distinguish foetal infection and Neospora-associated abortion are based not only on the demonstration of the parasite in the foetus but also on the extent and severity of the lesions in the foetus, foetal age and the assessment of neosporosis at the herd level. In the near future, new tools to diagnose infection should help to detect animals with parasite reactivation by testing the immune response to stage-specific antigens and lead to the development of molecular typing methods to characterise different parasite isolates. Finally, uniform diagnostic procedures need to be established between laboratories and countries in order to standardise result interpretation. The role of National or Regional Reference Laboratories is essential in countries or regions where control programmes for the disease are being developed.