Quantitative detection of Neospora caninum in bovine aborted fetuses and experimentally infected mice by real-time PCR

In vitro regulation of gene expression of pregnancy-associated proteins and cytokines in bovine endometrial epithelial cells and bovine trophoblastic cells by infection with Neospora caninum

Abortion caused by the parasite Neospora caninum is an important threat to the livestock industry worldwide. Trophoblasts and caruncular cells play major roles in initiating innate immune responses and controlling parasite infection at the fetal-maternal interface. In the present study, bovine uterine epithelial cells (BUECs) and bovine trophoblastic (BT) cells treated with bovine interferon-gamma (IFN-γ), IFN-alpha (IFN-α) and IFN-tau (IFN-τ) followed by infection with N. caninum were examined by measuring the mRNA expression levels of numerous pregnancy-associated proteins and observing parasite growth to elucidate the host-parasite interaction at the uteroplacental region. N. caninum infection increased the expression of prolactin-related protein 1 (PRP1), pregnancy-associated glycoprotein 1 (PAG1), and cytokines (TNF-α, IL-8 and IL-10) in BUECs and of IL-8 in BT cells. Bovine IFN-γ inhibited IL-8 and TNF-α expression in BUECs and IL-8 in BT cells. In contrast, the expression of the interferon-stimulated gene OAS1 was significantly increased by treatment of the infected BT cells with IFN-γ. However, treatment with bovine IFNs did not inhibit N. caninum growth in either cell line. In conclusion, our results suggest that bovine IFN-γ plays a crucial role in control of pathogenesis in uterus and induction of inflammatory response in the placental region following N. caninum infection, rather than growth inhibition of the parasites.

Construction of luciferase-expressing Neospora caninum and drug screening

BACKGROUND

Neospora caninum is an apicomplexan parasite that is particularly responsible for abortions in cattle and neuromuscular disease in dogs. Due to the limited effectiveness of currently available drugs, there is an urgent need for new therapeutic approaches to control neosporosis. Luciferase-based assays are potentially powerful tools in the search for antiprotozoal compounds, permitting the development of faster and more automated assays. The aim of this study was to construct a luciferase-expressing N. caninum and evaluate anti-N. caninum drugs.

METHODS

Luciferase-expressing N. caninum (Nc1-Luc) was constructed using clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR/Cas9). After testing the luciferase expression and phenotype of the Nc1-Luc strains, the drug sensitivity of Nc1-Luc strains was determined by treating them with known positive or negative drugs and calculating the half-maximal inhibitory concentration (IC50). The selective pan-rapidly accelerated fibrosarcoma (pan-RAF) inhibitor TAK-632 was then evaluated for anti-N. caninum effects using Nc1-Luc by luciferase activity reduction assay and other in vitro and in vivo studies.

RESULTS

The phenotypes and drug sensitivity of Nc1-Luc strains were consistent with those of the parental strains Nc1, and Nc1-Luc strains can be used to determine the IC50 for anti-N. caninum drugs. Using the Nc1-Luc strains, TAK-632 showed promising activity against N. caninum, with an IC50 of 0.6131 μM and a selectivity index (SI) of 62.53. In vitro studies demonstrated that TAK-632 inhibited the invasion, proliferation, and division of N. caninum tachyzoites. In vivo studies showed that TAK-632 attenuated the virulence of N. caninum in mice and significantly reduced the parasite burden in the brain.

CONCLUSIONS

In conclusion, a luciferase-expressing N. caninum strain was successfully constructed, which provides an effective tool for drug screening and related research on N. caninum. In addition, TAK-632 was found to inhibit the growth of N. caninum, which could be considered as a candidate lead compound for new therapeutics for neosporosis.

Establishment of an ultrasensitive and visual detection platform for Neospora caninum based-on the RPA-CRISPR/Cas12a system

Neospora caninum is a protozoan parasite that causes neosporosis in cattle, and leads to a high rate of abortion and severe financial losses. Rapid and accurate detection is particularly important for preventing and controlling neosporosis. In our research, a highly effective diagnostic technique based on the RPA-CRISPR/Cas system was created to successfully identify N. caninum against the Nc5 gene, fluorescent reporter system and the lateral flow strip (LFS) biosensor were exploited to display results. The specificity and sensitivity of the PRA-CRISPR/Cas12a assay were evaluated. We discovered that it was highly specific and did not react with any other pathogens. The limit of detection (LOD) for this technology was as low as one parasite per milliliter when employing the fluorescent reporter system, and was approximately ten parasites per milliliter based on the LFS biosensor and under blue or UV light. Meanwhile, the placental tissue samples were detected by our RPA-CRISPR/Cas12a detection platform were completely consistent with that of the nested PCR assay (59.4 %, 19/32). The canine feces were detected by our RPA-CRISPR/Cas12a detection platform were completely consistent with that of the nested PCR assay (8.6 %, 6/70). The RPA-CRISPR/Cas12a detection procedure was successfully finished in within 90 min and offers advantages of high sensitivity and specificity, speed and low cost. The technique was better suitable for extensive neosporosis screening in non-laboratory and resource-constrained locations. This study provided a new strategy for more rapid and portable identification of N. caninum.

Characterization of Neospora caninum virulence factors NcGRA7 and NcROP40 in bovine target cells

Bovine neosporosis is one of the major causes of reproductive failure in cattle worldwide, and differences in virulence between isolates have been widely shown. However, the molecular basis and mechanisms underlying virulence in Neospora caninum are mostly unknown. Recently, we demonstrated the involvement of NcGRA7 and NcROP40 in the virulence of N. caninum in a pregnant murine model using single knockout mutants in these genes generated by CRISR/Cas9 technology. In this study, the role of these proteins was investigated in two in vitro models using bovine target cells: trophoblast (F3 cell line) and monocyte-derived macrophages (BoMØ). The proliferation capacity of the single knockout mutant parasites was compared to the wild-type strain, the Nc-Spain7 isolate, using both cell populations. For the bovine trophoblast, no differences were observed in the growth of the defective parasites compared to the wild-type strain, neither in the proliferation kinetics nor in the competition assay. However, in naïve BoMØ, a significant decrease in the proliferation capacity of the mutant parasites was observed from 48 h pi onwards. Stimulation of BoMØ with IFN-γ showed a similar inhibition of tachyzoite growth in defective and wild-type strains in a dose-dependent manner. Finally, BoMØ infected with knockout parasites showed higher expression levels of TLR3, which is involved in pathogen recognition. These results suggest that NcGRA7 and NcROP40 may be involved in the manipulation of innate immune defense mechanisms against neosporosis and confirm the usefulness of the BoMØ model for the evaluation of N. caninum virulence mechanisms. However, the specific functions of these proteins remain unknown, opening the way for future research.

Congenital transmission of Neospora caninum in wild ungulates and foxes

Introduction

Neospora caninum is one of the main causes of abortion in cattle. In wildlife, the occurrence and relevance of vertical infection have not been yet clearly evaluated. The aim of this study was to verify the possibility of vertical transmission of N. caninum in three wild species extensively distributed in Europe, namely roe deer Capreolus capreolus, wild boar Sus scrofa and red fox Vulpes vulpes.

Methods

A total of 190 fetuses (72 wild boars, 67 foxes and 51 roe deer) from 61 females were included in the study. All animals, which were either found dead or culled within selective control plans in North-western Italy, were tested, in parallel by PCR on central nervous system, skeletal muscle and kidney.

Results and discussion

The efficiency of vertical transmission in the three target species was of 87.5% (95% CI 69.00-95.66).

Involvement of chemokine receptor CXCR3 in the defense mechanism against Neospora caninum infection in C57BL/6 mice

C-X-C motif chemokine receptor 3 (CXCR3) is an important receptor controlling the migration of leukocytes, although there is no report regarding its role in Neospora caninum infection. Herein, we investigated the relevance of CXCR3 in the resistance mechanism to N. caninum infection in mice. Wild-type (WT) C57BL/6 mice and CXCR3-knockout (CXCR3KO) mice were used in all experiments. WT mice displayed a high survival rate (100%), while 80% of CXCR3KO mice succumbed to N. caninum infection within 50 days. Compared with WT mice, CXCR3KO mice exhibited significantly lower body weights and higher clinical scores at the subacute stage of infection. Flow cytometric analysis revealed CXCR3KO mice as having significantly increased proportions and numbers of CD11c-positive cells compared with WT mice at 5 days post infection (dpi). However, levels of interleukin-6 and interferon-γ in serum and ascites were similar in all groups at 5 dpi. Furthermore, no differences in parasite load were detected in brain, spleen, lungs or liver tissue of CXCR3KO and WT mice at 5 and 21 dpi. mRNA analysis of brain tissue collected from infected mice at 30 dpi revealed no changes in expression levels of inflammatory response genes. Nevertheless, the brain tissue of infected CXCR3KO mice displayed significant necrosis and microglial activation compared with that of WT mice at 21 dpi. Interestingly, the brain tissue of CXCR3KO mice displayed significantly lower numbers of FoxP3⁺ cells compared with the brain tissue of WT mice at 30 dpi. Accordingly, our study suggests that the lack of active regulatory T cells in brain tissue of infected CXCR3KO mice is the main cause of these mice having severe necrosis and lower survival compared with WT mice. Thus, CXCR3⁺ regulatory T cells may play a crucial role in control of neosporosis.

ABORTION AND NEONATAL MORTALITY DUE TO TOXOPLASMA GONDII IN BIGHORN SHEEP (OVIS CANADENSIS)

Low lamb recruitment can be an obstacle to bighorn sheep (Ovis canadensis) conservation and restoration. Causes of abortion and neonate loss in bighorn sheep, which may affect recruitment, are poorly understood. Toxoplasma gondii is a major cause of abortion and stillbirth in domestic small ruminants worldwide, but no reports exist documenting abortion or neonatal death in bighorn sheep attributable to toxoplasmosis. Between March 2019 and May 2021, eight fetal and neonatal bighorn lamb cadavers from four western US states (Idaho, Montana, Nebraska, and Washington) were submitted to the Washington Animal Disease Diagnostic Laboratory for postmortem examination, histologic examination, and ancillary testing to determine the cause of abortion or neonatal death. Necrotizing encephalitis characteristic of toxoplasmosis was identified histologically in six of eight cases, and T. gondii infection was confirmed by PCR in five cases with characteristic lesions. Other lesions attributable to toxoplasmosis were pneumonia (3/5 cases) and myocarditis (2/5 cases). Protozoal cysts were identified histologically within brain, lung, heart, skeletal muscle, adipose tissue, or a combination of samples in all five sheep with PCR-confirmed T. gondii infections. Seroprevalence of T. gondii ranged from 40-81% of adult females sampled in the Washington population in October and November 2018-2021, confirming high rates of exposure before detection of Toxoplasma abortions in this study. Of 1,149 bighorn sheep postmortem samples submitted to Washington Animal Disease Diagnostic Laboratory between January 2000 and May 2021, 21 of which were from fetuses or neonates, a single case of chronic toxoplasmosis was diagnosed in one adult ewe. Recent identification of Toxoplasma abortions in bighorn sheep suggests that toxoplasmosis is an underappreciated cause of reproductive loss. Abortions and neonatal mortalities should be investigated through postmortem and histologic examination, particularly in herds that are chronically small, demographically stagnant, or exhibit reproductive rates lower than expected.

NcGRA7 and NcROP40 Play a Role in the Virulence of Neospora caninum in a Pregnant Mouse Model

The intraspecific variability among Neospora caninum isolates in their in vitro behaviour and in vivo virulence has been widely studied. In particular, transcriptomic and proteomic analyses have shown a higher expression/abundance of specific genes/proteins in high-virulence isolates. Consequently, the dense granule protein NcGRA7 and the rhoptry protein NcROP40 were proposed as potential virulence factors. The objective of this study was to characterize the role of these proteins using CRISPR/Cas9 knockout (KO) parasites in a well-established pregnant BALB/c mouse model of N. caninum infection at midgestation. The deletion of NcGRA7 and NcROP40 was associated with a reduction of virulence, as infected dams displayed milder clinical signs, lower parasite burdens in the brain, and reduced mortality rates compared to those infected with the wild-type parasite (Nc-Spain7). Specifically, those infected with the NcGRA7 KO parasites displayed significantly milder clinical signs and a lower brain parasite burden. The median survival time of the pups from dams infected with the two KO parasites was significantly increased, but differences in neonatal mortality rates were not detected. Overall, the present study indicates that the disruption of NcGRA7 considerably impairs virulence in mice, while the impact of NcROP40 deletion was more modest. Further research is needed to understand the role of these virulence factors during N. caninum infection.

Deleting ku80 improves the efficiency of targeted gene editing in Neospora caninum

CRISPR/Cas9 technology has been widely used for gene editing in organisms. Gene deletion of the ku80/ku70 complex can improve the efficiency of gene replacement in Arabidopsis thaliana, Cryptococcus neoformans, and Toxoplasma gondii, which remained elusive in Neospora caninum. Here, we knock out the ku80 gene in Nc1 strain by using CRISPR/Cas9, detect the growth rate and virulence of NcΔku80. Then we compare the efficiency of gene replacements between NcΔku80 and Nc1 strains by transfected with the same HA-tagged plasmids, and the percentage of HA-tagged parasites was investigated by IFA. The results showed that gene targeting efficiency was increased in the NcΔku80 strain via double crossover at several genetic loci, but its growth rate and virulence were unaffected. In conclusion, the NcΔku80 strain can be used as an effective strain for rapid gene editing of N. caninum.

Parasitemia and Associated Immune Response in Pregnant and Non-Pregnant Beef Cows Naturally Infected With Neospora caninum

The aim of this longitudinal study was to characterize the parasitemia of Neospora caninum and the associated immunological parameters in naturally infected beef cows for 10 months. The following groups were established: Neospora caninum seropositive pregnant cows (+Preg, n = 7), seropositive non-pregnant cows (+Npreg, n = 7), seronegative pregnant cows (−Preg, n = 4), and seronegative non-pregnant cows (−Npreg, n = 4). Several samples were obtained for absolute and relative leukocyte counting, cytokines IL-10, IL-12, α-TNF, and γ-IFN quantification, specific IgG, IgG1, and IgG2 and avidity and N. caninum DNA molecular detection and quantification. The +Preg group had a higher frequency and concentration of N. caninum DNA in PBMC in the last third of pregnancy compared to +Npreg (p <0.05), with 22 and 8% of detection, respectively. Parasitemia correlated positively with IgG titers and negatively with IgG1/IgG2 ratio (p <0.05). On day 222 of the assay, the +Preg group had the lowest total leukocyte counting (p <0.05). The +Preg group had a higher concentration of IgG and higher avidity in the last third of gestation compared to +Npreg (p <0.05). Avidity correlated with total IgG and IgG2 (p <0.05). All +Preg cows gave birth to clinically healthy but seropositive calves before colostrum intake, therefore, the congenital transmission was 100% efficient. Only a complete N. caninum genotype from a placenta and a partial genotype from cow #3 of the group +Preg were achieved by multilocus microsatellite analysis. Overall, N. caninum parasitemia is frequent in seropositive beef cows during the last third of gestation. This correlates with higher antibody levels and a decrease in total leukocyte counting. The precise timing of the parasitemia may be used for diagnosis purposes and/or for design strategies to avoid vertical transmission. Further studies are needed to identify the immune molecular mechanisms that favor parasitemia during gestation in chronically infected cattle.

Toxoplasma gondii and Neospora caninum Infections in Stray Cats and Dogs in the Qinghai–Tibetan Plateau Area, China

Simple Summary

Diseases caused by parasites have introduced serious threats to human health and the development of animal husbandry in the Qinghai–Tibetan Plateau Area (QTPA), such as toxoplasmosis caused by Toxoplasma gondii and neosporosis caused by Neospora caninum. However, information on the epidemiology of toxoplasmosis and neosporosis in stray cats and dogs which are the definitive hosts of T. gondii and N. caninum in the QTPA is limited. The aim of this study was to establish a detailed record of the seroprevalence of T. gondii and N. caninum-specific IgG and IgM antibodies in serum samples and the molecular epidemiology in feces from stray cats and dogs in the plateau area. The results revealed that stray cats and dogs in the QTPA, China present both T. gondii and N. caninum infection through the antibodies and antigen detection of the indirect ELISA tests and qPCRs. The present study suggests the prevalence of acute neosporosis and chronic re-emergence of toxoplasmosis in stray cats and dogs in the testing area. To the best of our knowledge, this is the first report of T. gondii and N. caninum infection in cats and dogs in the QTPA, and the first determination of N. caninum infection in cats in China. In conclusion, stray cats and dogs play key roles in the transmission and prevalence of T. gondii and N. caninum in the plateau area.

Abstract

Toxoplasma gondii and Neospora caninum belong to the Apicomplexan protozoa which is an obligate intracellular parasite, causing toxoplasmosis and neosporosis throughout the world. Cats and dogs are the definitive hosts of these two parasites. However, information on the epidemiology of toxoplasmosis and neosporosis in stray cats and dogs in the Qinghai–Tibetan Plateau Area (QTPA) is limited, and little is known about the diversity of the diseases. Therefore, the aim of this study was to perform indirect ELISA tests based on recombinant TgSAG1, TgGRA1, NcSAG1 and NcGRA7 proteins to establish a detailed record of the seroprevalence of T. gondii and N. caninum-specific IgG and IgM antibodies in serum samples and to develop qPCR amplification based on TgB1 and NcNc5 genes to conduct molecular epidemiology in feces from stray cats and dogs in the QTPA. In the current study, a total of 128 cat serum samples were analyzed through serological tests in which 53 (41.4%) and 57 (44.5%) samples were found positive for T. gondii specific-IgG and IgM antibodies, and 2 (1.6%) and 74 (57.8%) samples were confirmed positive for N. caninum specific-IgG and IgM antibodies, respectively. Out of 224 stray dog sera, 59.8% and 58.9% were recorded as positive against anti-Toxoplasma IgG and IgM antibodies, 17.9% and 64.7% were detected positive against Neospora IgG and IgM. On the other hand, 1 of 18 cat fecal samples was successfully amplified within the Ct value of 10 to 30 while no cat was positive for neosporosis. Moreover, a higher prevalence of toxoplasmosis in stray dogs (14.5%, 16/110) than of neosporosis (5.5%, 6/110) with different parasite numbers were found. Further analysis showed that no significant sex differences were found nor between the overall infection rates of T. gondii and N. caninum in this study. This study suggests that stray cats and dogs play key roles in the transmission and prevalence of T. gondii and N. caninum in the plateau area.

Neospora caninum infection in aborting bovines and lost fetuses: A systematic review and meta-analysis

Background

Neospora caninum (N. caninum) is known to be a major cause of reproductive failure in cattle herds around the world. Therefore, the current comprehensive study was performed to estimate the global prevalence of N. caninum infection in bovines that had an abortion and aborted fetuses.

Methods

In this study, PubMed, ScienceDirect, Web of Science, Scopus, and ProQuest databases were systematically searched for relevant studies up until November 4, 2021. Pooled prevalence and corresponding 95% confidence intervals (CI) were estimated using a random effect model. Other analyzes performed on the data of this study include sensitivity analysis, publication bias test, and quality assessment.

Results

The final analyses included 71 studies conducted on 2965 abortive cattle and 4805 aborted fetuses. The overall prevalence rates of N. caninum infection in bovines that had an abortion were 47% and 1% using serological and molecular methods. Furthermore, overall prevalence rates of N. caninum infection in bovine aborted fetuses globally were 35% (95% CI: 8%–62%) and 43% (95% CI: 35%–52%) using serological and molecular methods.

Conclusions

The results of this study showed the high prevalence of N. caninum infection in bovines that had an abortion and aborted fetuses. It is hoped that the results of this study will help prevent abortion in bovines around the world and encourage further studies to determine the impact of this parasite on the occurrence of abortion that may help reduce the economic damage caused by abortion worldwide.

The Protective Role of TLR2 Mediates Impaired Autophagic Flux by Activating the mTOR Pathway During Neospora caninum Infection in Mice

Autophagy has been shown to play an essential role in defending against intracellular bacteria, viruses, and parasites. Mounting evidence suggests that autophagy plays different roles in the infection process of different pathogens. Until now, there has been no conclusive evidence regarding whether host autophagy is involved in Neospora caninum infection. In the current study, we first monitored the activation of autophagy by N. caninum, which occurred mainly in the early stages of infection, and examined the role of host autophagy in N. caninum infection. Here, we presented evidence that N. caninum induced an increase in autophagic vesicles with double-membrane structures in macrophages at the early stage of infection. LC3-II expression peaked and decreased as infection continued. However, the expression of P62/SQSTM1 showed significant accumulation within 12 h of infection, indicating that autophagic flux was blocked. A tandem fluorescence protein mCherry-GFP-LC3 construct was used to corroborate the impaired autophagic flux. Subsequently, we found that N. caninum infection induced the activation of the TLR2–AKT–mTOR pathways. Further investigation revealed that TLR2–mTOR, accompanied by the blockade of autophagic flux, was responsible for impaired autophagy but was not associated with AKT. In vitro and in vivo, N. caninum replication was strongly blocked by the kinase inhibitor 3-methyladenine (3-MA, autophagy inhibitor). In contrast, rapamycin (Rapa, an autophagy inducer) was able to promote intracellular proliferation and reduce the survival rate of N. caninum-infected mice. On the other hand, the accumulation of autophagosomes facilitated the proliferation of N. caninum. Collectively, our findings suggest that activation of host autophagy facilitates N. caninum replication and may counteract the innate immune response of the host. In short, inhibition of the early stages of autophagy could potentially be a strategy for neosporosis control.

A short-term treatment with BKI-1294 does not protect foetuses from sheep experimentally infected with Neospora caninum tachyzoites during pregnancy

The Neospora caninum Calcium-dependent protein kinase 1 (NcCDPK1) inhibitor BKI-1294 had demonstrated excellent efficacy in a pregnant mouse model of neosporosis, and was also highly efficacious in a pregnant sheep model of toxoplasmosis. In this work, we present the efficacy of BKI-1294 treatment (dosed 5 times orally every 48 h) starting 48 h after intravenous infection of sheep with 10⁵ Nc-Spain7 tachyzoites at mid-pregnancy. In the dams, BKI-1294 plasma concentrations were above the IC₅₀ for N. caninum for 12-15 days. In treated sheep, when they were compared to untreated ones, we observed a minor increase in rectal temperature, higher IFNγ levels after blood stimulation in vitro, and a minor increase of IgG levels against N. caninum soluble antigens through day 28 post-infection. Additionally, the anti-NcSAG1 and anti-NcSAG4 IgGs were lower in treated dams on days 21 and 42 post-infection. However, BKI-1294 did not protect against abortion (87% foetal mortality in both infected groups, treated and untreated) and did not reduce transplacental transmission, parasite load or lesions in placentomes and foetal brain. The lack of foetal protection was likely caused by short systemic exposure in the dams and suboptimal foetal exposure to this parasitostatic drug, which was unable to reduce replication of the likely established N. caninum tachyzoites in the foetus at the moment of treatment. New BKIs with a very low plasma clearance and good ability to cross the blood-brain and placental barriers need to be developed.

Host defense against Neospora caninum infection via IL-12p40 production through TLR2/TLR3-AKT-ERK signaling pathway in C57BL/6 mice

Neospora caninum is an intracellular parasite which can cause neosporosis and significant economic losses in both dairy and beef industries worldwide. A better understanding of the immune response by host cells against N. caninum could help to design better strategies for the prevention and treatment of neosporosis. Although previous studies have shown TLR2/TLR3 were involved in controlling N. caninum infection in mice, the precise mechanisms of the AKT and MAPK pathways controlled by TLR2/TLR3 to regulate N. caninum-induced IL-12p40 production and the role of TLR2/TLR3 in anti-N. caninum infection in bovine macrophages remain unclear. In the present study, TLR2^-/- mice displayed more parasite burden and lower level of IL-12p40 production compared to TLR3^-/- mice. N. caninum could activate AKT and ERK signaling pathways in WT mouse macrophages, which were inhibited in TLR2^-/- and TLR3^-/- mouse macrophages. In N. caninum-infected WT mouse macrophages, AKT inhibitor or AKT siRNA could decrease the phosphorylation of ERK. AKT or ERK inhibitors reduced the production of IL-12p40 and increased the number of parasites. The productions of ROS, NO, and GBP2 were significantly reduced in TLR2^-/- and TLR3^-/- mouse macrophages. Supplementation of rIL-12p40 inhibited N. caninum proliferation and rescued the productions of IFN-γ, NO, and GBP2 in WT, TLR2^-/-, and TLR3^-/- mouse macrophages. In bovine macrophages, the expressions of TLR2, TLR3, and IL-12p40 mRNA were significantly enhanced by N. caninum, and N. caninum proliferation was inhibited by TLR2/TLR3 agonists. Taken together, the proliferation of N. caninum in mouse macrophages was controlled by the TLR2/TLR3-AKT-ERK signal pathway via increased IL-12p40 production, which in turn lead to the productions of NO, GBP2, and IFN-γ during N. caninum infection. And in bovine macrophages, TLR2 and TLR3 contributed to inhibiting N. caninum proliferation via increased IL-12p40 production.

Molecular Survey on Toxoplasma gondii and Neospora caninum Infection in Wild Birds of Prey Admitted to Recovery Centers in Northern Italy

Toxoplasma gondii and Neospora caninum (Apicomplexa, Sarcocystidae) are protozoan parasites infecting a wide range of intermediate hosts worldwide, including birds. Raptors acquire the infections through the ingestion of both infected preys and oocysts in the environment suggesting they might be used as indicators of the spread of these pathogens. Here, we report an epidemiological survey with the aim of determining the prevalence of T. gondii and N. caninum infections in wild birds of prey, hospitalized in two Wildlife Recovery Centres (WRCs) in Northern Italy. Genomic DNA extracted from brain tissue samples was submitted to Real Time PCR targeting T. gondii B1 and N. caninum Nc5 genes. T. gondii genotyping was then performed by multilocus sequence typing (MLST) analysis, targeting three polymorphic genes (GRA6, BTUB, and altSAG2). T. gondii DNA was found in 35 (62.5%) out of 56 examined samples; concerning genotyping, it was possible to amplify at least one gene for 26 animals, and obtained sequences belonged to Type II. N. caninum DNA was only detected in two (3.6%) common kestrels (Falco tinnunculus), adding a new species to the list of suitable intermediate hosts for this pathogen. Data obtained in the present study thus confirmed the spread of both T. gondiiand N. caninum in wild bird of prey, endorsing the role of WRCs in the epidemiological surveillance of wildlife.

Meningoencephalitis, Vasculitis, and Abortions Caused by Chlamydia pecorum in a Herd of Cattle

A cow dairy (n = 2000) in close proximity to a sheep flock had third-trimester abortions and fatalities in cows and calves over a 14-month period. Eighteen of 33 aborted fetuses (55%) had multifocal random suppurative or mononuclear meningoencephalitis with vasculitis. Seventeen of these affected fetuses had intracytoplasmic bacteria in endothelial cells, and 1 fetus with pericarditis had similar bacteria within mesothelial cells or macrophages. Immunohistochemistry for Chlamydia spp. or polymerase chain reaction (PCR) for Chlamydia pecorum or both, performed on brain or pooled tissue, were positive in all 14 tested fetuses that had meningoencephalitis and in 4/4 calves and in 3/4 tested cows that had meningoencephalitis and thrombotic vasculitis. In 1 calf and 11/11 fetuses, C. pecorum PCR amplicon sequences were 100% homologous to published C. pecorum sequences. Enzootic chlamydiosis due to C. pecorum was the identified cause of the late term abortions and the vasculitis and meningoencephalitis in fetuses, calves, and cows. C. pecorum, an uncommon bovine abortogenic agent, is a differential diagnosis in late-term aborted fetuses with meningoencephalitis, vasculitis, and polyserositis.

Microneme Protein 6 Is Involved in Invasion and Egress by Neospora caninum

BACKGROUND

Neospora caninum, is the etiological agent of neosporosis, an infection that causes abortions in cattle and nervous system dysfunction in dogs. Invasion and egress are the key steps of the pathogenesis of N. caninum infection. Microneme proteins (MICs) play important roles in the recognition, adhesion, and invasion of host cells in other apicomplexan parasites. However, some MICs and their functions in N. caninum infection have rarely been reported.

METHODS

The homologous recombination strategy was used to investigate the function of MIC6 in N. caninum infection.

RESULTS

ΔNcMIC6 showed a smaller plaque size and weakened capacities of invasion and egress than Nc1. Transcription levels of the egress-related genes CDPK1, PLP1, and AMA1 of ΔNcMIC6 were downregulated. Due to the lack of NcMIC6, virulence of the pathogen in the infected mouse was weakened. The subcellular localization of NcMIC1 and NcMIC4 in ΔNcMIC6, however, did not change. Nevertheless, the transcription levels of MIC1 and MIC4 in ΔNcMIC6 were downregulated, and the expression and secretion of MIC1 and MIC4 in ΔNcMIC6 were reduced compared with that in Nc1. Furthermore, the absence of NcMIC6 weakened the virulence in mice and lower parasite load detected in mice brains.

CONCLUSIONS

NcMIC6 is involved in host cell invasion and egress in N. caninum and may work synergistically with other MICs to regulate the virulence of the pathogen. These data lay a foundation for further research into the function and application of NcMIC6.

Pyroptosis executioner gasdermin D contributes to host defense and promotes Th 1 immune response during Neospora caninum infection

Neospora caninum (N. caninum) is an intracellular parasite and is the causative agent of neosporosis, which leads to reproductive failure in cattle. Pyroptosis is a recently discovered form of programmed cell death executed by gasdermin D (GSDMD). This cell death mechanism is an important host defense against intracellular pathogens. However, pyroptosis induced by N. caninum is poorly understood. The aim of this study was to explore the roles of GSDMD-mediated pyroptosis during N. caninum infection in vivo. N. caninum-infected wild type mice and GSDMD-deficient mice were used to evaluate host resistance and its ability to affect immune response against this parasite. The results showed that GSDMD deficiency significantly reduced survival and impaired the host's abilities to clear parasite loads in tissues, monocytes/macrophages and neutrophils. Additionally, GSDMD was essential for circulating IL-18 and IFN-γ production induced by N. caninum infection, indicating that GSDMD can mediate the Th 1 immune response against N. caninum infection. Additional data revealed that treatment with exogenous recombinant IL-18 in N. caninum-infected Gsdmd^-/- mice rescues the reduction of circulating IFN-γ production to help eliminate the parasite. Taken together, our data indicate that GSDMD-mediated pyroptosis plays a vital role in maintaining host resistance to N. caninum and is essential for clearing the parasite. This form of programmed cell death promotes the Th 1 immune response by controlling IL-18 release and is considered a host defense against N. caninum. This study expands our understanding of interactions between host immune response/defense and N. caninum infection.

ROS-mediated NLRP3 inflammasome activation participates in the response against Neospora caninum infection

Background

Neospora caninum is an obligate intracellular protozoan that causes neosporosis, N. caninum infection is a major cause of abortion in cattle worldwide. Currently, specific treatment for neosporosis is not available. The NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is a cytoplasmic protein complex that plays an important role in host defense against N. caninum infection, but the underlying mechanisms are poorly understood.

Methods

The reactive oxygen species (ROS) inhibitor and the ROS inducer, wild-type (WT) and NLRP3-deficient peritoneal macrophages or mice were used to investigate the role of ROS in NLRP3 inflammasome activation and controlling parasite burdens. ROS production, cell death and cell viability, production of inflammasome-mediated IL-1β or IL-18, cleavage of caspase-1 and NLRP3 expression, as well as parasite burdens were detected.

Results

In vitro, N. caninum induced ROS generation in a dose-dependent manner in peritoneal macrophages. The pretreatment of ROS inhibitor N-acetyl-l-cysteine (NAC) significantly attenuated N. caninum-induced ROS production, LDH release, IL-1β secretion and NLRP3 expression, whereas N. caninum proliferation was notably increased. In contrary, the ROS inducer pyrogallol (PG) significantly enhanced ROS production and NLRP3 inflammasome activity and decreased the parasite burden in N. caninum-infected peritoneal macrophages. NADPH-dependent ROS-mediated NLRP3 inflammasome activation induced by N. caninum can also be confirmed by using the NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI). However, the NAC or DPI pre-treatment or PG treatment did not significantly alter N. caninum-induced inflammasome activities and parasite proliferation in Nlrp3^−/− peritoneal macrophages. In vivo, IL-18 releases in serum and parasite burdens in peritoneal exudate cells were significantly increased in PG-treated WT mice after infection with N. caninum; however, IL-18 productions and parasite burdens were not changed in PG-treated Nlrp3^−/− mice. Furthermore, PG treatment in WT mice infected with N. caninum significantly decreased the mortality, weight loss and parasite burdens in tissues and histopathological lesions.

Conclusions

Neospora caninum-induced NADPH-dependent ROS generation plays an important role in NLRP3 inflammasome activation and controlling parasites. The ROS inducer PG can control N. caninum infection mainly by promoting NLRP3 inflammasome activation. ROS-mediated NLRP3 inflammasome axis can be a potential therapeutic target for neosporosis.

Neospora caninum DNA distribution in tissues of gerbils as experimental models of chronic neosporosis

ABSTRACT Neospora caninum is the main etiologic agent of neosporosis in domestic animals and its pathogenesis comprises two characteristic phases: acute and chronic. Rodents are used as experimental models to mimic acute and chronic bovine neosporosis. In this study, we inoculated a total of 27 female gerbils, with different doses of N. caninum tachyzoites aiming to induce chronic disease. DNA was extracted from different organs of each animal after spontaneous death or euthanasia. Encephalic tissues were submitted to a highly sensitive real time PCR aiming to detect chronically infected animals. All the other samples were submitted to standard PCR. A total of 11 gerbils died due to acute neosporosis, as confirmed by N. caninum DNA detection in organs. 5x103 tachyzoites/mL of N. caninum was the dosage of antigen that can induce chronic infection in gerbils. In the encephalon sections of some animals that showed clinical signs of persistent infection, we found 70% positive for the anterior encephalon section, suggesting this area as preferential for cyst formation. Therefore, we determined the doses of tachyzoites that cause acute or chronic infection and detection of positive tissues, preferably, systemic organs during acute and encephalon in chronic phases.

Research into Neospora caninum-What Have We Learnt in the Last Thirty Years?

BACKGROUND

Neospora caninum has been recognised world-wide, first as a disease of dogs, then as an important cause of abortions in cattle for the past thirty years. Over that time period, there have been improvements in the diagnosis of infection and abortion, new tests have been developed and validated, and it is timely to review progress to date.

METHODS

Bibliometric methods were used to identify major trends and research topics present in the published literature on N. caninum. The tools used were SWIFT-Review, VOSviewer and SciMAT, along with the published papers found in the MEDLINE, Dimensions and Web of Science databases. A systematic review of the published Neospora literature (n = 2933) was also carried out via MEDLINE and systematically appraised for publications relevant to the pathogenesis, pathology and diagnosis of Neospora abortions.

RESULTS

A total of 92 publications were included in the final analysis and grouped into four main time periods. In these four different time periods, the main research themes were "dogs", "abortion", "seroprevalence" and "infection". Diagnostics, including PCR, dominated the first two time periods, with an increased focus on transmission and abortions, and its risk factors in cattle.

CONCLUSIONS

Longitudinal analyses indicated that the main themes were consistently investigated over the last 30 years through a wide range of studies, with evolving emphasis initially on dogs and diagnostic test development, followed by application to cattle, the identification of the risk factors leading to abortion, and in the latter time periods, an understanding of the immunity and a search for vaccines.

Quantification of Toxocara canis DNA by qPCR in mice inoculated with different infective doses

The nematode Toxocara canis is of public health importance and is the main causative agent of toxocariasis in humans. This disease is difficult to diagnose due to several factors, including the possibility of cross-reactions with other nematodes in the ELISA. To overcome this problem, molecular tests have been recommended as an alternative to identify the parasite. The quantitative real-time polymerase chain reaction (qPCR) technique was used in this study to identify and quantify the parasite load of T. canis in the mouse brain. To this end, 24 mice were divided into six groups, five of which were challenged with different infective doses of T. canis larvae (L3) (1000, 500, 250, 100 and 50 larvae), while the sixth group, uninfected, acted as negative control. Forty-five days after infection, the animals were euthanized to collect the brain, from which two portions of 20 mg of tissue were taken for DNA extraction, while the rest of the brain tissue was digested to quantify the number of larvae by microscopy. The number of DNA copies was calculated from the standard DNA quantification curve, showing values of E = 93.4%, R2 = 0.9655 and Y = -3.415. A strong positive correlation (R = 0, 81; p < .001) was found between the number of copies and the recovery of larvae from brain. However, the parasite's DNA was also identified even in animals from whose brain no larvae were recovered after tissue digestion. The results of this study therefore confirm that the qPCR technique can be a valuable tool for the detection and quantification of T. canis DNA in murine hosts, even in animals whose with tissues contain very few parasites.

Inhibitory action of phenothiazinium dyes against Neospora caninum

Neospora caninum is an Apicomplexan parasite related to important losses in livestock, causing abortions and decreased fertility in affected cows. Several chemotherapeutic strategies have been developed for disease control; however, no commercial treatment is available. Among the candidate drugs against neosporosis, phenothiazinium dyes, offer a low cost-efficient approach to parasite control. We report the anti-parasitic effects of the phenothiaziums Methylene Blue (MB), New Methylene Blue (NMB), 1,9–Dimethyl Methylene Blue (DMMB) and Toluidine Blue O (TBO) on N. caninum, using in vitro and in vivo models. The dyes inhibited parasite proliferation at nanomolar concentrations (0.019–1.83 μM) and a synergistic effect was achieved when Methylene Blue was combined with New Methylene Blue (Combination Index = 0.84). Moreover, the phenothiazinium dyes improved parasite clearance when combined with Pyrimethamine (Pyr). Combination of Methylene Blue + 1,9–Dimethyl Methylene Blue demonstrated superior efficacy compared to Pyrimethamine based counterparts in an in vivo model of infection. We also observed that Methylene Blue, New Methylene Blue and 1,9–Dimethyl Methylene Blue increased by 5000% the reactive oxygen species (ROS) levels in N. caninum tachyzoites. Phenothiazinium dyes represent an accessible group of candidates with the potential to compound future formulations for neosporosis control.

Inducible Nitric Oxide Synthase is required for parasite restriction and inflammatory modulation during Neospora caninum infection

Neospora caninum infection is an important cause of neuromuscular disease in dogs and abortion in cattle, leading to significant economic losses in beef and dairy industries. The protective immunity against apicomplexan parasites, specifically Toxoplasma gondii and N. caninum, is typically achieved by inducing an IL-12-driven Th1 immune response. IL-12 stimulates IFN-γ production, which activates Inducible Nitric Oxide Synthase (iNOS) and promotes consequent Nitric Oxide (NO) synthesis, classically described as one of the main effector mechanisms for parasite elimination. Here, we aimed to evaluate the role played by iNOS during N. caninum infection. Our results show that N. caninum infection in C57BL/6 wild type (WT) mice induce NO production in vivo and in vitro. In agreement, iNOS deficient mice, as well as WT mice treated with iNOS inhibitor aminoguanidine, succumbed during acute infection with a dose lethal to 50 % of the WT mice, and presented significant increase in parasite load when submitted to sub-lethal infection protocols. Interestingly, the lack of control of parasite proliferation observed in iNOS^-/- mice was associated with notable CNS inflammation and increased production of the main systemic proinflammatory cytokines (IL-12, IFN-γ, IL-6, TNF and IL-17A). Taken together, our findings show that iNOS plays an important role in restricting N. caninum replication, while also modulates the inflammatory process induced by the infection.

Early Neospora caninum infection dynamics in cattle after inoculation at mid-gestation with high (Nc-Spain7)- or low (Nc-Spain1H)-virulence isolates

Early Neospora caninum infection dynamics were investigated in pregnant heifers intravenously inoculated with PBS (G-Control) or 107 tachyzoites of high (G-NcSpain7)- or low (G-NcSpain1H)-virulence isolates at 110 days of gestation. Serial culling at 10 and 20 days post-infection (dpi) was performed. Fever was detected at 1 dpi in both infected groups (P < 0.0001), and a second peak was detected at 3 dpi only in G-NcSpain7 (P < 0.0001). At 10 dpi, Nc-Spain7 was detected in placental samples from one animal related to focal necrosis, and Nc-Spain7 transmission was observed, although no foetal lesions were associated with this finding. The presence of Nc-Spain1H in the placenta or foetuses, as well as lesions, were not detected at 10 dpi. At 20 dpi, G-NcSpain7 animals showed almost 100% positive placental tissues and severe focal necrosis as well as 100% transmission. Remarkably, foetal mortality was detected in two G-NcSpain7 heifers. Only one animal from G-NcSpain1H presented positive placental samples. No foetal mortality was detected, and lesions and parasite transmission to the foetus were not observed in this group. Finally, 100% of G-NcSpain7 heifers at 20 dpi presented specific antibodies, while only 60% of G-NcSpain1H animals presented specific antibodies at 20 dpi. In addition, earlier seroconversion in G-Nc-Spain7 was observed. In conclusion, tachyzoites from Nc-Spain7 reached the placenta earlier and multiplied, leading to lesion development, transmission to the foetus and foetal mortality, whereas Nc-Spain1H showed delayed infection of the placenta and no lesional development or transmission during early infection.

Effects of challenge dose and inoculation route of the virulent Neospora caninum Nc-Spain7 isolate in pregnant cattle at mid-gestation

Parameters such as pathogen dose and inoculation route are paramount in animal models when studying disease pathogenesis. Here, clinical findings, including foetal mortality, parasite transmission rates and lesion severity, and immune responses were evaluated in Asturiana pregnant heifers at day 110 of gestation challenged with a virulent (Nc-Spain7) Neospora caninum isolate. Four different doses of parasite tachyzoites were inoculated intravenously (IV1, 10⁷ parasites, n = 6; IV2, 10⁵, n = 6; IV3, 10³, n = 6; and IV4, 10², n = 5), and the subcutaneous (SC) inoculation route was also assessed for the dose of 10⁵ tachyzoites (SC, n = 6). In addition, a control group (n = 4 pregnant heifers) was evaluated. Foetal death was observed in all infected groups from 25 to 62 days post-infection, varying with the dose (IV1:4/6, IV2:3/6; IV4:2/5, IV3:1/6), and was three times less frequently associated with the SC route than IV inoculation (1/6 vs. 3/6). A dose-dependent effect for parasite loads in placental and foetal brain tissues was also detected. After SC challenge, a reduced number of tachyzoites were able to reach foetal brain tissues, and no lesions were observed. In calves, specific IgG responses in precolostral sera were mainly associated with high-dose groups (IV1 [100.0%] and IV2 [66.7%]), and cerebral parasite DNA detection was scarce (3/18). In dams, IFN-γ production and the dynamics of anti-N. caninum IgG antibodies varied with the dose, and the cell-mediated immune response was also found to be route-dependent. Our results confirm the influence of parasite dose and inoculation route on the outcome and dynamics of bovine neosporosis at mid-gestation.

The pathogenicity of two Neospora caninum goat strains in a BALB/c mouse model

Goats are frequently described as an intermediate host for the protozoan Neospora caninum, manifesting the disease mainly by recurrent abortions with placentitis and encephalitis in fetuses. Several reports of natural and experimental infections in cattle and mice show differences in the immune response, and the outcome of the infection can be variable depending on the species affected and by the behavior of the infective strain. This study describes for the first time two Neospora caninum strains isolated from naturally infected goats from the state of Minas Gerais, Brazil. One placenta and one brain from different goats were processed for a first bioassay in gerbils (Meriones unguiculatus). Subsequently, a second bioassay was performed by inoculating the processed brain samples from gerbils into Interferon gamma (IFN-γ) knockout mice (KO mice). Tachyzoites collected from the peritoneal fluid of the KO mice were inoculated into VERO cell monolayers, where they presented a very slow growth rate. The tachyzoites were also inoculated into BALB/c mice with a dose of 10⁶ tachyzoites per animal. After a 5-week follow up, the animals infected with both of the strains developed a strong polarized Th1 response with increased serum and spleen gene expression levels of pro-inflammatory cytokines (mainly IFN-γ and TNF-α) in the first week. Tissue lesions were mild in the animals infected with both strains. Despite the strong immune response preventing an infection in the visceral organs, the parasite was able to reach the brain, causing progressive brain lesions from the second to fifth week post infection. The NC-goat1-infected mice presented with severe meningoencephalitis, but the NC-goat2-infected animals had considerable histological brain lesions only at week 5. Immunohistochemical analysis of the mouse brains revealed a different pattern of inflammatory cells compared to the naturally infected goats. A severe inflammatory infiltrate of CD3⁺ T lymphocytes was found in the NC-goat1-infected mice. A more discrete infiltrate of CD3⁺ T cells was found in the NC-goat2-infected animals. Additionally, IBA1 IHC revealed an intense microglial reaction and monocyte perivascular cuffs in the NC-goat1-infected animals and lower microglia/monocyte infiltrates in the NC-goat2-infected mice. This work contributes knowledge on the pathogenicity of new Neospora caninum strains in mice, comparable with other well-established mouse models of the disease, and demonstrates the importance of studying goats as an intermediate host of this parasite.

C57BL/6 mice immunized with synthetic peptides from Toxoplasma gondii surface and microneme immunodominant antigens are able to decrease parasite burden in the brain tissues

Toxoplasmosis is a disease caused by Toxoplasma gondii, an intracellular protozoan able to infect a wide range of hosts. The infection is particularly severe in immunocompromised patients or during pregnancy, circumstances in which the parasite could find a more favorable microenvironment to replicate and invade host tissues. The current treatment consists in toxic drugs for the patients, being not appropriate for the fetuses and immunodeficient patients. So far, there is a lack of available vaccine to prevent the disease. The present study aimed to evaluate the immune response induced by peptides derived from parasite immunodominant proteins from key components, as surface, rhoptry, microneme and dense granule antigens. A panel of eleven peptides was selected considering the highest scores for B cell epitope prediction by in silico analyses. The peptides were divided in groups, according to the parasite organelle locations, and used to immunize C57BL/6 mice. The animals were submitted to three doses of immunization and infected by 10 cysts of T. gondii ME49 strain. Blood samples were collected and used to measure the production of antibodies and cytokines, while the brains were collected to determine the parasite burden by quantitative polymerase chain reaction (qPCR). It was found that synthetic peptides from all targets were able to induce IgG synthesis in immunized mice, as well as to modulate the Th1/Th2 cytokine production, particularly the MIC and SRS groups, which presented the IFN-γ/IL-10 and TNF-α/IL-10 ratios 30 and 10 times higher, respectively, when compared with non-immunized group. Interestingly, the animals from MIC and SRS groups had significantly lower levels of T. gondii DNA in their brains. In summary, it can be concluded that peptides mainly from SRS and MIC parasite components constitute relevant targets to design vaccine candidates against parasite burden observed during chronic toxoplasmosis.

Differential Responses of Bovine Monocyte-Derived Macrophages to Infection by Neospora caninum Isolates of High and Low Virulence

Neospora caninum, a protozoan parasite closely related to Toxoplasma gondii, represents one of the main causes of abortion in cattle. Macrophages (MØs) are mediators of the innate immune response against infection and likely one of the first cells encountered by the parasite during the host infection process. In this study, we investigated in vitro how high or low virulent isolates of N. caninum (Nc-Spain7 and Nc-Spain1H, respectively) interact with bovine monocyte-derived MØs and the influence of the isolate virulence on the subsequent cellular response. Both isolates actively invaded, survived and replicated in the MØs. However, Nc-Spain7 showed a higher invasion rate and a replication significantly faster, following an exponential growth model, whereas Nc-Spain1H presented a delayed replication and a lower growth rate without an exponential pattern. N. caninum infection induced a hypermigratory phenotype in bovine MØs that was characterized by enhanced motility and transmigration in vitro and was accompanied by morphological changes and abrogated extracellular matrix degradation. A significantly higher hypermotility was observed with the highly virulent isolate Nc-Spain7. Nc-Spain1H-infected MØs showed elevated reactive oxygen species (ROS) production and IL12p40 expression, which also resulted in increased IFN-γ release by lymphocytes, compared to cells infected with Nc-Spain7. Furthermore, IL-10 was upregulated in MØs infected with both isolates. Infected MØs exhibited lower expression of MHC Class II, CD86, and CD1b molecules than uninfected MØs, with non-significant differences between isolates. This work characterizes for the first time N. caninum replication in bovine monocyte-derived MØs and details isolate-dependent differences in host cell responses to the parasite.

A probe-based real-time PCR assay for the detection of Neospora caninum in clinical samples from cattle

Neospora caninum is an apicomplexan protozoan parasite that is a leading cause of abortion in cattle. Detection of parasite-specific DNA by PCR is a highly sensitive method for identifying the presence of N. caninum in a variety of tissues. We developed and validated a probe-based real-time PCR assay targeting the conserved Nc5 gene of N. caninum. Using N. caninum strain Nc-1 genomic DNA and a synthetic gene fragment as amplification standards, we determined the PCR amplification efficiency and the limit of detection to be 95.60% and 3 copies, respectively. Five pathogens frequently associated with bovine abortions, namely bovine viral diarrhea virus types I and II, bovine alphaherpesvirus-1, Chlamydia, and Leptospira, were tested to ensure analytical exclusivity. A total of 103 clinical samples from aborted fetuses were tested concurrently with a standard conventional PCR and the new probe-based real-time PCR assay. All tested samples showed 100% agreement between these two assays. In conclusion, the probe-based real-time PCR assay facilitates accurate and rapid detection of N. caninum from abortions in cattle.

An investigation of the concurrency of anti-Neospora antibody and parasitemia in water buffalo (Bubalus bubalis) in northwest of Iran

Neospora caninum is an obligate intracellular parasite causing abortion and reproductive failure in ruminants. Here, the seroprevalence of Neospora DNA and anti-Neospora antibodies and the correlation between the DNA and the antibody using polymerase chain reaction (PCR) and a new developed whole cell-based enzyme-linked immunosorbent assay (ELISA) in water buffalo (Bubalus bubalis) were investigated. To determine the level of anti-Neospora antibody, 83 serum samples were collected from buffaloes in the northwest of Iran. Plates were coated with 2 × 10⁶ whole Neospora tachyzoites and the anti-Neospora antibody level was determined by calculating the ratio of sample/positive control (S/P) optical densities (ODs) in the ELISA. All samples with the ration of 0.50 or above were accounted as positive. To confirm the presence of Neospora DNA, the serum samples were directly subjected to PCR and nested PCR for detection of Neospora NC5 gene without the DNA isolation process. A total number of 83 buffalo serum samples were examined for the presence of anti-N. caninum immunoglobulin G and Neospora DNA. All samples with the S/P ratio of 0.50 or above (16 samples, 19.27%) were also positive for Neospora DNA. All samples with OD less than 0.50 (34 samples, 40.96%) were negative for Neospora DNA. However, 33 samples with the S/P ratio of bellow 0.50 (39.75%) showed a significant level of antibody. A 100% correlation was observed between high levels of the anti-Neospora antibody and Neospora DNA in the serum of water buffalo, and the whole N. caninum tachyzoites have the potency to be used as antigens for detection of the parasite in ELISA.

Virulence in Mice of a Toxoplasma gondii Type II Isolate Does Not Correlate With the Outcome of Experimental Infection in Pregnant Sheep

Toxoplasma gondii is an apicomplexan parasite that infects almost all warm-blooded animals. Little is known about how the parasite virulence in mice extrapolates to other relevant hosts. In the current study, in vitro phenotype and in vivo behavior in mice and sheep of a type II T. gondii isolate (TgShSp1) were compared with the reference type II T. gondii isolate (TgME49). The results of in vitro assays and the intraperitoneal inoculation of tachyzoites in mice indicated an enhanced virulence for the laboratory isolate, TgME49, compared to the recently obtained TgShSp1 isolate. TgShSp1 proliferated at a slower rate and had delayed lysis plaque formation compared to TgME49, but it formed more cyst-like structures in vitro. No mortality was observed in adult mice after infection with 1–10⁵ tachyzoites intraperitoneally or with 25–2,000 oocysts orally of TgShSp1. In sheep orally challenged with oocysts, TgME49 infection resulted in sporadically higher rectal temperatures and higher parasite load in cotyledons from ewes that gave birth and brain tissues of the respective lambs, but no differences between these two isolates were found on fetal/lamb mortality or lesions and number of T. gondii-positive lambs. The congenital infection after challenge at mid-pregnancy with TgShSp1, measured as offspring mortality and vertical transmission, was different depending on the challenged host. In mice, mortality in 50% of the pups was observed when a dam was challenged with a high oocyst dose (500 TgShSp1 oocysts), whereas in sheep infected with the same dose of oocysts, mortality occurred in all fetuses. Likewise, mortality of 9 and 27% of the pups was observed in mice after infection with 100 and 25 TgShSp1 oocysts, respectively, while in sheep, infection with 50 and 10 TgShSp1 oocysts triggered mortality in 68 and 66% of the fetuses/lambs. Differences in vertical transmission in the surviving offspring were only found with the lower oocyst doses (100% after infection with 10 TgShSp1 oocysts in sheep and only 37% in mice after infection with 25 TgShSp1 oocysts). In conclusion, virulence in mice of T. gondii type II isolates may not be a good indicator to predict the outcome of infection in pregnant sheep.

Endogenous transplacental transmission of Neospora caninum during successive pregnancies across three generations of naturally infected sheep

Endogenous transplacental transmission, which occurs during pregnancy as the result of reactivation of a latent infection in the dam, is the main mechanism of propagation of Neospora caninum within cattle herds. However, the importance of this propagation mechanism has not yet been evaluated in relation to ovine neosporosis. In this study, involving three generations of ewes naturally infected by N. caninum, we demonstrated that endogenous transplacental transmission may also be highly efficient in the ovine host since transmission of infection occurred in 96.6% of gestations and the congenital infection rate ranged between 66.7 and 93%. Nevertheless, parasite burdens decreased gradually in consecutive generations. Reactivation of latent infections had a strong impact on the pregnancy outcome, with high mortality rates recorded in the offspring of the two first generations of ewes (21.4-46.1%). Histological examination of the brain revealed that all aborted foetuses had characteristic lesions of neosporosis (necrotic glial foci) and a few parasite cysts, whereas most stillborn and newborn lambs that died shortly after birth had non-specific lesions (mild glial foci without necrosis) and parasite cysts were more frequent. Microsatellite analysis revealed scarce genetic variability in the N. caninum population, in accordance with a scenario in which infections were of a single origin and were exclusively maintained by clonal propagation through endogenous transplacental transmission.

NLRP3 Inflammasome Participates in Host Response to Neospora caninum Infection

Neospora caninum is an intracellular protozoan parasite closely related to Toxoplasma gondii that mainly infects canids as the definitive host and cattle as the intermediate host, resulting in abortion in cattle and leading to financial losses worldwide. Commercial vaccines or drugs are not available for the prevention and treatment of bovine neosporosis. Knowledge about the hallmarks of the immune response to this infection could form the basis of important prevention strategies. The innate immune system first responds to invading parasite and subsequently initiates the appropriate adaptive immune response against this parasite. Upon infection, activation of host pattern-recognition receptors expressed by immune cells triggers the innate immune response. Toll-like receptors, NOD-like receptors, and C-type lectin receptors play key roles in recognizing protozoan parasite. Therefore, we aimed to explore the role of the NLRP3 inflammasome during the acute period of N. caninum infection. In vitro results showed that N. caninum infection of murine bone marrow-derived macrophages activated the NLRP3 inflammasome, accompanied by the release of IL-1β and IL-18, cleavage of caspase-1, and induction of cell death. K⁺ efflux induced by N. caninum infection participated in the activation of the inflammasome. Infection of mice deficient in NLRP3, ASC, and caspase-1/11 resulted in decreased production of IL-18 and reduced IFN-γ in serum. Elevated numbers of monocytes/macrophages and neutrophils were found at the initial infection site, but they failed to limit N. caninum replication. These findings suggest that the NLRP3 inflammasome is involved in the host response to N. caninum infection at the acute stage and plays an important role in limiting parasite growth, and it may enhance Th1 response by inducing production of IFN-γ. These findings may help devise protocols for controlling neosporosis.

A novel recombinase polymerase amplification (RPA) assay for the rapid isothermal detection of Neospora caninum in aborted bovine fetuses

The development of a method to rapidly diagnose Neospora caninum infection is highly desirable. Recombinase polymerase amplification (RPA), combined with lateral flow (LF) strips, is a novel approach to rapidly amplify and visualize DNA. We have developed a prototype LF-RPA assay, using primers and a probe that targeted a specific sequence in the N. caninum NC-5 gene. The N. caninum-specific LF-RPA assay was first tested on purified DNA from oocysts and amplified N. caninum DNA to detectable levels in 10 min, at a constant temperature and without the need for an expensive thermocycler. The designed RPA primers and probe displayed 100% specificity for detecting N. caninum without any cross-reaction with DNA from nine related protozoan spp. (eg Toxoplasma gondii, Sarcocystis gigantean, Sarcocystis zuoi, Hammondia hammondi, Hammondia heydorni, Eimeria cylindrica, Plasmodium falciparum, Theileria annulata and Babesia bigemina). Although, LF-RPA assay detected amounts as low as 50 fg of N. caninum DNA, it was nearly 5-fold less sensitive than previously published qPCR and nested PCR assays. We tested the diagnostic performance of the LF-RPA assay for the detection of N. caninum DNA in aborted bovine fetal tissue samples, and compared the results with those obtained from nested PCR. Out of the 75 samples examined, 18 (24%) and 17 (22.6%) tested positive using LF-RPA and nested PCR, respectively. Our results indicate that LF-RPA is a suitable assay for the rapid and reliable detection of N. caninum.

Influence of dose and route of administration on the outcome of infection with the virulent Neospora caninum isolate Nc-Spain7 in pregnant sheep at mid-gestation

Experimental infections in pregnant sheep have been focused on studying the effect of the time of challenge on the outcome of N. caninum infection, whereas the impact of the dose and route of challenge has not been studied in depth. Therefore, clinical outcome, immune responses, parasite detection and burden, and lesion severity in placental tissues and foetal brains were investigated in 90-day-pregnant sheep inoculated intravenously with 10⁵ (G1), 10⁴ (G2), 10³ (G3), or 10² (G4) tachyzoites or subcutaneously with 10⁴ (G5) tachyzoites of the virulent Nc-Spain7 isolate and an uninfected group (G6). Comparing challenge doses, G1 was the only group that had 100% abortion. Likewise, IFNγ levels in G1 increased earlier than those in other intravenously infected groups, and IgG levels on day 21 post-infection (pi) were higher in G1 than those in other intravenously infected groups. Concerning vertical transmission, G1 shows a higher parasite burden in the foetal brain than did G2 and G3. Comparing routes of administration, no differences in foetal survival rate or parasite load in the foetal brain were found. Although G2 had higher IFNγ levels than G5 on day 10 pi, no differences were found in humoral immune responses. Because the outcome after intravenous infection with 10⁵ tachyzoites was similar to that observed after intravenous infection with 10⁶ tachyzoites used in a previous work (100% abortion and vertical transmission), we conclude that it may be reasonable to use 10⁵ tachyzoites administered by the intravenous route in further experiments when assessing drugs or vaccine candidates.

Safety and efficacy of the bumped kinase inhibitor BKI-1553 in pregnant sheep experimentally infected with Neospora caninum tachyzoites

Neospora caninum is one of the main causes of abortion in cattle, and recent studies have highlighted its relevance as an abortifacient in small ruminants. Vaccines or drugs for the control of neosporosis are lacking. Bumped kinase inhibitors (BKIs), which are ATP-competitive inhibitors of calcium dependent protein kinase 1 (CDPK1), were shown to be highly efficacious against several apicomplexan parasites in vitro and in laboratory animal models. We here present the pharmacokinetics, safety and efficacy of BKI-1553 in pregnant ewes and foetuses using a pregnant sheep model of N. caninum infection. BKI-1553 showed exposure in pregnant ewes with trough concentrations of approximately 4 μM, and of 1  μM in foetuses. Subcutaneous BKI-1553 administration increased rectal temperatures shortly after treatment, and resulted in dermal nodules triggering a slight monocytosis after repeated doses at short intervals. BKI-1553 treatment decreased fever in infected pregnant ewes already after two applications, resulted in a 37–50% reduction in foetal mortality, and modulated immune responses; IFNγ levels were increased early after infection and IgG levels were reduced subsequently. N. caninum was abundantly found in placental tissues; however, parasite detection in foetal brain tissue decreased from 94% in the infected/untreated group to 69–71% in the treated groups. In summary, BKI-1553 confers partial protection against abortion in a ruminant experimental model of N. caninum infection during pregnancy. In addition, reduced parasite detection, parasite load and lesions in foetal brains were observed.

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BKI-1553 showed excellent exposure in pregnant ewes and foetuses.

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BKI-1553 confers partial protection against abortion in N. caninum infected ewes.

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Treatment reduces parasite detection, parasite load and lesions in foetal brains.

Neospora caninum bioassay in gerbils using placental tissues from naturally infected goats

Neospora caninum is one of the main agents that causes abortions in cattle worldwide. However, little is known about the pathogenesis of neosporosis in small ruminants, especially goats. Gerbils (Meriones unguiculatus) have been used as a model for neosporosis, and this species is highly susceptible to infection by bovine N. caninum strains. The present study aimed to evaluate the susceptibility of gerbils to a N. caninum isolate from goats. The placentas were obtained from naturally infected goats, that presented with mild to severe lymphoplasmacytic and histiocytic infiltrate, foci of necrosis, calcification and protozoan-like structures. Immunosuppressed gerbils bioassayed with N. caninum-infected placental tissues showed severe neurological signs. Microscopic lesions in these gerbils were characterized by encephalitis, myocarditis, myositis and pancreatitis. These lesions were often associated with a small to moderate number of N. caninum tachyzoites, confirmed by immunohistochemistry and PCR. This is the first report showing that goat N. caninum strains could infect immunocompetent gerbils and cause severe lesions and clinical signs in immunosuppressed gerbils.

Differential susceptibility of bovine caruncular and trophoblast cell lines to infection with high and low virulence isolates of Neospora caninum

Background

Neospora caninum, one of the main causes of abortion in cattle, is very effective at crossing the placental barrier and placental damage is crucial in the pathogenesis of abortion. Bovine trophoblast and caruncular cell layers are key cellular components in the maternal-foetal interface in placentomes, playing a fundamental role in placental functionality.

Methods

We studied tachyzoite adhesion, invasion, proliferation and egress of high- (Nc-Spain7) and low- (Nc-Spain1H) virulence N. caninum isolates in established cultures of bovine caruncular epithelial (BCEC-1) and trophoblast (F3) cells. The parasite invasion rate (pInvR) and the cell infection rate (cInfR) were determined by immunostaining plaque assay at different time points and multiplicities of infection (MOIs), respectively. In addition, tachyzoite growth kinetics were investigated using real-time PCR (qPCR) analysis and immunostaining plaque assay at different times.

Results

Neospora caninum invaded and proliferated in both cell lines. The pInvR was higher in F3 compared to BCEC-1 cells for the Nc-Spain7 isolate (P < 0.05), and higher for the Nc-Spain7 than the Nc-Spain1H in F3 cells (P < 0.01). The cInfR was also higher in F3 cells than in BCEC-1 cells for both isolates (P < 0.0001), and the cInfR for the Nc-Spain7 isolate was higher than for the Nc-Spain1H isolate in both cell lines (P < 0.05). Tachyzoite growth kinetics showed tachyzoite exponential growth until egress at 58 hpi for both isolates in F3, whereas Nc-Spain1H showed a non-exponential growth pattern in BCEC-1. Asynchronous egress of both isolates was observed from 22 h post-infection onwards in BCEC-1. In addition, the tachyzoite yield (TY_58h) was higher in F3 than in BCEC-1 infected by both isolates (P < 0.0001), highlighting better replication abilities of both parasites in F3. Nc-Spain7 showed shorter doubling times and higher TY_58h compared to Nc-Spain1H in F3 cells; adhesion, invasion and proliferation mechanisms were very similar for both isolates in BCEC-1.

Conclusions

Our results indicate a highly similar behavior of high- and low-virulence isolates in their interactions with maternal caruncular cells and suggest an important role of foetal trophoblasts in the pathogenesis of N. caninum infection.

Development of a loop-mediated isothermal amplification technique and comparison with quantitative real-time PCR for the rapid visual detection of canine neosporosis

Background

Dogs are the definitive hosts of Neospora caninum and play an important role in the transmission of the parasite. Despite the high sensitivity of existing molecular tools such as quantitative real-time PCR (qPCR), these techniques are not suitable for use in many countries because of equipment costs and difficulties in implementing them for field diagnostics. Therefore, we developed a simplified technique, loop-mediated isothermal amplification (LAMP), for the rapid visual detection of N. caninum.

Methods

LAMP specificity was evaluated using a panel containing DNA from a range of different organisms. Sensitivity was evaluated by preparing 10-fold serial dilutions of N. caninum tachyzoites and comparing the results with those obtained using qPCR. Assessment of the LAMP results was determined by recognition of a colour change after amplification. The usefulness of the LAMP assay in the field was tested on 396 blood and 115 faecal samples from dogs, and one placenta from a heifer collected in Lopburi, Nakhon Pathom, Sa Kaeo, and Ratchaburi provinces, Thailand.

Results

Specificity of the LAMP technique was shown by its inability to amplify DNA from non-target pathogens or healthy dogs. The detection limit was the equivalent of one genome for both LAMP and qPCR. LAMP and qPCR detected positive N. caninum infection in 15 of 396 (3.8%) blood samples; LAMP detected 9/115 (7.8%) positive faecal samples, while qPCR detected 5/115 (4.3%) positive faecal samples. The placental tissue was shown to be positive by both techniques. Agreement between LAMP and qPCR was perfect in blood samples (kappa value, 1.00) and substantial in faecal samples (kappa value, 0.697).

Conclusions

This is the first known LAMP assay developed for the amplification of N. caninum. The technique effectively and rapidly detected the parasite with high sensitivity and specificity and was cost-effective. This assay could be used in the field to confirm the diagnosis of canine or bovine neosporosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2330-2) contains supplementary material, which is available to authorized users.

NLRP3 inflammasome activation in murine macrophages caused by Neospora caninum infection

Background

Neospora caninum is an intracellular parasite that causes significant economic losses in cattle industry. Understanding the host resistance mechanisms in the innate immune response to neosporosis could facilitate the exploration of approaches for controlling N. caninum infection. The NLR inflammasome is a multiprotein platform in the cell cytoplasm and plays critical roles in the host response against microbes.

Methods

Neospora caninum-infected wild-type (WT) macrophages and Nlrp3^−/− macrophages, and inhibitory approaches were used to investigate inflammasome activation and its role in N. caninum infection. Inflammasome RT Profiler PCR Arrays were used to identify the primary genes involved in N. caninum infection. The expression of the sensor protein NLRP3, processing of caspase-1, secretion of IL-1β and cell death were detected. Neospora caninum replication in macrophages was also assessed.

Results

Many NLR molecules participated in the recognition of N. caninum, especially the sensor protein NLRP3, and further study revealed that the NLRP3 distribution became punctate in the cell cytoplasm, which facilitated inflammasome activation. Inflammasome activation-mediated caspase-1 processing and IL-1β cleavage in response to N. caninum infection were observed and were correlated with the time of infection and number of infecting parasites. LDH-related cell death was also observed, and this death was regarded as beneficial for the clearance of N. caninum. Treatment of N. caninum-infected macrophages with caspase-1, pan-caspase and NLRP3 inhibitors led to the impaired release of active IL-1β and a failure to restrict parasite replication. And Neospora caninum infected peritoneal macrophages from Nlrp3-deficient mice displayed greatly decreased release of active IL-1β and the failure of caspase-1 cleavage.

Conclusions

The NLRP3 inflammasome can be activated in N. caninum-infected macrophages, and plays a protective role in the host response to control N. caninum.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2197-2) contains supplementary material, which is available to authorized users.

Differential Gamma Interferon- and Tumor Necrosis Factor Alpha-Driven Cytokine Response Distinguishes Acute Infection of a Metatherian Host with Toxoplasma gondii and Neospora caninum

Toxoplasma gondii and Neospora caninum (both Apicomplexa) are closely related cyst-forming coccidian parasites that differ significantly in their host ranges and ability to cause disease. Unlike eutherian mammals, Australian marsupials (metatherian mammals) have long been thought to be highly susceptible to toxoplasmosis and neosporosis because of their historical isolation from the parasites. In this study, the carnivorous fat-tailed dunnart (Sminthopsis crassicaudata) was used as a disease model to investigate the immune response and susceptibility to infection of an Australian marsupial to T. gondii and N. caninum The disease outcome was more severe in N. caninum-infected dunnarts than in T. gondii-infected dunnarts, as shown by the severity of clinical and histopathological features of disease and higher tissue parasite burdens in the tissues evaluated. Transcriptome sequencing (RNA-seq) of spleens from infected dunnarts and mitogen-stimulated dunnart splenocytes was used to define the cytokine repertoires. Changes in mRNA expression during the time course of infection were measured using quantitative reverse transcription-PCR (qRT-PCR) for key Th1 (gamma interferon [IFN-γ] and tumor necrosis factor alpha [TNF-α]), Th2 (interleukin 4 [IL-4] and IL-6), and Th17 (IL-17A) cytokines. The results show qualitative differences in cytokine responses by the fat-tailed dunnart to infection with N. caninum and T. gondii Dunnarts infected with T. gondii were capable of mounting a more effective Th1 immune response than those infected with N. caninum, indicating the role of the immune response in the outcome scenarios of parasite infection in this marsupial mammal.

Isolation and partial characterization of Streptococcus suis from clinical cases in cattle

Sixteen isolates of gram-positive, coccoid bacteria were obtained from clinical cases of diverse conditions in cattle and identified as Streptococcus suis using 16S ribosomal DNA gene sequencing and other bacterial identification methods. None of the isolates could be assigned to any of the known S. suis capsular types. Virulence-associated gene profiling that targeted muramidase-released protein, extracellular protein factor, suilysin, 89-kb pathogenicity island, and arginine deiminase ( arcA) genes were negative except for 1 isolate that was arcA positive. The arcA-positive isolate caused severe widespread lesions, including multiorgan suppurative and hemorrhagic inflammation in the meninges, lung, liver, spleen, lymph nodes, and serosae of heart and intestines. The other isolates were primarily associated with meningitis, bronchopneumonia, and multifocal acute necrotizing hepatitis. The isolates differed from each other by 4-6 fragments when examined by pulsed-field gel electrophoresis, indicating they are possibly related. The isolates were susceptible to ampicillin, penicillin, and tiamulin. Resistance was noted to sulfadimethoxine (93%), oxytetracycline (86%), chlortetracycline (86%), neomycin (67%), tilmicosin (47%), clindamycin (47%), enrofloxacin (33%), gentamicin (13%), florfenicol (7%), trimethoprim-sulfamethoxazole (7%), and spectinomycin (53%). Multi-drug resistance (defined as resistance to at least 1 agent in 3 or more antimicrobial classes) was detected in 67% of the isolates. The pathology observations provide evidence that S. suis may be an important pathogen of bovine calves. S. suis is an agent that clinical bacteriology laboratories should consider when dealing with cases involving cattle.

Neonatal neosporosis in a 2-week-old Bernese mountain dog infected with multiple Neospora caninum strains based on MS10 microsatellite analysis

Neonatal neosporosis is a challenging disease to diagnose in neonatal and young puppies because the first signs of this condition may not be strongly suggestive of an infectious aetiology. Within two weeks of birth, three of four pups died with a subacute clinical course, some with dyspnea, some with diarrhoea and some with neurologic signs. Neosporosis was diagnosed post-mortem, but only after microscopic examination of tissues collected at necropsy. Histological findings consisted of (i) necrotizing, diffuse interstitial pneumonia associated with intralesional protozoa and (ii) necrotizing multifocal myocarditis with mineralization and intralesional protozoa. No significant alterations were found in the cerebrum or cerebellum (spinal cord was not examined). Immunohistochemistry confirmed protozoal stages and cysts were Neospora caninum. Immunohistochemistry for Toxoplasma gondii was negative. Lung and heart were the most severely affected tissues with large numbers of free zoites, BAG5 positive bradyzoites and tissue cysts of N. caninum further confirmed by N. caninum-specific quantitative real-time PCR. One affected pup which displayed knuckling, ataxia and diarrhoea were treated with trimethoprim sulfadiazine and clindamycin, and made a complete recovery. This surviving pup (at 8 weeks-of-age) and dam were both positive for N. caninum antibody (reciprocal titres 4096 and 256, respectively). Three other intact bitches on the same property were seropositive for N. caninum, suggesting horizontal transmission and a common source of infection, possibly due to consumption of infected meat. Analysis using microsatellite-10 (MS10) demonstrated that multiple strains of N. caninum were present. It was likely that all MS10 N. caninum strains were transplacentally transmitted from dam to pups. This is the first time that multiple N. caninum strains have been demonstrated to be vertically transmitted in dogs. N. caninum should be considered in the differential diagnosis for acute to subacute death in neonatal pups even when neurological signs suggestive of neosporosis are absent.

Besnoitia besnoiti lytic cycle in vitro and differences in invasion and intracellular proliferation among isolates

Background

Bovine besnoitiosis, caused by the protozoan Besnoitia besnoiti, reduces productivity and fertility of affected herds. Besnoitiosis continues to expand in Europe and no effective control tools are currently available. Experimental models are urgently needed. Herein, we describe for the first time the kinetics of standardised in vitro models for the B. besnoiti lytic cycle. This will aid to study the pathogenesis of the disease, in the screening for vaccine targets and drugs potentially useful for the treatment of besnoitiosis.

Methods

We compared invasion and proliferation of one B. tarandi (from Finland) and seven B. besnoiti isolates (Bb-Spain1, Bb-Spain2, Bb-Israel, Bb-Evora03, Bb-Ger1, Bb-France, Bb-Italy2) in MARC-145 cell culture. Host cell invasion was studied at 4, 6, 8 and 24 h post infection (hpi), and proliferation characteristics were compared at 24, 48, 72, 96, 120, and 144 hpi.

Results

In Besnoitia spp., the key parameters that determine the sequential adhesion-invasion, proliferation and egress steps are clearly distinct from those in the related apicomplexans Toxoplasma gondii and Neospora caninum. Besnoitia spp. host cell invasion is a rather slow process, since only 50 % of parasites were found intracellular after 3–6 h of exposure to host cells, and invasion still took place after 24 h. Invasion efficacy was significantly higher for Bb-France, Bb-Evora03 and Bb-Israel. In addition, the time span for endodyogeny to take place was as long as 18–35 h. Bb-Israel and B. tarandi isolates were most prolific, as determined by the tachyzoite yield at 72 hpi. The total tachyzoite yield could not be predicted neither by invasion-related parameters (velocity and half time invasion) nor by proliferation parameters (lag phase and doubling time (dT)). The lytic cycle of Besnoitia was asynchronous as evidenced by the presence of three different plaque-forming tachyzoite categories (lysis plaques, large and small parasitophorous vacuoles).

Conclusions

This study provides first insights into the lytic cycle of B. besnoiti isolates and a standardised in vitro model that allows screening of drug candidates for the treatment of besnoitiosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1405-9) contains supplementary material, which is available to authorized users.

Immunization with Neospora caninum profilin induces limited protection and a regulatory T-cell response in mice

Profilins are actin-binding proteins that regulate the polymerization of actin filaments. In apicomplexan parasites, they are essential for invasion. Profilins also trigger the immune response of the host by activating TLRs on dendritic cells (DCs), inducing the production of pro-inflammatory cytokines. In this study we characterized for the first time the immune response and protection elicited by a vaccine based on Neospora caninum profilin in mice. Groups of eight BALB/c mice received either two doses of a recombinant N. caninum profilin expressed in Escherichia coli. (rNcPRO) or PBS, both formulated with an aqueous soy-based adjuvant enriched in TLR-agonists. Specific anti-profilin antibodies were detected in rNcPRO-vaccinated animals, mainly IgM and IgG3, which were consumed after infection. Splenocytes from rNcPRO-immunized animals proliferated after an in vitro stimulation with rNcPRO before and after challenge. An impairment of the cellular response was observed in NcPRO vaccinated and infected mice following an in vitro stimulation with native antigens of N. caninum, related to an increase in the percentage of CD4+CD25+FoxP3+. Two out of five rNcPRO-vaccinated challenged mice were protected; they were negative for parasite DNA in the brain and showed no histopathological lesions, which were found in all PBS-vaccinated animals. As a whole, our results provide evidence of a regulatory response elicited by immunization with rNcPRO, and suggest a role of profilin in the modulation and/or evasion of immune responses against N. caninum.

A review of neosporosis and pathologic findings of Neospora caninum infection in wildlife

Neospora caninum is an apicomplexan parasite that is the etiologic agent of neosporosis, a devastating infectious disease regarded as a major cause of reproductive loss in cattle and neuromuscular disease in dogs worldwide. This protozoan pathogen is maintained in the environment by a heteroxenous life cycle that involves a definitive canid host and a wide range of intermediate hosts. In recent years, a number of wildlife species have been investigated for their possible involvement in the N. caninum life cycle and many have been implicated as intermediate hosts. However, in many instances these studies have utilized serological and molecular techniques to detect infection in clinically normal animals, and investigation of possible associated morbidity, mortality, and pathology has been neglected. As such, the occurrence and importance of Neospora-associated disease in wildlife species are unknown. In order to improve our understanding of the significance of N. caninum infection in nondomestic species, the present review provides an up-to-date summary of clinical neosporosis and N. caninum-associated pathologic lesions in naturally and experimentally infected wildlife species. We provide a list of all free-ranging and captive wildlife species identified with N. caninum infection to date using currently available diagnostic tools. The advantages and disadvantages of diagnostic methods in wildlife are addressed in order to recommend optimal diagnosis of confirming N. caninum infection and neosporosis in nondomestic species. Although current data would suggest that N. caninum infection does not adversely impact wildlife populations, there is a need for greater international uniformity in the diagnosis of N. caninum infection and neosporosis in nondomestic species in order to assess the true consequences of parasite infection.

Influence of the gestational stage on the clinical course, lesional development and parasite distribution in experimental ovine neosporosis

Neospora caninum is considered one of the main causes of abortion in cattle, yet recent studies have also emphasised its relevance as an abortifacient in small ruminants. In order to gain deeper insight into the pathogenesis of ovine neosporosis, pregnant ewes were intravenously inoculated with 10⁶ tachyzoites of the Nc-Spain7 isolate at days 40, 90 or 120 of gestation. Infection during the first term resulted in the death of all foetuses between days 19 and 21 post-infection, showing mainly necrotic lesions in foetal liver and the highest parasite DNA detection and burden in both placenta and foetal viscera. After infection at day 90, foetal death was also detected in all ewes, although later (34–48 days post-infection). In this group, lesions were mainly inflammatory. Foetal livers showed the lowest frequency of lesions, as well as the lowest parasite detection and burden. All ewes infected at day 120 delivered viable lambs, although 3 out of 9 showed weakness and recumbency. Neospora DNA was detected in all lambs but one, and parasite burden was similar to that observed in day 90 group. Lesions in this group showed more conspicuous infiltration of inflammatory cells and higher frequency in foetal brain and muscle when compared to both previous groups. These results highlight the crucial role that the stage of gestation plays on the course of ovine neosporosis, similar to that reported in bovine neosporosis, and open the doors to consider sheep as a valid model for exogenous transplacental transmission for ruminant neosporosis.