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

Ovine placental explants: A new ex vivo model to study host‒pathogen interactions in reproductive pathogens

Reproductive failure is one of the main performance constraints in ruminant livestock. Transmissible agents such as Toxoplasma gondii and Neospora caninum are commonly involved in the occurrence of abortion in ruminants, but little is known about the mechanisms involved. While in vivo models are optimal for the study of abortion pathogenesis, they have a high economic cost and come with ethical concerns. Unfortunately, alternative in vitro models fail to replicate the complex in vivo placental structure. To overcome the limitations of currently available models, we developed an ex vivo model based on the cultivation of fresh and cryopreserved sheep placental explants, enabling the biobanking of tissues. Reproducible and simple markers of tissue integrity (histology, RNA concentrations), viability (resazurin reduction), and functionality (synthesis of steroid hormones) were also investigated, allowing a clear quality assessment of the model. This work shows that, similar to fresh explants, tissues cryopreserved in ethylene glycol using slow freezing rates maintain not only their structure and function but also their receptivity to T. gondii and N. caninum infection. In addition, the findings demonstrate that explant lifespan is mainly limited by the culture method, with protocols requiring improvements to extend it beyond 2 days. These findings suggest that cryopreserved tissues can be exploited to study the initial host‒pathogen interactions taking place in the placenta, thus deepening the knowledge of the specific mechanisms that trigger reproductive failure in sheep. Importantly, this work paves the way for the development of similar models in related species and contributes to the reduction of experimental animal use in the future.

Experimental infection with Neospora caninum in Texel ewes at different stages of gestation

In this study Texel sheep, at different stages of pregnancy, were experimentally infected with Neospora caninum. Eleven ewes, seronegative for N. caninum and Toxoplasma gondii, were inoculated 30 days before breeding (Group A), or at 65, 100, and 120 days of gestation (Groups B, C, and D). The group E (control) was inoculated with PBS. Blood samples were collected at -2, 2, 5, and 7 days post-infection (dpi), and weekly up to 42 dpi, for hematology, parasitemia (PCR), and serology (RIFI) assessments. Blood and tissue samples were collected from the lambs for molecular and histological analyses. All animals in Groups B, C, and D were seroconverted, whilst those in groups A and E remained seronegative. Parasitic DNA was detected in the blood of two ewes (groups B and D) and a lamb (group D), and in the brain of a lamb (group B). The parasitemia-positive ewe in group B delivered a weak and seropositive lamb, and had parasitic DNA in its placenta. These results confirm the vertical transmission of N. caninum in ewes inoculated at the beginning and end of pregnancy. The absence of abortions and other clinical signs suggest that Texel sheep may potentially have resistance to N. caninum.

Detection of Anti-Neospora caninum IgG in Blood Serum and Colostrum Samples in Naturally Infected Sheep and in Their Newborn Offspring

The aim was to detect correlations of IgG antibodies against N. caninum in serum and colostrum samples from ewes, through the IFAT, and to evaluate the presence of this immunoglobulin in the serum of newborn lambs after colostrum ingestion. Blood samples from 162 ewes that did not show any disease in the general physical examination and from their newborn lambs, not more than five days postpartum, along with 162 colostrum samples and 182 blood samples from the neonates, were analyzed. In total, 27.8% (45/162) of the mothers were positive for anti-N. caninum IgG, among which antibodies were detected in the colostrum in 46.7% (21/45). All the ewes with positive colostrum had reactive offspring. The kappa agreement for the correlation between the serological tests on the ewes and the colostrum results was 0.558. This correlation increased as the antibody titers of the mothers increased, and reached 1.000 from the titer of 1:400 from the mothers. Comparison of the antibody detection results between the offspring's serum and colostrum showed a kappa agreement of 1.000. In conclusion, there was a good agreement regarding the detection of anti-N. caninum IgG between the colostrum samples and the lambs' serum; the use of colostrum forms a noninvasive alternative for diagnosing N. caninum in sheep herds.

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.

One health therapeutics: Target-Based drug development for cryptosporidiosis and other apicomplexa diseases

This is a review of the development of bumped-kinase inhibitors (BKIs) for the therapy of One Health parasitic apicomplexan diseases. Many apicomplexan infections are shared between humans and livestock, such as cryptosporidiosis and toxoplasmosis, as well as livestock only diseases such as neosporosis. We have demonstrated proof-of-concept for BKI therapy in livestock models of cryptosporidiosis (newborn calves infected with Cryptosporidium parvum), toxoplasmosis (pregnant sheep infected with Toxoplasma gondii), and neosporosis (pregnant sheep infected with Neospora caninum). We discuss the potential uses of BKIs for the treatment of diseases caused by apicomplexan parasites in animals and humans, and the improvements that need to be made to further develop BKIs.

Maternal immune response in the placenta of sheep during recrudescence of natural congenital infection of Neospora caninum

In order to gain further insight into the pathogenesis and transmission of ovine neosporosis, the serological response of 13 naturally infected pregnant sheep was monitored. All sheep were euthanized upon the detection of a sharp increase in the level of specific antibodies against N. caninum in order to study the maternal immune response after the recrudescence of a chronic infection. Ten sheep were euthanized between 84 and 118 days of gestation, whereas the three remaining and three control not infected, pregnant sheep were euthanized at 135 days of gestation after no sharp increase in antibodies was detected. Vertical transmission was confirmed in 11 sheep by detection of N. caninum-DNA in at least one fetus, confirming recrudescence. Not all of fetuses showed pathologic microscopic lesions, however, multifocal non-purulent encephalitis was the main finding. Furthermore, nine out of the 11 vertical transmission positive sheep had lesions in placentomes (mainly multifocal necrotic foci), and the parasite was detected in eight out of 11 placentas by PCR and/or immunohistochemestry. The placentomes from sheep that suffered recrudescence showed an increased number of T lymphocytes CD3+ (CD4/CD8 < 1) and macrophages (MHC-II+), assessed by immunohistochemestry, together with an up-regulation of IFN-γ, IL-10, IL-4, TNFα, IL-2 and IL-18. IL-17 was only upregulated in the three infected sheep that did not have a sharp increase in antibody levels. In the sheep that showed fetal death at the time of euthanasia (n = 3) the placental microscopic lesions were more severe, the inflammatory infiltrate was higher, and the upregulation of cytokines was greater than in those sheep carrying viable fetuses. This study suggests that, similarly to bovine neosporosis, the time of gestation when recrudescence occurs determines the viability of the fetuses and, thus, seems to be related to the severity of lesions and immune response in the placenta. These results suggest that there might be a correlation, either as cause or as a consequence, between protection against vertical transmission of the parasite and a milder maternal serological response together with a high level of transcription of IL-17 in the placenta.

Toxoplasma gondii and Neospora caninum infections in South American camelids in Switzerland and assessment of serological tests for diagnosis

Background

Little is known about the epidemiology of Toxoplasma gondii and Neospora caninum infections in alpacas (Vicugna pacos) and llamas (Lama glama) outside South America. The study aimed to estimate the seroprevalence of T. gondii and N. caninum infections in South American camelids (SAC) in Switzerland, to optimize serological tests for SAC and to identify risk factors, which may favour infection.

Methods

A total of 571 sera from 132 Swiss farms (374 alpacas and 197 llamas, mean 4.3 animals/farm) were obtained. Four commercial enzyme-linked immunosorbent assays (ELISA) for detecting antibodies against T. gondii (ID Screen^® Toxoplasmosis Indirect (TOXO-MS)) or N. caninum (i.e. ID Screen^® Neospora caninum Indirect Multi-species (NCS-MS); ID Screen^® Neospora caninum Competition (NCC) and ID Screen^® Neospora caninum Indirect (NCS)) were first assessed for their use on SAC comparing their results with those in immunoblot, and optimizing cut-offs. Subsequently, two kits (TOXO-MS and NCS-MS) were selected for seroprevalence estimation. Additionally, a risk factor analysis for infection was performed on 41 farms, which agreed to participate in a web-based survey.

Results

Three kits (TOXO-MS, NCS-MS and NCC) showed almost perfect agreement (kappa > 0.901) with immunoblot results when the cut-offs were optimized, and one kit (NCS) proved not to be useful for detecting N. caninum seropositive SAC. By TOXO-MS ELISA, 82.3% (308/374) of the alpacas and 84.8% (167/197) of the llamas were seropositive for T. gondii, and 131/132 (99.2%) farms had seropositive animals. By NCS-MS ELISA, 3.5% (13/374) of the alpacas and 2.5% (5/197) of the llamas evidenced antibodies against N. caninum, and 9.1% (12/132) of the farms had seropositive animals. The variables “age” and “female sex” were identified as risk factors for T. gondii infection and “absence of cats in the farm during the last two years” as a protective factor. No risk or protective factors for N. caninum infection could be identified.

Conclusions

This nationwide cross-sectional study demonstrated for the first time the presence of antibodies against T. gondii and N. caninum in the Swiss SAC population, highlighting a high seroprevalence for T. gondii, the presence of cats as a risk factor and suggesting that SAC meat might represent an additional infection source for humans.

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.