Experimental ruminant models for bovine neosporosis: what is known and what is needed

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.

The role of genetic variability of the host on the resistance to Neospora caninum infection in cattle

Neospora caninum is one of the most frequently diagnosed abortifacient pathogens in cattle. There is abundant genomic information about the parasite itself, but very little is known about the genetic variability of resistance in the most common intermediate host. The aim of this review was to compile all the available information about the genetic variability associated with the resistance to N. caninum both between and within cattle breeds. We systematically searched for published studies that investigated the influence of genetics of the host on the prevalence of N. caninum and risk of abortion. Beyond the potential confounding effects of feeding systems, management and animal density, some lines of evidence suggest that Holstein, the most popular breed for milk production, has a comparatively higher risk of abortion due to infections by N. caninum, whereas some beef breeds from Continental Europe seem to be more resistant. It is still not clear if different genetic mechanisms of resistance are involved in the two known routes of infection: postnatal ingestion of oocysts or transplacental transmission from the infected dam to the fetus. Genomic information associated with susceptibility to infection and risk of abortion in different cattle breeds is still scarce. The information reported here could be useful to identify new research alternatives and to define novel strategies to deal with this major problem of animal production.

Reactivation and Foetal Infection in Pregnant Heifers Infected with Neospora caninum Live Tachyzoites at Prepubertal Age

Neospora caninum is recognised for causing cattle abortion, provoking severe economic losses in the livestock industry worldwide. The aim of the present study was to evaluate the reactivation and foetal infection in pregnant heifers inoculated with live N. caninum tachyzoites before puberty. A total of 15 30-month-old pregnant heifers were allocated into four groups: animals inoculated with live tachyzoites of NC-Argentina LP1 isolate before puberty and challenged with live tachyzoites of NC-1 strain at 210 days of gestation (DG) (Group A); animals mock inoculated before puberty and challenged with NC-1 strain at 210 DG (Group B), animals inoculated before puberty but not subsequently challenged (Group C); and noninfected and nonchallenged animals (Group D). The results of this study showed that 100% of animals infected before puberty (Groups A and C) suffered reactivation of the infection at the seventh month of gestation. In addition, in three and two calves from Groups A and C, respectively, congenital infection was confirmed. Interestingly, we provide evidence that the use of live N. caninum tachyzoites in young animals as a strategy to induce protection is neither safe nor effective.

Neospora caninum and Toxoplasma gondii as causes of reproductive losses in commercial sheep flocks from Argentina

The aim of this study is to provide preliminary data about the occurrence of Neospora caninum- and Toxoplasma gondii-related abortions and perinatal deaths in sheep from Argentina. Thirty ovine aborted foetuses and 33 perinatal deaths were submitted to the Veterinary Diagnostic Service at INTA EEA Balcarce (Argentina) during 2017–2019. A complete necropsy was performed on all specimens submitted, and foetal and placental tissues were examined. Foetal cavity fluids were collected for assessment of antibodies to N. caninum and T. gondii by indirect fluorescent antibody technique (IFAT). Placental and foetal tissue samples were collected for DNA extraction and histopathological analysis. The differential diagnosis with other causes of abortion was carried out. Of the sampled specimens, 20.63% (13/63) displayed evidence for N. caninum infection by IFAT and PCR, and in 61.5% (8/13) of the positive specimens the parasite was confirmed as the cause of abortion/perinatal death based on the presence of compatible histological lesions and/or positive immunohistochemistry test, positive PCR and/or positive IFAT, and no other infectious agents diagnosed. In contrast, T. gondii infection was confirmed in 9.52% (6/63) of the analysed specimens, but only in 2 lambs T. gondii was determined as the death cause. Neosporacaninum and T. gondii co-infections were confirmed in 4 analysed specimens (2 aborted foetuses and 2 perinatal deaths). These results demonstrated that N. caninum is efficiently transmitted and a frequent cause of ovine reproductive failure in the commercial analysed flocks compared with T. gondii. Despite T. gondii congenital infection was detected in some specimens (6/63), it was confirmed as the cause of death in only two of them. Thus, and considering the limited availability of confirmed samples, we could not determine whether toxoplasmosis is a major problem in Argentinian sheep flocks or not. More studies on a greater number of specimens from different ovine production systems under different management conditions are necessary to assess the real impact of neosporosis and toxoplasmosis in Argentina.

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Neospora caninum congenital infection was found in 13 of the 63 analysed specimens.

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In 8 of these 13 cases, N. caninum was confirmed as the cause of abortion/perinatal death.

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Toxoplasma gondii was determined as the perinatal death cause in 2 lambs.

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Co-infections with N. caninum + T. gondii were only confirmed in 4 analysed specimens.

Vaccination with Neospora caninum-cyclophilin and -profilin confers partial protection against experimental neosporosis-induced abortion in sheep

The purpose of this study was to evaluate the protective efficacy of a vaccine consisting of recombinant Neospora caninum-cyclophilin (NcCyP) and -profilin (NcPro) in sheep. At 42 d and 21 d prior to mating, adult Dorset ewes were immunized with the rNcCyP-rNcPro vaccine (Group 1) or co-purifying non-recombinant (NR) control vaccine (Group 2). At 90 days post-mating, all immunized ewes and were challenged by intravenous injection with 10⁶Nesopora caninum Illinois tachyzoites (NcTZ). Significant protection (P < 0.05) was observed in Group 1 with 9 out of 13 ewes giving birth to live-born lambs (69.2%), whereas all Group 2 ewes aborted (6/6). Neospora caninum was detected by PCR in both fetal and placental tissues from all Group 2 aborting ewes and in the placental tissues of Group 1 aborting ewes. In contrast, tissues and placentas of Group 1 live-born lambs were Neospora DNA-negative. Immunoreactive Neospora antigens were demonstrated in placentas associated with abortions, but not in tissues of aborted fetuses or those of the live-born lambs and their associated placentas. Anti-NcCyP and anti-NcPro titers were high in sera from Group 1 ewes and were further boosted by challenge infection, resulting in long-lasting (≥14.5 mos.) elevated titers. Lambs born to Group 1 ewes also had high NcCyP and NcPro titers in pre-colostrum sera. Immunofluorescence staining (IFA) of NcTZ with Group 1 post-immunization sera revealed both surface and internal TZ staining, a pattern consistent with that observed with rabbit sera to rNcCyP or rNcPro. Infection of NR-vaccinated ewes produced high but transient anti-NcCyP and anti-NcPro Ab titers. The results indicate that the NcCyP-NcPro vaccine elicited strong anti-N. caninum responses and conferred significant protection against abortion and transplacental transmission of N. caninum TZ in sheep.

Maternal and Foetal Cellular Immune Responses in Dams Infected With High- and Low- Virulence Isolates of Neospora caninum at Mid-Gestation

Bovine neosporosis is currently considered one of the main causes of abortion in cattle worldwide and the outcome of the infection is, in part, determined by Neospora caninum isolate virulence. However, the dam and foetal immune responses associated with this factor are largely unknown. We used a model of bovine infection at day 110 of gestation to study the early infection dynamics (10- and 20-days post-infection, dpi) after experimental challenge with high- and low-virulence isolates of N. caninum (Nc-Spain7 and Nc-Spain1H, respectively). In the present work, dam peripheral cellular immune responses were monitored twice a week from -1 to 20 dpi. At different time points, IFN-γ and IL-4 production was investigated in stimulated dam blood and the percentage of monocytes, NK cells, B cells and T cells (CD4+, CD8+ and γδ) in peripheral blood mononuclear cells (PBMC) were determined by flow cytometry. In addition, maternal iliofemoral lymph nodes and foetal spleen and thymus were collected at 10 and 20 dpi for the study of the same cell subpopulations. Peripheral immune response dynamics were similar after the infection with both isolates, with a significant increase in the percentage of CD4+ T cells at 6 and 9 dpi in PBMC, coincident with the higher levels of IFN-γ and IL-4 release. However, the levels of IFN-γ were significantly higher and an increase in CD8+ T cells at 9, 13 and 20 dpi was observed in the dams infected with Nc-Spain7. Nc-Spain1H infection induced higher IL4 levels in stimulated blood and a higher CD4+/CD8+ ratio in PBMC. The analysis of the maternal iliofemoral lymph node showed a significant enhancement in the percentage of NK, CD4+ and CD8+ T cells for the animals infected with the highly virulent isolate and euthanized at 20 dpi. Regarding the foetal responses, the most remarkable result was an increase in the percentage of monocytes at 20 dpi in the spleen of foetuses from both infected groups, which suggests that foetuses were able to respond to N. caninum infection at mid gestation. This work provides insights into how isolate virulence affects the maternal and foetal immune responses generated against N. caninum, which may influence the course of infection.

Modeling the Ruminant Placenta-Pathogen Interactions in Apicomplexan Parasites: Current and Future Perspectives

Neospora caninum and Toxoplasma gondii are one of the main concerns of the livestock sector as they cause important economic losses in ruminants due to the reproductive failure. It is well-known that the interaction of these parasites with the placenta determines the course of infection, leading to fetal death or parasite transmission to the offspring. However, to advance the development of effective vaccines and treatments, there are still important gaps on knowledge on the placental host-parasite interactions that need to be addressed. Ruminant animal models are still an indispensable tool for providing a global view of the pathogenesis, lesions, and immune responses, but their utilization embraces important economic and ethics restrictions. Alternative in vitro systems based on caruncular and trophoblast cells, the key cellular components of placentomes, have emerged in the last years, but their use can only offer a partial view of the processes triggered after infection as they cannot mimic the complex placental architecture and neglect the activity of resident immune cells. These drawbacks could be solved using placental explants, broadly employed in human medicine, and able to preserve its cellular architecture and function. Despite the availability of such materials is constrained by their short shelf-life, the development of adequate cryopreservation protocols could expand their use for research purposes. Herein, we review and discuss existing (and potential) in vivo, in vitro, and ex vivo ruminant placental models that have proven useful to unravel the pathogenic mechanisms and the host immune responses responsible for fetal death (or protection) caused by neosporosis and toxoplasmosis.

Delayed-type hypersensitivity skin test against Neospora caninum in heifers with undetectable specific antibodies

Delayed-type hypersensitivity (DTH) has been used in human and veterinary medicine as a skin testing for evaluating in vivo cell-mediated immune responses (CMIR). Whereas CMIR is a key process to control intracellular pathogens, its value at identifying cattle exposed to the abortigenic intracellular coccidian parasite Neospora caninum is unknown. In this work, we have evaluated a DTH skin testing in cattle exposed to N. caninum and still seronegative. Female calves were experimentally sensitized by subcutaneous (SC) inoculation with live tachyzoites of N. caninum (NC-Argentina LP1) in sterile phosphate-buffered saline (PBS) (group A; n: 8) whereas other calveswere mock-sensitized with PBS (group B; n: 6). Two DTH skin tests were performed by intradermal inoculation with a soluble lysate of N. caninum tachyzoites (NC-Argentina LP1) in the neck region at 60d and 960 d after sensitization. Skinfold thickness at the intradermal inoculation site was measured at 0, 24, 48 h post each DTH skin test and skin biopsies taken for microscopic evaluation. Specific N. caninum antibodies kinetics was evaluated all throughthe experiment. We found that whereas N. caninum specific antibodies remained below the ELISA cut-off, a distinctive skinfold thickness increase was detected in sensitized animals (group A) at the DTH skin test site, showing induration, swelling and inflammatory infiltration. Mock sensitized animals (group B) showed no skinfold thickness growth and lacked specific antibody response. Thus, N. caninum DTH skin testing could be a useful diagnostic tool for the detection of CMIR during N. caninum infection in non-humoral responders.

Comparative tachyzoite proteome analyses among six Neospora caninum isolates with different virulence

The biological variability among Neospora caninum isolates has been widely shown, however, the molecular basis that determines this diversity has not been thoroughly elucidated to date. The latest studies have focused on a limited number of isolates. Therefore, the goal of the present study was to compare the proteome of a larger number of N. caninum isolates with different origins and virulence. Label-free LC-MS/MS was used to investigate the tachyzoite proteomic differences among Nc-Bahia, Nc-Spain4H and Nc-Spain7, representing high virulence isolates and Nc-Ger6, Nc-Spain2H and Nc-Spain1H, representing low virulence isolates. Pairwise comparisons between all isolates and between high virulence and low virulence groups identified a subset of proteins with higher abundance in high virulence isolates. These proteins were involved in energy and redox metabolism, and DNA/RNA processing, which might determine the faster growth rates and parasite survival of the high virulence isolates. Highlighted proteins included a predicted member of the rhoptry kinase family ROP20 specific for N. caninum, Bradyzoite pseudokinase 1 and several dense granule proteins. DNA polymerase, which was more abundant in all high virulence isolates in all comparisons, might also be implicated in virulence. These results reveal insights into possible mechanisms involved in specific phenotypic traits and virulence in N. caninum, and the relevance of these candidate proteins for N. caninum virulence deserves further investigation.

Added value of IgM detection and low avidity index as markers of acute bovine besnoitiosis

Early in vivo diagnosis of bovine besnoitiosis is crucial for the success of control programmes. However, diagnosis in acutely infected animals is hindered by the low sensitivity of the available serological tools. In this study, a novel ELISA to detect specific anti-Besnoitia besnoiti IgM antibodies was developed. The usefulness of this tool together with an avidity ELISA were studied with a well-coded sera panel from experimentally and naturally infected cattle. First, the kinetics of specific IgM levels were determined in experimentally infected calves during the acute and chronic infection. Next, IgM levels were determined in naturally infected cattle with either acute or chronic infection. Finally, the IgG avidity index was monitored in both experimentally and naturally infected cattle. Specific IgM antibodies were detected prior to specific IgG antibodies (7-19 days vs. 17-26 days post-infection). A prompt IgM response was associated with the end of the febrile stage in experimentally infected calves. Naturally and experimentally infected animals with acute clinical signs tested IgM-positive but IgG-negative, followed by IgG seroconversion 2-3 weeks later. Chronically infected cattle developed both IgM and IgG specific antibodies. Moreover, a progressive increase in the avidity index (AI) was observed in all experimentally infected calves during the course of the experimental trials. However, a low AI coincided with visible tissue cysts. Low avidity values were also detected when naturally infected cattle with acute clinical signs seroconverted, in contrast to a high AI detected in chronically infected cattle. In summary, IgM and avidity ELISAs improved the early in vivo diagnosis of bovine besnoitiosis. IgM-positive but IgG-negative results were indicative of an acute infection, whereas IgG positive results accompanied by low avidity values confirmed a recent 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.

A model for chronic bovine besnoitiosis: Parasite stage and inoculation route are key factors

In this work, an experimental model for chronic besnoitiosis in bovine was developed and characterized. Using a previously established calf model, two new variables (parasite stage and inoculation route) were combined and used. Twelve Holstein Friesian 3-month-old male calves were randomly divided into four groups of three animals each. Bradyzoites were obtained from a chronically infected bull and used for inoculation via three different inoculation routes. Three groups were inoculated with 10⁶ bradyzoites by intravenous (G1), subcutaneous (G2) and intradermal (G3) routes, and a non-infected control group (G4) was inoculated with PBS. The trial lasted for 90 days and included daily clinical monitoring as well as weekly skin biopsies and blood sampling. Sera were obtained to analyse both cellular and humoral responses. Once the calves were euthanized, tissues from the skin, eyes, respiratory and reproductive tracts, among others, were collected to study presence of the parasite. Clinically, the infection was classified as mild to moderate for the acute stage since all infected calves showed lymphadenopathy from four days post-infection (pi) and fever from one week pi until 24 days pi. However, the most relevant results were achieved during the chronic stage that was classified as moderate to severe. In fact, pathognomonic conjunctival cysts were observed in all infected calves from 40 days pi onwards and were more abundant in G3. Moreover, one calf from this group developed skin lesions (49 days pi). The microscopic tissue cysts and Besnoitia DNA were detected primarily in skin, reproductive tract and respiratory tissue samples, and parasite load was higher in G3. In conclusion, the parasite stage (bradyzoite) and the inoculation route are key factors that influence the outcome of an infection. In particular, the intradermal route led to more severe clinical signs of the chronic phase in the inoculated calves.

Immune response to Neospora caninum live tachyzoites in prepubertal female calves

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

Treatment of Toxoplasmosis and Neosporosis in Farm Ruminants: State of Knowledge and Future Trends

Toxoplasmosis and neosporosis are closely related protozoan diseases that lead to important economic impacts in farm ruminants. Toxoplasma gondii infection mainly causes reproductive failure in small ruminants and is a widespread zoonosis, whereas Neospora caninum infection is one of the most important causes of abortion in cattle worldwide. Vaccination has been considered the most economic measure for controlling these diseases. However, despite vaccine development efforts, only a live-attenuated T. gondii vaccine has been licensed for veterinary use, and no promising vaccines against ne-osporosis have been developed; therefore, vaccine development remains a key goal. Additionally, drug therapy could be a valuable strategy for disease control in farm ruminants, as several drugs that limit T. gondii and N. caninum proliferation and dissemination have been evaluated. This approach may also be relevant to performing an initial drug screening for potential human therapy for zoonotic parasites. Treat-ments can be applied against infections in adult ruminants to minimize the outcomes of a primo-infection or the reactivation of a chronic infection during gestation or in newborn ruminants to avoid infection chronification. In this review, the current status of drug development against toxoplasmosis and neosporo-sis in farm ruminants is presented, and in an effort to promote additional treatment options, prospective drugs that have shown efficacy in vitro and in laboratory animal models of toxoplasmosis and neosporosis are examined

The route of Besnoitia besnoiti tachyzoites inoculation does not influence the clinical outcome of the infection in calves

In a previous attempt, an experimental model of bovine besnoitiosis was established in calves that were intravenously inoculated with different doses of Besnoitia besnoiti tachyzoites. Despite the fact that all infected calves developed the acute stage of disease, only microscopic findings characteristic of chronic besnoitiosis were reported. In the present study, calves were inoculated by subcutaneous and intradermal routes with B. besnoiti tachyzoites with the aim of developing clinical signs and macroscopic lesions characteristic of chronic besnoitiosis. Nine 3-month-old male calves were randomly distributed into three groups of three animals each. Next, 10⁶ tachyzoites were inoculated by either the subcutaneous (G1) or intradermal route (G2). The negative control group (G3) was inoculated with PBS. Daily clinical monitoring and regular blood collection were performed. At 70 days post-infection (pi), animals were euthanized, and tissues were collected to investigate lesions and parasites. Infected animals developed mild-moderate acute besnoitiosis characterized by lymphadenopathy from four days to 47 days pi, and sporadic fever peaks were only observed in one calf from G2. However, other clinical signs and macroscopic lesions characteristic of chronic besnoitiosis were not detected. Only nine tissue samples were B. besnoiti-DNA-positive, eight of which belonged to reproductive and respiratory tracts tissues from G1. Finally, the kinetics of the immune responses were similar in both infected groups. However, delayed and lower cellular and humoral immune responses were observed in G1 followed by G2 and were compared with intravenously inoculated calves. The differences observed among the three inoculation routes could be due to different effector mechanisms of the host early innate immune response against B. besnoiti. Accordingly, the inoculation route of B. besnoiti tachyzoites does not significantly influence the clinical outcome of the infection in calves. Thus, a further refinement of this experimental model of bovine besnoitiosis is needed to reproduce macroscopic lesions characteristic of chronic stage disease.

A Descriptive Study of Lectin Histochemistry of the Placenta in Cattle following Inoculation of Neospora caninum

The aim of this study was to describe the lectin-binding pattern in the placentas of cows infected experimentally with Neospora caninum. Four cows were inoculated intravenously with 1 × 10⁸ tachyzoites of the NC-1 strain of N. caninum at 150 ± 7 days of pregnancy. Two control cows were administered a placebo. An indirect fluorescence antibody test (IFAT) was performed on serum samples obtained before and after the inoculation. The cows were killed at 30 and 37 days post inoculation. Samples of placenta were taken for histopathology and lectin histochemistry. Fetal tissues and fluids were collected for histopathology and IFAT, respectively. All infected cows had high antibody titres. All fetuses had characteristic histopathological lesions, including non-suppurative meningoencephalitis, myocarditis, hepatitis and myositis, suggesting N. caninum infection. Only two infected fetuses developed specific antibodies. Mild non-suppurative inflammatory infiltrates were recorded in the placentae. Differences in the lectin-binding pattern were observed between infected animals and controls in the glycocalyx (CON-A and WGA) and apical cytoplasm (RCA-I and CON-A) of the trophoblastic cells; giant trophoblastic cells (CON-A and DBA); glycocalyx (PNA, WGA) and apical cytoplasm (CON-A, WGA, PNA, DBA and RCA-I) of endometrial cells; trophoblast of the interplacentomal region (WGA); endothelium (CON-A, SBA, RCA-1 and WGA); and finally, mesenchyme (CON-A, RCA-1, SBA, PNA and DBA). These findings indicate that there is a distinctive pattern of lectin binding in the placenta of cattle infected with N. caninum. The direct effect of the presence of the protozoa as well as the altered expression of cytokines could explain these changes in the maternofetal interface.

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.

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.

Experimental ovine toxoplasmosis: influence of the gestational stage on the clinical course, lesion development and parasite distribution

The relation between gestational age and foetal death risk in ovine toxoplasmosis is already known, but the mechanisms involved are not yet clear. In order to study how the stage of gestation influences these mechanisms, pregnant sheep of the same age and genetic background were orally dosed with 50 oocysts of Toxoplasma gondii (M4 isolate) at days 40 (G1), 90 (G2) and 120 (G3) of gestation. In each group, four animals were culled on the second, third and fourth week post infection (pi) in order to evaluate parasite load and distribution, and lesions in target organs. Ewes from G1 showed a longer period of hyperthermia than the other groups. Abortions occurred in all groups. While in G2 they were more frequent during the acute phase of the disease, in G3 they mainly occurred after day 20 pi. After challenge, parasite and lesions in the placentas and foetuses were detected from day 19 pi in G3 while in G2 or G1 they were only detected at day 26 pi. However, after initial detection at day 19 pi, parasite burden, measured through RT-PCR, in placenta or foetus of G3 did not increase significantly and, at in the third week pi it was lower than that measured in foetal liver or placenta from G1 to G3 respectively. These results show that the period of gestation clearly influences the parasite multiplication and development of lesions in the placenta and foetus and, as a consequence, the clinical course in ovine toxoplasmosis.

Experimental caprine neosporosis: the influence of gestational stage on the outcome of infection

Here, we assessed outcome of experimental infection by Neospora caninum in goats intravenously inoculated with 10(6) tachyzoites of the Nc-Spain7 isolate at 40 (G1), 90 (G2) and 120 (G3) days of gestation. Infected goats had fever between 5 and 9 days post inoculation (dpi); all were seropositive at the time of abortion/birth. Foetal death occurred in G1 from 10 to 21 dpi (n = 7) and in G2 from 27 to 35 dpi (n = 4). Goats in G2 also had seropositive stillbirth (n = 1) and healthy kids (n = 2). G3 goats (n = 7) had 3 seropositive and 3 seronegative weak kids, and 2 seronegative healthy kids. Parasite DNA detection in placentomes was 100% in G2, 85.7% in G3 and in G1 was detected only in placentomes from the goats with foetal losses from 17 dpi (100%). Parasites were detected in foetal/kid brain (>85.7%) and liver (≥ 50%) of G2 and G3, and in G1 after 17 dpi (100%). The highest parasite loads were detected in the placentomes of G1 from 17 dpi and G2, and in foetal tissues of G1 from 17 dpi and G3. Multifocal necrotic lesions were observed in the placentas of the three groups, but they were larger and more frequent in G1 and G2. Similar lesions were observed in foetal tissues, but they were more frequent in G3. These findings suggest that, as observed in cattle and sheep, the clinical consequences of N. caninum in pregnant goats are dependent in part on the time of gestation when animals were infected.

Systemic and local immune responses in sheep after Neospora caninum experimental infection at early, mid and late gestation

Besides its importance in cattle, Neospora caninum may also pose a high risk as abortifacient for small ruminants. We have recently demonstrated that the outcome of experimental infection of pregnant sheep with 10(6) Nc-Spain7 tachyzoites is strongly dependent on the time of gestation. In the current study, we assessed peripheral and local immune response in those animals. Serological analysis revealed earlier and higher IFN-γ and IgG responses in ewes infected at early (G1) and mid (G2) gestation, when abortion occurred. IL-4 was not detected in sera from any sheep. Inflammatory infiltrates in the placenta mainly consisted of CD8+ and, to a lesser extent, CD4+ T cells and macrophages (CD163+). The infiltrate was more intense in sheep infected at mid-gestation. In the foetal mesenchyme, mostly free tachyzoites were found in animals infected at G1, while those infected in G2 displayed predominantly particulate antigen, and parasitophorous vacuoles were detected in sheep infected at G3. A similar pattern of placental cytokine mRNA expression was found in all groups, displaying a strengthened upregulation of IFN-γ and IL-4 and milder increases of TNF-α and IL-10, reminiscent of a mixed Th1 and Th2 response. IL-12 and IL-6 were only slightly upregulated in G2, and TGF-β was downregulated in G1 and G2, suggestive of limited T regulatory (Treg) cell activity. No significant expression of TLR2 or TLR4 could be detected. In summary, this study confirms the pivotal role of systemic and local immune responses at different times of gestation during N. caninum infection in sheep.

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.

Comparison of host cell invasion and proliferation among Neospora caninum isolates obtained from oocysts and from clinical cases of naturally infected dogs

In a previous study we have shown that the in vitro invasion rate (IR) and tachyzoite yield (TY) are associated with the virulence phenotypes of Neospora caninum isolates of bovine origin. In addition, we recently observed marked differences in virulence when canine isolates were compared in a pregnant BALB/c mouse model. In this study, we investigated whether invasion and proliferation capacities could be used as virulence-related N. caninum phenotypic traits. Of the isolates compared in mice, four canine isolates obtained from oocysts (Nc-Ger2, Nc-Ger3, Nc-Ger-6, Nc-6 Arg) had shown a low-moderate virulence, and two further isolates obtained from dogs with neurological signs (Nc-Bahia, Nc-Liv) were highly virulent. The IR for each isolate was determined by a plaque assay and the counting of immunofluorescence-labeled parasitophorous vacuoles at 3 days post-inoculation (p.i.). The TY was determined by the quantification of tachyzoites at 56 h p.i. by real-time PCR. Most of the canine isolates showed similar IR values under controlled invasion conditions for 4h and 72 h p.i., indicating a limited time period for invasion similar to that observed for bovine isolates. The Nc-Ger3, Nc-Bahia, and Nc-Liv isolates showed a significantly higher IR and TY than the Nc-Ger2 and Nc-Ger6 isolates (P<0.0001). A correlation was found between the IRs and TY (ρ>0.885, P<0.033), as well as between the TY and both dam morbidity (ρ=0.8452, P<0.033) and pup mortality (ρ>0.8117, P<0.058) in mice. These results demonstrate the importance both the invasive and proliferative capacities have on the virulence of canine N. caninum isolates.