Neospora caninum in persistently infected, pregnant cows: spontaneous transplacental infection is associated with an acute increase in maternal antibody

Review: Bovine foetal mortality - risk factors, causes, immune responses and immuno-prophylaxis

This review of bovine foetal mortality (>42 d gestation) concluded that while the majority of risk factors associated with sporadic loss operate at animal-level, e.g. foetal plurality, those that operate at herd-level, e.g. some foetopathogenic infections, are more likely to result in abortion outbreaks. While the causes of foetal mortality have traditionally been classified as infectious and non-infectious, in fact, the latter category is a diagnosis of exclusion, generally without determination of the non-infectious cause. This review has also established that the traditional dichotomisation of infectious agents into primary and secondary pathogens is based on a flawed premise and these terms should be discontinued. The delicate balance of the maternal gestational immune system between not rejecting the allograft (conceptus) but rejecting (attacking) foetopathogens is stage-of-pregnancy-dependent thus the timing of infection determines the clinical outcome which may result in persistent infection or foetal mortality. Utilisation of our knowledge of the materno-foetal immune responses to foetopathogenic infection has resulted in the development of numerous mono- and polyvalent vaccines for metaphylactic or prophylactic control of bovine foetal mortality. While some of these have been shown to significantly contribute to reducing the risk of both infection and foetal mortality, others have insufficient, or conflicting evidence, on efficacy. However, recent developments in vaccinology, in particular the development of subunit vaccines and those that stimulate local genital tract immunity, show greater promise.

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.

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.

The Utility of Serological Analysis for Neospora caninum Infection in Dairy Cattle Farms Management: Serological Investigation and Evaluation of the Effects on Reproductive and Productive Performances in Two Study Herds in Northern Italy

Simple Summary

Among infectious agents triggering reproductive disorders in cattle, Neospora caninum, an obligate intracellular protozoan parasite, is a major cause of abortion in cows worldwide. A serosurvey was designed in two cattle herds, both located in northern Italy and with similar reproductive management features, recruited as a case study. The clinical outcome and the effects on herd performances were evaluated in association with the seropositivity to N. caninum. This study showed that the integration of serological analysis results for N. caninum, the reproductive and productive parameters, and the information on herd performances, could give indications for the application of control strategies.

Abstract

Neospora caninum is recognized as a major cause of abortion in cattle, determining economic losses, particularly in dairy industries. To evaluate the impact of neosporosis on herd efficiency, and to understand how the serological analysis for N. caninum is explicative of the farm picture, an epidemiological study was designed in two dairy farms recruited as a case study. Blood samples were collected from 540 animals, including cows and heifers over 12 months, and analyzed by an indirect immunofluorescent antibody test with subsequent antibody titration. Overall, 94 animals (17.4%) were identified as positive to N. caninum antibodies (15.5% and 18.5% in Farm 1 and Farm 2), with differences between the farms concerning the antibody titers (Chi-square, p-value = 0.04), particularly in cows (Chi-square, p-value = 0.018). Consequently, a different pattern of abortion episodes was depicted in the two investigated farms. Considering reproductive and productive performances, the number of inseminations necessary to make an animal pregnant was higher in seropositive cows (2.4 and 2.9 in Farm 1 and 2, respectively) than in seronegative ones (2.1 and 2.4 in Farm 1 and 2, respectively). Similarly, particularly in Farm 1, the number of days in milk of not-pregnant cows was higher in seropositive (167.7) than seronegative animals (133.4). Moreover, although the association between N. caninum infection and milk production is still unclear, both the daily milk production and the 305-mature equivalent milk yield were lower in seropositive (31.02 and 11,838.94) than seronegative cows (33.59 and 12,274.88) in Farm 1; an opposite pattern was otherwise depicted in Farm 2. The study showed that even if N. caninum circulated equally in the two herds, the dynamics of the parasite infection and its outcome may be different, also depending on the specific situation of the farm. In this way, the integration of serological analysis for N. caninum, the reproductive and productive parameters, and the information on herd performances, could give specific indications for the application of control strategies.

Neospora caninum and Toxoplasma gondii infections and their relationship with reproductive losses in farmed red deer (Cervus elaphus)

The aims of the present study were to determine the Neospora caninum and Toxoplasma gondii seropositivity rates in farmed red deer hinds from Argentina and their relationship with reproductive losses. Over a 2-year period, 449 hinds from 4 commercial farms were serologically tested at late gestation for N. caninum and T. gondii by IFAT. During the first year, a sequential serological analysis was carried out at 3 different time points to analyze antibody dynamics from mating until the end of the gestation period. Fetal and postnatal mortality rates were estimated by 3 successive ultrasound scannings (us) annually and a breeding control carried out after the calving period. Ultrasound fetal measurements were used to estimate conception date and gestational age of abortions. The seropositivity rate for N. caninum was 25.5% (37/145) for the yearlings and 34.2% (104/304) for the adults, while for T. gondii was 64.3% (93/145) and 78.3% (238/304), respectively. Abortions detected at us1 and us2 were 13/21 (61.9%) with a range of gestational age of 30-87 days, while abortions detected at us3 were 8/21 (38.1%) with a range of gestational age of 49-209 days. The fetal mortality rate was 4% and 5.8%, while the postnatal mortality rate was 18.8% and 4.1% of 101 yearlings and 294 adult pregnant hinds, respectively. Most seropositive hinds to both protozoans showed a stable antibody titer pattern from mating to the end of gestation, and a lower proportion developed an increase in titers suggesting infection recrudescence. Seroconversion during the gestational period was demonstrated in 6 and 50 hinds for N. caninum and T. gondii, respectively. Hinds with fetal mortality were more likely to be seropositive to N. caninum (OR = 3.1) or have N. caninum titers ≥400 (OR = 27.4) than hinds that weaned a fawn. No statistical associations were detected for T. gondii seropositivity and reproductive losses. The pregnancy rate was not affected by N. caninum or T. gondii infection, while the serological evidence of N. caninum causing postnatal mortality was marginal. Based on serological evidence, N. caninum would be a potential abortigenic agent in red deer hinds.

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.

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.

Isolation of Neospora caninum from a beef cattle fetus from Argentina: Immunopathological and molecular studies

Neospora caninum is an important abortifacient agent affecting mainly cattle worldwide. The aim of the present work was to describe the histopathological findings in a naturally infected beef cow and its midterm fetus caused by a genetically defined N. caninum isolate in Argentina. A N. caninum seropositive multiparous Aberdeen Angus pregnant cow and its fetus in the sixth month of gestation were submitted for histopathological, immunohistochemical, serological, and molecular studies and parasite isolation. The cow belonged to a beef herd under extensive management, with a N. caninum seroprevalence of 11%, and low level of annual abortion rate (≤ 5%). The dam had mild lymphocytic infiltrate in CNS, heart and uterus and no parasites were detected by Immunohistochemistry (IHC). No parasitic DNA was detected in the dam's brain, and gamma interferon knockout mice inoculated with brain material did not become infected. Clusters of tachyzoites and parasitic DNA were detected in the placenta by IHC and PCR, respectively. However, isolation from the placenta was unsuccessful. The fetus developed specific antibodies and an inflammatory response was detected in multiple organs. Furthermore, in vitro and in vivo isolation was achieved from gamma interferon knockout mice inoculated with CNS from the fetus. Multilocus-microsatellite typing revealed a genetically defined N. caninum isolate similar to the previously reported as MLG 72. We report the first N. caninum isolate from beef cattle in Argentina.

Age, gender and climate associations with the seroprevalence of Neospora species infection in horses in Jordan

A cross-sectional study was carried out on a sample of 379 horses to determine the seroprevalence of Neospora spp. in Jordan using the indirect fluorescent antibody test. Five variables, namely locality (n=10), climatic zone (n=4), age group (n=3), gender, and breed were tested as risk factors for Neospora-immunoglobulin (Ig)G seropositivity at four cutoff titers (1:50, 1:200, 1:400, and 1:800) using univariate and multivariate logistic regression analyses. A total of 122 (32%; 95% CI: 28, 37) sera samples had anti-Neospora-IgG at a cutoff titer of 1:50. Increased Neospora-IgG seropositivity was found in horses in three localities (Madaba, Zarka, and Petra) and was associated with the following variables: cool temperate climate; age >14 years; and female gender. Seropositivity was found among horses from Madaba at all cutoff titers, Zarka at titers >1:200, and Petra at titers <1:200. Cool temperate climate was associated with titers <1:400. Horses aged >14 years were found to be associated with seropositivity at titers ≥1:200. Female gender was associated with high seropositivity at >1:800.

Evidence of reduced vertical transmission of Neospora caninum associated with higher IgG1 than IgG2 serum levels and presence of IFN-γ in non-aborting chronically infected cattle under natural condition

Neospora caninum infection of cattle can be vertically transmitted, resulting in abortion or birth of infected calves. Vertical transmission occurs both in acutely or chronically infected cattle. There is little information on the immune response needed to prevent endogenous transplacental transmission, particularly from chronically infected cattle to their offspring in a natural environment. In this study, N. caninum seropositive pregnant cattle from three different farms with high avidity antibodies and low IgM titers were selected and their newborn colostrum-deprived calves were tested for anti-N. caninum antibodies. Based on these results, dams were grouped according to their congenital transmission status. The analysis of the immune profile of the chronically-infected pregnant cattle revealed that higher ratio between IgG1 and IgG2 anti-N. caninum serum titers and higher levels of systemic IFN-γ were associated with diminished vertical transmission rates, compared to dams with the opposite profile. Our results evidenced an association between the immune profile and vertical transmission in non-aborting chronically infected dams, and confirm that vertical transmission, even when not leading to abortion, is related to a defined immune profile. This is important information to accomplish successful vaccine development efforts.

Immunization with a cocktail of antigens fused with OprI reduces Neospora caninum vertical transmission and postnatal mortality in mice

OprI is an outer membrane lipoprotein from Pseudomonas aeruginosa, and when fused to a recombinant antigen, will exert adjuvant properties by engaging Toll-like receptor 2, leading to dendritic cell activation. Previous studies have shown that the Neospora caninum (Nc) antigens NcPDI, NcROP2 and NcROP40 are implicated in host cell interactions and are promising vaccine candidates. In two independent experiments, the efficacy of a polyvalent vaccine formulation composed of OprI-NcPDI, OprI-NcROP2 and OprI-NcROP40 (collectively named O-Ags) was assessed in non-pregnant and pregnant Balb/c mouse models challenged with tachyzoites of the high-virulence isolate Nc-Spain7. Parameters that were investigated were clinical signs, fertility, parasite burden in adult mice, humoral and cellular immune responses at different time-points prior to and after challenge infection, vertical transmission and post-natal survival of offspring mice, all to explore potential correlations with efficacy. Vaccination of mice with O-Ags induced a mixed Th1/Th2 immune response in adult mice and led to significantly increased protection against cerebral infection. Vaccination with O-Ags also resulted in reduced vertical transmission, and postnatal disease in offspring was significantly inhibited at a rate not observed in mice infected with a high-virulence isolate to date. However, O-Ags mixed with TLR ligands targeting TLR3 and TLR7, which are known to induce clear Th1-biased responses, or vaccination with OprI fused to the non-N. caninum antigen ovalbumin (OprI-OVA) did not confer protection.

Using beef-breed semen in seropositive dams for the control of bovine neosporosis

A program for controlling bovine neosporosis based only on the use of beef semen, without culling seropositive animals, was evaluated in a closed dairy cattle herd over a 5-year period (2013-2017). The program was based on individual and periodic serological screenings to identify seropositive breeders. Seropositive cows were inseminated with beef-breed semen, thus excluding their descendants from the remount in order to prevent the vertical transmission of the disease. Seronegative animals, as well as heifers at first insemination, were tested before each insemination. Sera of 1097 cattle were examined by a commercial indirect ELISA for the detection of antibodies anti-Neospora caninum. To verify the difference in seropositivity values among years of sampling, statistical analysis through generalized estimation equations (GEEs) was performed, also considering the effects of age, lineages, and occurrence of abortion. A seroprevalence of 33.8% was found in the first screening. The prevalence and incidence of the infection within the herd decreased significantly in 2017 (P = 28.9%, I = 1.4%) (p-value = 0.0001). The family line investigation detected a higher risk of being seropositive for a cow born to a seropositive dam (p-value = 0.0001) than to a seronegative dam, decreasing both the apparently vertical and horizontal transmissions. The number of spontaneous abortions decreased after the first year of the study (23 in 2013 to 6 in 2017). Seropositive animals were associated with abortion events (p-value = 0.0001). Although an eradication of N. caninum was not achieved at the end of the study period, a significant reduction in prevalence and incidence of neosporosis in the herd and a reduction of the abortion rate was achieved with the application of this control plan in five years, without culling a high number of seropositive potential milk-producing animals.

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.

Immune response in bovine neosporosis: Protection or contribution to the pathogenesis of abortion

Neospora caninum is a protozoan parasite with a preference for cattle and dogs as hosts. When N. caninum infection occurs in cattle it induces abortion, bovine neosporosis being a main cause of abortion worldwide. In dairy cattle, the economic burden of neosporosis-associated abortion is so great that it might results in closure of a farm. However, not all infected cows abort and it is not yet understood why this occurs. At present there is no effective treatment or vaccine. This review provides insights on how immune response against the parasite determines protection or contribution to abortion. Aspects on markers of risk of abortion are also discussed. Humoral immune responses are not protective against N. caninum but seropositivity and antibody level can be good markers for a diagnosis of bovine neosporosis and its associated abortion risk. In addition, humoral mechanisms against N. caninum infection and abortion differ in pure-breed and cross-breed pregnant dairy and beef cattle. Concentrations of Pregnancy Associated glycoprotein -2 (PAG-2) can also be used to predict abortion. A partially protective immune response encompasses increased IFN-γ expression, which has to be counterbalanced by other cytokines such as IL-12 and IL-10, especially towards the end of pregnancy. Although IFN-γ is required to limit parasite proliferation a critical threshold of the IFN-γ response is also required to limit adverse effects on pregnancy. In clinical terms, it may be stated that IFN-γ production and cross-breed pregnancy can protect Neospora-infected dairy cows against abortion.

Serology-Based Diagnostics for the Control of Bovine Neosporosis

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

DINÂMICA SOROLÓGICA DE ANTICORPOS CONTRA Neospora caninum DURANTE A GESTAÇÃO DE VACAS NATURALMENTE INFECTADAS

Resumo Neosporose é uma das maiores causas de perdas reprodutivas em rebanhos bovinos. O estágio da gestação em que ocorre a infecção ou o recrudescimento das formas bradizoítas, que se reflete no nível de anticorpos, é um dos fatores que define o futuro da gestação. Portanto, este trabalho visa a traçar um esboço do perfil sorológico de fêmeas naturalmente infectadas durante a gestação. Para isso, amostras séricas de 25 vacas da raça holandesa foram coletadas desde o dia da inseminação artificial até a véspera do parto, em intervalos mensais. Essas amostras foram testadas por imunofluorescência indireta em busca de IgG. Dos 25 animais, somente 13 foram utilizados na análise, por serem soropositivos desde o início ou por se soroconverteram durante a gestação. Observou-se um aumento gradual dos níveis de anticorpos ao longo da gestação, mais evidente na metade final do período. Observou-se também diferença significativa nos títulos de anticorpos entre os períodos iniciais e finais da gestação, sugerindo a reativação de formas bradizoítas. Tais resultados reforçam a ideia da flutuação nos níveis de anticorpos ao longo da gestação, influenciado pela reativação de N. caninum. O conhecimento dessa dinâmica é importante para a patogenia e epidemiologia da infecção bem como para o diagnóstico.

Investigation of Neospora caninum seroprevalence and potential impact on reproductive success in semi-free-ranging Père David's deer (Elaphurus davidianus)

This study aimed to determine the prevalence and reproductive impact of Neospora caninum in a herd of semi-free-ranging Père David's deer (Elaphurus davidianus) at a conservation facility, following a suspected abortion storm in 2008. Serum samples (n=103) collected from 60 individuals between 2002 and 2011 were evaluated using competitive ELISA for the detection of N. caninum-specific antibodies. Of the 103 samples, 73 (70.9 per cent) were positive for N. caninum antibodies, with a mean±sd competitive inhibition (CI) of 77.6±19.8 per cent. Thirty (29.1 per cent) samples were seronegative, with mean CI of 15.2±9.70 per cent. A significant negative linear relationship was noted between the proportion of seropositive animals and age (R(2)=0.228, P<0.001). Calving rates of adult females from 2005 to 2011 ranged from 15.4 per cent to 52 per cent (mean 35.5±11.3 per cent), and did not correlate with mean CI values (Spearman's rank correlation coefficient=0.072, P=0.878). While both horizontal and transplacental transmission are likely contributing to persistent herd seropositivity, the role of N. caninum in reproductive success in this and other populations of endangered ungulates remains to be explored.

Prevalence and dynamics of antibodies against Toxoplasma gondii in kids born from naturally infected goats

We investigated the presence of antibodies against Toxoplasma gondii in domesticated goats intended for human consumption in a rural suburb of Rajshahi, Bangladesh. Antibodies to T. gondii were found in 55.1% (80/145) of the goats tested in our sample. The seroprevalence among goats aged <1 year, 1-2 years, 2-3 years and ≥3 years were 36.7%, 66.0%, 59.1% and 100%, respectively. Our results demonstrated that seroprevalence increased with age. Among the seropositive goats, a subsample of eight free-ranging female goats with access to male goats was placed under continuous observation. During the observation period, these seropositive female goats delivered 11 kids, all of which were found to be seronegative before suckling colostrum. This finding strongly suggested that trans-placental infection rarely occurs in female goats that have acquired an infection before pregnancy. Our results indicate that infection via ingestion of oocysts plays a more important role than endogenous trans-placental infection in maintaining the endemicity of T. gondii among goats in Bangladesh.

Markers related to the diagnosis and to the risk of abortion in bovine neosporosis

Bovine neosporosis has emerged as a main cause of abortion in cattle worldwide. An important question to understand the disease is why not all infected cows abort. In the present review we summarize the knowledge on markers related to the diagnosis and more importantly to the risk of abortion in the infected cow. Markers considered herein include those based on specific antibodies, antibody titers and antibody subtypes, cellular immunological markers, hormones and other proteins related to gestation. The identification of parasite molecules that are specifically identified in the aborting cows might help to understand the mechanism of parasite-associated abortion and control the disease.

Neosporosis in naturally infected pregnant dairy cattle

Neosporosis caused by caused by the apicomplexan parasite Neospora caninum is one of the major causes of infectious abortion in bovines worldwide. A long-term prospective study was performed in a dairy herd endemic for N. caninum in order to analyze the impact of neosporosis on the proportion of aborting cows. A total of 1078 pregnant cows were tested for presence of antibodies and the proportion of abortions was calculated. The overall seroprevalence of N. caninum found in the herd was 35.5%. The percentage of abortions in seropositive cows was 3 times higher than in their seronegative counterparts (21.6 and 7.3%, respectively). No statistically significant association was found between the antibody level of positive during pregnancy and the proportion of aborting cows. However, 41.2% of the dams with antibody titers of 1:12,800 aborted. The risk of abortion for such dams was 2.7 times higher than for other seropositive cows which had lower titers of antibodies (p=0.0072). In the follow-up examinations of the seropositive cows during several pregnancies, the overall percent of abortions observed was significantly higher than in seronegative individuals (49.3 and 16.9%, respectively; p<0.0001). Moreover, the proportion of repetitive abortion observed was 5 to 1 (17.4 and 3.5%) in seropositive and seronegative dams, respectively (p<0.001). The rate of vertical transmission in positive dams was 61.0% and it appeared to be directly associated with antibody levels: the higher the titer in the dams during pregnancy, the higher the percentage of sero-positivity in their calves. Increased proportion of abortions was observed in seropositive cows both in summer and winter in comparison with spring and autumn. It was found that in seropositive cows, an increased number of pregnancies, which was directly related to the age of the dam, has been associated with an increased number of abortions.

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

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

Transmission paths of Neospora caninum in a dairy herd of crossbred cattle in the northeast of Brazil

The aim of this study was to determine the transmission paths of Neospora caninum in a dairy herd of crossbred cattle. Two hundred and ninety animals were grouped according to the year of their birth to verify the distribution of infection according to age. The blood of 196 cattle was collected thrice, with an average interval of 210 days, to evaluate the existence of horizontal transmission in the herd. To evaluate vertical transmission, the blood of 64 calves was collected prior to ingestion of colostrum and from their mothers at parturition. Moreover, 63 family trees were built. The presence of anti-N. caninum antibodies was detected using an indirect fluorescent antibody test. The chi-square test (χ(2)) with Yates' correction or Fisher's exact test was used to evaluate the relation between the serology and age groups and between the serostatus of cows and their progeny in different calvings. A higher seropositivity (p=0.035) was found in animals born in 2008 compared to those born in 1997-2007. The serological status of only 13 animals presented changes, of which six (3.1%) became seropositive, indicating a low proportion of horizontal transmission. All seropositive cows gave birth to seropositive calves, resulting in 100% vertical transmission. Sixty-three family trees were constructed. In 29 (46%) of these families, there were animals seropositive for N. caninum. Congenital infection in relation to the number of births was estimated from the relation of Mother+ and Daughter+, without significant differences (p=0.84) between the number of births and the transmission of the parasite from infected cows to their progeny. The low proportion of horizontal transmission combined with the high proportion of vertical transmission allowed us to conclude that transplacental transmission is the principal route of N. caninum infection in the herd.

Gamma interferon production and plasma concentrations of pregnancy-associated glycoproteins 1 and 2 in gestating dairy cows naturally infected with Neospora caninum

Gamma interferon (IFN-γ) production and cross-breed pregnancy have been attributed a role in protecting dairy cows infected with Neospora caninum against abortion. Plasma levels of pregnancy-associated glycoproteins-1 (PAG-1) are a marker of placental/foetal well-being and of PAG-2 is an abortion risk indicator in chronically N. caninum-infected animals. The present study examines, in cross-breed pregnancies, interactions between IFN-γ production and levels of PAG-1 and PAG-2 in non-aborting naturally Neospora-infected dairy cows. Data were obtained from 60 pregnant Holstein-Friesian cows: 44 Neospora-seropositive and 16 Neospora-seronegative; 12 became pregnant using Holstein-Friesian semen and 48 using Limousin semen. Blood samples were collected on Days 40, 90, 120, 150, 180 and 210 of gestation. Gamma interferon was only detected in the plasma of nine of the 44 Neospora-seropositive cows, all of them became pregnant using Limousin semen. Through GLM procedures, in cows inseminated with Limousin semen and Neospora-seropositive cows showing no IFN-γ production, PAG-1 concentrations were high and increased throughout gestation compared to the levels detected in cows inseminated with Holstein-Friesian semen and Neospora-seropositive cows producing IFN-γ, respectively. In Neospora-seronegative cows and in Neospora-seropositive cows showing no IFN-γ production, significantly increased PAG-2 concentrations were observed on gestation Day 120. Our findings indicate that IFN-γ production correlates negatively and the production of antibodies against N. caninum is uncorrelated with plasma PAG concentrations during gestation in Neospora-infected dairy cows. Accordingly, IFN-γ production could be linked to the transplacental migration of tachyzoites, which may cause a reduction in PAG levels.

Adaptation of a commercial ELISA to determine the IgG avidity in sheep experimentally and naturally infected with Neospora caninum

Recent reports indicate Neospora caninum has a possible role in causing abortions in sheep in New Zealand. Knowledge about the epidemiology of neosporosis in sheep is limited. This study aimed to adapt and validate a commercially available ELISA assay as an IgG avidity assay to discriminate between acute (primary and re-inoculated) and chronic N. caninum infections in sheep. In addition, it was used to compare the antibody avidity values between lambs from ewes inoculated with N. caninum either during the pregnancy or in the previous year. The avidity assay was undertaken by using 6M urea for the first wash after incubation with the primary antibody in the commercial ELISA (Chekit* Neospora antibody test kit, IDEXX Laboratories, Australia). Sequential serum samples were obtained from naïve ewes (n=16) experimentally inoculated with live N. caninum tachyzoites. All ewes were seropositive by two weeks post-inoculation and remained seropositive for 20 weeks post-inoculation. There was a linear relationship between time after inoculation and avidity values (p<0.05) over the first 24 weeks. In Week 4, all animals had avidity values <35% and by Week 8, 8/16 animals had avidity values of >35%. These results suggest that an avidity value of <35% indicates a recent primary infection while a value of >35% is indicative of a chronic infection. The assay was then validated using samples from other groups of experimentally inoculated sheep as well as samples from naturally infected ewes. When comparing sample to positive ratio (S/P) and avidity values from lambs born from recently inoculated ewes with those from ewes inoculated the previous year and re-inoculated in the current year, it was possible to differentiate the lambs at 2 weeks of age. Lambs from recently inoculated ewes had low S/P and avidity values at 2 weeks of age which increased by 12 weeks of age. In comparison, lambs from re-inoculated ewes had high S/P and avidity values at 2 weeks of age, due to maternal antibody influence but values were similar to those from lambs that were born from recently inoculated ewes at 12 weeks of age. Avidity values for four naturally infected ewes were all >60% indicating chronic infection. These results suggest that the assay is able to discriminate between recent and chronic infection in sheep as well as able to differentiate lambs with maternal immunity compared to their own de novo immunity. As such it can be utilized to understand the kinetics of N. caninum infection in sheep.

Kinetics of anti-Neospora antibodies during the period of two consecutive pregnancies in chronically infected dairy cows

The course of anti-Neospora antibody kinetics during two consecutive pregnancies has been evaluated in five chronically infected dairy cows. The blood samples of cows were collected monthly. Anti-Neospora antibodies in blood sera were detected by indirect ELISA (ID-VET, France). During whole period of the study cows remained seropositive; with S/P% values (iELISA) ranging from 94 to 214%. The antibody kinetics determined by iELISA showed a significant increase (P<0.0059) of specific IgG antibodies in the third trimester of both pregnancies. The monitored cows gave birth to 10 healthy calves (4 steers and 6 heifers). To confirm the occurrence of vertical transmission of Neospora from mothers to offspring in the herd, dam-daughter serology was performed. Anti-Neospora antibodies was found in 4 from 6 heifers (>6 months old). Study presents original data reporting on the very similar persistent pattern of anti-Neospora antibody levels during the third trimester of pregnancies in all five dairies. Based on the high seropositivity of female offspring, the reactivation of a latent infection of cows rather than a re-infection can be supposed.

Phenotypic characterisation of the cellular immune infiltrate in placentas of cattle following experimental inoculation with Neospora caninum in late gestation

Despite Neospora caninum being a major cause of bovine abortion worldwide, its pathogenesis is not completely understood. Neospora infection stimulates host cell-mediated immune responses, which may be responsible for the placental damage leading to abortion. The aim of the current study was to characterize the placental immune response following an experimental inoculation of pregnant cattle with N. caninum tachyzoites at day 210 of gestation. Cows were culled at 14, 28, 42 and 56 days post inoculation (dpi). Placentomes were examined by immunohistochemistry using antibodies against macrophages, T-cell subsets (CD4, CD8 and γδ), NK cells and B cells. Macrophages were detected mainly at 14 days post inoculation. Inflammation was generally mild and mainly characterized by CD3⁺, CD4⁺ and γδ T-cells; whereas CD8⁺ and NK cells were less numerous. The immune cell repertoire observed in this study was similar to those seen in pregnant cattle challenged with N. caninum at early gestation. However, cellular infiltrates were less severe than those seen during first trimester Neospora infections. This may explain the milder clinical outcome observed when animals are infected late in gestation.

Performance of a commercial serum ELISA for the detection of antibodies to Neospora caninum in whole and skim milk samples

Control of Neospora caninum infection in cattle depends on specific, ante-mortem detection of infected animals and limiting their use as breeding stock or by culling. The objective of the present study was to determine appropriate cut-off values and diagnostic performance of a milk ELISA test using whole and skim milk in a commercial serum ELISA test (IDEXX Neospora Ab). Serum and milk samples were obtained from a total of 475 lactating cows from two herds with and two herds without a previous history of N. caninum-associated abortion. Overall seroprevalence determined by the ELISA was 18.3%. Compared to serum ELISA values, correlation and overall performance assessed by receiver operating characteristic analysis was higher when either whole or skim milk samples were diluted 1:2 compared to undiluted or 1:5 diluted samples. Diagnostic performance for analysis of whole and skim milk was compared at cut-off values that achieved a desired operating characteristic of at least 95% specificity. For whole milk diluted 1:2 and a cut-off of 0.14 (S/P ratio), sensitivity and kappa values were 74.7% (95% CI 64.3-83.4) and 0.70 (95% CI 0.61-0.78), respectively. For skim milk diluted 1:2 and a cut-off of 0.30, sensitivity and kappa values were 77.0% (95% CI 66.8-85.4) and 0.72 (95% CI 0.64-0.80), respectively. Using the selected cut-offs, the IDEXX Neospora Ab Test is equally suited for the analysis of whole and skim milk as a screening tool in neosporosis control programs.

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

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

Up regulation of the maternal immune response in the placenta of cattle naturally infected with Neospora caninum

Neospora caninum is an intracellular protozoan parasite which is a major cause of abortion in cattle worldwide. It forms persistent infections which recrudesce during pregnancy leading to foetal infection and in a proportion of cases, abortion. The mechanisms underlying abortion are not understood. In this study, recrudescence of a persistent infection in eight naturally infected cows occurred between 20 and 33 weeks of gestation. Animals were killed at the time of recrudescence and parasites were detected in the placentae and foetuses. An active maternal immune response consisting of an infiltration of CD4+ and CD8+ T cells and a 46–49 fold increase in interferon-γ and interleukin-4 mRNA was detected. Other cytokines, notably interleukin-12 p40, interleukin-10 and tumour necrosis factor-α were also significantly increased and Major Histocompatibility Class II antigen was expressed on maternal and foetal epithelial and stromal fibroblastoid cells. Significantly, despite the presence of an active maternal immune response in the placenta, all the foetuses were alive at the time of maternal euthanasia. There was evidence of parasites within foetal tissues; their distribution was restricted to the central nervous system and skeletal muscle and their presence was associated with tissue necrosis and a non-suppurative inflammatory response involving lymphocytes and macrophages, irrespective of the gestational age of the foetus. Whilst an active maternal immune response to a pathogen in the placenta is generally considered to be damaging to the foetal trophoblast, our findings suggest that the presence of a parasite-induced maternal immune response in the placenta is not detrimental to foetal survival but may contribute to the control of placental parasitosis.

Fetal death in cows experimentally infected with Neospora caninum at 110 days of gestation

Neospora caninum is a major cause of abortion in cattle, but the reasons why some animals abort and not others remain unclear. Most of the N. caninum experimental primary infections in cattle late in gestation, after 120 days of pregnancy, result in birth of full-term congenitally infected fetuses. In the present study, the distribution of parasites and pathogenesis of infection in both dams and fetuses after inoculation with 10(7) culture derived tachyzoites of N. caninum NC-Illinois cattle strain at 110 days of gestation were analyzed at 3 weeks, 6 weeks and 9 weeks after infection (WAI) in eight Angus heifers. One dam from the group euthanized at 6 WAI had a dead fetus at necropsy. Extensive lesions were observed in the placenta and tachyzoites were detected in both the placenta and the fetus. The fetus was seropositive and had high IFN-gamma g production in fetal fluids. Another fetus, still alive when euthanized at 3 WAI, had severe lesions and high IFN-gamma production and a similar fate could have been expected if the experimental period would have been longer. Lesions in the placenta of the remaining six dams that had live fetuses at necropsy were mild. In those dams, the fetal and maternal placentas had not separated and contained focal areas of placentitis at the materno-fetal junction. Transplacental infection took place on all fetuses based on detection of parasitic DNA in fetal tissues. The present study shows that experimental N. caninum infection of naïve dams after 110 days of pregnancy can lead to fetal death. The results suggest that the severity of placental lesions and the strong IFN-gamma response in some fetuses, possibly as part of the immune response trying to control the high parasitemia, might, in fact, be the cause of their death.

Ultrastructural and molecular confirmation of the development of Sarcocystis neurona tissue cysts in the central nervous system of southern sea otters (Enhydra lutris nereis)

In 2004, three wild sea otters were diagnosed with putative Sarcocystis neurona-associated meningoencephalitis by histopathology and immunohistochemistry. Schizonts, free merozoites and tissue cysts were observed in the brains of all three infected animals. Tissue cysts walls from sea otter 1 (SO1) stained positively using anti-S. neurona polyclonal antiserum. However, positive staining does not preclude infection by closely related or cross-reactive tissue cyst-forming coccidian parasites. Two immature tissue cysts in the brain of SO1 were examined using transmission electron microscopy. Ultrastructural features included cyst walls with thin villous projections up to 1 microm long with tapered ends and a distinctive, electron-dense outer lining layer composed of linearly-arranged, semi-circular structures with a "hobnailed" surface contour. Small numbers of microtubules extended down through the villi into the underlying granular layer. Metrocytes were short and plump with an anterior apical complex, 22 sub-pellicular microtubules, numerous free ribosomes and no rhoptries. Some metrocytes appeared to be dividing, with two adjacent nuclear profiles. Collectively these ultrastructural features were compatible with developing protozoal cysts and were similar to prior descriptions of S. neurona tissue cysts. Panspecific 18S rDNA primers were utilized to identify protozoa infecting the brains of these otters and DNA amplification and additional sequencing at the ITS1 locus confirmed that all three otters were infected with S. neurona. No other Sarcocystis spp. were detected in the brains or skeletal muscles of these animals by immunohistochemistry or PCR. We believe this is the first ultrastructural and molecular confirmation of the development of S. neurona tissue cysts in the CNS of any animal.

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

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

Specific anti-Neospora caninum IgG1 and IgG2 antibody responses during gestation in naturally infected cattle and their relationship with gamma interferon production

Gamma interferon (IFN-gamma) production has been attributed a protective role against abortion in Neospora-infected dairy cows. This study investigate possible relationships between plasma levels of the N. caninum-specific immunoglobulin (Ig) isotypes IgG1 and IgG2 and IFN-gamma production throughout gestation in dairy cows naturally infected with the parasite. Data were obtained from 31 pregnant Neospora-seropositive animals. Blood samples were collected on gestation days 40, 90, 120, 150, 180 and 210 or until abortion. Ten pregnancies ended in abortion. One of the 11 cows producing IFN-gamma suffered abortion (9.1% of the cows producing IFN-gamma). Non-aborting cows producing IFN-gamma (n=10) showed a significantly higher IgG2/IgG1 antibody ratio throughout the gestation period than cows not producing IFN-gamma (n=11). A significant negative effect of IFN-gamma production on IgG1 antibodies was also observed, while IFN-gamma production did not affect IgG2 antibody levels. In contrast, higher levels of IgG2 antibodies compared to IgG1 antibodies were observed over the whole of gestation in aborting animals, both in those not producing IFN-gamma and in the single aborting cow that produced the cytokine. Our findings indicate that a Th1 immune response, in which IgG2 antibodies prevail, could be protective against N. caninum abortion, but only in the presence of IFN-gamma production. On their own, elevated IgG2 antibody titres appear to be insufficient to protect dams chronically infected with N. caninum against abortion.

The host-parasite relationship in pregnant cattle infected with Neospora caninum

The protozoan parasite Neospora caninum is an important cause of reproductive disease in cattle worldwide. The dog is a definitive host for the parasite and the oocyst stage, shed in the faeces, is a source of infection for cattle through consumption of contaminated feed or water. In addition, transplacental transmission of N. caninum is a very efficient means of the parasite infecting a new host and this can occur in successive pregnancies and over several generations. Neospora parasites may cause disease during pregnancy resulting in death of the foetus or birth of live congenitally infected calves that may show some neurological clinical signs at birth. The stage of pregnancy at which infection/parasitaemia occurs is an important factor in determining disease severity. Neospora infection in the first trimester of pregnancy may have more severe consequences for the foetus compared with infection occurring in the final trimester. The host-parasite relationship during pregnancy is a fascinating interaction and research in this area will improve understanding of disease pathogenesis and the various consequences of the host immune response, being host-protective, parasite protective and contributing to disease pathology. Pregnancy poses an interesting problem for the immune system of the dam as she is essentially carrying a semi-allogeneic tissue graft (the foetus) without immunological rejection taking place. To facilitate the pregnancy the cytokine environment in the placenta favours the regulatory Th-2-type cytokines, whose role is to counteract the pro-inflammatory Th1-type immune responses. Protective immunity to N. caninum, similar to many other intracellular parasites, involves Th1-type immune responses, which may pose problems for the dam trying to control a Neospora infection during pregnancy. This paper will discuss the host-parasite relationship at different stages of gestation in pregnant cattle and review the implications of this research for our understanding of disease pathogenesis, parasite transmission and host protection.

Dense-granule protein NcGRA7, a new marker for the serodiagnosis of Neospora caninum infection in aborting cows

To investigate whether the production of an antigen-specific antibody is associated with Neospora caninum-induced bovine abortion, 62 serum samples were tested with an enzyme-linked immunosorbent assay using the recombinant antigens NcSAG1, NcSRS2, and NcGRA7. Our study suggested that NcGRA7 would be a new marker for the serodiagnosis of N. caninum infection resulting in abortion.

The extent of parasite-associated necrosis in the placenta and foetal tissues of cattle following Neospora caninum infection in early and late gestation correlates with foetal death

The protozoan parasite Neospora caninum is the most frequently diagnosed abortifacient in the UK and a leading cause of abortion worldwide but the mechanisms leading to abortion are not fully understood. The distribution of parasites and the histopathological changes in the placenta and foetus were compared in 12 cows following experimental infection of cattle with N. caninum in early (n=6) and late (n=6) gestation, by PCR, immunohistology, light microscopy and transmission electron microscopy. Twelve uninfected pregnant cattle were used as controls. Infection in early gestation led to foetal death. In the placentae of cattle immediately following foetal death, N. caninum DNA was detected and there was evidence of widespread parasite dissemination. This was associated with extensive focal epithelial necrosis, serum leakage and moderate maternal interstitial mononuclear cell infiltration. In the foetuses, parasites were evident in all tissues examined and were associated with necrosis. In the placenta of cattle infected in late gestation, N. caninum DNA was detected sporadically but parasites were not evident immunohistologically. Small foci of necrosis were seen associated with mild interstitial mononuclear cell infiltration. Detection of N. caninum DNA in the foetuses was sporadic and parasites were demonstrated immunohistologically in brain and spinal cord only, with an associated mononuclear cell infiltration. This data is consistent with uncontrolled parasite spread in an immunologically immature foetus and could, via multiparenchymal necrosis of foetal tissues or the widespread necrosis and inflammation observed in the placenta, be the cause of Neospora-associated abortions.