Protection against abortion linked to gamma interferon production in pregnant dairy cows naturally infected with Neospora caninum

Many immunological aspects of pregnancy, such as the role played by gamma interferon (IFN-gamma) in abortion, are not well understood. Neospora caninum is an intracellular protozoan considered to be among the main causes of abortion in cattle worldwide. The present study analyzes the interaction between IFN-gamma production and N. caninum infection in naturally infected pregnant cows. Data were obtained from 126 pregnant cows: 86 seropositive and 40 seronegative for the parasite. Pregnancy diagnosis and blood sample collection were performed on days 40, 90, 120, 150, 180 and 210 post-insemination or until the time of abortion detection. Plasma was tested for antibodies against N. caninum and IFN-gamma. Interferon-gamma was detected at some point along the pregnancy in 16 (19%) of the 86 Neospora-seropositive cows yet was undetectable in the 40 seronegative animals. Of the 126 pregnancies examined, 22 (17.5%) ended in abortion. Abortion occurred in 24.4% of seropositive cows (21/86) and in 2.5% of seronegative animals (1/40). Significant (P<0.0001) interaction was observed between Neospora-seropositivity and IFN-gamma production. Based on the odds ratio, the risk of abortion was 15.6 times higher in seropositive cows not producing IFN-gamma than in seronegative animals, whereas neosporosis had no effect in seropositive cows with IFN-gamma production. A significant (P=0.001) negative effect of IFN-gamma production on the Neospora titer was furthermore observed in the 65 non-aborting seropositive animals. These results indicate that IFN-gamma production affords protection against abortion in Neospora-infected cows and also point to a reduced humoral immune response to N. caninum during gestation in cows producing IFN-gamma.     

Evidence of post-natal transmission of Neospora caninum in Dutch dairy herds

Eighteen dairy herds with neosporosis-associated abortions were analysed for antibodies against Neospora caninum. Blood samples of all cows, heifers and calves were collected on the same day for each farm. A total of 2430 heads of cattle were examined. For each herd, the seropositive and seronegative animals were plotted against month of birth. Analysis of seroprevalence in relation to age showed an equal distribution of seropositives in all age-groups in 10 herds. In contrast, in eight herds an age-group could be identified which had a significantly higher seroprevalence than the other animals in the herd. Most seropositive animals in the high seroprevalence age-groups had either seronegative dams or seronegative offspring, whereas there was a strong relationship between the serostatus of dams and offspring in the other animals in the herd. Aborting animals were mainly part of the high seroprevalence age-group. These findings strongly indicate a post-natal infection of the animals in the high seroprevalence age-groups, probably due to a point source exposure to N. caninum.     

Plasma pregnancy-associated glycoprotein-1 (PAG-1) concentrations during gestation in Neospora-infected dairy cows

The aim of this study was to determine whether plasma pregnancy-associated glycoprotein-1 (PAG-1) concentrations in pregnancy are affected by persistent Neospora caninum infection in dairy cows. The data analyzed were derived from 22 multiparous cows: 16 N. caninum-seropositive and 6 N. caninum-seronegative animals (used as controls). Three of the 16 seropositive cows aborted during the study period and the corresponding data were analyzed separately. Pregnancy diagnoses were performed on day 40 post-insemination by transrectal ultrasound, and by palpation per rectum on days 90, 120, 150, 180 and 210. Blood samples were collected from each animal immediately before each pregnancy diagnosis, and then at parturition or at the time of abortion detection. Plasma was tested for antibodies against N. caninum and PAG-1 concentrations were determined by radioimmunoassay. In non-aborting animals, the effects of neosporosis (seropositive versus seronegative), N. caninum antibody levels, semen providing bull, sex of the newborn, and day of gestation on PAG-1 concentrations were evaluated by GLM repeated measures analysis of variance. The effect of the gestation period (first half versus second half) on the N. caninum antibody titer was established by the Student's t-test in seropositive cows. A significant positive effect of gestation day on PAG-1 concentrations was observed (d.f.=6; F=12.6; P<0.0001). For all cows, PAG-1 concentrations increased steadily during the course of gestation, with peak concentrations recorded at parturition. Neosporosis (P=0.493), N. caninum antibody levels (P=0.921), sex of the newborn (P=0.856) and semen providing bull (P=0.087) had no effect on plasma PAG-1 concentration. There was a significant 52% increase (P<0.0001) in N. caninum antibody titers during the second half of gestation compared to the first half. The fates of the three aborting cows were abortion on gestation day 215 in one, and fetus mummification diagnosed on gestation days 180 and 210, respectively, in the remaining two cows. A luteolytic dose of prostaglandin was applied 30 days after mummification diagnosis in these last two cows, and fetus expulsion was detected on days 215 and 250, respectively. Two of the aborted fetuses were submitted to laboratory analysis and the presence of N. caninum was confirmed by specific PCR. In the cows with a mummified fetus, PAG-1 concentrations were low or undetectable when the diagnosis was made. These findings suggest that N. caninum infection has no effect on placental function in chronically infected, cows not suffering abortion, while PAG-1 measurements in aborting animals provide a useful indication of feto-placental status.     

Review of Neospora caninum and neosporosis in animals

Neospora caninum is a coccidian parasite of animals. It is a major pathogen for cattle and dogs and it occasionally causes clinical infections in horses, goats, sheep, and deer. Domestic dogs are the only known definitive hosts for N. caninum. It is one of the most efficiently transmitted parasite of cattle and up to 90% of cattle in some herds are infected. Transplacental transmission is considered the major route of transmission of N. caninum in cattle. Neospora caninum is a major cause of abortion in cattle in many countries. To elicit protective immunity against abortion in cows that already harbor a latent infection is a major problem. This paper reviews information on biology, diagnosis, epidemiology and control of neosporosis in animals.     

Increase in the occurrence of abortions associated with exposure to the Bluetongue virus serotype 8 in naïve dairy herds

The transplacental transmission capacity demonstrated for Bluetongue virus serotype 8 (BTV-8) in cattle probably is associated with an increased occurrence of abortions. The objectives of this study were to quantify the effect of BTV-8 exposure on the occurrence of abortions in previously naive dairy cow herds under natural infection conditions, and to determine a possible risk period during pregnancy associated with this increase. Two criteria were considered in order to estimate the occurrence of abortion: late return-to-service after a first artificial insemination (AI), and short gestations. A late return-to-service was defined as a return taking place 90 to 200 days after a first AI. These criteria were compared between cows in herds exposed during the 2007 epizootic in France and cows in herds that were not exposed. To determine the risk period during a pregnancy, variations in the occurrence of abortions were quantified according to the stage of the pregnancy during which the exposure took place. Survival analyses were used to estimate the risk of increased occurrence of abortion associated with BTV-8 exposure, adjusted by the principal factors known to influence the risk of abortion. Exposure to the BTV-8 virus under natural conditions in previously naive dairy herds notified after clinical suspicion during the 2007 epizootic was associated with an increase in the occurrence of abortions, regardless of the stage of pregnancy. The at-risk gestation period depended on the criteria used to detect abortions. The mean effect of BTV-8 exposure in the ensemble of detected outbreaks corresponded to an increase of 6.7% in late return-to-service. BTV-8 exposure during the first 3 mo of gestation was associated with a 15% increase in late return-to-service for cows with no return-to-service at 90 days, while this increase was 6% for exposure starting from the third month of gestation (in outbreaks detected in September). BTV-8 exposure from the third month of gestation was associated with a 1.9% increase of short gestations. The effect of exposure was more pronounced for outbreaks detected early in the epizootic compared with those detected later.     

Use of purified tachyzoite surface antigen p38 in an ELISA to diagnose bovine neosporosis

Affinity-purified 38 kDa surface antigen of Neospora caninum tachyzoites was used to develop an enzyme-linked immunosorbent assay (ELISA) to diagnose N. caninum-associated abortion in cattle. The specificity of this antigen was demonstrated by using sera from cattle experimentally infected with other apicomplexan parasites. In a panel of field sera, serological differences could be demonstrated between herds with epidemic and endemic abortions. Optimal ELISA cut-offs were determined for the detection of association between seropositivity and abortion in herds with N. caninum-associated abortions. These optimal cut-offs differed markedly when only sera from either endemic or epidemic cases were used for cut-off determination. It may thus be appropriate to apply different cut-offs in serological tests depending on the abortion pattern to be analysed.     

Serological differences in Neospora caninum-associated epidemic and endemic abortions.

A sandwich enzyme-linked immunosorbent assay (ELISA) for the sensitive and specific detection of bovine antibodies to Neospora caninum was developed and evaluated using sera from cattle experimentally infected with N. caninum, Toxoplasma gondii, Sarcocystis cruzi, Sarcocystis hominis, Sarcocystis hirsuta, Eimeria bovis, Cryptosporidium parvum, Babesia divergens, and field sera from naturally exposed animals. Field sera were classified using a gold standard that included the results from an indirect fluorescent antibody test (IFAT) and an immunoblot (IB). Based on these gold standard results, i.e., IFAT-IB results, an equal relative sensitivity and specificity of 94.2%(theta0) was reached when a cutoff of 0.034 (d0) was employed. The analysis of IFAT-IB-positive field sera showed that within groups of aborting and nonaborting dams, the animals from herds with endemic N. caninum-associated abortions had significantly higher ELISA indices than animals from herds with N. caninum-associated epidemic abortions. By contrast, IFAT-IB-positive aborting dams from herds with endemic N. caninum-associated abortions had significantly lower IFAT titers than IFAT-IB-positive aborting dams from herds with epidemic N. caninum-associated abortions. This is the first time that statistically significant serological differences between herds exhibiting epidemic and endemic N. caninum-associated abortions are described.     

Characteristics of Neospora caninum-associated abortion storms in diary herds in The Netherlands (1995 to 1997)

Abortion storms in 50 dairy herds in The Netherlands were reported in which there was a strong association with Neospora caninum-infection. The duration of the abortion storms ranged from 6 to 65 d (mean 41.5 d). The cumulative proportion of aborting cows ranged from 0.11 to 0.57 (mean 0.26) of the animals at risk. An apparent seasonal influence was noted as most abortion storms occurred during the summer and early autumn. The prevalence of antibodies to N. caninum in 50 herds which had had an abortion storm was compared with that of 100 control herds which had no history of an abortion storm. Seroprevalence was estimated by testing a 20% cross sectional herd sample using a tachyzoite lysate-based ELISA method. Seroprevalence in case herds (range 17 to 87%, mean 51.5%) was significantly higher than that in control herds (range 0 to 53%, mean 13.9%). For most herds the seroprevalence levels were equal across all age groups, which suggests that the infection had been perpetuated by vertical transmission. In these herds, the abortion storms appeared to be induced by factors causing recrudescence of a N. caninum-infection in chronically infected animals rather than being the result of a recent introduction. In 6 case herds the seroprevalence in the dairy cows was significantly higher than in the young stock, which may have been attributable to superimposed postnatal infection.     

Seroprevalence of Neospora caninum infection in dairy and beef cattle in Spain

In recent years, neosporosis has been identified as a major cause of abortion in dairy and beef cattle. Although the disease has been described worldwide, there is a Jack of information concerning the prevalence of this infection in different cattle production systems. The aim of this study was to investigate the seroprevalence of Neospora caninum infection in a representative area of beef and dairy cattle production in Spain. A cross-sectional study was undertaken in which herds constituted the initial sampling unit and two strata (dairy and beef herds) were considered. Using a 95% level of confidence and setting 5% (beef) and 5.4% (dairy) error limits, 216 beef and 143 dairy herds were randomly selected and sampled. Nine animals (> 1 year old) were randomly sampled in each herd to detect the presence of the infection. A herd was considered infected when at least one animal was seropositive. In total, serum samples from 1121 dairy and 1712 beef animals were collected and tested for specific anti-N. caninum IgG using an ELISA. Specific antibodies were detected in 55.1% (119/216) beef and 83.2% (119/143) dairy herds. Individual prevalences obtained were 17.9% (306/1712) for beef and 35.9% (402/1121) for dairy animals. Presence of N. caninum infection was higher in dairy than in beef herds and the association between infection and the cattle production system (dairy or beef) was statistically significant [(chi2)Y= 29.21, P < 0.001, OR = 4.04 (2.35-6.99)]. Herd size of dairy cattle did not appear to be associated with N. caninum infection. On the contrary, infection was associated with herd size in beef cattle (chi2 = 12.79, P < 0.01). Finally, no association was found between replacement or pasture management and infection in beef herds.     

Increased risk of abortion following Neospora caninum abortion outbreaks: a retrospective and prospective cohort study in four dairy herds

Explosive abortion outbreaks in 4 Dutch dairy herds during 1992 to 1994 are reported. In 50 of 51 fetuses submitted during the first 3 wk of the outbreaks characteristic histological lesions compatible for infection with Neospora caninum were seen. Diagnosis of infection was confirmed by immunohistochemistry in 40 fetuses (78%). No evidence for other abortifacients was found. The abortion risk of the herds was investigated in a prospective and retrospective cohort study. The prospective study showed that cows aborting during the outbreaks and N. caninum seropositive nonaborting cows had a two- to three-fold increased risk of abortion compared with N. caninum seronegative cows. Retrospective examination showed that seropositive nonaborting cows had an increased risk of abortion before the outbreaks, which may indicate that these animals were infected with N. caninum prior to the outbreaks. It is concluded that serostatus can be used for selective culling of cows to decrease future risk of abortion in dairy herds.     

A retrospective study of 932 second trimester terminations using gemeprost (16,16 dimethyl-trans delta 2 PGE1 methyl ester).

A retrospective study of 932 second trimester terminations between 12-27 weeks gestation was carried out to determine the efficacy of gemeprost for second trimester termination. A single course of 5 x 1 mg gemeprost pessaries was administered every three hours. If abortion had not occurred after the first course of pessaries, a further course of 5 x 1 mg pessaries was administered. Intravenous oxytocin was administered after 36 hours if abortion had not occurred. Eighty per cent and ninety five per cent of patients aborted within 24 and 48 hours respectively. Of the remaining 5 per cent of women, 3 per cent aborted with escalating doses of oxytocin. In the remaining 18 (2 per cent) women, the pregnancies were electively terminated with an alternative method. The median induction-abortion interval was 18.0 hours and 15.0 hours in nulliparous and parous women respectively (P less than 0.0001). The number of pessaries required to induce abortion was not influenced by parity. Significantly more parous women bled more than 500 ml. The incidence of pelvic sepsis (0.1 per cent) and cervical tear (0.1 per cent) was low. Twenty six per cent of women had diarrhoea and 23 per cent vomited following administration of prostaglandin. This study confirmed the efficacy of gemeprost for second trimester termination of pregnancy. This method of termination is safe, non-invasive, simple and has a low complication rate.     

Influence of management factors on pregnancy attrition in dairy cattle

The present study was conducted to determine the influence of management factors on pregnancy attrition in dairy cattle. Data from 3162 diagnosed pregnancies in parous cows and 1050 in heifers at 9 commercial dairy herds in northeastern Spain were used. Pregnancy diagnosis by palpation per rectum was performed from 30 to 70 d post insemination. Pregnancy attrition was registered when pregnancy diagnosis resulted negative in a second palpation carried out between 120 and 150 d following insemination. Overall proportion of pregnancy losses was 7.9% (9.6% in parous cows and 2.8% in heifers). Data analysis was performed by multiple logistic regression methods. For all animals, effect of time of pregnancy diagnosis was shown (Odds ratio = 0.97 for 1 d increase; P = 0.0042). Conceptus loss in heifers was lower than in parous cows (Odds ratio = 0.28; P = 0.0001), and a higher proportion of pregnancy attritions was detected in animals inseminated in spring, summer and winter, compared to those inseminated in autumn (P < 0.04). Herd effect on pregnancy attrition was also significant. Similar results were observed in the subanalysis for parous cows and, furthermore, no effect of lactation number and of interval from previous calving to pregnancy was shown in this group. In heifers, no effect of time of pregnancy diagnosis and of insemination season on pregnancy attrition was shown, and only a herd effect was observed. Our data suggest that the influence of parity status (heifer vs cow) could affect the proportion of pregnancy attrition rather than early diagnosis, and, in pregnant cows, adaptation to seasonal changes associated with temperature decreases seem more efficient.     

Effect of neosporosis on productive and reproductive performance of dairy cattle in Costa Rica

A cross-sectional study was conducted to assess the effect of neosporosis on productive and reproductive parameters in dairy cows. Cows (n=2743) from 94 farms located in the most important dairy areas in Costa Rica were used in the study. The size of the herds ranged from 32 to 379 females (mean=110, median=125). An indirect ELISA was used to determine the serostatus of the cows towards Neospora caninum. The effect of neosporosis on milk production was analysed by a mixed linear model. In addition, the effects on calving interval (days) and calving to conception interval (days) were analysed by survival analysis. The risk of abortion in relation to N. caninum serostatus was assessed by logistic regression, with herd as a random effect. Overall, 1185 of 2743 cows (43.3%) were seropositive for Neospora. Eighty-nine of 94 (94.7%) farms were classified as Neospora-seropositive. It was estimated that cows seronegative to Neospora produced an additional 84.7L of milk (P=0.6). Serostatus did not have a significant effect on the length of the calving interval in the Cox proportional hazard survival analysis (Hazard ratio=1.2, 95% CI: 0.9, 1.4). The logistic regression model had a weak positive association between serostatus and abortion (OR 1.7, 95% CI: 0.8, 3.9), but did not show a strong association between serostatus and the number of services per conception (OR=0.95, 95% CI: 0.7, 1.3). In conclusion, there were no significant effects of Neospora serostatus on production and reproductive performance in this study.     

Seroprevalence of Neospora caninum and Brucella abortus in dairy cattle herds with high abortion rates

The protozoan Neospora caninum and the bacterium Brucella abortus are well-recognized causes of abortion in dairy cattle. Serum samples (n = 240) from aborting (n = 141) and at-risk (n = 99) animals from 5 herds with high abortion rates in Punjab Province, Pakistan, were tested for antibodies to N. caninum using monoclonal antibody-based ELISA and for antibodies to B. abortus using the serum agglutination test. Antibodies to N. caninum and B. abortus were detected in 105 (43.8%) and 135 (56.3%) cattle, respectively. Prevalences of antibodies to N. caninum and B. abortus were higher in aborting cows (46.8% and 76.6%, P < 0.05) than in animals at risk (39.4% and 27.3%, P > 0.05). Sixty-six animals (27.5%) were seropositive to both N. caninum and B. abortus , and results showed no significant difference (P > 0.05) with respect to geographical district, breed, and age. This is the first report of N. caninum infection among dairy cattle herds in Pakistan.     

Serological survey of Neospora caninum infection in cattle herds from Western Romania

Serum samples from 376 randomly selected adult cattle, from 25 farms located in 3 counties (Arad, Bihor, and Timi?) from western Romania, were sampled for Neospora caninum antibodies using a commercial ELISA-kit. Seroprevalence values and risk factors for neosporosis (cow age, breed, herd size, farming system, previous abortion, and number of farm dogs) were examined using a generalized linear mixed model with a binomial distribution. Overall, the seroprevalence of N. caninum was 27.7% (104/376) with a prevalence of 27.9% (24/86) in Arad, 26.9% (25/93) in Bihor, and 27.9% (55/197) in Timi?. Of 25 cattle herds, 23 were seropositive with a prevalence ranging from 10.0 to 52.2%. No correlation was found between N. caninum seropositivity and age, breed, herd size, breeding system, and previous abortion. The number of farm dogs was the only factor (P(Wald) = 0.03) positively associated with seroprevalence in cows and can be considered the risk factor in the acquiring of infection. The present work is the first regarding serological evidence of N. caninum infection in cattle from western Romania.     

Congenital neosporosis in goats from the State of Minas Gerais, Brazil

Congenital Neospora caninum infection was diagnosed in two Saanen goat kids from two distinct herds with a history of abortion and weak newborn goat kids in the Southern region of the State of Minas Gerais, Brazil. The first kid was weak at birth, had difficulty to rise and was unable to nurse. Gross lesions of porencephaly and hydrocephalus ex vacuo were seen. Multifocal necrosis, gliosis and non-supurative encephalitis were observed in the brain. Several parasitic cysts with a thick wall that reacted strongly only with polyclonal antiserum to Neospora caninum were seen in the cerebral cortex, brain stem and cerebellum. The second kid was born from a Neospora caninum seropositive mother that aborted in the last pregnancy. It was born without clinical signs. The diagnosis of neosporosis was based on antibody titer of 1:800 to N. caninum by indirect fluorescence antibody test obtained from blood collected before the goat kid ingested the colostrum and Neospora caninum DNA was detected by polymerase chain reaction and sequenced from placenta. This is the first report of neosporosis in goats in the southeast region of Brazil.     

Low seroprevalence of Neospora caninum infection associated with the limousin breed in cow-calf herds in Andorra, Europe

Neospora caninum seroprevalence and risk factors affecting seroprevalence in beef cattle in Andorra were investigated. Antibodies to N. caninum were evaluated by enzyme-linked immunosorbent assay performed on a yearly basis in 1,758 animals older than 6 mo, belonging to 26 herds. Mean seroprevalence of antibodies to N. caninum for the herds was 7.4 +/- 1.2% (130/1,758). Logistic regression analyses were performed on data from each animal, considering N. caninum seropositivity as the dependent variable, and herd, grazing area, year of sampling, repeat-test animal (animals sampled twice or more), sex, breed, age (animals <4 yr old or > or =5 yr old), and country of birth as possible risk factors. Based on the odds ratio, the prevalence of infection was 2.1 times higher (P < 0.01) in animals from the Ordino grazing area, 1.64 times higher in animals older than 5 yr (P < 0.01), and 6.7 times (1/0.15) lower in Limousin-mixed Limousin cattle (P < 0.002). The results suggest that the particular grazing location could promote the horizontal transmission of this parasite and that certain breeds are less susceptible to N. caninum infection than others.     

Abortion risk in progeny of cows after a Neospora caninum epidemic

A study was done of the descendants of cows from 4 dairy herds in which there had been N. caninum abortion outbreaks. Precolostral antibodies to N. caninum were demonstrated in 34 of 50 (68%) F1 calves and in 14 of 17 (82%) F2 calves from cows that aborted during the outbreaks. In 214 F1 progeny, N. caninum seroprevalence was nearly 50%, and there was a significant association between serostatus of the offspring and serostatus of dams. These observations indicated that congenital infection was an important mode of transmission after abortion outbreaks in these herds. A total of 52 abortions was recorded in 293 pregnancies of F1 progeny cows (1 to 3 pregnancies per animal). It was found that seropositive F1 cows had a three-fold increased abortion risk compared with seronegative F1 cows. In 2 of 10 abortions in seronegative cows evidence for N. caninum infection was found, suggesting that a low level of postnatal infection may also have occurred. It is concluded that N. caninum-infected calves should not be used as replacement stock, to decrease the future risk of abortion in dairy herds.     

Prevalence of Neospora caninum infection in dairy cows and its consequences for reproductive management

This study was carried out to determine the prevalence of neosporosis in an area of intensive dairy production, in Portugal. Sera samples were obtained in a random basis from 114 cows in 49 herds (group A), and from 1237 cows in 36 herds with a history of abortion outbreaks (group B). All sera samples were tested for neosporosis by direct agglutination test (DAT). Additionally, attempts to isolate Neospora caninum in 42 aborted bovine fetuses from 38 dairy herds (group C) were carried out, utilizing a bioassay with immuno-depressed Swiss Webster mice. Parasitological confirmation was done by indirect fluorescent antibody test (IFAT). The prevalence of neosporosis in the group A was 28%. Group B had a significantly (P < 0.001) higher prevalence (46%) and Neospora caninum was isolated in 36% of the aborted fetuses (group C). These results indicate that neosporosis, a disease only recently (2001) diagnosed in Portugal, has a high prevalence in the country, particularly in populations with a story of abortion. Thus, neosporosis should systematically be considered in the differential diagnosis of abortion. In the context of embryo transfers, the importance of selecting Neospora-free embryo recipients is discussed, as well as the pertinence of assessing the Neospora status of traded and imported cattle.     

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.