Evaluation of Immunodiagnostic Performances of Neospora caninum Peroxiredoxin 2 (NcPrx2), Microneme 4 (NcMIC4), and Surface Antigen 1 (NcSAG1) Recombinant Proteins for Bovine Neosporosis

Bovine neosporosis is among the main causes of abortion in cattle worldwide, causing serious economic losses in the beef and dairy industries. A highly sensitive and specific diagnostic method for the assessment of the epidemiology of the disease, as well as it surveillance and management, is imperative, due to the absence of an effective treatment or vaccine against neosporosis. In the present study, the immunodiagnostic performance of Neospora caninum peroxiredoxin 2 (NcPrx2), microneme 4 (NcMIC4), and surface antigen 1 (NcSAG1) to detect IgG antibodies against N. caninum in cattle were evaluated and compared with that of the indirect fluorescent antibody test (IFAT). The results revealed that NcSAG1 had the highest sensitivity and specificity, with values of 88.4% and 80.7%, respectively, followed by NcPrx2, with a high sensitivity of 87.0% but a low specificity of 67.0%, whereas NcMIC4 showed sensitivity and specificity of 84.1% and 78.9%, respectively, when compared with IFAT. A high degree of agreement was observed for NcSAG1 (k = 0.713) recombinant protein, showing the highest diagnostic capability, followed by NcMIC4 (k = 0.64) and NcPrx2 (k = 0.558). The present study demonstrates that NcSAG1 is helpful as an antigen marker and also demonstrates the potential immunodiagnostic capabilities of NcPrx2 and NcMIC4, which could serve as alternative diagnostic markers for detecting N. caninum infection in cattle. These markers may find utility in future treatment management, surveillance, and risk assessment of neosporosis in livestock or other animal host species. Further research should be directed toward understanding the in vivo immune response differences resulting from immunization with both recombinant proteins.

Fluctuations of antibody serum titers for Toxoplasma gondii and Neospora caninum in naturally infected crossbred cows during gestation

This study aimed to assess the fluctuations of antibody serum titers for Toxoplasma gondii and Neospora caninum in naturally infected crossbred cows during gestation and to investigate transplacental transmission of T. gondii; 51 cows were monitored during pregnancy by monthly serologic testing by indirect fluorescent antibody test. 33 cows were seronegative for both N. caninum and T. gondii, 10 were seropositive only for N. caninum, 5 were seropositive only for T. gondii, and 3 were seropositive for both N. caninum and T. gondii. In both protozoan infections, great variation in antibody levels in pregnant cows was observed, and there was significant increase (p<0.05) in the comparison between the averages of serological titration per trimester. There was a significant correlation (p<0.05) between month and probability of seropositivity for T. gondii. We conclude that pregnancy influences antibody titers of crossbred cows naturally infected with N. caninum and/or T. gondii, and that serologic testing for T. gondii in pregnant cows from the sixth month of gestation onward may decrease the number of false negative results.

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.

Evaluation of Neospora caninum serodiagnostic antigens for bovine neosporosis

Abortion and reproductive failure caused by Neospora caninum infection has a dramatic negative economic impact on the cattle industry. To date, no definitive serodiagnostic tool for assessing N. caninum abortion has been reported. In this study, we evaluated the diagnostic performance of numerous N. caninum antigens in relation to abortion in cattle. Five recombinant proteins with potential as diagnostic antigens (NcGRA6, NcGRA7, NcGRA14, NcCyP, and NcSAG1) were compared by indirect enzyme-linked immunosorbent assay (iELISA) using sera from mice and cattle experimentally infected with N. caninum. The best-performing three antigens (NcSAG1, NcGRA7, and NcGRA6) were evaluated by IgG-iELISAs to assess their utility in diagnosing Neospora abortion using sera from confirmed N. caninum-aborted dams based on immunohistochemical assays (IHC). Additionally, all samples were tested using a commercial N. caninum antibody competitive ELISA (cELISA). The iELISAs against both NcSAG1 and NcGRA7 could efficiently distinguish IHC positive and negative samples compared with iELISAs against NcGRA6 and the cELISA. Furthermore, antibody levels against NcSAG1 and NcGRA7 were significantly higher in aborting cows comparing with infected but non-aborted dams in a herd experiencing a Neospora abortion outbreak. Tracking the dynamics of antibody levels during pregnancy revealed a marked increase in NcSAG1- and NcGRA7-specific antibodies at the last trimester of pregnancy. In contrast, no marked differences in antibody levels against either antigen were noted in neurologically symptomatic calves compared with non-symptomatic infected calves. Our data suggests NcSAG1 and NcGRA7 as indicators for Neospora abortion.

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.

Identification of a highly antigenic region of subtilisin-like serine protease 1 for serodiagnosis of Neospora caninum infection

Neospora caninum is an apicomplexan parasite that causes abortion in cattle; hence, accurate diagnosis of this pathogen is important to the cattle farming industry. Our previous proteomics and immunoscreening analyses revealed that the N. caninum subtilisin-like serine protease 1 (NcSUB1) has potential as a serodiagnostic tool for Neospora. Consequently, we expressed two fragments containing five NcSUB1 tandem repeat copies covering amino acids (aa) 524 to 843 (NcSUB1t) and 555 to 679 (NcSUB1tr) to identify the antigenic regions. The serodiagnostic performances of NcSUB1t and NcSUB1tr were compared with that of N54, which contains a single copy of the repeats (aa 649 to 784), and with the truncated NcSAG1 (NcSAG1t), which lacks a signal peptide and C-terminal hydrophobic regions, as a positive reference. Serum samples from N. caninum experimentally infected cattle and mice and cattle from a farm with confirmed cases of Neospora abortion were tested by enzyme-linked immunosorbent assay (ELISA) with the four antigens. In the N. caninum experimentally infected cattle, the highest IgG1 antibody titers were detected against NcSUB1t, while specific IgG1 antibodies were detectable from 16 days postinfection (dpi), with levels peaking at 36 dpi for all of the antigens. On the other hand, the levels of anti-NcSUB1 IgG2 antibodies were lower than those of anti-SAG1t IgG2 antibodies. The ELISA with NcSUB1t and NcSUB1tr had good sensitivity (94.59 to 95.95%) and specificity (80 to 100%) with bovine serum field samples compared to NcSAG1t and showed no cross-reactions with sera from Toxoplasma gondii experimentally infected mice. Moreover, IgG antibodies against NcSUB1t were detected during parturition in the NcSAG1t antibody-positive cattle, and NcSUB1t-specific antibody transfer was observed from a mother to her calf. Our results show that the NcSUB1 tandem repeat is potentially useful for serodiagnosis of N. caninum.

What is the global economic impact of Neospora caninum in cattle - the billion dollar question

Neospora caninum is regarded as one of the most important infectious causes of abortions in cattle worldwide, yet the global economic impact of the infection has not been established. A systematic review of the economic impact of N. caninum infections/abortions was conducted, searching PubMed with the terms 'cattle' and 'Neospora'. This yielded 769 publications and the abstracts were screened for economically relevant information (e.g. abortion prevalence and risk, serological prevalence). Further analysis was restricted to countries with at least five relevant publications. In total, 99 studies (12.9%) from 10 countries contained data from the beef industry (25 papers (25.3%)) and 72 papers (72.8%) from the dairy industry (with the remaining two papers (2.0%) describing general abortion statistics). The total annual cost of N. caninum infections/abortions was estimated to range from a median US $1.1 million in the New Zealand beef industry to an estimated median total of US $546.3 million impact per annum in the US dairy population. The estimate for the total median N. caninum-related losses exceeded US $1.298 billion per annum, ranging as high as US $2.380 billion. Nearly two-thirds of the losses were incurred by the dairy industry (US $842.9 million). Annual losses on individual dairy farms were estimated to reach a median of US $1,600.00, while on beef farms these costs amounted to just US $150.00. Pregnant cows and heifers were estimated to incur, on average, a loss due to N. caninum of less than US $20.00 for dairy and less than US $5.00 for beef. These loss estimates, however, rose to ∼US $110.00 and US $40.00, respectively, for N. caninum-infected pregnant dairy and beef cows. This estimate of global losses due to N. caninum, with the identification of clear target markets (countries, as well as cattle industries), should provide an incentive to develop treatment options and/or vaccines.

Potential involvement of Neospora caninum in naturally occurring ovine abortions in New Zealand

Neospora caninum is an obligate intracellular parasite and is recognised as the leading cause of bovine abortion worldwide. Natural infection with N. caninum has been described in sheep but it has generally not been regarded as a significant cause of abortion. Recently, there have been several New Zealand cases of foetal abortions where N. caninum was detected which strongly suggested the involvement of Neospora in these abortions. However, there is minimal information about the prevalence of N. caninum infection naturally occurring in New Zealand sheep flocks and particularly its impact on reproduction success. Thus, this present study provides preliminary data on the role that Neospora is playing in ovine reproductive failure by establishing the prevalence of N. caninum antibodies and DNA in ewe blood and foetal material present in 21 New Zealand sheep farms with ongoing unexplained abortion problems and 10 farms with consistently high fertility levels. The results of this study demonstrated an overall seroprevalence of 1.4% which varied between Aborting/non-pregnant (1.8%), age-matched pregnant controls (0.6%) and high fertility (2.1%) ewes. However, despite the variation observed, there was no statistical difference between the three groups. In addition, Neospora DNA was detected by PCR in 13% of submitted foetal brains and in ewe blood from aborting/non-pregnant (6.9%), age-matched pregnant controls (3.6%) and high fertility pregnant (2.1%) ewes. When the PCR results were considered with the IFAT and IDEXX ELISA results, there was no correlation between serology positive and PCR positive blood samples. Taken together, these results reveal that reliance on ELISA-based serology or PCR alone may underestimate the involvement of Neospora. Furthermore, determining the involvement of Neospora appears to require a multi-facetted approach where diagnostic methods and serological cut-off values may need to be adjusted as further information about the effect of natural infections with N. caninum in the ovine host is elucidated.

Seroprevalence and risk factors associated with neosporosis in sheep and dogs from farms

This study aimed to establish the seroprevalence and risk factors associated with neosporosis in sheep and dogs from rural properties. 1497 blood samples were collected from sheep and 42 from dogs that cohabited with sheep from 16 farms located in the central region of São Paulo State, Brazil. For the detection of N. caninum antibodies it was performed the indirect fluorescent antibody test (IFAT ≥ 25). For the epidemiological study it was applied a questionnaire for the owners or responsible from the sheep and dogs regarding informations related to neosporosis. The seroprevalence obtained out of the 1497 sheep sera tested was 8.0% (CI95%=6.7-9.2%) and out of the 42 dogs 4.8% (CI95%=0-7.2%). Variables statistically related to seropositivity for N. caninum in sheep were: dams well as water supply (P=0.0004; OR=2.15), presence of other domestic canids (P=0.0013; OR=2.38) and presence of reproductive problems (P=0.0031; OR=1.75).

Comparison between immunohistochemistry and two PCR methods for detection of Neospora caninum in formalin-fixed and paraffin-embedded brain tissue of bovine fetuses

The objective of this study was to identify the presence of the parasite by comparing immunohistochemistry (IHC) with two polymerase chain reaction (PCR) methods for the detection of the pNc5 gene and the internal transcribed spacer 1 (ITS1) of N. caninum in brain tissue of bovine fetuses that had previously been fixed in formalin and paraffin-embedded. In 29 out of 48 brains (60.4%), microscopic lesions consistent with Neospora infection were observed, and 21 of the 29 cases (72.41%) were positive for IHC. Fifteen of the 29 cases positive for IHC (51.72%) were also positive on the ITS1 PCR, and 12 cases were also positive on the pNc5 PCR (41.37%). The sensitivity of the PCR assays was 71.42% and 57.14%, respectively, and the specificity was 100% for both. The concordance between histopathology and IHC and the ITS1 PCR was 85%, and in the case of the pNc5 PCR it was 77.5%. When the number of fetuses positive by IHC and both PCR tests was compared, no statistically significant difference was found (P>0.05). It is concluded that the use of formalin-fixed and paraffin-embedded bovine fetal tissues allows the detection of N. caninum by IHC or PCR. Nevertheless, it is recommended that more than one technique is used to increase the diagnostic sensitivity, and preferably tests that show better performance in the individual laboratory should be selected.

Some factors affecting the abortion rate in dairy herds with high incidence of Neospora-associated abortions are different in cows and heifers

The aim of this study was to determine if the factors affecting the abortion rate in dairy herds with high incidence of Neospora-associated abortions are different in pregnancies of cows and heifers chronically infected with Neospora caninum. In heifers (n = 229), an increase in the cumulative number of days with a mean relative humidity (RH) lower than 60% during the second trimester of gestation increases the risk of abortion. Yet, the likelihood of abortion was 7.6 times lower for pregnant heifers inseminated with Limousin bull semen, compared with those inseminated with Holstein-Friesian bull semen. In pregnancies of parous cows (n = 521), an increase in rainfall and in the cumulative number of days with a mean RH lower than 60% during the second trimester of gestation increased the abortion rate. However, in contrast, an increase in the lactation number produced a decrease in the abortion rate, with a likelihood of abortion 4.8 times lower for pregnant cows inseminated with Limousin bull semen, and three times lower for those inseminated with Belgian Blue bull semen, compared with dairy cows inseminated with Holstein-Friesian bull semen. Finally, the likelihood of abortion was 3.2 times lower for pregnancies of parous cows with low antibody titres against N. caninum (6-30 units) as compared to those with high antibody titres (>/=30 units), whereas in heifers this variable had no effect. The practical recommendations of the present study include the control of the cow environment during the second trimester of gestation, the priority of culling for parous cows with higher antibody titres against N. caninum and the insemination of Neospora-seropositive cows with semen from the Limousin breed.

Seroprevalence of Neospora caninum antibodies in cattle and water buffaloes in India

Neospora caninum is now recognized as a major cause of abortion in cattle worldwide, but there is no report of N. caninum infection in cattle in India. Serum samples from 427 dairy cattle and 32 dairy water buffaloes from 7 organized dairy farms located in Punjab, India, were tested for N. caninum antibodies using a commercial monoclonal antibody-based competitive enzyme-linked immunosorbent assay (ELISA). Antibodies to N. caninum were found in 35 of 427 cattle from 6 of the 7 farms; 9.6% of cows, 5.1% of heifers, and 5.0% of calves were seropositive, suggesting postnatal transmission of N. caninum on the farm. Antibodies to N. caninum were found in 16 of 32 buffaloes tested from 2 dairy farms. In total, 64 cattle and 16 buffalo sera already tested by ELISA were also evaluated by an indirect fluorescent antibody test (IFAT) to verify ELISA results. Of the 64 cattle samples, 29 sera were negative by both tests and of the 35 ELISA-positive sera, 12 had IFAT titers of 1:100 or higher (1 had IFAT titer of 100, 2 had IFAT titer of 200, and 9 had IFAT titers of 400 or higher). Of the 16 buffalo sera positive by ELISA, 1 had an IFAT titer of 1:400. Thus, antibodies to N. caninum were demonstrated in cattle sera by 2 serologic methods. To our knowledge this is the first report of N. caninum infection in cattle and buffaloes in India.

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.

Epidemiology of neosporosis in dairy cattle in Galicia (NW Spain)

This comprehensive study of neosporosis in dairy cattle in Galicia (NW Spain) included: (1) a comparative study of three serological techniques for detection of Neospora caninum antibodies (direct agglutination, enzyme-linked immunosorbent assay and indirect immunofluorescence); (2) a cross-sectional serological survey in which 276 herds and 5,196 animals were tested; (3) a study of N. caninum antibody dynamics; (4) the isolation of viable tachyzoites of N. caninum. Data were analysed to determine the risk factors associated with the infection. A total of 219 herds (79.3%) and 816 heads of cattle (15.7%) were found to be seropositive. Seropositivity was higher on farms with dogs than on farms without dogs, and there was a negative correlation between the size of the herds and seroprevalence. Co-infection with Toxoplasma gondii increased the risk of seropositivity. Cows infected with N. caninum were 5.3 times more likely to abort than non-infected cows. The dynamics study showed an increase in anti-N. caninum antibody titres during the third trimester of pregnancy. Viable tachyzoites were isolated from brain samples. These results indicate that the economic impact of N. caninum is high in Galicia, and therefore, the inclusion of control measures for neosporosis in the official control health programmes is strongly recommended.

Comparison of serological methods for the diagnosis of Neospora caninum infection in cattle

The aims of this study were to evaluate the performance and agreement of various commercial and in-house Neospora caninum antibody assays used in dairy cattle in North America, and to investigate reproducibility of two assays performed in different laboratories. From 1998 to 2005, three enzyme linked immunosorbent assays (ELISAs, a competitive ELISA-VMRD Inc., an indirect ELISA-Biovet Inc., and another indirect ELISA-Herdchek IDEXX Corp.), two indirect fluorescent antibody tests (IFATs, VMRD Inc., and in-house USDA) and one N. caninum agglutination test (NAT, in-house USDA) were utilized to test 397 randomly selected dairy cattle serum samples from 34 herds in eastern Canada for antibodies to N. caninum. The manufacturers' recommended cut-off values were used to evaluate test performance and agreement between tests. One IFAT (VMRD Inc.) performed well (sensitivity and specificity: 0.97 and 0.97, respectively) using reference sera (n = 452), therefore, results from this IFAT on the 397 samples could subsequently be used as the reference standard to calculate test characteristics for the other assays. Only 11% of the 397 sera were found to be N. caninum-positive with the IFAT. Prevalence-adjusted bias-adjusted kappa (PABAK) ranged from 0.06 to 0.99. Positive agreement was moderate to very good (P(pos) = 0.25-0.96). Negative agreement was very good for all assays (P(neg) > 0.94) except NAT (P(neg) = 0.66). Sensitivity was > or =0.89 for all assays except the NAT, which had a significantly lower sensitivity (0.66). Specificity was high (>0.94) for all assays except for one indirect ELISA (specificity = 0.52). This indirect ELISA did not perform satisfactorily when used in 1998, but an improved version of the ELISA performed as one of the best assays in 2004. Reproducibility of the competitive ELISA was excellent, but the reproducibility of the indirect ELISA that was improved was low (concordance correlation coefficient = 0.90 and 0.36, respectively). The performance characteristics observed for most assays in this study make them useful for screening antibodies to N. caninum in cattle.

Seroprevalence of neosporosis in beef and dairy cattle breeds in Northeast Hungary

In order to assess the seroprevalence of bovine neosporosis with indirect fluorescent antibody test (IFAT), blood samples were collected randomly from 1063 beef and dairy cattle belonging to 12 different breeds in Northeast Hungary. Antibodies to Neospora caninum were detected in 27 (2.5%) of the animals, kept on 19 of the 42 settlements included in this survey. Since samples were collected on 50 farms, herd prevalence amounted to 38%. The percentage of cattle with seroconversion increased with age, suggesting a postnatal source of infection. The highest rate of positivity was detected in Aberdeen Angus (3.3%) and Holstein-Friesian cows (3.2%), and the lowest in Limousine (0.9%), but no breed predisposition was statistically substantiated. Neosporosis was more prevalent in dairy (3.4%) than in beef (1.9%) cattle, although the difference was not significant. Only three out of the seropositive cows, all of them Holstein-Friesians, had a history of abortion.

Neosporosis, Toxoplasmosis, and Sarcocystosis in Ruminants

Neospora caninum, Sarcocystis spp, and Toxoplasma gondii are related coccidian parasites that can cause abortion and neonatal mortality in animals. In addition, T gondii and certain species of Sarcocystis are zoonotic. This article reviews information on the etiology, diagnosis, control, and prevention of these diseases.

Diagnosis of bovine neosporosis

The protozoan parasite Neospora caninum is a major cause of abortion in cattle. The diagnosis of neosporosis-associated mortality and abortion in cattle is difficult. In the present paper we review histologic, serologic, immunohistochemical, and molecular methods for dignosis of bovine neosporosis. Although not a routine method of diagnosis, methods to isolate viable N. caninum from bovine tissues are also reviewed.

Seronegative conversion in four Neospora caninum-infected cows, with a low rate of transplacental transmission

Four Neospora-seropositive pregnant cows (prebreeding indirect fluorescent antibody (IFA) titers between 1:400 and 1:1600) were confined and observed until parturition. All cows gave birth to normal calves. Selected tissues were tested for NC by histopathology, immunohistochemical (IHC) and polymerase chain reaction (PCR). Parasite isolation was attempted in vero cell cultures. At parturition, all cows were seronegative at 1:200 and two of four cows had a titer of 1:100 when further tested. Three of four calves were not infected, as determined by negative results of precolostral serology (1:25 cut-off), histopathology, IHC and PCR. One calf was congenitally infected, as shown by the presence of a thick-walled cyst labelled by IHC in its brain, positive PCR of brain and a precolostral IFA titer of 1:100. It was concluded that NC antibody titers may drop or convert to seronegative status in chronically infected cows by the time of parturition and this finding in four of four cows indicates that this could be a common occurrence. Similarly, the finding of an infected calf with a low antibody titer indicates that precolostral serology may not be a fool-proof means of identifying calves with congenital Neospora caninum infections. These findings call into question conclusions of other studies that have estimated rates of congenital transmission of this parasite based on serological tests at calving. This study is the first confirmed report of congenital NC infection in a calf in Thailand.

The use of beef bull semen reduced the risk of abortion in Neospora-seropositive dairy cows

There is an evidence that the epidemiology of neosporosis differs in dairy and beef cattle, such that beef cattle carry a lower risk of abortion. The aim of the present study was to establish whether artificial insemination using semen from beef bulls could reduce the risk of abortion in dairy cows seropositive for the Neospora caninum parasite. Our study was based on yearly serological screening for neosporosis and on the confirmation of Neospora infection in aborted fetuses in two high-producing dairy herds with a mean 28% seroprevalence of N. caninum antibodies. The study population comprised of 273 pregnancies in seropositive animals: 156 pregnancies monitored after insemination using Holstein-Friesian semen and 117 after insemination using beef bull semen. Abortion rates for these animals were 28.2% (77 of 273), 34.6% (54 of 156) and 19.7% (23 of 117). Logistic regression analysis indicated no significant effects of lactation number and previous abortion on the abortion rate. Based on the odds ratio, a 1-unit increase in the Neospora antibody titre yielded a 1.01-fold increase in the abortion rate. The likelihood of abortion was two times higher for cows in one of the two herds and 2.8 times lower (one of 0.36) for pregnant cows inseminated with beef bull semen rather than Holstein-Friesian semen. Our results indicate that the use of beef bull semen can reduce the risk of abortion in dairy cows, and suggest that annual screening for neosporosis, specifically the antibody titre to the protozoan, could be an useful predictor of abortion risk in reproductive health programmes.

Neospora-associated abortion episode over a 1-year period in a dairy herd in north-east Spain

This report describes a retrospective study based on serological screening, performed on a Neospora-associated abortion episode over a 12-month period in a dairy herd in north-east Spain. During the 1-year study period, the overall abortion rate for the herd was 23.2% (38 abortions of 164 diagnosed pregnancies). The data analysed were those derived from blood samples collected from the whole herd (n = 237) and from diagnosed pregnancies. Antibodies to Neospora caninum were found in 35.4% of the cattle with 44% of seropositive pregnant animals aborting over 1-year period. Based on the odds ratio, the risk of abortion was 12.2 times higher (P < 0.0001) in the Neospora-seropositive animals than in seronegative animals and significantly higher during the second term of gestation (P < 0.01) than during the first and third terms. Abortions were not found to be associated with parity status or season of pregnancy, and the common risk factors associated with pregnancy loss in the geographical area of the study. Age-related differences in N. caninum seroprevalence were not statistically significant, indicating vertical transmission as the main route of infection. Indeed, a high percentage of congenitally infected offspring was observed (90.6%) and the farm had been free of dogs for the last 7 years. Our results suggest that, when a dairy herd shows an increased incidence of abortions due to Neosporosis, maternal serology can be a good indicator of the abortion risk in individual cows, and that the effects of factors normally related to abortion, such as parity and pregnancy season, may be masked.

Comparison of three techniques for the serological diagnosis of Neospora caninum in the dog and their use for epidemiological studies

An enzyme-linked immunosorbent assay (ELISA) was developed in our laboratory and used to determine the seroprevalence of Neospora caninum in three different dog populations in Belgium: healthy dogs from cattle farms and urban dogs with or without various neurological disorders. The test was validated and compared with two other tests: an indirect fluorescent antibody test (IFAT) and a commercially available competitive enzyme-linked immunosorbent assay (C-ELISA). The study showed a good correlation between the IFAT and the ELISA developed. When the two tests were compared with the C-ELISA, moderate positive and negative agreement indices were observed. Using our ELISA and the IFAT techniques, a high prevalence was found in farm dogs. This result showed that the neurological symptoms are not usually associated with the Neospora infection. In conclusion, the ELISA developed in our laboratory could replace the IFAT for the screening of a large number of dogs' sera.

Neospora caninum infection does not affect early pregnancy in dairy cattle

This study was designed to evaluate the relationship between Neospora caninum infection prior to pregnancy, as determined through maternal serology, and the subsequent occurrence of abortion in dairy cattle. Special emphasis was placed on pregnancy losses in the first trimester of pregnancy. Neospora caninum antibodies were analyzed by commercial ELISA in 2773 pregnant animals (2022 parous cows and 751 heifers) from six herds. The mean seroprevalence of antibodies to N. caninum in the herds was 15.1% (n = 419). From gestation Day 34 to the 90th day of pregnancy, there were 183 abortions (6.6% of all pregnancies) (23 in Neospora positive animals). After 90 days of pregnancy, the number of abortions was 146 (5.3%); 126 occurring during the second and 20 during the third trimester of pregnancy (105 in Neospora positive animals). Multiple logistic regression analyses were performed on data from each animal using abortion before or after 90 days of pregnancy as the dependent variable, and Neospora positivity, herd, pregnancy season, and parity (parous or nonparous) as independent factors. No significant effects of Neospora positivity and herd were found on the abortion rate before 90 days of pregnancy. Based on the odds ratio, the abortion rate was 4 times higher (P < 0.0001) in animals that became pregnant in the warm than in the cool period, and 3.7 times higher (P < 0.0001) in parous than in nonparous animals. Neospora positivity was the only variable included in the logistic regression model for abortions occurring after 90 days of pregnancy. Seropositivity in an animal increased the probability of abortion by an odds ratio of 18.9 (P < 0.0001; 95% confidence interval 12.9-27.8). Season, parity, and herd showed no effect. The results of the present study suggest that chronic N. caninum infection prior to pregnancy appears not to affect the early fetal period, but does have a significant abortive effect after 90 days of gestation.

Comparison and standardisation of serological methods for the diagnosis of Neospora caninum infection in bovines

Various existing serological tests were compared with a standard panel of 523 sera in a multicentred study across Europe. Well characterised sera from animals that were experimentally or naturally infected with Neospora caninum as well as sera from cattle deemed uninfected with N. caninum were provided by the participants of the study and analysed in several commercial (CHEKIT Dr. Bommeli/Intervet, CIVTEST BOVIS NEOSPORA Hipra, Cypress Diagnostics C.V., Herd Check IDEXX, Mastazyme MAST Diagnostics, P38-ELISA Animal Welfare and Food Safety GmbH (AFOSA)) as well as in-house assays (five ELISAs and one IFAT). Most tests showed a high level of agreement in the interpretation of the test results (positive or negative). A further distinct increase in agreement between tests was obtained after the application of standardised cut-offs offered by a two-graph receiver operating characteristic analysis. This procedure allows a standardised interpretation of results obtained with different tests used in independent, parallel seroepidemiological studies.

Seroprevalence of Neospora caninum in aborting dairy cattle in the Czech Republic

A serological survey for antibodies against Neospora caninum in aborting cattle was carried out in the Czech Republic. Serum samples from 463 aborting dairy cows originated from 137 farms from different parts of the Czech Republic were tested for presence of N. caninum antibodies by use of an enzyme-linked immunosorbent assay (ELISA) and an indirect fluorescent antibody test (IFAT). Antibodies (> or = 1:640) to N. caninum were found in 18 (3.9%) of 463 aborting cows. Farm prevalence in aborting cows was 12.4% (17/137). The antibody titres of cows were 1:200 (9 cows), 1:640 (7 cows), 1:1280 (3 cows), 1:2560 (3 cows), 1:5120 (3 cows), 1:10,240 (2 cows) and 1:20,480 (0 cow). A case-control study was conducted to estimate the association of N. caninum infection and abortion. For this 407 serum samples were collected from cows on five dairy farms with repeated occurrence of endemic and sporadic abortion of unidentified etiology. These samples were obtained from aborting cattle (n=44) and normally calving cattle (control group; n=363) and tested for N. caninum antibodies by an immunofluorescent antibody test (IFAT). Overall, 3.19% (13/407) of cows sampled had positive N. caninum fluorescence with a cut-off titre of 1:200. The prevalence of N. caninum was significantly higher (P<0.05) in the aborting group (13.64%; 95% confidence interval (CI): 5.2, 27.4) than in the control group (1.93%; 95% CI: 0.8, 3.9). A strong association between seropositivity and abortion was found, with seropositive cows being eight times more likely to abort than seronegative cows (odds ratio=8; 95% CI: 2.6, 25.1). This first report on the serological prevalence of N. caninum in cows in the Czech Republic verified a strong association between N. caninum infection and abortions in five dairy farms. Thus, the neosporosis should be considered in differential diagnosis of bovine abortion.

The effect of the dam-calf relationship on serostatus to Neospora caninum on 20 Costa Rican dairy farms

An epidemiological study was conducted on 20 dairy herds previously diagnosed as seropositive for Neospora caninum. The number of females per farm varies from 41 to 296. All females present on the farms were bled once in the period of July and August 2000. A total of 3002 females were bled. An indirect ELISA was used to determine the serostatus of the animals. The analysis of the data was performed in four steps: (1) descriptive statistics about the serological status and general characteristics of the cattle; (2) calculation of vertical and horizontal transmission; (3) an univariate analysis and, (4) a multivariate logistic regression analysis with herd as random effect. The within-herd seroprevalence varied between 25.0% (34/136) and 70.5% (203/288). Seven hundred and forty-seven dam-daughter pairs were available, involving daughters of any age. Daughters in the specific age-class of 2- and 3-years old had a higher seroprevalence (P<0.01) compared with younger and older age-classes. The risk of being seropositive when being born to a mother that tested seropositive (prevalence ratio (PR)) was 2.8-fold increased which coincides with a 5.3-fold increased odds. The probability of horizontal infection amounts to 0.22. The probability of a seropositive offspring due to vertical transmission was 0.64 (attributable fraction among exposed (AFexp)). The multivariate logistic regression showed a significant 6.0-fold increased odds for being seropositive when born from a seropositive mother. Also the within-herd seroprevalence level was significantly associated with the serostatus of the daughters. In the specific conditions of the dairy herds involved in this study, the serostatus of the cows should be not used as a predictor of the serostatus of daughters due to the increased probability of horizontal transmission.

Neospora caninum antigens recognized by mouse IgG at different stages of infection including recrudescence

Western blotting was performed to analyze Neospora caninum tachyzoite antigens recognized by mouse IgG at different stages of infection including recrudescence. At the early stage of infection, a 36-38 kDa antigen was clearly recognized by the mouse antisera. After day 48 postinoculation, the signal of the 36-38 kDa antigen gradually weakened. Meanwhile, a 43 kDa antigen was intensely and continuously recognized from 48 to 125 days postinoculation. This 43 kDa antigen was clearly detectable with the antisera from the mice under immunosuppression. Sera from naturally infected cattle strongly reacted with the 43 kDa antigen. Therefore, the 43 kDa antigen may be useful for immunological reactions to detect infected animals except in the early stage of the infection.

Validation of a Neospora caninum iscom ELISA without a gold standard

Neospora caninum is an intracellular parasite which causes abortion in cattle worldwide. One problem in the validation of the different methods for demonstration of this parasite is the lack of an appropriate gold standard. To validate an immunostimulating complex (iscom) enzyme-linked immunoassay (ELISA) used to detect antibodies to N. caninum, sera from 244 cattle in five Swedish dairy herds infected with N. caninum were analysed. The sera also were analysed by a standard indirect-fluorescent antibody test (IFAT). The results obtained by the two tests were compared using the Gibbs sampler. Gibbs sampling is a latent-class approach based on Bayesian statistics; neither test is assumed to be more correct in stating the true status of infection. The Gibbs sampler was run using both informative and non-informative prior probabilities. We also simulated different cut-offs in the iscom ELISA (providing data to inform selection of optimal cut-off values for different applications). The ELISA produced fewest incorrect test results over all at a cut-off value of 0.200. The sensitivity and specificity at this cut-off were 99 and 96%, respectively. The IFAT had a high specificity (99%) but a lower sensitivity (78%) than expected-confirming that the IFAT cannot be treated as a true gold standard. Sensitivity and specificity of the ELISA were presented in a two-graph receiver operating characteristic (TG-ROC) plot. Any cut-off between 0.150 and 0.300 will have both sensitivity and specificity > or =95%. Optical densities of < or =0.150 and > or =0.550 (or > or =0.350) were suggested as limits to rule out and rule in infection, respectively.

Fetal infection with Neospora caninum in dairy and beef cattle in Belgium

Neospora caninum is a protozoan parasite, which causes fetal and neonatal mortality in livestock and companion animals. In 224 abortions in Belgian cattle, different diagnostic methods were used to demonstrate infection, and the presence of N. caninum. An indirect fluorescent antibody test (IFAT) was used to analyze fetal and maternal sera and immunohistochemistry (IHC) was performed when lesions consistent with neosporosis were observed in the brain, heart or liver. Twenty dairy cattle sera out of 70 (29%) and 13 beef cattle sera out of 93 (14%) were positive by IFAT. A positive titer to N. caninum was found in seven and three fetuses born to beef and dairy cows, respectively. Lesions consistent with N. caninum infection were observed in 17 fetuses. Of nine positive beef fetuses, five were confirmed by IHC while, all but one dairy fetus were confirmed using the same technique. Age had no influence on the serological status of the mother (P = 0.486) whereas husbandry system had a borderline influence (P = 0.082). However, a strong association (P = 0.004) between the level of antibodies in the dam and the occurrence of lesions in the fetus was observed and lesions were more prominent in dairy than in beef fetuses. Additionally, the distribution of intra-cerebral lesions was more extensive in dairy than in beef fetuses (P < 0.0001). Age and serological status of the fetus were found to influence the occurrence of lesions in beef fetuses (both P < 0.001) but no such significant relationships could be demonstrated in dairy fetuses. The study indicated that N. caninum must be considered as an important cause of bovine abortion in Belgium.

An analysis of the performance characteristics of serological tests for the diagnosis of Neospora caninum infection in cattle

AIMS

To analyse the performance characteristics (sensitivity/specificity) of two enzyme-linked immunosorbent assays (ELISA) against the indirect fluorescent antibody test (IFAT).

METHODS

A total of 1199 sera were tested in two ELISAs and the IFAT and results analysed utilising software that performed a receiver-operating characteristic (ROC) analysis.

RESULTS

Sensitivity and specificity for the two ELISAs were calculated for a range of different cut-offs. Minimal misclassification was achieved at cut-offs that, in the case of the Central Animal Health Laboratory (CAHL)-ELISA were in line with previously published cut-off values. In the case of the IDEXX-ELISA lower cut-off values than suggested by the manufacturer were calculated.

CONCLUSIONS

ROC-analysis resulted in optimised, as compared to the IFAT, cut-off thresholds for the CAHL and IDEXX-ELISA which can be further adjusted depending on the purpose of the investigation.

Control options forNeospora caninuminfections in cattle — current state of knowledge

This article reviews control options for Neospora caninum infection and abortion in cattle, drawing on published literature and the authors' own research in this field. Apart from the successful use of embryo transfer to prevent congenital infection in calves born to infected cows, there are currently no accepted control methods for the prevention of abortions in cattle. The epidemiological data at hand suggest that concomitant infections with bovine pestivirus increase the risk of abortion significantly and that these infections, for which effective vaccines exist, should therefore be controlled. While vertical transmission appears to be the major route of infection in cattle, there is also a role for postnatal transmission, involving a definitive host. Presently, the control of dogs and their access to bovine tissues, particularly potentially infected placentae and other foetal tissues, appear to be the most prudent control methods. There are some indications that vaccination against N. caninum may aid in the prevention of abortions. Suggestions for control options are limited by our current lack of actual experiences with control strategies. Further practical fieldwork is needed in this area.

Sensitive and specific identification of Neospora caninum infection of cattle based on detection of serum antibodies to recombinant Ncp29

Neosporosis is an economically important disease of dairy cattle caused by the protozoan Neospora caninum. Diagnostic tests for neosporosis are complicated by the potential for cross-reaction of antibodies to antigens that are similar between N. caninum and closely related parasites Toxoplasma gondii and Sarcocystis cruzi. To provide a sensitive and specific assay for detecting antibodies to N. caninum in the serum of infected animals, we have investigated a recombinant form of the antigen known as Ncp29 (rNcp29), which is a major surface protein of the parasite. Ncp29 is encoded by a gene that is homologous to the SAG1 gene previously characterized from T. gondii. An enzyme-linked immunosorbent assay (ELISA) was used to screen animals for the presence of serum antibodies specific to rNcp29. The rNcp29 ELISA readily distinguished between cattle known to be infected with N. caninum (optical density [OD] > 1.2 at 1:500 or greater dilution) and negative controls (OD < 0.5 at 1:500). Additionally, sera from animals that were infected with T. gondii or S. cruzi were negative. The rNcp29 ELISA developed here provides a specific and sensitive assay for detecting neosporosis in cattle.

Evidence of point-source exposure to Neospora caninum and protective immunity in a herd of beef cows

OBJECTIVE

To determine whether cows with evidence of previous infection with Neospora caninum were less likely to abort or give birth prematurely during an outbreak of neosporosis, compared with herdmates with evidence of primary infection.

DESIGN

Cohort study.

ANIMALS

208 pregnant beef cows.

PROCEDURES

Aborted fetuses and calves born prematurely were examined during an outbreak of neosporosis in a herd of beef cows. Sera were collected from all cows during the outbreak and again 71 days later. Cows were classified into groups on the basis of normal and abnormal reproductive outcomes. Sera were examined, using an avidity ELISA procedure for N caninum, and results were compared between groups and among time points.

RESULTS

Antibody concentrations decreased significantly and IgG avidity values increased significantly over time. During the outbreak, cows with normal reproductive outcomes were significantly more likely to have high IgG avidity values than cows with abnormal reproductive outcomes.

CONCLUSIONS AND CLINICAL RELEVANCE

The herd had numerous abortions and premature births with evidence of recent point-source exposure to N caninum. Therefore, to reduce risk of transmission of N caninum to cattle, attempts should be made to prevent canine feces from contaminating feed, especially feedstuffs used to prepare mixed rations for cattle. Cows with evidence of previous exposure to N caninum were less likely to abort or give birth prematurely during the outbreak than cows with primary infections with N caninum; this finding suggests development of protective immunity in previously infected cows.

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.

A European perspective on Neospora caninum

Since the identification of Neospora caninum in 1984 as a parasite separate from Toxoplasma gondii by Bjerkas et al., and its subsequent characterization and classification in 1988 by Dubey and co-workers, this parasite has attracted increasing attention, primarily as an important causative agent of abortion in cattle and neuromuscular disease in dogs, but also as a complementary model system to T. gondii for investigating the basic biology of intracellular parasitism. During November 11-14, 1999, the COST 820 Annual meeting (Vaccines against coccidioses) took place in Interlaken, Switzerland. Almost half of the papers presented at that meeting were on N. caninum and neosporosis, reflecting the increasing awareness of the importance of this parasite on part of the scientific community in Europe. On the occasion of the meeting, participants in this COST Action involved in Neospora research in Europe were asked to participate in this invited review in order to document the growing interest in N. caninum and the disease it causes. Thus, this paper is a unique collection of contributions provided by several European experts in the field. It is comprised of 10 reviews or original papers on different aspects of Neospora research including epidemiology, immunology, application and development of serological tools, and molecular characterisation of the parasite currently carried out throughout Europe. In addition, two distinguished invited speakers from overseas (Milton McAllister and John Ellis) provided valuable contributions. This invited review demonstrates that the COST 820 Action has brought together scientists from all over Europe and other parts of the world, and has laid the basis for many fruitful collaborations. The studies described here will contribute in assessing the relevance of neosporosis as a potential risk factor not only for animals, but also for human health.

Serologic survey of Neospora caninum infection in a closed dairy cattle herd in Maryland: risk of serologic reactivity by production groups

Prevalence of antibodies to Neospora caninum was determined in a cross-sectional consensus survey of 1029 bovines in a dairy herd with endemic Neospora-induced abortion. Sera were screened by indirect fluorescent antibody test (IFAT). The prevalence of N. caninum antibody in the IFAT was 17.9% in 107 neonates, 26.2% in 233 yearling heifers and steers, 39.07% in 218 mature heifers, and 26.9% in 465 milking cows. Serologic reactivity was associated with production grouping on the farm with the greatest risk of serologic reactivity appearing in the yearling and mature heifers. There was an increasing risk of serologic reactivity with increasing age only in the parity one and greater animals in the herd. Castrated males were at half the risk of similarly aged females of possessing antibodies to N. caninum. There was no clear relationship between the serologic status of dams and offspring.

Neospora caninum seroprevalence and associated risk factors in beef cattle in the northwestern United States

A Neospora caninum seroprevalence and risk factor survey of 2585 cows was conducted in 55 beef cow-calf herds located in five northwestern states of the USA. Blood samples were collected by private veterinary practitioners and management practices were surveyed using a mail questionnaire. Producers were randomly selected from those that employed these veterinarians to perform annual herd pregnancy examinations. Questions were asked about animal management, grazing and feeding, immunization and record keeping practices. Blood was collected from a systematically selected sample of cows in each herd, and age, origin, and pregnancy status were recorded. Blood samples were analyzed for antibodies against N. caninum antigen using a monoclonal antibody-based competitive inhibition (CI) ELISA. Overall seroprevalence was 24% and within herd seroprevalence ranged from 3 to 67% with a median of 19%. Within herd seroprevalence and mean inhibition percentage were different between the five states. Herds that managed their cows on range for summer grazing had lower seroprevalence than those that did not, while increased seroprevalence was associated with higher winter stocking density. Cows less than 3 years of age had higher CI ELISA inhibition percent values than cows greater than 6 years of age. No relationship was noted between serologic status and individual cow origin (purchased or raised), or pregnancy status at the time of sampling.

Seroprevalence of Neospora caninum infection following an abortion outbreak in a dairy cattle herd

OBJECTIVE

To investigate the seroprevalence of Neospora caninum infection in a commercial dairy cattle herd, 15 months after detection of an abortion outbreak.

PROCEDURE

Sera from the whole herd (n = 266) were examined for N caninum antibodies by indirect fluorescent antibody test (IFAT) and immunoblot analysis. Herd records were reviewed to collate serological results with abortion history, proximity to calving, and pedigree data.

RESULTS

The seroprevalence of N caninum infection was 24% (63/266) for IFAT titre > or = 160, 29% (78/266) for immunoblot positive (+ve), and 31% (82/266) for IFAT > or = 160 and/or immunoblot +ve; 94% (59/63) of animals with IFAT > or = 160 were immunoblot +ve. The association between seropositivity (IFAT > or = 160 and/or immunoblot +ve) and history of abortion was highly significant (P < 0.001); the seroprevalence was 86% (18/21) in aborting cows, compared with 30% (50/164) in non-aborting animals. The abortion rate for seropositive cows was 26% (18/68) compared with 3% (3/117) for seronegative animals. IFAT titres of infected cows were higher within 2 months of calving than at other times (P < 0.001). The association between seropositivity in dams and daughters was highly significant (P = 0.009).

CONCLUSIONS

The abortions were associated with N caninum infection and there was evidence of reactivation of latent infection close to calving and congenital transmission of infection. Immunodominant antigens identified by immunoblots may prove useful for improved diagnostic tests.

Progress in the serodiagnosis of Neospora caninum infections of cattle

Neospora caninum is an apicomplexan protozoan that has become the focus of significant research attention worldwide. This organism infects a range of host species, including dogs, from which it was originally reported in 1984, but it is most important as a major cause of bovine abortion. As a result of the global importance of N. caninum, researchers have developed a number of serological tests to investigate the epidemiology of infection and disease. In this article, Robert Atkinson, Peter Harper, Michael Reichel and John Ellis consider progress made in the serodiagnosis of N. caninum.

Serological diagnosis of Neospora caninum infection

Since the first isolation of the apicomplexan parasite Neospora caninum, a range of serological assays have been developed for use in dogs, cattle and a variety of other potential host species. The tests include the indirect fluorescent antibody test, the direct agglutination test and different enzyme-linked immunosorbent assays. This article reviews the principles and properties of the available tests which are discussed in relation to different applications.

Bovine neosporosis: comparison of serological methods using outbreak sera from a dairy herd in New Zealand

Serological methods developed to detect Neospora caninum specific bovine antibodies were compared using sera from an abortion outbreak on a dairy farm in New Zealand. These methods included four ELISAs, IFAT and immunoblot. The abortions (n = 16) on the farm were restricted to one of two groups of the herd which consisted of 194 adult dairy cows. All ELISAs, IFAT and immunoblot (applying stringent cut-off levels) revealed a statistically significant association between seropositivity and abortion among the adult cows from the afflicted group 1. The strength of this association varied between different tests, and different seroprevalences were determined for various animal groups. Among the different ELISAs, the strength of the relationship between single test results was characterised by a considerable variation in the determinants of correlation. Discrepancies in positive-negative classification between the two commercial ELISAs and one of the in-house ELISAs were due mainly to differences in the cut-off selection.

Oral infection of calves with Neospora caninum oocysts from dogs: humoral and cellular immune responses

Neospora caninum has been identified as a major cause of abortion in cattle in a number of countries throughout the world. Until the recent demonstration that dogs can serve as a definitive host of this parasite, it was not possible to study the infection in cattle orally exposed to oocysts. The aim of this study was to investigate the potential of N. caninum oocysts to infect calves, and to define initial immune responses that arise after oral infection. Seven calves were fed approximately 10(4)-10(5) N. caninum oocysts, three calves served as uninfected controls. Before infection, all calves were serologically negative for anti-Neospora antibodies and the calves were non-reactive to Neospora antigen in an in vitro lymphocyte proliferation assay. Peripheral blood lymphocytes from inoculated calves were able to mount in vitro proliferative responses to crude N. caninum antigen extract as early as 1 week p.i. Within 2 and 4 weeks p.i., Neospora-specific IgG1 and IgG2 antibodies were detected by IFAT and ELISA in serum from infected calves but not from sham-infected calves. The continued presence of reactive cells in the blood, spleen and mesenteric, inguinal, bronchial lymph nodes was seen as late as 2.5 months p.i., and parasite DNA was detected in the brain and spinal cord of the infected animals by PCR, indicating that the cattle were infected by oral inoculation of N. caninum oocysts collected from dogs, and that the animals were systematically sensitised by parasite antigen.

Neospora caninum infections in bovine foetuses and dairy cows with abortions in Argentina

Antibodies to Neospora caninum were measured in bovine foetuses, dairy cows and beef cows in Argentina using the IFAT, the N. caninum agglutination test, and the recombinant NCDG1 and NCDG2 ELISA. Serum antibodies (IFAT titre 1:80) were found in 20 of 82 (24.4%) dairy cow foetuses and one of 22 (4.5%) beef cow foetuses. Microscopic lesions suggestive of neosporosis were seen in brains of seven of eight foetuses with IFAT titres of 1:80. Antibodies (IFAT) were found in 122 of 189 (64.5%) dairy cows that aborted. Serum antibody titres (IFAT) of 189 dairy cows that aborted were: < 1:25 (67 cows), 1:25 (four cows), 1:50 (16 cows), 1:200 (seven cows), 1:> or = 800 (95 cows). Of the 87 sera with IFAT titres of < or = 1:50, 57 had no antibodies in 1:40 dilution and 30 had titres of 1:40 in the N. caninum agglutination test. Thus, sera from at least 56 dairy cows which had aborted were seronegative both in the N. caninum agglutination test and the IFAT. The distribution of positive and negative sera was similar when measured by ELISA, except that, depending on cut-off titre, the ELISA indicated a greater number of seropositive cows that were negative by the IFAT and N. caninum agglutination test. These results suggest that transplacental transmission of N. caninum in dairy cows in Argentina is frequent.

Serum antibody profile and reproductive performance during two consecutive pregnancies of cows naturally infected with Neospora caninum

The objective of this study was to record how the antibody levels change over time during pregnancy in dairy cows naturally infected with the protozoan parasite Neospora caninum, and relate this to the reproductive performance. Eighteen cows with antibodies to N. caninum were serum sampled monthly during their first pregnancy and 13 of them were also followed for a second pregnancy. In all, five pregnancies ended in abortion and two in stillbirth. Antibodies to N. caninum in serum were demonstrated by immune stimulating complex enzyme-linked immunosorbent assay (iscom ELISA). The N. caninum antibody titres remained well above the 1:100 cut-off limit for the test used during 2 years in all cows. In the non-aborting cows, mean values of antibody titres to N. caninum rose 1.5-2.5 dilution steps to reach a plateau 4-5 months before parturition, and thereafter decreased from 2 months before parturition. These changes were statistically significant (p < 0.001). The same pattern was seen in the aborting cows. The consistent pattern of rise in antibody titres observed during both pregnancies in all cows indicated a reactivation rather than a reinfection of the parasite at mid-gestation.

Recent advances in Neospora and neosporosis

Neospora caninum has emerged as a major cause of abortion in cattle in many countries. This paper reviews recent advances in the life cycle and biology of Neospora with the emphasis on bovine neosporosis. The role of the recently discovered oocyst stage of N. caninum in the epidemiology of neosporosis is discussed. Progress made in serologic diagnosis of N. caninum infection is discussed. There is no vaccine for preventing Neospora-induced abortions in cattle or to prevent oocyst shedding in dogs.