Detection of Neospora caninum in the semen and blood of naturally infected bulls

Assessment of Neospora caninum infection in bulls using serological and molecular techniques

Neospora caninum is a significant cause of abortion and economic losses in cattle worldwide. The main aim of the present work was to detect the prevalence of N. caninum infection in bulls in Hamedan (Iran) using serology and molecular techniques. All blood samples (n = 792) were screened for detecting the antibodies to N. caninum using enzyme-linked immunosorbent assay (ELISA). Then seropositive animals were rechecked using the immunofluorescent antibody test (IFAT). Also, blood, epididymis, and spinal cord samples were collected from animals for molecular analysis using nested PCR. In serology, using ELISA, 3.91% of animals were seropositive for N. caninum. Additionally, true prevalence based on the sensitivity and specificity of the ELISA was calculated 1.25% (95% CI: 0.48-2.02%). Neospora-infection in animals, calculated as the number of bulls seropositive and/or one sample positive to nested PCR, was 3.40%; and 19 bulls tested positive by both serology and molecular diagnostic methods. The overlaps between ELISA and molecular results were observed in 74.19% of whole blood samples, 80.64% of the epididymis, and 87.09% of the spinal cord. Using ELISA, the seroprevalence of N. caninum was detected 1.8% in ≤2 and 5.45% in >2 years old group of animals (p = 0.009, PR = 3.1). In addition, the seropositivity in Holstein and native breed animals was calculated 6.57% and 2.93%, respectively (p = 0.019, PR = 2.3). Seven sequences with 94.9-99.3% similarity were detected in multiple alignments of positive PCR products. Our work was the first comprehensive evaluation of Neospora-infection/neosporosis in Iranian bulls. We detected a low prevalence of infection in animals compared to previous reports. The ELISA is a sensitive serological technique for detecting the highest number of positive bulls in the present investigation and, the nested PCR is a reliable technique to identify Neospora-DNA.

Neospora caninum and Toxoplasma gondii infections in one-humped camels (Camelus dromedarius) in central desert of Iran

The protozoan parasite Neospora caninum infects carnivores as definitive and a wide range of mammals as intermediate hosts. This parasite is regarded as an important cause of abortion in cattle worldwide, causing significant economic losses. Although there is serological evidence of infection in Old World camelids, the significance of N. caninum in these animal species is still poorly understood. The aim of this study was to use molecular and histological methods to detect N. caninum in the blood and tissues of 100 slaughtered one-humped camels (Camelus dromedarius) in Iran. For this, genomic DNA was extracted from blood, brain, portal lymph node and liver of the camels, and nested-PCR assay followed by sequencing were performed. Besides, paraffin-embedded tissue sections were stained with hematoxylin and eosin (H&E) and studied microscopically. In addition, immunohistochemical staining for N. caninum was attempted on brain samples with positive PCR results. All animals were tested for antibodies against N. caninum and Toxoplasma gondii by whole tachyzoite-agglutination tests. N. caninum DNA was detected in blood, brain, and portal lymph node, but not in the liver of two (2%) camels. Histopathological examination revealed cysts resembling N. caninum in brain samples of one of these camels; however, immunohistochemical staining for N. caninum and T. gondii did not allow a morphological identification. IgG antibodies to N. caninum and T. gondii were detected in 36% and 35% of the camels, respectively. This study provides the first insight into direct detection of N. caninum in C. dromedarius in Iran. Further molecular studies on aborted fetuses, stillborn animals and cases of perinatal mortality are needed to understand the possible involvement of N. caninum in cases of reproductive failure. As the definitive hosts of N. caninum are domestic and wild canids, producers should be advised to monitor and limit exposure of their camelids to these species and their feces.

Parasitemia and Associated Immune Response in Pregnant and Non-Pregnant Beef Cows Naturally Infected With Neospora caninum

The aim of this longitudinal study was to characterize the parasitemia of Neospora caninum and the associated immunological parameters in naturally infected beef cows for 10 months. The following groups were established: Neospora caninum seropositive pregnant cows (+Preg, n = 7), seropositive non-pregnant cows (+Npreg, n = 7), seronegative pregnant cows (−Preg, n = 4), and seronegative non-pregnant cows (−Npreg, n = 4). Several samples were obtained for absolute and relative leukocyte counting, cytokines IL-10, IL-12, α-TNF, and γ-IFN quantification, specific IgG, IgG1, and IgG2 and avidity and N. caninum DNA molecular detection and quantification. The +Preg group had a higher frequency and concentration of N. caninum DNA in PBMC in the last third of pregnancy compared to +Npreg (p <0.05), with 22 and 8% of detection, respectively. Parasitemia correlated positively with IgG titers and negatively with IgG1/IgG2 ratio (p <0.05). On day 222 of the assay, the +Preg group had the lowest total leukocyte counting (p <0.05). The +Preg group had a higher concentration of IgG and higher avidity in the last third of gestation compared to +Npreg (p <0.05). Avidity correlated with total IgG and IgG2 (p <0.05). All +Preg cows gave birth to clinically healthy but seropositive calves before colostrum intake, therefore, the congenital transmission was 100% efficient. Only a complete N. caninum genotype from a placenta and a partial genotype from cow #3 of the group +Preg were achieved by multilocus microsatellite analysis. Overall, N. caninum parasitemia is frequent in seropositive beef cows during the last third of gestation. This correlates with higher antibody levels and a decrease in total leukocyte counting. The precise timing of the parasitemia may be used for diagnosis purposes and/or for design strategies to avoid vertical transmission. Further studies are needed to identify the immune molecular mechanisms that favor parasitemia during gestation in chronically infected cattle.

Molecular identification of Neospora caninum and co-infection with Toxoplasma gondii in genital apparatus of naturally infected cows in North Tunisia

The aim of this study was to estimate the molecular prevalence of Toxoplasma gondii, Neospora caninum and the co-infection by both Apicomplexan parasites in uterus tissues of cows. PCR was used to detect T. gondii and N. caninum DNA in uterus from 140 uteri of slaughtered cows in the regional slaughterhouse of Béja (Northwest Tunisia). Positive PCR products were sequenced and used for the phylogenetic analysis. The overall molecular prevalence of T. gondii and N. caninum in cows' uterus was 5 and 15.57%, respectively. Co-infection prevalence by the two parasites was estimated to be 2.85%. Risk factors including the age categories significantly affected the molecular prevalence of T. gondii and N. caninum in cows' uterus. The highest molecular prevalence of T. gondii (11.5 ± 3.1) and N. caninum (21.1 ± 11.1; p = 0.038) was observed in cows aged of more than 8 years. There were no differences depicted according to cow's breeds and localities. Comparison of the partial sequences of the ITS1 gene revealed 100% similarity among our N. caninum sequence (MW136256) and those deposited in GenBank. The T. gondii sequence described in this study (MW260335) was 99.4-100% homologous to T. gondii sequences published in the GenBank.To the best of our knowledge, this is the first molecular evidence of N. caninum and T. gondii co-infection in naturally infected cows in North Africa. This information is pertinent in designing control programmes that would reduce economic losses in the livestock industry.

Neosporosis in bulls: potential for venereal transmission, and effect on semen quality and production

Neospora caninum caninum is a protozoan parasite that can cause abortions, birth of congenitally infected calves, and reduced milk production in cattle. Neosporosis in cattle can be transmitted through vertical transplacental transmission from dam to calf, or through horizontal transmission between animals. While it is well established that horizontal transmission from dogs (the definitive host) to cattle (an intermediate host) occurs, it is not clear whether horizontal transmission may occur between cows and bulls during mating. Transmission via infected semen of seropositive bulls was suggested when N. caninum DNA was found in bull semen. The primary objective of this article is to critically evaluate the evidence for venereal transmission of N. caninum between cattle, to determine whether this transmission route is likely to occur. A secondary objective is to review and evaluate published evidence for whether neosporosis in bulls may affect semen quality and production. N. caninum DNA can be detected by PCR in occasional batches of semen straws from bulls that are seropositive for N. caninum. Insemination of heifers with semen experimentally infected with 5 × 10⁴ N. caninum tachyzoites has caused persistent seroconversion in some animals. However, the highest concentration of parasites in the semen of naturally infected bulls was estimated, using quantitative PCR, as 10 tachyzoites. Thus it appears that, whether used for natural or artificial insemination, the semen of bulls naturally infected with N. caninum, does not contain the necessary intrauterine dose of tachyzoites to cause persistent seroconversion in a heifer or cow. Thus, based on the available evidence, the venereal transmission of N. caninum via bull semen is extremely unlikely. Nevertheless, neosporosis in bulls may influence semen quality and production. Epididymal semen concentration, viability, and motility appeared "to be" significantly decreased in N. caninum-seropositive bulls compared to seronegative bulls. Furthermore, semen production could be altered if neosporosis affects the thyroid gland. The thyroid hormones such as triiodothyronine and thyroxine (T4) may affect testicular development. Significantly lower concentrations of T4 were observed in the blood of N. caninum-seropositive, compared with those of seronegative bulls. Longitudinal studies are needed to confirm the long-term effect and significance of neosporosis on semen quality and thyroid hormone concentrations in bulls.

Neospora caninum Natural Infection in Tunisian Rams: Serological Study and Molecular Identification of Infection in Semen

PURPOSE

The aim of this study was to estimate the seroprevalence and molecular prevalence and perform a molecular identification of Neospora caninum in semen of Tunisian rams.

METHODS

A total of 92 blood samples were collected from four farms located in four Tunisian governorates (Jendouba, Kairouan, Zaghouan and Ben Arous) and samples were screened with a commercial ELISA kit for N. caninum antibodies. For the same rams, semen samples were collected and tested for the presence of N. caninum ITS1 gene using PCR. Five amplicons were randomly selected for sequencing. A phylogenetic tree was constructed to compare the partial sequences of the ITS1 gene with sequences deposited in GenBank.

RESULTS

The seroprevalence of N. caninum infection was 25% (23/92) and PCR revealed that the molecular infection prevalence in semen was 11.95% (11/92). Kappa test showed an average agreement between seroprevalence and parasite prevalence in semen (κ = 0.44). The highest molecular prevalence was for rams that accomplished more than two mating seasons (21.0 ± 12.1%) compared to those performed less than two mating seasons and yearling individuals (4.0 ± 5.5%) (P = 0.01). There were no differences in N. caninum molecular prevalence according to either breed or locality. Comparison of the partial sequences of the ITS1 gene revealed 99-100% similarity with those deposited in GenBank.

CONCLUSION

To the best of our knowledge, this is the first detection and molecular identification of N. caninum in semen from rams in North Africa. Our findings indicate that N. caninum infection rate was high in rams.

An investigation of the concurrency of anti-Neospora antibody and parasitemia in water buffalo (Bubalus bubalis) in northwest of Iran

Neospora caninum is an obligate intracellular parasite causing abortion and reproductive failure in ruminants. Here, the seroprevalence of Neospora DNA and anti-Neospora antibodies and the correlation between the DNA and the antibody using polymerase chain reaction (PCR) and a new developed whole cell-based enzyme-linked immunosorbent assay (ELISA) in water buffalo (Bubalus bubalis) were investigated. To determine the level of anti-Neospora antibody, 83 serum samples were collected from buffaloes in the northwest of Iran. Plates were coated with 2 × 10⁶ whole Neospora tachyzoites and the anti-Neospora antibody level was determined by calculating the ratio of sample/positive control (S/P) optical densities (ODs) in the ELISA. All samples with the ration of 0.50 or above were accounted as positive. To confirm the presence of Neospora DNA, the serum samples were directly subjected to PCR and nested PCR for detection of Neospora NC5 gene without the DNA isolation process. A total number of 83 buffalo serum samples were examined for the presence of anti-N. caninum immunoglobulin G and Neospora DNA. All samples with the S/P ratio of 0.50 or above (16 samples, 19.27%) were also positive for Neospora DNA. All samples with OD less than 0.50 (34 samples, 40.96%) were negative for Neospora DNA. However, 33 samples with the S/P ratio of bellow 0.50 (39.75%) showed a significant level of antibody. A 100% correlation was observed between high levels of the anti-Neospora antibody and Neospora DNA in the serum of water buffalo, and the whole N. caninum tachyzoites have the potency to be used as antigens for detection of the parasite in ELISA.

Development of a loop-mediated isothermal amplification technique and comparison with quantitative real-time PCR for the rapid visual detection of canine neosporosis

Background

Dogs are the definitive hosts of Neospora caninum and play an important role in the transmission of the parasite. Despite the high sensitivity of existing molecular tools such as quantitative real-time PCR (qPCR), these techniques are not suitable for use in many countries because of equipment costs and difficulties in implementing them for field diagnostics. Therefore, we developed a simplified technique, loop-mediated isothermal amplification (LAMP), for the rapid visual detection of N. caninum.

Methods

LAMP specificity was evaluated using a panel containing DNA from a range of different organisms. Sensitivity was evaluated by preparing 10-fold serial dilutions of N. caninum tachyzoites and comparing the results with those obtained using qPCR. Assessment of the LAMP results was determined by recognition of a colour change after amplification. The usefulness of the LAMP assay in the field was tested on 396 blood and 115 faecal samples from dogs, and one placenta from a heifer collected in Lopburi, Nakhon Pathom, Sa Kaeo, and Ratchaburi provinces, Thailand.

Results

Specificity of the LAMP technique was shown by its inability to amplify DNA from non-target pathogens or healthy dogs. The detection limit was the equivalent of one genome for both LAMP and qPCR. LAMP and qPCR detected positive N. caninum infection in 15 of 396 (3.8%) blood samples; LAMP detected 9/115 (7.8%) positive faecal samples, while qPCR detected 5/115 (4.3%) positive faecal samples. The placental tissue was shown to be positive by both techniques. Agreement between LAMP and qPCR was perfect in blood samples (kappa value, 1.00) and substantial in faecal samples (kappa value, 0.697).

Conclusions

This is the first known LAMP assay developed for the amplification of N. caninum. The technique effectively and rapidly detected the parasite with high sensitivity and specificity and was cost-effective. This assay could be used in the field to confirm the diagnosis of canine or bovine neosporosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2330-2) contains supplementary material, which is available to authorized users.

No detection of Besnoitia besnoiti DNA in the semen of chronically infected bulls

Bovine besnoitiosis is a chronic and debilitating disease observed in many European countries that may cause important economic losses in cattle. The recent widespread of the parasite in Europe had led the European Food Safety Authority to declare bovine besnoitiosis as a re-emerging disease in Europe. Many aspects of the epidemiology of bovine besnoitiosis such as the main routes of transmission are still unclear and need to be further studied. Among the different hypotheses, a sexual transmission has not yet been investigated. Therefore, the aim of this study was to evaluate the presence of Besnoitia besnoiti DNA in the semen of naturally infected bulls by using a highly sensitive method (real-time qPCR). Both pre-sperm and sperm fractions of 40 bulls, including seronegative (n = 11), seropositive subclinically (n = 17), and seropositive clinically (n = 12) infected animals, were collected by electroejaculation and analyzed by real-time qPCR. No B. besnoiti DNA was detected in 27 pre-sperm and 28 sperm fractions of the 40 examined bulls, suggesting that the transmission of B. besnoiti infection by the semen of chronically infected bulls is very unlikely.

Effect of vaccination of cattle with the low virulence Nc-Spain 1H isolate of Neospora caninum against a heterologous challenge in early and mid-gestation

Live vaccines have emerged as one of the most potentially cost-effective measures for the control of bovine neosporosis. Previous studies have shown that Nc-Spain 1H is a naturally attenuated isolate of Neospora caninum and that immunisation with live Nc-Spain 1H tachyzoites generated a protective immune response in mice. The aim of this study was to evaluate the safety and efficacy of immunisation in cattle. N. caninum-seronegative heifers were immunised subcutaneously twice with 10⁷ live Nc-Spain 1H tachyzoites prior to artificial insemination. No adverse reactions or negative effects on reproductive parameters were recorded following immunisation. In immunised and non-challenged heifers, no foetal deaths were observed, and none of the calves was congenitally infected. The efficacy against N. caninum-associated foetal death and vertical transmission was determined after challenge with high doses of the Nc-1 isolate at 70 and 135 days of gestation, respectively. After the challenge in early gestation, the immunisation induced a protection of 50% against foetal death. In addition, the microsatellite analysis performed in PCR-positive tissue samples from foetuses that died after challenge infection showed that the profiles corresponded to the challenge isolate Nc-1. A degree of protection against vertical transmission was observed after challenge at mid-gestation; calves from immunised heifers showed significantly lower pre-colostral Neospora-specific antibody titres than calves from the non-immunised/challenge group (P < 0.05). Strong antibody and interferon gamma responses were induced in the immunised heifers. This study indicates that the immunisation before pregnancy with the Nc-Spain 1H vaccine isolate appeared to be safe and reduced the occurrence of N. caninum-associated abortion and vertical transmission in experimentally infected cattle. In light of these encouraging results, the next step for testing this live attenuated candidate should be the assessment of its efficacy and safety in naturally infected cattle.

Detection ofNeospora caninumin aborted bovine fetuses and dam blood samples by nested PCR and ELISA and seroprevalence in Beijing and Tianjin, China

Neospora caninuminfection is a significant cause of abortion in cattle. We investigated the tissue distribution ofN. caninumin aborted bovine fetuses and dam blood samples by a nested PCR assay, and compared the nested PCR with ELISA in the diagnosis ofN. caninuminfection. In total, 26 aborted fetuses and 813 blood samples were collected from 8 dairy herds in Beijing (n=212) and Tianjin (n=601), China. Fifteen fetuses (57·7%) were testedN. caninum-positive by the nested PCR.N. caninumDNA was detected from the brain of 52%, kidneys of 22%, skeletal muscle of 18%, and heart of 4% of the aborted fetuses. The PCR-positive cases (55%, 11/20) were higher than seropositive cows (40%, 8/20) in a subset of 20 fetuses, but the PCR results of blood samples of the 20 cows were all negative. The seroprevalence of the 813 samples was 15·5% (43·4% of samples from Beijing, 5·7% of samples from Tianjin), compared to the PCR-positive blood samples of 0·9%. Our study showed that the nested PCR is a valuable diagnostic tool for the primary diagnosis ofN. caninumin aborted fetuses, while ELISA is the preferred assay for testing blood samples collected from cows. The two assays are complementary in determining whether abortions are associated withN. caninuminfection in cattle.

Experimental infection with a low virulence isolate of Neospora caninum at 70 days gestation in cattle did not result in foetopathy

The Nc-Spain 1H isolate of Neospora caninum, which was newly obtained from the brain of a congenitally asymptomatic infected calf, demonstrated a reduced in vitro tachyzoite yield and viability rate, as well as low virulence in mouse models. The objective of the present study was to determine the ability of this isolate to induce foetal death in a pregnant bovine model. For this purpose, 13 naïve pregnant heifers were divided into three groups and were experimentally challenged with either 10⁷ tachyzoites of Nc-1 (group 1, n = 5), Nc-Spain 1H (group 2, n = 5) isolates or phosphate-buffered saline (group 3, n = 3) intravenously at 70 days of gestation. After inoculation, pregnancy was monitored and dams were sacrificed when foetal death was detected. The remaining animals were slaughtered at 45 days post-infection. Maternal and foetal samples were collected for examination by histology and parasite DNA detection. Parasitaemia, specific anti-N. caninum IgG and interferon γ responses were also studied. At 3–4 weeks after infection, foetal death was detected in 3 out of 5 Nc-1-infected dams. However, no evidence of foetal death was observed in either Nc-Spain 1H-infected or control groups during the period studied. The most severe histopathological lesions were observed in the placenta and foetal organs from Nc-1-infected cattle that exhibited foetal death. It was in these animals that N. caninum DNA was more frequently detected. Parasitaemia was observed in all Nc-1-infected dams and in only 3 out of 5 Nc-Spain 1H-infected animals. The magnitude of the immune response was significantly higher in the Nc-1-inoculated group than in the group inoculated with the Nc-Spain 1H isolate. These data reveal the reduced virulence of the Nc-Spain 1H isolate in cattle.

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

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

Quantitative analysis of parasite DNA in the blood of immunized and naïve mice after infection with Neospora caninum

Real-time PCR was used to study the duration and level of parasitaemia in mice immunized with immune-stimulating complexes (iscoms) containing recombinant NcSRS2, one of the immunodominant surface antigens of Neospora caninum. After challenge infection, blood was collected daily for 9 days. During this period the amounts of parasite DNA detected in immunized mice were significantly lower (P<0.001), and the duration of parasitaemia appeared to be shorter, than in non-immunized controls. Furthermore, the degree of parasitaemia seemed to correlate well with the amount of N. caninum DNA in the brain 3 weeks post-inoculation and with disease severity measured as changes in body weight. These results indicate that the protective immunity induced by the NcSRS2-iscoms was sufficient to reduce the level of parasitaemia, which probably reduced the number of parasites reaching the brain, and could be the reason for the reduction in brain parasite load and clinical symptoms. Furthermore, real-time PCR was found to be a sensitive means for rapid assessment of N. caninum in blood.

Experimental neosporosis in bulls: Parasite detection in semen and blood and specific antibody and interferon-gamma responses

AIM

To investigate the presence of Neospora caninum in semen and blood, and the development of specific antibody and interferon-gamma (IFN-gamma) responses in experimentally infected bulls.

METHODS

Eight bulls were intravenously infected with 10(8) live N. caninum tachyzoites of NC-1 isolate. The presence of N. caninum in semen and blood was assessed using a nested-PCR procedure. PCR-positive semen samples were bioassayed using a BALB/c nu/nu mouse model. Specific anti-N. caninum antibody and IFN-gamma responses were also examined. In parallel, eight seronegative bulls were studied as non-infected controls. All bulls were monitored for 26 weeks.

RESULTS

All eight experimentally infected bulls showed N. caninum DNA in their semen and/or blood samples at some time during the course of the study. Parasite load in semen ranged from 0.1 to 14.5 parasites/ml (mean 6.0). N. caninum could not be detected in BALB/c nu/nu mice inoculated with PCR-positive semen samples. A significant increase in mean serum specific IgM antibody response to N. caninum was detected between 10 and 28 days post-infection (p.i.). Serum specific IgG, IgG1, and IgG2 antibody levels in experimentally infected bulls were significantly different after 21, 10, and 14 days p.i. as compared to controls, respectively. Specific anti-N. caninum IgG were detected in seminal plasma from infected bulls and values obtained were different from controls after 25 days p.i. Mean specific IFN-gamma responses in experimentally infected bulls were significantly higher than controls 3 days p.i.

CONCLUSIONS

This is the first study to report the presence of N. caninum DNA in the semen and blood of experimentally infected bulls. Our observations indicate an intermittent presence of N. caninum in low numbers in semen and associated with chronic stage of the infection. This study is also the first to report the detection of anti-N. caninum IgG in seminal plasma of experimentally infected bulls.

Epidemiology and control of neosporosis and Neospora caninum

Neospora caninum is a protozoan parasite of animals. Until 1988, it was misidentified as Toxoplasma gondii. Since its first recognition in dogs in 1984 and the description of the new genus and species Neospora caninum in 1988, neosporosis has emerged as a serious disease of cattle and dogs worldwide. Abortions and neonatal mortality are a major problem in livestock operations, and neosporosis is a major cause of abortion in cattle. Although antibodies to N. caninum have been reported, the parasite has not been detected in human tissues. Thus, the zoonotic potential is uncertain. This review is focused mainly on the epidemiology and control of neosporosis in cattle, but worldwide seroprevalences of N. caninum in animals and humans are tabulated. The role of wildlife in the life cycle of N. caninum and strategies for the control of neosporosis in cattle are discussed.

Intrauterine Neospora caninum inoculation of heifers and cows using contaminated semen with different numbers of tachyzoites

OBJECTIVE

To investigate the potential of different Neospora caninum tachyzoite doses to infect heifers (experiment 1) and cows (experiment 2) when administered in utero by artificial insemination via contaminated semen.

METHODS

In experiment 1, five groups of 5, 7, 8, 9, and 5 cyclic heifers were hormonally synchronized and artificially inseminated with semen containing 0 (A, controls), 10(2) (B), 5 x 10(3) (C), 5 x 10(4) (D), and 5 x 10(5) (E) live N. caninum NC-1 isolate-tachyzoites, respectively. Experimental infection was followed for 100 days. Parasitaemia and specific serum IgG, and interferon-gamma (IFN-gamma) responses were studied. In experiment 2, four groups of 9, 10, 9, and 9 adult multiparous cows with confirmed infertility problems of diverse aethiology were hormonally synchronized and artificially inseminated with semen containing 0 (a, controls), 10(2) (b), 5 x 10(3) (c), and 5 x 10(5) (d) live N. caninum NC-1 isolate-tachyzoites, respectively. Experimental infection was followed for 63 days. Parasitaemia and specific serum IgG responses were studied.

RESULTS

In experiment 1, parasitaemia was detected in 1, 2, and 3 heifers from groups B, C, and D, respectively, between 9 and 23 days after insemination. Persistent specific serum antibody responses were detected in 2 and 3 heifers from groups D and E, respectively. Transient specific serum antibody responses were detected in 2, 1 and 1 heifers from groups C, D, and E, respectively. In addition, 1 heifer from group B showed a serum-specific antibody level higher than cut off value at 21 days post-insemination. Heifers seroconverted between 23 and 47 days after insemination. Specific IFN-gamma levels were detected in 1, 4, 6, and 3 heifers from groups B, C, D, and E, respectively, between 9 and 55 days after insemination. Pregnancy rate in the control group (60%) was higher than those observed in inoculated heifers (0-42.9%). Pregnancy rates in inoculated heifers were lower when the tachyzoite dose was increased (B 42.9%, C 12.5%, D 11.1%, and E 0%). In experiment 2, no Neospora DNA in blood nor specific serum IgG to N. caninum were detected in any of the cows studied, except in one cow inoculated with 5 x 10(5) tachyzoites (group d) which showed a relative index x100 (RIPC) values of 9.4, 18.9, and 18.1 at 42, 56, and 63 days after insemination, respectively.

CONCLUSIONS

This study provides evidence that the intrauterine infection via contaminated semen using 5 x 10(4) and 5 x 10(5) tachyzoites caused persistent serum-specific antibody responses in some heifers. On the basis of serological data, a dose-response effect was also observed. In addition, N. caninum would be a probable cause of early foetal death in inoculated heifers. In contrast, results obtained in a similar experiment with cows showing confirmed infertility indicate that higher doses, such as of 5 x 10(5) tachyzoites, were necessary to induce seroconversion in at least one animal.

Neospora caninum detected in feral rodents

The role of rodents in the epidemiology of neosporosis was investigated by assaying brain tissue of feral mice (Mus musculus) and rats (Rattus norvegicus) for Neospora caninum. Both mouse and rat brain tissue were extracted for total DNA, and subjected to two different N. caninum-specific nested polymerase chain reaction (PCR) assays. A portion of brain tissue from the mice and rats were also assayed for N. caninum in gerbils or gamma-interferon gene knockout (KO) mice. Of the 105 feral mice tested, 10% were positive in the N. caninum-specific PCR assays. Of the 242 rats tested, 30% were positive in both assays. Although mice and rats had N. caninum by PCR testing, clinical signs of N. caninum infection were not observed nor were N. caninum parasites observed in gerbils or KO mice inoculated with the rodent brain tissue.

Simulating the impact of four control strategies on the population dynamics of Neospora caninum infection in Swiss dairy cattle

A dynamic deterministic simulation model was developed to assess the impact of different putative control strategies on the seroprevalence of Neospora caninum in female Swiss dairy cattle. The model structure comprised compartments of "susceptible" and "infected" animals (SI-model) and the cattle population was divided into 12 age classes. A reference model (Model 1) was developed to simulate the current (status quo) situation (present seroprevalence in Switzerland 12%), taking into account available demographic and seroprevalence data of Switzerland. Model 1 was modified to represent four putative control strategies: testing and culling of seropositive animals (Model 2), discontinued breeding with offspring from seropositive cows (Model 3), chemotherapeutic treatment of calves from seropositive cows (Model 4), and vaccination of susceptible and infected animals (Model 5). Models 2-4 considered different sub-scenarios with regard to the frequency of diagnostic testing. Multivariable Monte Carlo sensitivity analysis was used to assess the impact of uncertainty in input parameters. A policy of annual testing and culling of all seropositive cattle in the population reduced the seroprevalence effectively and rapidly from 12% to <1% in the first year of simulation. The control strategies with discontinued breeding with offspring from all seropositive cows, chemotherapy of calves and vaccination of all cattle reduced the prevalence more slowly than culling but were still very effective (reduction of prevalence below 2% within 11, 23 and 3 years of simulation, respectively). However, sensitivity analyses revealed that the effectiveness of these strategies depended strongly on the quality of the input parameters used, such as the horizontal and vertical transmission factors, the sensitivity of the diagnostic test and the efficacy of medication and vaccination. Finally, all models confirmed that it was not possible to completely eradicate N. caninum as long as the horizontal transmission process was not interrupted.

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.

Neosporosis in dairy cattle: An update from an epidemiological perspective

Our understanding of the epidemiology of bovine neosporosis is advancing rapidly with considerable research activity being facilitated by improving methods. The dynamics of the infection in the known definitive hosts, the dog and the coyote, are being described. Improved procedures for production of oocysts enables the horizontal transmission to intermediate hosts and the subsequent more natural infection process to be studied. Details of the sylvatic cycles, potentially involving other animals in the dairy environment, are also emerging.

Pathogenesis of bovine neosporosis

The protozoan parasite Neospora caninum is a major pathogen of cattle and dogs, being a significant cause of abortion in cattle in many countries. It is one of the most efficiently transmitted parasites, with up to 90% of cattle infected in some herds. The pathogenesis of abortion due to Neospora is complex and only partially understood. Losses occur after a primary infection during pregnancy but more commonly as the result of recrudescence of a persistent infection during pregnancy. Parasitaemia is followed by invasion of the placenta and fetus. It is suggested that abortion occurs when primary parasite-induced placental damage jeopardises fetal survival directly or causes release of maternal prostaglandins that in turn cause luteolysis and abortion. Fetal damage may also occur due to primary tissue damage caused by the multiplication of N. caninum in the fetus or due to insufficient oxygen/nutrition, secondary to placental damage. In addition, maternal immune expulsion of the fetus may occur associated with maternal placental inflammation and the release of maternal pro-inflammatory cytokines in the placenta. Thus N. caninum is a primary pathogen capable of causing abortion either through maternal placental inflammation, maternal and fetal placental necrosis, fetal damage, or a combination of all three. The question of how N. caninum kills the fetus exposes the complex and finely balanced biological processes that have evolved to permit bovine and other mammalian pregnancies to occur. Defining these immunological mechanisms will shed light on potential methods of control of bovine neosporosis and enrich our understanding of the continuity of mammalian and protozoal survival.

Artificial insemination of cows with semen in vitro contaminated with Neospora caninum tachyzoites failed to induce neosporosis

Neosporosis is a major cause of abortion in cattle all over the world. Congenital transmission as well as horizontal transmission by ingestion of oocysts has been described. The detection of Neospora caninum DNA in bull semen warrants the investigation of possible transmission through the use of contaminated semen. In this experiment four cows were artificially inseminated with frozen-thawed semen contaminated in vitro with viable N. caninum tachyzoites (group A) and four control cows were inseminated with tachyzoites-free frozen-thawed semen, from the same bull (group B). Serum samples were collected 15 days before the artificial insemination (AI) and at days 10, 14, 21, 28, 45, 60 and 75 post-insemination. All sera samples were tested for neosporosis by direct agglutination test (DAT). Three of the cows from group A had negative DAT titers (< or =1:20) in all of the samples, while the fourth cow from this group had a low titer of antibodies (1:80) at day 10, and became negative at day 45, suggesting a stimulation of the immune system by the tachyzoites placed in uterus, rather than the induction of an infection. All of the cows from group B had negative DAT titers (< or =1:20) in all of the samples. These results suggest that transmission of neosporosis by artificial insemination with frozen-thawed semen is an unlikely event.

Diagnosis of bovine neosporosis: Recent advances and perspectives

Neospora caninum is considered a major cause of abortion in cattle. Appropriate techniques for diagnosis of bovine neosporosis, both in vivo and in aborted foetuses, have been developed in the last ten years and some of them are commercially available. For diagnosis in live animals, detection of antibodies in serum or milk has been shown to be the best option both at the herd and the individual level. These techniques are excellent tools to examine N. caninum-associated abortion problems and to adopt some basic herd-control measures. Concerning foetal diagnosis, detection of compatible lesions by histological examination and parasites by PCR in brain (as well as heart and liver) are the best choices. Diagnostic criteria to distinguish foetal infection and Neospora-associated abortion are based not only on the demonstration of the parasite in the foetus but also on the extent and severity of the lesions in the foetus, foetal age and the assessment of neosporosis at the herd level. In the near future, new tools to diagnose infection should help to detect animals with parasite reactivation by testing the immune response to stage-specific antigens and lead to the development of molecular typing methods to characterise different parasite isolates. Finally, uniform diagnostic procedures need to be established between laboratories and countries in order to standardise result interpretation. The role of National or Regional Reference Laboratories is essential in countries or regions where control programmes for the disease are being developed.

Intrauterine Neospora caninum inoculation of heifers

Here, we studied the potential of Neospora caninum tachyzoites to infect heifers when administered in utero by artificial insemination via contaminated semen. Eighteen primiparous cyclic heifers were hormonally synchronized and artificially inseminated. Nine of them, which were inseminated with semen containing 10(7) live N. caninum NC-1 isolate-tachyzoites, reacted with seroconversion and a specific IFN-gamma response. Moreover, N. caninum DNA was demonstrated by a nested-PCR in the blood of all nine heifers and in brain, lungs, liver and uterine horn of several of them. In contrast, nine heifers inseminated with tachyzoite-free semen developed no antibody or IFN-gamma responses, and no parasite DNA was detected in blood or organs. At necropsy, viable embryos were detected in one and six of the infected and non-infected heifers, respectively. No specific Neospora DNA was detected in any of the embryos. This study provides evidence that intrauterine inoculation via contaminated semen cause N. caninum infection in cattle.