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

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.

Neospora caninum infection in aborting bovines and lost fetuses: A systematic review and meta-analysis

Background

Neospora caninum (N. caninum) is known to be a major cause of reproductive failure in cattle herds around the world. Therefore, the current comprehensive study was performed to estimate the global prevalence of N. caninum infection in bovines that had an abortion and aborted fetuses.

Methods

In this study, PubMed, ScienceDirect, Web of Science, Scopus, and ProQuest databases were systematically searched for relevant studies up until November 4, 2021. Pooled prevalence and corresponding 95% confidence intervals (CI) were estimated using a random effect model. Other analyzes performed on the data of this study include sensitivity analysis, publication bias test, and quality assessment.

Results

The final analyses included 71 studies conducted on 2965 abortive cattle and 4805 aborted fetuses. The overall prevalence rates of N. caninum infection in bovines that had an abortion were 47% and 1% using serological and molecular methods. Furthermore, overall prevalence rates of N. caninum infection in bovine aborted fetuses globally were 35% (95% CI: 8%–62%) and 43% (95% CI: 35%–52%) using serological and molecular methods.

Conclusions

The results of this study showed the high prevalence of N. caninum infection in bovines that had an abortion and aborted fetuses. It is hoped that the results of this study will help prevent abortion in bovines around the world and encourage further studies to determine the impact of this parasite on the occurrence of abortion that may help reduce the economic damage caused by abortion worldwide.

Research into Neospora caninum-What Have We Learnt in the Last Thirty Years?

BACKGROUND

Neospora caninum has been recognised world-wide, first as a disease of dogs, then as an important cause of abortions in cattle for the past thirty years. Over that time period, there have been improvements in the diagnosis of infection and abortion, new tests have been developed and validated, and it is timely to review progress to date.

METHODS

Bibliometric methods were used to identify major trends and research topics present in the published literature on N. caninum. The tools used were SWIFT-Review, VOSviewer and SciMAT, along with the published papers found in the MEDLINE, Dimensions and Web of Science databases. A systematic review of the published Neospora literature (n = 2933) was also carried out via MEDLINE and systematically appraised for publications relevant to the pathogenesis, pathology and diagnosis of Neospora abortions.

RESULTS

A total of 92 publications were included in the final analysis and grouped into four main time periods. In these four different time periods, the main research themes were "dogs", "abortion", "seroprevalence" and "infection". Diagnostics, including PCR, dominated the first two time periods, with an increased focus on transmission and abortions, and its risk factors in cattle.

CONCLUSIONS

Longitudinal analyses indicated that the main themes were consistently investigated over the last 30 years through a wide range of studies, with evolving emphasis initially on dogs and diagnostic test development, followed by application to cattle, the identification of the risk factors leading to abortion, and in the latter time periods, an understanding of the immunity and a search for vaccines.

Combined control evaluation for Neospora caninum infection in dairy: Economic point of view coupled with population dynamics

Neospora caninum infection is regarded as one of the most important infectious causes of abortion in dairy cattle. To intervene in its spread, four potential controls including test-and-cull, medication, vaccination, and selective breeding are considered and assessed in this study. The cost of each control, together with the inevitable annual loss due to population dynamics, is adopted as an assessment criterion from an economic point of view. By performing simulation and sensitivity analysis, our results demonstrate that compared with each single control, combined controls are worthwhile with better financial outcomes. For farm affected with significant prevalence (equal to or greater than 30%), vaccine treatment is the most effective and economical option among all control strategies. On the other hand, for farm where prevalence is relatively low (around 10%), combined control, by applying vaccination followed with test-and-cull, medication or selective breeding, could be alternative treatment to provide better financial outcome against single control in an observed period.

Evaluation of abortions spontaneously induced by Neospora caninum and risk factors in dairy cattle from Lima, Peru

Our objective was to identify the direct and indirect presence of Neospora caninum in dairy cattle and their aborted fetuses from Lima, Peru. A total 219 blood samples obtained from dairy cattle with records of spontaneous abortion were collected to detect antibodies against N. caninum in serum with indirect ELISA and search for risk-factor associations. 68 fetal aborted tissue samples of these cows were analyzed by PCR, indirect ELISA and histopathology assay to detect N. caninum presence. The prevalence ratio (PR) and 95% confidence intervals (CI) were estimated. Univariate analysis was performed using the chi-squared test. Among the 68 aborted fetuses collected, 10 (15%) were positive in at least two diagnostic tests. Among 219 serum samples, 46.6% (95% CI: 40.0%-53.3%) were positive. Cows with 4 years or older (PR: 7.10; 95% CI: 4.89-10.67) and multiparous (PR: 1.76; 95% CI: 1.11-2.80) were found to be more likely to possess N. caninum antibodies. This study detects presence of N. caninum in dairy cattle and their aborted fetus from Lima valley, suggesting biosecurity management improve to neosporosis control.

Relation between Neospora caninum and abortion in dairy cows: Risk factors and pathogenesis of disease

Neosporosis is a parasitic disease cause by Neospora caninum, a parasite of great importance in livestock. This study aimed to evaluate the presence of antibody against N. caninum in dairy cattle with history of abortion, as well as to identify associated risk factors for neosporosis. Animals suspected of neosporosis (n = 130) after clinical examination were randomly selected. Sera samples from 29 farms were submitted to indirect immunofluorescence technique (IFA) in order to detect antibodies against N. caninum, and animals were considered positive if ≥ IFA 1:200. An epidemiological questionnaire was used to verify probable risk factors for neosporosis and their cause-effect relation. Serological results showed that 43.8% of the animals were seropositives for N. caninum. The univariate statistical analysis found a significant relation between neoporosis and age. The number of pregnancies and the number of years that the farms had been producing milk were found as associated risk factors for the disease either by univariate or by multivariate analyses. The cause-effect model found a possible relation between reproductive problems and positive serology for neosporosis (P = 0.06). Therefore, it was concluded that approximately 44% of dairy cows with history of abortion were seropositives for N. caninum and that age and the number of years that the farms had been producing milk are risk factors for parasite infection in dairy cattle.

Control options for Neospora caninum--is there anything new or are we going backwards?

Recent work has highlighted and enumerated the economic annual losses due to Neospora caninum abortions worldwide, which should provide strong motivation for the control of bovine neosporosis. However, with the recent withdrawal from sale of the only commercially available vaccine, control options for N. caninum have become more restricted. While researchers continue to work on developing alternative efficacious vaccines, what are the control options presently available for the cattle industries? At the practical level, recommendations for 'Test-and-cull', or 'not breeding from seropositive dams' stand diametrically opposed to alternative options put forward that suggest a primary producer is better advised to keep those cows in the herd that are already seropositive, i.e., assumed to be chronically infected, and indeed those that have already aborted once. Treatment with a coccidiostat has been recommended as the only economically viable option, yet no such treatment has gained official, regulatory approval. Dogs are central to the life cycle of N. caninum and have repeatedly been associated with infection and abortions in cattle by epidemiological studies. Knowledge and understanding of that pivotal role should be able to be put to use in control programmes. The present review canvasses the relevant literature for evidence for control options for N. caninum (some of them proven, many not) and assesses them in the light of the authors' knowledge and experience with control of N. caninum.

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.

Development of maternal and foetal immune responses in cattle following experimental challenge with Neospora caninum at day 210 of gestation

This study examined the immunological responses of pregnant cattle and their foetuses following an experimental challenge with live Neospora caninum tachyzoites at day 210 of gestation. Animals were bled prior to and weekly throughout the experiment and sacrificed at 14, 28, 42 and 56 days post inoculation (dpi). At post mortem examination, samples of lymph nodes and spleen were collected from both dam and foetus for immunological analysis. Subcutaneous (sc) inoculation over the left prefemoral (LPF) lymph node of pregnant cattle at day 210 of gestation, led to the vertical transmission of parasites by 14 dpi, however no foetal deaths were observed in the infected animals. Foetuses from infected dams mounted Neospora-specific humoral and cell-mediated immune (CMI) responses by 14 dpi. These responses involved anti-Neospora IgG, antigen-specific lymphocyte proliferation, and the production of the cytokines IFN–γ, interleukin (IL)-4 and IL-10. There was also evidence of innate immunity during the response against Neospora from infected dams, with statistically significant (p < 0.05) increases in mean expression of toll like receptors (TLR)-2 on 56 dpi in maternal spleen, LPF, right prefemoral (RPF), left uterine (LUL) and right uterine (RUL) lymph nodes and TLR-9 in retropharyngeal (RLN), LPF and RPF lymph nodes from 28 dpi. Statistically significant (p < 0.05) increases in mean TLR-9 were detected in spleen samples from foetuses of infected dams, compared to the foetuses from control animals. Our results show that vertical transmission of the parasite occurred in all infected dams, with their foetuses showing effective Neospora-specific cell mediated, humoral and innate immune responses.

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.

Maternal and foetal immune responses of cattle following an experimental challenge with Neospora caninum at day 70 of gestation

The immune responses of pregnant cattle and their foetuses were examined following inoculation on day 70 of gestation either intravenously (iv) (group 1) or subcutaneously (sc) (group 2) with live NC1 strain tachyzoites or with Vero cells (control) (group 3). Peripheral blood mononuclear cell (PBMC) responses to Neospora antigen and foetal viability were assessed throughout the experiment. Two animals from each group were sacrificed at 14, 28, 42 and 56 days post inoculation (pi). At post mortem, maternal lymph nodes, spleen and PBMC and when possible foetal spleen, thymus and PBMC samples were collected for analysis. Inoculation with NC1 (iv and sc) lead to foetal deaths in all group 1 dams (6/6) and in 3/6 group 2 dams from day 28pi; statistically significant (p ≤ 0.05) increases in cell-mediated immune (CMI) responses including antigen-specific cell proliferation and IFN-γ production as well as increased levels of IL-4, IL-10 and IL-12 were observed in challenged dams compared to the group 3 animals. Lymph node samples from the group 2 animals carrying live foetuses showed greater levels of cellular proliferation as well as significantly (p ≤ 0.05) higher levels of IFN-γ compared to the dams in group 2 carrying dead foetuses. Foetal spleen, thymus and PBMC samples demonstrated cellular proliferation as well as IFN-γ, IL-4, IL-10 and IL-12 production following mitogenic stimulation with Con A from day 14pi (day 84 gestation) onwards. This study shows that the generation of robust peripheral and local maternal CMI responses (lymphoproliferation, IFN-γ) may inhibit the vertical transmission of the parasite.

Cytokine gene expression profiles in peripheral blood mononuclear cells from Neospora caninum naturally infected dams throughout gestation

Neospora caninum is a major cause of abortion in cattle but it is not known why some infected animals suffer abortion while others do not. An essential role in protective immunity against N. caninum has been proposed for Th1 cytokines such as IFN-γ and IL-12 although cytokine patterns in N. caninum infected pregnant cattle have been scarcely addressed. In this study, gene expression of the cytokines IFN-γ, IL-12, IL-10, IL-4 and TNF-α was analyzed by real time RT-PCR in peripheral blood mononuclear cells in N. caninum naturally infected dams throughout pregnancy. Blood samples were drawn from 18 cows (13 N. caninum seropositive and 5 N. caninum seronegative) on Days 45, 90, 120, 150, 180 and 210 of pregnancy or until abortion. Four seropositive animals aborted. Compared to the seronegative animals, N. caninum infected dams showed up-regulated mRNA levels of the Th1 cytokines, IFN-γ, TNF-α and IL-12p40, along with up-regulation of the T regulatory (Treg) cytokine IL-10. In contrast, expression levels of IL-4 (Th2 cytokine) did not differ significantly among the different groups throughout the study period. Our findings indicate clear differences in peripheral blood cytokine gene expression levels during pregnancy between animals naturally infected with N. caninum and seronegative control animals. To the best of our knowledge, this is the first study to examine the gene expression of Th1, Th2 and regulatory cytokines in the peripheral blood of pregnant cows naturally infected with N. caninum.

Peripheral white blood cell counts throughout pregnancy in non-aborting Neospora caninum-seronegative and seropositive high-producing dairy cows in a Holstein Friesian herd

Pregnancy is characterized by transient changes in the maternal immune system, also evident at peripheral level. The present study analyzes the kinetics and possible factors affecting peripheral white blood cell populations throughout pregnancy in a herd of high-producing dairy cows chronically infected or not with Neospora caninum. We examined 54 pregnant parous cows: 29 Neospora-seronegative and 25 Neospora-seropositive cows. Blood samples were collected on Days 90, 120, 150, 180 and 210 of gestation. General Linear Model (GLM) repeated measures analysis of variance showed that the interaction Neospora-seropositivity × parity significantly affected total leukocyte, neutrophil and monocyte counts with lower levels of total leukocytes, lower neutrophil and higher monocyte counts recorded in primiparous Neospora-seropositive cows. In addition, N. caninum-seropositive cows had significantly increased monocyte counts on Day 180 of gestation compared to seronegative ones. Other factors significantly associated with changes in total and/or differential leukocyte profiles were period of pregnancy, season, twin pregnancy and milk production. In conclusion, a parity-associated effect of chronic N. caninum infection was observed on peripheral blood cell profiles in dairy cattle during gestation.

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

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

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.

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

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

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

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

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

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

Comparative host–parasite relationships in ovine toxoplasmosis and bovine neosporosis and strategies for vaccination

Toxoplasma gondii and Neospora caninum are important causes of reproductive loss in ruminant species worldwide. Both parasites cause disease during pregnancy that may result in foetal death or birth of live congenitally infected offspring. T. gondii is also an important human pathogen with the main risk groups including pregnant women and immuno-compromised individuals, although clinical disease has also been observed in outbreaks among immuno-competent people. While the two parasites are closely related there are distinct differences between the two in their interactions with different host species and subsequent clinical outcome. This paper discusses the respective host-parasite relationships in ovine toxoplasmosis and bovine neosporosis and how the immune response may be host-protective, parasite-protective or contribute to disease pathogenesis, and how this knowledge may help in the development of more effective and targeted vaccination strategies.

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.

Vaccination as a control strategy against the coccidial parasitesEimeria,ToxoplasmaandNeospora

The protozoan parasitesEimeriaspp.Toxoplasma gondiiandNeospora caninumare significant causes of disease in livestock worldwide andT. gondiiis also an important human pathogen. Drugs have been used with varying success to help control aspects of these diseases and commercial vaccines are available for all three groups of parasites. However, there are issues with increasing development of resistance to many of the anti-coccidial drugs used to help control avian eimeriosis and public concerns about the use of drugs in food animals. In addition there are no drugs available that can act against the tissue cyst stage of eitherT. gondiiorN. caninumand thus cure animals or people of infection. All three groups of parasites multiply within the cells of their host species and therefore cell mediated immune mechanisms are thought to be an important component of host protective immunity. Successful vaccination strategies for bothEimeriaandToxoplasmahave relied on using a live vaccination approach using attenuated parasites which allows correct processing and presentation of antigen to the host immune system to stimulate appropriate cell mediated immune responses. However, live vaccines can have problems with safety, short shelf-life and large-scale production; therefore there is continued interest in devising new vaccines using defined recombinant antigens. The major challenges in devising novel vaccines are to select relevant antigens and then present them to the immune system in an appropriate manner to enable the induction of protective immune responses. With all three groups of parasites, vaccine preparations comprising antigens from the different life cycle stages may also be advantageous. In the case ofEimeriaparasites there are also problems with strain-specific immunity therefore a cocktail of antigens from different parasite strains may be required. Improving our knowledge of the different parasite transmission routes, host-parasite relationships, disease pathogenesis and determining the various roles of the host immune response being at times host-protective, parasite protective and in causing immunopathology will help to tailor a vaccination strategy against a particular disease target. This paper discusses current vaccination strategies to help combat infections withEimeria,ToxoplasmaandNeosporaand recent research looking towards developing new vaccine targets and approaches.

Effect of Neospora caninum-serostatus on culling, reproductive performance and milk production in Dutch dairy herds with and without a history of Neospora caninum-associated abortion epidemics

We quantified the effect of Neospora caninum (NC)-serostatus on culling and (re)production in 83 herds randomly selected from the Dutch dairy herd population (random group) and in 17 herds that had experienced an abortion epidemic associated with NC infection (epidemic-abortion group). In the random group, a single whole-herd blood sampling was done during the spring of 2003, while in the epidemic-abortion group whole-herd blood sampling was done repeatedly at least once a year starting after the abortion epidemic during the period 1997-2000 until the summer of 2004. Serological test-results for NC were given as 'negative' (N), 'low-positive' (LP) and 'high-positive' (HP). For analysing the time to culling, calving interval and age of first calving, survival analysis was used. For categorical reproduction parameters either a logistic-regression model (abortion, non-return after 1st insemination) or a Poisson-regression model (number of inseminations per pregnancy) was used. For milk production a linear-mixed model was used. All models were controlled, if applicable, for confounding variables like parity, production, season, year and abortion and adjusted for within-herd clustering. In random herds, HP serostatus increased the hazard for culling 1.73-fold (95% CI: 1.37-2.19) compared to N and LP serostatus. Compared to N serostatus, LP and HP serostatus in epidemic-abortion herds increased the odds for abortion 1.88-fold (95% CI: 1.41-2.52) and 1.72-fold (95% CI: 1.38-2.14), respectively. No other reproduction parameters were associated with NC-serostatus in the random or epidemic-abortion herds. We found no effect of serostatus on milk production in the random group. In contrast, milk production of LP and HP serostatus in the epidemic-abortion group was respectively, 0.72kgmilk/day (95% CI: 0.15-1.03) and 0.59kgmilk/day (95% CI: 0.13-1.30), less during the first 100 days of lactation in the first year after the abortion epidemic compared with N serostatus.

If control of Neospora caninum infection is technically feasible does it make economic sense?

Recent work on Neospora caninum, a protozoan parasite that causes abortions in dairy cattle has focused on a number of different control options. Modelling has suggested the most effective options for control but the present paper argues that the most effective option might not necessarily be optimal from an economic point of view. Decision trees, using published quantitative data, were constructed to choose between four different control strategies. The costs of these interventions, such as 'test and cull', therapeutic treatment with a pharmaceutical, vaccination or "doing nothing" were compared, and modelled, in the first instance, on the New Zealand and Australian dairy situation. It is argued however, that the relative costs in other countries might be similar and that only the availability of a registered vaccine will change the decision tree outcomes, as does the within-herd prevalence of N. caninum infection. To "do nothing" emerged as the optimal economic choice for N. caninum infections/abortions up to a within-herd prevalence of 18%, when viewed over a 1-year horizon, or 21% when costs were calculated over a 5 years horizon. For a higher (>or=21%) within-herd prevalence of N. caninum infection vaccination provided the best (i.e. most economic) strategy. Despite being the most efficacious solutions, 'test and cull' or therapeutic treatment never provided a viable economic alternative to vaccination or "doing nothing". Decision tree analysis thus provided clear outcomes in terms of economically optimal strategies. The same approach is likely to be applicable to other countries and the beef industry, with only minor changes expected in the relationships of decisions versus within-herd prevalence of N. caninum infection.

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.

Variations of Neospora caninum antibody levels in milk during lactation in dairy cows

A longitudinal study was performed to investigate the variations of Neospora caninum antibody levels in individual milk during lactation as well as the association between antibody levels in serum and milk. Serum and milk samples of 15 milking cows were collected between February 2003 and September 2004 in three smallholder dairy farms in Khon Kaen province in northeast Thailand. All samples were analyzed for presence of antibodies by an N. caninum iscom ELISA test kit and the results were given as percent positivity (PP). The effects of time between calving and sampling, lactation number, and season on milk and serum PP were studied using Generalized Estimation Equations methods. All cows were antibody positive in either milk or serum at the first two consecutive samplings. Although serum and milk PP varied considerably, milk PP was consistently positive throughout the study. Cows of all lactation groups had a higher adjusted mean of milk PP at calving compared to later months after calving although the only significant difference was in first lactation. Serum and milk PP were always lower in first lactation than in second and later lactations. An adjusted mean of milk PP for cows classified as having serum PP> or =55 was significantly (P<0.05) higher than that of cows classified as having lower serum PP. Our results indicate that individual milk can be an alternative material to demonstrate presence of N. caninum antibodies in lactating cows.

Proportion of abortions due to neosporosis among dairy cattle in Japan

A retrospective cohort study was conducted to clarify the association between seropositive reactions to Neospora caninum and subsequent reproductive disorders among dairy cattle in Japan. A statistically significant association between Neospora seropositive reactions and abortions was observed (P=0.016), and seropositive cattle were 6.1 times more likely to abort compared to seronegative cows. No significant differences were observed between seropositive reactions and other reproductive disorders such as conception failure, perinatal death and calf mortality. As indicated by estimation of the attributable fraction, 83.6% of abortions in Neospora seropositive animals may be attributed to N. caninum. Considering seroprevalence of N. caninum in the cattle which aborted in Japan, 21.8% of abortions were estimated to be caused by neosporosis in Japan.

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.

Recent advances in understanding the epidemiology of Neospora caninum in cattle

INTRODUCTION

Neospora caninum is the most frequently diagnosed cause of cattle abortion in New Zealand and is an important pathogen worldwide. The parasite has been found in aborted bovine foetuses and in puppies with neurological disease. Recent developments have provided new insights into the epidemiology of the disease that are reviewed in this article.

TRANSMISSION

Transplacental infection is of major importance in the spread of N. caninum overseas. Most congenital infections result in the birth of apparently healthy calves. Seroepidemiological studies indicate introduced point-source infections are also likely, as do investigations of abortion outbreaks in cattle herds attributed to N. caninum. Horizontal transmission is an important determinant of the stability of infection prevalence in a herd. Two potential sources of horizontal transmission that have recently been reported are: via a canine definitive host and; cow-to-calf transmission through pooled colostrum or milk. Transmission parameters for the organism have been estimated using mathematical modeling, to explore the epidemiology and options for control of N. caninum infection in dairy cattle in the absence of precise epidemiological data. LIFE-CYCLE: Seroepidemiologic studies, combined with the knowledge that dogs can be a definitive host, provide evidence supporting a dog-cattle life-cycle. The importance of dogs in the epidemiology of bovine neosporosis is not yet clear. It is likely that N. caninum oocysts in dog faeces could serve as a source of infection for cattle and recent studies have shown that the canine and bovine isolatesflare the same organism. Infection of cattle orally exposed to oocysts has been demonstrated experimentally but not in nature. It is not known if other wild carnivores may serve as definitive hosts of N. caninum.

CONCLUSION

Despite active research for over a decade, very little is known about the mechanisms of transmission of N. caninum. Vertical transmission is well documented but horizontal spread and the pathogenesis of abortion from this disease need further investigation. It is evident that, even with a very high probability of vertical transmission, some form of horizontal transmission is required for the disease to persist in a herd.

Evaluation of three enzyme-linked immunosorbent assays for detection of antibodies to Neospora caninum in bulk milk

Three ELISAs for the detection of antibodies against Neospora caninum in bulk milk were evaluated in 162 Dutch dairy herds. The first ELISA was the Dutch Animal Health Service (AHS) in-house ELISA, developed from the routine in-house serum ELISA. The other two ELISAs were commercial milk ELISAs from IDEXX and LSI. Blood samples of all lactating cows in 162 dairy herds were tested using the AHS in-house serum ELISA. Based on previous studies in the Netherlands a within-herd N. caninum seroprevalence of 15% was associated with increased risk for reproductive losses. This percentage was therefore used as positive seroprevalence cut-off value. Repeatability of the ELISAs was evaluated by testing on three different days. The AHS in-house ELISA lacked specificity, probably due to use of a different batch of antigen on the second and third test-day. Cut-off values were determined using misclassification costs term calculations. At cut-off values 0.6 for the IDEXX and 0.2 for the LSI, a herd sensitivity of 61% (95% CI: 49--73%) and 47% (95% CI: 35--60%) was estimated. Herd specificity at these cut-off values was 92% (95% CI: 87--98%) for the IDEXX and 94% (95% CI: 90--99%) for the LSI ELISA. The positive and negative predictive values were 84% (95% CI: 68--100%) and 86% (95% CI: 79--94%) for the IDEXX ELISA, and 85% (95% CI: 67--100%) and 82% (95% CI: 74--90%) for the LSI ELISA. The agreement between all possible combinations of test-days was expressed by kappa values. These were found to be slightly higher for the IDEXX than for the LSI ELISA. It is concluded that both commercial ELISAs performed satisfactorily to detect a within-herd seroprevalence of N. caninum in lactating cows of at least 15%.

Reduced infection and protection from clinical signs of cerebral neosporosis in C57BL/6 mice vaccinated with recombinant microneme antigen NcMIC1

NcMIC1 is a 460 amino acid Neospora caninum microneme protein implicated in host cell adhesion and invasion processes. In this study, we assessed the potential protectivity of NcMIC1-based vaccination against experimental N. caninum infection in mice, employing both recombinant antigen vaccines and DNA vaccines. Recombinant NcMIC1 (recNcMIC1) was expressed in Escherichia coli as gluthatione-S-transferase-fusion protein. The corresponding NcMIC1 cDNA was cloned into the pcDNA3.1 expression plasmid (pcDNA-MIC1), and expression was checked in transfected Vero cells. Mice (10 animals/group) were vaccinated either with recNcMIC1 antigen suspended in Ribi-adjuvant (3 intraperitoneal injections), pcDNA-NcMIC1 (3 intramuscular injections), or pcDNA-NcMIC1 (twice intramuscularly), followed by 1 intraperitoneal recNcMIC1 antigen boost. Control groups included corresponding treatments with adjuvant, pcDNA3.1 without insert, and PBS (= infection control). All vaccinated and control groups were then challenged intraperitoneally with 2 x 10(6) N. caninum tachyzoites. Animals were inspected daily for a period of 3 wk postinfection (PI). At day 21, all animals were killed and assessed for infection. Before day 21 PI, clinical signs such as walking disorders, rounded back, apathy, and paralysis occurred in infection controls (50% of the mice), pcDNA and adjuvant controls (20% each), and the combined pcDNA-NcMIC1/recNcMIC1-treated group (30%). No clinical symptoms were observed in the recNcMIC1 and pcDNA-NcMIC1 vaccinated groups. All mice were positive for cerebral N. caninum infection as assessed by PCR of brain tissue. However, quantitative real-time PCR revealed that the infection intensity was significantly reduced in the group vaccinated with recNcMIC1 antigen. Immunohistochemistry confirmed these findings. In contrast, the infection intensity was highest in the group vaccinated with the pcDNA-NcMIC1/recNcMIC1 combination, indicating that the sequential application of the DNA vaccine and recombinant antigen had a deleterious effect. Serological analysis showed that only recNcMIC1-immunized animals generated detectable antibody levels recognizing native NcMIC1. Thus, of all protocols applied here, only recNcMIC1 vaccination appears to be suited to reduce cerebral infection in mice challenged with N. caninum tachyzoites.

Relationship between rainfall and Neospora caninum-associated abortion in two dairy herds in a dry environment

The possible direct relationship between climate variations and abortion in Neospora caninum-infected cows has not been studied. The objective of this study was to determine whether climate changes could be a risk factor for abortion in N. caninum-infected cows, and was based on yearly serological screening for neosporosis and on the confirmation of N. caninum infection on aborted fetuses in two high-producing dairy herds with a mean 27% seroprevalence of N. caninum antibodies. The final population study was comprised of 357 pregnancies in seropositive animals. Logistic regression analysis indicated no significant effects of herd, N. caninum antibody titre, climate variables during the first and third trimesters of gestation, mean and maximum temperature-humidity index values during the second trimester of gestation, and previous abortion on the abortion rate. Based on the odds ratio, a 1-unit increase in lactation number yielded a 0.85-fold decrease in the abortion rate. The likelihood of abortion was 1.9 times (1/0.54) lower for pregnant cows inseminated with beef bull semen compared with Holstein-Friesian bull semen. The likelihood of abortion decreased significant and progressively by factors of 0.5, 0.41 and 0.3 for the respective classes 40-49, 30-39 and <30 rainfall mm during the second trimester of gestation (using the class >or=60 rainfall mm as reference). As a general conclusion, it seems that increased rainfall in a dry environment can compromise the success of gestation in N. caninum-infected cows. Attempts should therefore be made to reduce environment effects during the second trimester of gestation, a period in which the immune response of cows is diminished.

Serologic immunoreactivity to Neospora caninum antigens in dogs determined by indirect immunofluorescence, western blotting and dot-ELISA

Neospora caninum, is a coccidian protozoan known as a major cause of bovine abortion and canine neuropathies. The aim of the present study was to develop a reliable and quick test to detect antibodies to N. caninum in dog sera. Sixty-five serum samples from dogs, including 35 positive and 30 negative for N. caninum antibodies were used for standardization of the test. In parallel, immunoreactivity of the sera to Toxoplasma gondii antigens was investigated using a passive agglutination test. A dot-ELISA test, using soluble extract of N. caninum tachyzoites on nitrocellulose ester membranes, was developed and standardized. SDS-PAGE and complementary analysis of reactivity by Western blotting were used for the characterization of the immunoreactive fractions of all tested sera. The sensitivity and specificity of the dot-ELISA were 94 and 73%, respectively, compared to IFAT at a cut-off of 1:50, and 87 and 100% compared to IFAT at a cut-off of 1:25. Among the sera that tested positively for both IFAT and dot-ELISA, only 8.6% were reactive to T. gondii. The most immunoreactive fractions in Western blots were the 14-, 33-, 42- and 55 kDa bands, with percentages of 42, 60, 42 and 37%, respectively. The 60 kDa band showed a non-specific reaction in 43% of neosporosis-negative animals by both dot-ELISA and IFAT. These results indicate that the dot-ELISA using N. caninum antigen present good sensitivity and specificity, and might be used as a screening test to detect antibodies to N. caninum in dogs.

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.

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

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

Seroprevalence of Neospora caninum in dairy and beef cattle with reproductive disorders in Japan

Serum samples from 145 dairy and 65 beef cattle with reproductive disorders and 54 normally calving dairy cattle (controls) in Japan were tested for presence of Neospora caninum antibodies by use of an indirect fluorescent antibody test (IFAT, titer 1:200). Overall, seroprevalence of N. caninum was significantly higher (P < 0.001) in dairy cattle (20.0%, 29/145) than in beef cattle (1.5%, 1/65). In cattle which aborted, seroprevalence of N. caninum was significantly higher (P = 0.041) in dairy cattle (26.1%, 23/88, compared with controls (3.7%, 2/54)) than in beef cattle (5.0%, 1/20), indicating that neosporosis might be a more common problem in dairy cattle than in beef cattle in Japan. Seropositive cattle were 9.2 times more likely to abort compared to seronegative cows. Abortions associated with N. caninum seropositivity in this study were most frequently observed in the second trimester, and the mean gestational age of the fetuses aborted from seropositive dams was 5.7 months. In conclusions, N. caninum seems to be causing serious economic losses in the dairy industry in Japan. This is the first report on an objective comparison of seroprevalence of dairy and beef cattle with reproductive disorders in Asia.

Associations between pregnancy outcome and serological response toNeospora caninumamong a group of dairy heifers

AIM

To monitor pregnancy in a group of rising 2-year-old dairy heifers on a farm on which abortion due to Neospora caninum was known to occur in previous years.

METHODS

A prospective cohort study group of 164 rising 2-year-old heifers was pregnancy-tested and blood-sampled at 4-5-week intervals throughout gestation. Sera were tested for antibodies to N. caninum at 3-4-month intervals, using an enzyme-linked immunosorbent assay (ELISA). When loss of pregnancy was detected, an N. caninum indirect fluorescent antibody test (IFAT) was conducted retrospectively on stored sera collected the month before abortion, the month abortion was detected, and for the following 2 months, from heifers that aborted. All fetal and placental material detected following abortion was subjected to gross post-mortem and histopathological examination.

RESULTS

Eleven of 18 (61%) heifers that were seropositive and 4/146 (3%) heifers that were seronegative to N. caninum by ELISA, aborted. The relative risk for abortion among ELISA-positive heifers was 23.6. Abortion occurred predominantly between Days 120 and 152 gestation among the ELISA-positive heifers and throughout gestation among the ELISA-negative heifers. IFAT titres rose around the time of abortion in most of the heifers that were previously seropositive by ELISA, but dropped rapidly again in post-abortion samples. IFAT titres among 4/6 ELISA-positive heifers that did not abort increased, but later in gestation than the time other heifers aborted. IFAT titres remained negative in heifers that aborted that were ELISA negative.

CONCLUSIONS

Heifers that were seropositive to N. caninum by ELISA had a much greater risk of abortion than seronegative heifers. Most seropositive heifers showed evidence of a reactivation of infection during pregnancy. High (> or =1:2,000) N. caninum IFAT titres also occurred in non-aborting heifers.

CLINICAL RELEVANCE

Culling of replacement heifers seropositive to N. caninum may be a cost-effective strategy for minimising risk of abortion. Pregnancy testing heifers before 5 months gestation may overestimate the number that calve in N. caninum-infected herds, but would assist in documenting the occurrence of abortion. Reliance on a high (>1:2,000) IFAT titre to rule-in N. caninum as a cause of abortion is likely to produce false-positive results.

Serological prevalence of Neospora caninum in healthy and aborted dairy cattle in Mashhad, Iran

A total of 810 dairy cattle were blood sampled and used to evaluate serological screening for Neospora caninum infection in dairy cattle herds in Mashhad (Khorasan province, Iran). In 4 herds, of the 810 cattle, 123 (15.18%) were seropositive by IFA Test (VMRD Inc., Pullman, WA 99163, USA) with titer 1:200 and range of prevalence per herd from 9.92 to 19.60%. Seroprevalence was not significantly different between Holstein breed (14.88%) and Brown Swiss breed (19.60%). Comparison of N. caninum serological status with age groups (< or =2 years, 2-4 years, > or =4 years) showed no significant difference. Of the 139 aborted cattle sampled, 19.42% were seropositive for N. caninum.

Risk factors associated with Neospora caninum abortion in Ontario Holstein dairy herds

The objective of this epidemiological study was to identify risk factors for Neospora caninum-related abortions in Ontario Holstein dairy herds. A total of 88 herds, consisting of 5080 cattle, and utilizing Dairy Herd Improvement (DHI) services, were divided into three groups. Case (n = 30) and first control (n = 31) herds were selected from 1998 and 1999 fetal abortion submissions to the Animal Health Laboratory, University of Guelph, that were histopathologically positive or negative, respectively, for N. caninum. A second control group (n = 27) was selected from multiple sources of herds sampled within the previous 4 years that had a low seroprevalence (<7%) to N. caninum. Between May and December 1999, all available cows on all farms, in parity one or greater, were blood sampled. The sera were then analyzed for antibody to N. caninum using a kinetic ELISA. A survey administered at the time of sampling recorded information on housing, animal species present, manure management, reproduction, biosecurity practices, wildlife observations, peri-parturient cow management, herd disease history and nutrition. Production and other herd parameters were obtained from DHI records. Logistic regression indicated that the following parameters were positively associated with a N. caninum abortion in a herd: the N. caninum herd seroprevalence (OR = 1.1), the total number of dogs on a farm (OR = 2.8), the frequency that dogs were observed defecating in mangers (OR = 2.8), the number of horses on a farm (OR = 3.1), the observed annual rate of retained fetal membranes (OR = 1.2) and the observed annual rate of cows returning to estrus after pregnancy confirmation (OR = 1.2). Factors negatively associated were the frequency of stray cats and wild canids observed on a farm (OR = 0.4 and OR = 0.7, respectively) and the housing of heifers on loafing packs (a housing pen divided into feed manger, scrape alley and bedded pack areas, OR = 0.1).

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.

Genetic Susceptibility to Neospora caninum Infection in Holstein Cattle in Ontario

Neospora caninum has been reported to be an important cause of endemic fetal loss and occasional abortion epidemics in cattle around the world. This study examined 12,016 sera collected from 9723 Holstein cows on 125 herds across Ontario in 1998, 1999, and 2000. An enzyme-linked immunosorbent assay was used to examine the sera for antibodies to N. caninum. The overall prevalence of N. caninum antibodies in the cattle was 11.2% and the prevalence in individual herds varied from 0 to 70.4%. Among 3109 daughter-dam pairs, 619 positive dams had 252 positive daughters, giving a detected vertical transmission rate of 40.7%. In contrast, there were only 6.7% positive daughters from negative dams (167 of 2490). Pedigree edits left 8031 cows with 1463 sires for estimation of heritability. Five genetic models (sire model, animal model, sire-dam model, a sire-maternal grandsire model, and a maternal effects model) with fixed effects of bleeding year-month, age of the animals, and herd were fitted to the data. The estimated heritability of susceptibility to N. caninum ranged between 0.084 and 0.124. The sire-maternal grandsire model and the maternal effects model provided better fit than the other models because the maternal genetic variance was much greater than the direct genetic variance. To reduce the incidence of N. caninum infection, more emphasis should be placed on management practices than on genetic selection.

Maternal and fetal immune responses of cattle inoculated with Neospora caninum at mid-gestation

The humoral and cell-mediated immune responses of pregnant cattle and their fetuses were examined at intervals after infection with Neospora caninum tachyzoites at mid-gestation (day 140). All cattle seroconverted and interferon gamma was detected in supernatants of peripheral blood mononuclear cells stimulated with specific antigen. At day 14 post-inoculation (pi), specific cell proliferation responses were detected in the lymph node draining the site of inoculation and in the uterine lymph node. The peak response was recorded in the majority of maternal lymph nodes by day 28 pi and cells from the maternal retropharyngeal lymph node, which in part drains the central nervous system, showed no specific activity to N. caninum until day 42 pi. This changing pattern of immune responsiveness may reflect parasite invasion and development within different host tissues. Fetal lymph node cells showed mitogen responsiveness from day 14 pi (day 154 of gestation) and also showed N. caninum-specific cell proliferation and interferon-gamma responses by day 28 pi (day 168 of gestation). At day 42 pi, specific cell-mediated immune responses were not apparent; however, N. caninum-specific fetal IgG and IgM antibodies were detected.

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.