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

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

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

Seroprevalence and associated risk factors of bovine neosporosis in the Khomas region of Namibia

Neospora caninum is a coccidian parasite that occurs worldwide and is one of the most important causes of abortion, especially in cattle. However, no studies have been performed in Namibia to determine the N. caninum status in livestock. Therefore, this study aimed to determine the seroprevalence of N. caninum in cattle and the associated risk factors in the Khomas region of Namibia. A total of 736 sera were collected from cows in 32 farming establishments. These comprised 698 beef and 38 dairy cattle sera and were tested using a commercial enzyme-linked immunosorbent assay (ELISA) kit. Questionnaires were concurrently administered to determine possible risk factors associated with N. caninum seropositivity. A total of 42 sera were positive (all beef), giving an animal-level seroprevalence rate of 5.7%. Eight of the 32 establishments had at least one positive animal, giving a herd-level seroprevalence of 25%. There was no significant association between seropositivity and the presence of dogs, jackals, history of abortions, farm size, number of cattle or average annual rainfall. The establishments with moderate to high numbers of Feliformia were 9.8 times more likely to be seropositive to N. caninum than those with none to low levels of the former (p = 0.0245). The authors concluded that the seroprevalence level of N. caninum in the Khomas region was relatively low compared with other parts of the world and that the role of Feliformia in the epidemiology of bovine neosporosis needed to be further investigated.Contribution: Serological evidence of bovine neosporosis and the associated risk factors are reported in Namibia for the first time. This study contributes to the scientific body of knowledge on N. caninum in Africa, which is currently limited.

Development and application of an indirect ELISA to detect antibodies to Neospora caninum in cattle based on a chimeric protein rSRS2-SAG1-GRA7

Neospora caninum is an important apicomplexan parasite causing neosporosis in cattle. The disease is recognized as one of the most important cause of reproductive problems and abortion in cattle worldwide. In this context, we developed an indirect enzyme-linked immunosorbent assays (ELISA) with chimeric protein rSRS2-SAG1-GRA7 to diagnose antibodies to Neospora-infection. This indirect ELISA was compared to indirect fluorescent antibody test (IFAT) and western blotting (WB), and the sensitivity and specificity results of ELISA were calculated to be 86.7 and 96.1%, respectively. The overall coincidence rate was 92.6% using IFAT and WB. Additionally, 329 aborting dairy cattle serum samples were tested using this ELISA to evaluate the prevalence of N. caninum in Ningxia, China. The positive rate of N. caninum in these farms was from 19.05 to 57.89%, and the mean rate was 41.64% (±11.01%), indicating that infection with N. caninum may be one of the important causes of cattle abortion in this region. This established rSRS2-SAG1-GRA7 indirect ELISA is capable for detecting the antibodies against N. caninum, and it could be a useful screening tool for monitoring the epidemiology of neosporosis in cattle.

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.

Retrospective study of factors associated with bovine infectious abortion and perinatal mortality

Abortion and perinatal mortality, leading causes of economic loss in cattle industry, are the consequence of both non-infectious and a wide range of infectious causes. However, the relative contribution of pathogens to bovine abortion and perinatal mortality is poorly documented, since available studies involved only a limited number of pathogens. Therefore, the objectives of the present monitoring study were to determine the prevalence of infectious agents associated with bovine abortion and perinatal mortality, and to identify differences in production type, gestation length, parity and seasonality by using mixed effect models (logistic regression). A pre-established sampling protocol based on the collection of the aborted fetus/calf and a corresponding maternal blood sample, involving diagnostic testing for 10 pathogens, was performed. At least one potential causal agent of the abortion or perinatal mortality was detected in 39 % of cases. In these diagnosed cases, Neospora caninum was the most detected pathogen, followed by Trueperella pyogenes, BVDv, Escherichia coli, and Aspergillus fumigatus. Neospora caninum [odds ratio (OR): 0.4; 95 % confidence interval (CI): 0.3-0.7] and Aspergillus fumigatus (OR: 0.1; 95 % CI: 0.1-0.3) were detected less in late versus early gestation. Aspergillus fumigatus was less common in dairy in comparison to beef abortion cases (OR: 0.2; 95 % CI: 0.1-0.6). Winter was associated with a lower positivity for Neospora caninum and BVDv in comparison to warmer seasons. Despite extensive diagnostic testing, an etiological diagnosis was not reached in 61 % of cases, highlighting the need for even more extensive (non-)infectious disease testing or more accurate tests.

Risk factor analysis associated with Neospora caninum in dairy cattle in Western Brazilian Amazon

Neospora caninum is considered to be one of the main causes of abortion among cattle. The present survey was conducted in the municipality of Rolim de Moura, Rondônia State, Brazil. A questionnaire that investigates the epidemiological aspects of neosporosis was used in the analysis of risk factors associated with the animal-level and herd-level prevalence in dairy cattle. A total of 416 bovine blood samples were collected from 30 farms, and N. caninum antibody levels were measured by Indirect Fluorescent Antibody Test (IFAT). Analysis of dairy cattle serum samples revealed the presence of anti-N. caninum antibodies to be 47.36% (n = 197). Risk factors associated with N. caninum infection were the management system and access locations of dogs. The results of the present survey indicated that infection of dairy cattle with N. caninum is widespread in the studied region of Western Amazon, which has implications for prevention and control of neosporosis in this region. Therefore, integrated control strategies and measures are recommended to prevent and control N. caninum infection in dairy cattle. In addition, direct contact between dairy cattle, dogs and wild animals, which can influence the epidemiology of neosporosis, should be investigated further.

Endogenous transplacental transmission of Neospora caninum in successive generations of congenitally infected goats

Neospora caninum is a protozoan that is considered an important agent of reproductive disorders in ruminants worldwide, and vertical transmission is the main form of infection and maintenance of neosporosis in herds. In goats, there have been no studies that have evaluated the transmission of N. caninum between successive generations. Thus, the objective of this study was to evaluate, through IFAT and PCR, the endogenous transplacental transmission of N. caninum in up to five generations of six families of dairy goats naturally infected by the parasite and whether it was possible for dairy goats to become free of infection over successive generations. Ninety-five serum samples from positive animals and 75 samples from negative animals were analyzed for N. caninum. Of the 95 samples analyzed, 93 contained anti-N. caninum antibodies (97.8 %). Titers of anti-N. caninum antibodies varied (increasing or decreasing) in the offspring; however, with an increase in the number of the goat generations, the offspring tended to have lower titers (p = 0.021) at the day of birth. Reproductive disorders such as abortions, stillbirth or fetal retention occurred at a rate of 10.4 % and were not influenced by the mother's titer of anti-N. caninum antibodies at the day of parturition or abortion. The results showed that infection by N. caninum persists throughout generations in congenitally infected goats.

Serological and molecular detection of Neospora caninum and Toxoplasma gondii in human umbilical cord blood and placental tissue samples

Neosporosis primarily affects cattle and dogs and is not currently considered a zoonotic disease. Toxoplasmosis is a zoonosis with a worldwide distribution that is asymptomatic in most cases, but when acquired during pregnancy, it can have serious consequences. The seropositivity rates determined by the indirect fluorescent antibody test for Neospora caninum (N. caninum) and Toxoplasma gondii (T. gondii) were 24.3% (49 samples) and 26.8% (54 samples), respectively. PCR positivity for N. caninum was observed in two samples of cord blood (1%) using the Nc5 and ITS1 gene, positivity for T. gondii was observed in 16 samples using the primer for the B1 gene (5.5% positivity in cord blood and 2.5% positivity in placental tissue). None of the samples showed structures characteristic of tissue cysts or inflammatory infiltrate on histopathology. Significant associations were observed only between N. caninum seropositivity and the presence of domestic animals (p = 0.039) and presence of dogs (p = 0.038) and between T. gondii seropositivity and basic sanitation (p = 0.04). This study obtained important findings regarding the seroprevalence and molecular detection of N. caninum and T. gondii in pregnant women; however, more studies are necessary to establish a correlation between risk factors and infection.

Neospora caninum, A potential cause of reproductive failure in dairy cows from Northern Greece

Neospora caninum infection has been reported in a large number of intermediate hosts, such as ruminants, rabbits, mice, etc. but neosporosis has emerged as a serious disease in cattle and dogs worldwide. Abortions and other infertility issues have been reported in the infected cows, leading to great economic losses in farmers. The aim of our study was to assess N. caninum seroprevalence in dairy cattle from Northern Greece (region of Xanthi) by using the indirect fluorescent antibody technique. Blood samples were collected from 875 Holstein – Friesian dairy cows and tested for Neospora caninum antibodies. Among the cows that were studied, 184 (21.03%) were positive for N. caninum antibodies and concurrently their farms had a known previous history of infertility problems, such as abortions, increased number of artificial inseminations needed for conception, increased rate of returning to estrus and retention of fetal membranes.

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Neosporis is a common parasitosis in dairy cows.

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The number of abortions was significantly higher in seropositive cows.

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In seropositive cows the number of artificial inseminations was increased.

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The birth interval was much more longer in the N. caninum seropositive cows.

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Significant economic loss was observed in the infected farms.

Neospora caninum is the leading cause of bovine fetal loss in British Columbia, Canada

The protozoan pathogen Neospora caninum is recognized as a leading cause of infectious abortions in cattle worldwide. To evaluate the impact of neosporosis on dairy and beef herd production, a retrospective, longitudinal study was performed to identify the impact of neosporosis alongside other causes of fetal abortion in British Columbia, Canada. Retrospective analysis of pathology records of bovine fetal submissions submitted to the Animal Health Centre, Abbotsford, British Columbia, a provincial veterinary diagnostic laboratory, from January 2007 to July 2013 identified 182 abortion cases (passive surveillance). From July 2013 to May 2014, an active surveillance program identified a further 54 abortion cases from dairy farmers in the Upper Fraser Valley, British Columbia. Of the total 236 fetal submissions analyzed, N. caninum was diagnosed in 18.2% of cases, making it the most commonly identified infectious agent associated with fetal loss. During active surveillance, N. caninum was associated with 41% of fetuses submitted compared to 13.3% during passive surveillance (p<0.001). Breed of dam was significantly associated with N. caninum diagnosis, with a higher prevalence in dairy versus beef breeds, and fetuses of 3-6 months gestational age had the highest prevalence of N. caninum. There was no significant association with dam parity. N. caninum was diagnosed in every year except 2009 and cases were geographically widespread throughout the province. Furthermore, the active surveillance program demonstrates that N. caninum is highly prevalent in the Upper Fraser Valley and is a major causal agent of production losses in this dairy intensive region.

Neosporosis in naturally infected pregnant dairy cattle

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

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.

Neospora spp. antibodies in horses from two geographical regions of the state of Santa Catarina, Brazil

The aims of this study were to determine occurrences ofNeospora spp. IgG antibodies in horses from two geographical regions of the state of Santa Catarina, southern Brazil, and identify risk factors for infection. Analyses were performed on 615 samples using the immunofluorescent antibody test (IFAT ≥ 1:50). Out of the 615 samples, 25 (4.1%) were positive for Neospora spp. The titers for Neospora spp. were distributed as follows: 1:50 (13), 1:100 (eight), 1:200 (three) and 1:400 (one). Out of the 311 samples taken in the mountain region, eight were positive (2.6%). Among the samples from the coastal region (304), 17 had Neospora spp. antibodies, thus indicating occurrence of 5.6%. Although no statistically significant difference was observed (P = 0.06704), the prevalence among animals of the coast was 2.2 times higher than that of the mountain region. Contact with dogs and/or cattle (P = 0.007596) were identified as risk factor forNeospora spp. infection.

Prevalence of Neospora caninum antibodies in dairy cattle and water buffaloes and associated abortions in the plateau of Southern Peninsular India

A seroprevalence study of bovine neosporosis was conducted among 1,927 dairy cattle and 341 water buffaloes from Karnataka and Andhra Pradesh states in plateau of southern peninsular India by employing competitive enzyme-linked immunosorbent assay. Overall, 12.61 and 9.97 % sera samples were found positive for the presence of Neospora caninum antibody, respectively, among cattle and water buffaloes. Out of 1,927 sera samples from cattle, 912 and 1,015 samples were collected from unorganized and organized herds, respectively. The cattle screened were of upgraded Holstein-Friesian and water buffaloes were of graded Surti breed. Significantly (p < 0.05) higher prevalence was found in the cattle in unorganized herds (16.66 %) in comparison to organized herds (8.96 %). The highest seroprevalence was recorded in the age group of 4 years and above in both type of cattle herds and water buffaloes. There was a significant variation of seroprevalence (p < 0.05) observed between different age groups of cattle. The rate of seroprevalence increased with the increment in the age of the animals suggesting a possibility of horizontal mode of transmission of the infection from the environment. The percentage of abortion history was more in seropositive group (51.65 %) in comparison to the seronegative group (5.84 %) and the seropositive cattle were 8.84 times more likely to experience abortion than the seronegative cattle. The occurrence of abortion among different age groups varied significantly (p < 0.05). The findings revealed the presence of neosporosis in the southern peninsular India among cattle and water buffaloes and a strong association between the seroprevalence and abortion.

Geographical distribution modelling for Neospora caninum and Coxiella burnetii infections in dairy cattle farms in northeastern Spain

Maximum entropy ecological niche modelling and spatial scan statistic were utilized to predict the geographical range and to investigate clusters of infections for Neospora caninum and Coxiella burnetii in dairy cattle farms in Catalonia, northeastern Spain, using the Maxent and SaTScan programs, respectively. The geographical distribution of Neospora and Coxiella with the highest level of probability (P > 0·60) covers central Catalonia and spreads towards northeastern Catalonia which contains a high concentration of dairy cattle farms. The most important environmental factor that contributed to the ecological niche modelling was precipitation of driest month followed by elevation. Significant clusters (P < 0·001) were detected for Neospora and Coxiella infections in the western and eastern regions of Catalonia, respectively.

Tunicamycins, a class of nucleoside antibiotics similar to corynetoxins of the Rathayibacter toxicus, increase susceptibility of mice to Neospora caninum

Neosporosis is the leading cause of abortion in cattle. Neospora caninum-associated abortion may exhibit both endemic and epidemic patterns. It was reported that the epidemic outbreaks took place in the form of "abortion storms" and were not significantly correlated with seasonal changes or consumption of any particular feeds; and thus, the mechanisms by which the epidemic "abortion storms" are triggered remain unclear. Annual ryegrass toxicity (ARGT) is a severe or fatal neurological disorder of livestock of Australia and South Africa. This disorder is caused by the ingestion of several plant genera (Lolium, Polypogon, and Agrostis) colonized by a nematode (Anguina sp.) and a bacterium, Rathayibacter toxicus. Corynetoxins (CTs) produced by R. toxicus contaminate plants which are in turn ingested by sheep and cattle, causing severe or often fatal hepatocerebral disorders in affected animals. We hypothesize that N. caninum-associated fetal deaths and abortions in cattle may be potentiated by pre-exposure of sublethal levels of CT-contaminated plants prior to N. caninum infection or reactivation of a latent infection. The exposure of sublethal CTs may not cause clinical diseases, but may increase susceptibility to pathogens such as N. caninum. Indeed, CT poisoning surviving pregnant sheep can have up to 10% abortions. The present study investigated whether animals pre-exposed to tunicamycins (TMs), a functional substitute for CTs, had a lowered resistance to sublethal experimental infection by N. caninum tachyzoites in mice. The results showed that sublethal doses of TMs or N. caninum alone did not cause significant deaths. Sublethal doses of N. caninum induced high mortality in TM-treated mice in a dose dependent manner. When mice were treated with a low dose of TMs (5 μg/mouse), as few as 2.5 × 10(6) tachyzoites were needed to induce more than 30% of mortality which is equivalent to the mortality rate caused by 40 × 10(6) tachyzoites. Spleen cells of mice treated with TMs had reduced (p<0.05) Neospora antigen-induced interferon-gamma (IFN-g) production and Con A-stimulated proliferation. The results suggest that CT contaminated plants, when exposed to animals under natural conditions, may contribute to lowered host resistance and increased N. caninum-associated fetal morbidity and mortality in affected animals.

The first report of ovine cerebral neosporosis and evaluation of Neospora caninum prevalence in sheep in New South Wales

Presence of Neospora caninum DNA was detected in the brain and spinal cord of an adult Merino sheep suspected of dying with acute non-suppurative meningoencephalitis and mild to moderate non-suppurative myelitis. The most severe neurological lesions were found in the midbrain at the rostral coliculi with moderate to severe multifocal vasculitis and gliosis. As this was the first known occurrence of cerebral disease in sheep in Australia caused by N. caninum, we surveyed sera from five sheep properties in New South Wales (NSW) to obtain information on the likely prevalence of N. caninum infection in NSW sheep flocks. Serology using a commercial indirect enzyme-linked immunosorbent assay (ELISA) revealed no N. caninum antibody-positive sheep (n=184). However an observed prevalence for N. caninum antibodies using a commercially available competitive ELISA was 2.2% (5/232). We conclude that although the diagnosis of fatal ovine cerebral neosporosis is of importance to our surveillance program for transmissible spongiform encephalopathy (TSE) exclusion, sheep in NSW are not commonly infected with N. caninum and this species likely plays only a minor role in the life cycle of this parasite in Australia.

Risk factors associated with Neospora caninum seropositivity in randomly sampled Canadian dairy cows and herds

Our objective was to determine cow- and herd-level risk factors associated with seropositivity for Neospora caninum in a large number of randomly selected Canadian dairy herds, controlling for important confounding variables and co-infections with bovine leukemia virus (BLV), bovine viral diarrhea virus (BVDV) and Mycobacterium avium subspecies paratuberculosis (MAP). Serum samples were obtained from 30 randomly selected cows, where available, in 240 herds using monthly milk testing, within 6 of 10 provinces, and these samples were tested for antibodies against BLV, MAP and N. caninum using commercially available ELISA test kits. Five unvaccinated cattle >6 months old from each herd were tested for antibodies to BVDV using virus neutralization. Most herd-level predictors were obtained through personal interviews with questionnaires administrated to each farm manager. A mixed logistic-regression model was built using N. caninum serostatus at the cow-level as the outcome variable, with herd as a random effect and province as a fixed effect. A BLV seropositive cow was 1.50 times more likely to be seropositive for N. caninum than a BLV-seronegative cow, and this was the only cow-level variable to remain in the final model. Regarding herd-level variables, with "no on-farm dogs" as the baseline, "presence of dogs but not known to eat placentas and/or fetuses" increased the odds of seropositivity for N. caninum by a factor of 1.66. For "presence of dogs known to eat placentas and/or fetuses", the odds ratio (OR) was 2.75, demonstrating a dose-response relationship. "Using embryo transfer" (OR=0.69), "asking for a BVDV-negative test before introducing an animal" (OR=0.30), "using monensin in dry cows" (OR=0.71), and "heifers having nose-to-nose contact with calves" (OR=0.73) were all dichotomous variables negatively associated with seropositivity for N. caninum. "Number of milk cows on the farm" (OR=0.99), and "area (acres) used for forage production" (OR=0.99) were continuous variables negatively associated with N. caninum seropositivity.

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

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

Isolation and molecular characterisation of Neospora caninum in cattle in New Zealand

AIM

To isolate Neospora caninum from the brains of naturally infected cattle and use molecular techniques to characterise the isolates.

METHODS

Neospora caninum tachyzoites were isolated in Vero cell culture from the brains of a cow and two calves. The isolates were characterised using polymerase chain reaction (PCR) methods, DNA sequencing, an immunofluorescent antibody test (IFAT), transmission electron microscopy (TEM), and immunohistochemistry (IHC). The brains of the three cattle were subjected to histopathological examination. A pathogenicity study was conducted in 120 BALB/c mice.

RESULTS

Neospora caninum tachyzoites were isolated from all three cases and first observed in vitro between 14 and 17 days post-inoculation. Parasites were sub-cultured and maintained in Vero cell culture for more than 6 months. PCR products were generated for all three isolates, using two different primers. Sequencing of the PCR products and a subsequent BLAST search identified the isolates as N. caninum. In addition, the isolates tested positive using IFAT and IHC, and ultrastructure revealed by TEM was characteristic of N. caninum. Histopathological examination revealed lesions characteristic of N. caninum in 1/3 brains. In the pathogenicity study using BALB/c mice, the mortality rate was 3-7%.

CONCLUSION

This was the first successful isolation of N. caninum in New Zealand confirmed using molecular characterisation tests.

Serological evidence of Neospora caninum infection in mithun (Bos frontalis) from India

Studies conducted on mithuns maintained at National Research Centre on mithun, Indian Council of Agricultural Research (ICAR), Nagaland, India and mithuns found in free-ranging condition of Nagaland revealed that the overall prevalence of antibodies to Neospora caninum in mithun was 10% (95% CI=5-15) when detected by a commercially available competitive enzyme-linked immunosorbent assay test. Highest (prevalence rate=16, 95% CI=8-24) seroprevalence was found in mithuns above 3 years of age and lowest (prevalence rate=2, 95% CI=0-6) in mithuns of 2-12 months old. No statistically significant difference was observed between male (prevalence rate=7, 95% CI=0-14) and female (prevalence rate=12, 95% CI=6-18) seroprevalences. The seroprevalence was found to be higher (prevalence rate=20, 95% CI=9-31) in mithuns found in free-ranging condition in comparison to mithuns kept in semi-intensive system (prevalence rate=5, 95% CI=1-9). This is probably the first report on serological evidence of N. caninum infection in mithun. The possible role of sylvatic fauna in the epidemiology of N. caninum infection mithun is also discussed in brief.

Neospora caninuminfection in birds: experimental infections in chicken and embryonated eggs

Neospora caninumcauses economical impact in cattle-raising farms since it is implicated as the major cause of bovine abortions. Although infection by the parasite has been widely described in mammals, the role of birds in its life-cycle is still obscure. Therefore, this work aimed to evaluate the infection byN. caninumin different chicken models. Experimental infections were conducted in 7-day-old chicks, laying hens and embryonated eggs, where samples were analysed for parasite burden, IgG antibodies and lesions promoted. Chickens demonstrated an asymptomatic infection, although with seroconversion and systemic replication of the parasite. In laying hens, no signs of vertical transmission were observed. However, embryonated eggs inoculated by the allantoic cavity route demonstrated susceptibility to infection, with mortality rates around 50% independent of the inoculum dose. Additionally, dogs became infected after ingestion of different amounts of inoculated eggs, producing either oocysts or specific IgG antibodies. The results herein presented demonstrate that chickens may be intermediate hosts ofN. caninumand that embryonated eggs could be a useful model to study the parasite's biology.

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.

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

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

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.

The first detection of Neospora caninum DNA in the colostrum of infected cows

Limited data is available on the vertical transmission of Neospora caninum via the colostrum. The results of our previous research revealed the presence of N. caninum DNA in the milk of seropositive cows. The aim of the present work is to demonstrate parasite DNA in colostrum samples. A polymerase chain reaction using Np21 and Np6 primers was applied to DNA isolated from the colostrum sediment in order to amplify the corresponding genomic Nc-5 region. The expected 328-bp product was obtained in colostrum samples collected both on the calving day and the day after. This is the first detection of N. caninum DNA in the colostrum of seropositive cows, and these findings implicate the possibility of N. caninum transmission through the colostrum.

Seroepidemiology of Neospora caninum and Toxoplasma gondii in cattle and water buffaloes (Bubalus bubalis) in the People's Republic of China

A seroepidemiological survey of Neospora caninum and Toxoplasma gondii in cattle and water buffaloes was carried out in the People's Republic of China. Serum samples were obtained from dairy (n=262, 9 herds in 9 provinces) and beef cattle (n=10, 1 herd) and water buffaloes (n=40) in China. All sera were tested for antibodies to N. caninum and T. gondii by an enzyme-linked immunosorbent assay (ELISA) and an indirect agglutination test (IAT), respectively. The overall seroprevalence of N. caninum in dairy cattle was 17.2% (45/262), and the herds seroprevalence of N. caninum was 88.9% (8/9), and antibodies to T. gondii were present in 6 cows (2.3%). None of the cows had antibodies against both T. gondii and N. caninum. Antibodies to T. gondii or N. caninum were not found in beef cattle or water buffaloes. The seroprevalence of N. caninum in aborting cows (20.2%) was higher than that in non-aborting cows (16.6%) with an odds ratio of 1.26 (95% CI, 0.54-2.95), but the difference was not statistically significant (P>0.05). There was no apparent association of N. caninum seropositivity with age or number of pregnancies. This is the first report on the seroprevalence of N. caninum in cattle and water buffaloes in China.

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.

Cellular and immunological basis of the host-parasite relationship during infection with Neospora caninum

Neospora caninum is an apicomplexan parasite that is closely related to Toxoplasma gondii, the causative agent of toxoplasmosis in humans and domestic animals. However, in contrast to T. gondii, N. caninum represents a major cause of abortion in cattle, pointing towards distinct differences in the biology of these two species. There are 3 distinct key features that represent potential targets for prevention of infection or intervention against disease caused by N. caninum. Firstly, tachyzoites are capable of infecting a large variety of host cells in vitro and in vivo. Secondly, the parasite exploits its ability to respond to alterations in living conditions by converting into another stage (tachyzoite-to-bradyzoite or vice versa). Thirdly, by analogy with T. gondii, this parasite has evolved mechanisms that modulate its host cells according to its own requirements, and these must, especially in the case of the bradyzoite stage, involve mechanisms that ensure long-term survival of not only the parasite but also of the host cell. In order to elucidate the molecular and cellular bases of these important features of N. caninum, cell culture-based approaches and laboratory animal models are being exploited. In this review, we will summarize the current achievements related to host cell and parasite cell biology, and will discuss potential applications for prevention of infection and/or disease by reviewing corresponding work performed in murine laboratory infection models and in cattle.

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.

Supranational comparison of Neospora caninum seroprevalences in cattle in Germany, The Netherlands, Spain and Sweden

Herd, within-herd and animal prevalences for Neospora caninum in beef and dairy cattle were compared between four countries. In randomly selected herds from regions of Germany, The Netherlands, Spain and Sweden that were representative for the cattle production of these countries, all animals > or = 2 years were examined serologically by enzyme-linked immunosorbent assays (ELISAs) with high test specificity (> 98.0%). In a previous study, the ELISAs had been validated against each other. Single reacting animals within a herd were confirmed by immunobloting. At the time of sampling, animal (age, breed, herdtype, sex, lactation stage) and herd data (region) were collected. Considerable differences in N. caninum herd, within-herd, and overall animal prevalence estimations were observed between countries, regions, herdtype, age categories and breeds. Herd prevalences, based on confirmation of single reactors, for dairy herds were estimated to be 16% (95%CI: 10-24%) in Sweden, 49% (95%CI: 39-59%) in Germany, 63% (95%CI: 57-69%) in Spain and 76% (95%CI: 67-84%) in The Netherlands and for beef herds 41% (95%CI: 31-50%) in Germany, 46% (95%CI: 41-51%) in Spain and 61% (95%CI: 50-72%) in The Netherlands. No beef herds were examined in Sweden. The lowest animal true prevalence was estimated in dairy cattle in Sweden (0.5% (95%CI: 0.1-0.8%)) while the highest animal true prevalence was estimated for dairy cattle in Spain (16.2% (95%CI: 14.9-17.5%)). Within-herd prevalences varied greatly, with very few farms in Sweden having more than 10% seropositive animals while in Spain more than 10% of the herds had within-herd prevalences between 50 and 100%. Seropositivity was significantly associated with herdtype (beef versus dairy), age, breed and region within countries. The results of this supranational comparative study showed that the importance of N. caninum infection varied greatly within in Europe. Estimates of prevalence can be used to calculate the economic impact of N. caninum infection as well as to evaluate the effect of prevention and control strategies over time.

Prevalence of antibodies to Neospora caninum in dogs of rural or urban origin in central New Zealand

AIM

To investigate the seroprevalence of Neospora caninum infection in populations of dogs from dairy farms, sheep/beef farms and urban areas in the central part of New Zealand. It was postulated seroprevalence would be higher for farm dogs than urban dogs if the life-cycle of this parasite involves transmission between dogs and cattle.

METHODS

Serum samples were obtained from dogs that lived on dairy farms (n=161), sheep/beef farms (n=154) and in urban situations (n=150). The relative risk of detecting antibodies to N. caninum using an immunofluorescent antibody test (IFAT) was compared between farm and urban dogs.

RESULTS

The relative risk of having a titre of > or = 1:200 to N. caninum was 2.43 (95% CI=1.88-3.14) for dairy-farm dogs and 3.16 (95% CI=2.48-4.02) for sheep/beef-farm dogs, compared with urban dogs. At this titre, which is currently used in New Zealand to indicate seropositivity, seroprevalence of N. caninum infection was 30.7% in urban dogs, 74.5% in dairy-farm dogs and 96.8% in sheep/beef-farm dogs.

CONCLUSION

This observation is consistent with a cycling of this disease between cattle and dogs on farms in New Zealand and with higher exposure of dogs to N. caninum on farms than occurs in urban environments. The prevalence of antibodies in all three groups of dogs tested in this study (dairy-farm dogs, sheep/beef-farm dogs and urban dogs) is higher than has generally been reported elsewhere. New Zealand farm dogs have a higher serological prevalence of N. caninum infection than urban dogs.

CLINICAL RELEVANCE

Management and disease control practices that break the life-cycle of transmission between cattle and dogs should assist in controlling cattle abortion due to N. caninum.

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%.

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.

Neospora abortions in dairy cattle: diagnosis, mode of transmission and control

AIM

To determine the contribution of Neospora caninum to abortions on a dairy farm in NSW (Australia), determine the mode of transmission and develop and trial a control option for infection.

METHODS

Two whole herd bleeds were conducted 12 months apart and the association between serological status and abortion events were calculated for a number of bovine abortifacients. Family trees were constructed for N. caninum seropositive cattle in the herd. Some N. caninum seropositive cows were culled from the herd and no female offspring was retained from seropositive cows.

RESULTS

At the first whole-herd bleed in December 2002 a seroprevalence of 10.2% for N. caninum infection was detected. Cows with N. caninum infection were 13 times more likely to abort than uninfected ones. Seventy-five percent of seropositive animals in the herd were related, suggesting a high degree of congenital infection/transmission. Only 15% of infections were likely to be postnatally acquired. Selective culling of seropositive cows and not breeding from them reduced the number of seropositive animals. Only one newly sero-converted cow was detected at the second whole-herd bleed 12 months later.

CONCLUSIONS

Seroepidemiological approaches were able to establish a high degree of association between N. caninum infection and low-level abortion in the dairy herd. Vertical transmission of infection was the predominant mode of infection and hence control efforts aimed at selectively culling seropositive animals from the herd were highly successful in reducing the level of infection.

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.

Neospora caninum in pastured cattle: determination of climatic, environmental, farm management and individual animal risk factors using remote sensing and geographical information systems

A cross-sectional serological survey was conducted on cattle pasturing in an area of the southern Italian Apennines to evaluate the seroprevalence to Neospora caninum, and to investigate the climatic, environmental, farm management, and individual animal factors that influence the distribution of this protozoan. Blood samples were collected from 864 pastured cattle raised on 81 farms. Serum samples were tested for antibodies to N. caninum using an ELISA assay (HerdCheck), IDEXX). A geographical information system (GIS) for the study area was constructed using the following remote sensing (RS) and landscape feature data: autumn-winter, spring and summer normalized difference vegetation index (NDVI), land cover, elevation, slope, aspect, mean rainfall and minimum, mean, and maximum temperature in spring, summer, autumn and winter. Data on each of these features were then extracted for "buffer zones" consisting of the area included in a circle of 3 km diameter centered on the 81 geo-referenced centroids of the main cattle pastures. Climatic and environmental data obtained from RS and GIS and individual animal characteristics and farm management data obtained from a questionnaire were analyzed in relation to N. caninum seropositivity and antibody titres both by linear and logistic regression models. Out of the 81 farms sampled, 63 (77.8%) had at least one tested animal positive for N. caninum. Out of the 864 bovine sera samples, 266 (30.8%) were found to have antibodies to N. caninum. The results of the logistic regression model show that significantly high seroprevalence to N. caninum was found in heifers/steers and adults, in cattle raised on farms having a large number of dogs, and in cattle raised in buffer zones having high minimum temperatures in the spring, and a narrow extension of summer NDVI. In addition, positive linear correlations were found between N. caninum antibody titres and the number of dogs on farm, and the minimum temperature in spring. All the above determined risk factors for N. caninum seroprevalence indicate that horizontal infection resulting from the ingestion of oocysts shed by dogs is the most probable route of N. caninum infection in pastured cattle of the southern Italian Apennines.

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.

Neospora caninum seroprevalence in dairy cattle in central Thailand

The seroprevalence, in dairy cattle, of antibodies to Neospora caninum, the relationship between seropositivity and age (heifer versus cow), the relationship of herd infection with herd size and the relationship of herd infection with the presence of dogs on the farm were studied. The study involved 549 cows and 82 dogs in 59 dairy herds in Nakhon Pathom, Thailand. A competitive enzyme-linked immunosorbent assay (cELISA) with NC-specific monoclonal antibody was used to detect the NC antibodies in the sera. Individual and herd seroprevalence of NC were 5.5% (30/549) and 34% (20/59), respectively. No significant relationships between NC seropositivity with the age of the cows (heifer versus cow; P > 0.05) and between herd infection and the presence of dogs on the farm (P > 0.05) were found. Herd size significantly affected herd infection (P < 0.05) with higher infection in large than small herds (> or = 21 versus < or = 20 cows). Of 12 cows with a history of abortion, one was seropositive to NC. The seroprevalence of NC antibodies in dogs was 1.2% (1/82). This is the first NC seroprevalence study in dogs in Thailand. It was concluded that Neospora infection was more common at the herd level rather than the individual level in Thailand and the presence of dogs on the farm was not related to the level of herd infection. Caution should be taken in the interpretation of serological tests from the farm dogs.

Udder health in dairy cattle infected with Neospora caninum

Blood samples were collected from 3449 cows on 57 representative Ontario dairy herds during the summer of 1998 and analysed for antibody to Neospora caninum using an ELISA. Forty-eight herds (2742 cattle) contained at least one N. caninum-seropositive animal. Two composite milk samples were collected from all cattle: the first on the day of blood collection and the second 68 to 365 days later. All milk samples were submitted for bacteriological culture. Ontario Dairy Herd Improvement Corporation (DHI) data were available for 3162 cattle in the 57 herds at the time of bleeding. Furthermore, complete DHI data were available for 1658 cattle that were culled between 12 and 24 months following blood collection. Using a standardised ELISA sample-to-positive (S/P) cut-off of > or = 0.45, the corrected seroprevalence was 8.2% overall and 10.1% within seropositive herds. At blood collection the odds of N. caninum-seropositive cows having a high linear score (> or = 4.0; equivalent to a somatic cell count > or = 200,000 cells/ml) was 27% less than for seronegative animals. Similarly, at the time of culling, the odds of having a high linear score was 22% less in N. caninum-seropositive cattle. Overall, linear score was lower in N. caninum-seropositive cattle at culling. After controlling for herd, parity, days in milk, and the interval between collection of milk samples, the odds of N. caninum-seropositive cattle testing positive for an environmental pathogen (i.e. environmental Streptococcus species and coliforms) on the second milk sample was 56% less than for seronegative animals. The odds were 83% less at a higher ELISA S/P cut-off of > or = 0.70. Finally, the odds of N. caninum-seropositive cattle developing a new infection with a major pathogen (environmental or contagious) were 60% less than seronegative cows using the higher ELISA S/P cut-off.