Neospora caninum in dogs: detection of antibodies by ELISA using an iscom antigen

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.

Importance of serological cross-reactivity among Toxoplasma gondii, Hammondia spp., Neospora spp., Sarcocystis spp. and Besnoitia besnoiti

Toxoplasma gondii, Neospora spp., Sarcocystis spp., Hammondia spp. and Besnoitia besnoiti are genetically related cyst-forming coccidia. Serology is frequently used for the identification of T. gondii, Neospora spp. and B. besnoiti-exposed individuals. Serologic cross-reactions occur in different tests among animals infected with T. gondii and H. hammondi, as well as among animals infected by T. gondii and N. caninum. Infections caused by N. caninum and N. hughesi are almost indistinguishable by serology. Neospora caninum, B. besnoiti and Sarcocystis spp. infections in cattle show some degree of serologic cross-reactivity. Antibody cross-reactivity between Neospora spp. and H. heydorni-infected animals is suspected, but not proven to occur. We review serologic cross-reactivity among animals and/or humans infected with T. gondii, Neospora spp., Sarcocystis spp., Hammondia spp. and B. besnoiti. Emphasis is laid upon antigens and serological methods for N. caninum diagnosis which were tested for cross-reactivity with related protozoa. Species-specific antigens, as well as stage-specific proteins have been identified in some of these parasites and have promising use for diagnosis and epidemiological surveys.

Development of a disperse dye immunoassay technique for detection of antibodies against Neospora caninum in cattle

In this study a disperse dye immunoassay method was standardized and evaluated for detection of antibodies against Neospora caninum in cattle. Sera from 150 cattle with a recent history of abortion were collected and tested by commercial ELISA kit and a standardized in-house dye immunoassay system. The positivity rate for the sera used in this study was 34.6% for the disperse dye immunoassay (DDIA) compared to 32% obtained by ELISA kit. This study showed no significant difference between DDIA and ELISA. The results indicated that the DDIA provide an economic, simple, rapid and robust test for detection of N. caninum infection in cattle.

Functionalization of immunostimulating complexes (ISCOMs) with lipid vinyl sulfones and their application in immunological techniques and therapy

Background

Immunostimulating complexes (ISCOM)-type nanocapsules have been functionalized with lipid vinyl sulfones that anchor to them via the hydrophobic zone of their structure and can be charged with pharmacologically active molecules or macromolecules. These functionalized nanocapsules can incorporate protein A and bind to G immunoglobulins (IgGs) to make vehicles directed at the surface antigens of infectious agents, tumor cells, or receptor cells and deliver the encapsulated molecules in a highly specific way. They may be of particular use in pharmacological treatments with highly toxic molecules that should not be used in solution whenever it can be avoided. When bound to antibodies they can be used in biological processes that require the delivery or presentation of macromolecules to certain specific cells, in immunization processes for instance, or in diagnostic immunological techniques, as they are able to transport both the secondary antibodies and the reaction labels.

Methods and results

We describe the preparation of ISCOMs, the binding to the ISCOMS of newly synthesized compounds composed of chain alkyl vinyl sulfone, and the subsequent binding of the vinyl-sulfone compounds to IgGs. Within this context, a compound deriving from cholesterol functionalized with vinyl sulfone and used together with cholesterol in varying proportions has been linked to the structure of the ISCOMs and bound to protein A–IgG. This functionalization in no way altered the form or structure of the ISCOMs and allowed the nanocapsules carrying the specific IgGs to bind to forms of Trypanosoma cruzi against which antibodies had been developed. The fact that functionalized ISCOMs containing antibodies could deliver actinomycin D directly to the parasite meant that the effective dose of the antibiotic could be reduced very significantly.

Conclusion

We have developed ISCOM-type nanocapsules functionalized with lipid vinyl sulfone capable of anchoring to the surface of functional IgGs, which favors the recognition and transport of these nanocapsules precisely to certain kinds of cell.

Prevalence of antibodies against Neospora caninum in dogs from urban areas in Central Poland

Neospora caninum is a protozoan parasite which causes abortion in cattle as well as reproduction problems and neurological disorders in dogs. To assess the prevalence of the parasite in urban dogs in the Mazovian Voivodeship, Central Poland, serum samples from 257 dogs were analyzed for the presence of specific IgG antibodies. The examined dogs visited three private veterinary clinics located in Warsaw due to control tests, vaccinations, or other reasons not directly connected with neosporosis. Using ELISA and Western blot, antibodies against the parasite were detected in 56 out of 257 dogs, giving a prevalence of 21.7%. A greater prevalence was observed in female dogs than in males, 28% and 17.3%, respectively, and the differences were statistically significant (p < 0.05). There were no significant differences in seroprevalence of Neospora infection within the age groups (p > 0.05). This study indicates the presence of N. caninum in the Mazovian Voivodeship, in dogs which live in urban areas and exposure of these dogs to the parasite. The fact that seropositive dogs had no contact with cattle confirms the important role of dogs in the parasite’s epidemiology.

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.

A longitudinal study of seroprevalence and seroconversion of Neospora caninum infection in dairy cattle in northeast Thailand

A long-term study was carried out in 11 dairy herds in the Khon Kaen province of northeast Thailand between August 2001 and November 2004. The objective was to investigate seroprevalence dynamics of Neospora caninum infection in the herds and to demonstrate patterns of seroconversion in individual cattle. Each herd was visited once a year, in total four times, and sera from cattle > 3 months of age and farm dogs as well as a sample from the bulk milk were collected. All samples were analysed for presence of specific antibodies by an N. caninum iscom ELISA. The overall percentage of antibody-positive cattle was constant and varied only between 10 and 13% over the 4 years, but the variation in within-herd seroprevalence between herds was substantial. Two herds had > or = 20% seropositive animals at all samplings and consistently high bulk milk OD, whereas two herds had no seropositive animal at the last two samplings and low bulk milk OD. Five herds had a decreasing trend of within-herd seroprevalence, whereas the remaining six herds had a higher portion of test-positive individuals at the end of the study. A total of 424 individuals were sampled more than once; 344 (81%) and 32 (8%) were consistently antibody-negative and antibody-positive, respectively. The proportions of animals that changed from being seronegative to seropositive and from being seropositive to seronegative between the years were 3.9-4.6% and 19-39%, respectively. Apparent vertical and horizontal transmission rates were 58% (95% CI; 44-71%) and 5% (95% CI; 3-7%), respectively. In conclusion, the overall percentage of N. caninum antibody-positive cattle was constant over the years, but the within-herd seroprevalence varied substantially between the herds. Seroconversions were likely to occur in individual cattle although most animals had consistent serological status throughout the study.

Study on the prevalence of Toxoplasma gondii and Neospora caninum and molecular evidence of Encephalitozoon cuniculi and Encephalitozoon (Septata) intestinalis infections in red foxes (Vulpes vulpes) in rural Ireland

Thoracic fluid (pleural fluid and clotted blood) from 206 foxes were examined for antibodies to Toxoplasma gondii and 220 thoracic fluid samples were tested for Neospora caninum antibodies using indirect immunofluorescent antibody tests (IFAT). A total of 115 (56%) and six (3%) foxes had antibodies to T. gondii and N. caninum, respectively. The brains from 148 foxes were examined for histological lesions and pathological changes suggestive of parasitic encephalitis were observed in 33 (22%). Two thirds of these foxes had antibodies to T. gondii and one fox had antibodies to both T. gondii and N. caninum. PCR assays carried out on DNA extracted from the 33 brains with histological lesions were negative for N. caninum but one of the brains was positive for T. gondii. Microsporidian DNA was also amplified from the brains of two of these foxes. Sequencing these amplicons revealed 100% homology with Encephalitozoon (Septata) intestinalis in one fox and Encephalitozoon cuniculi in the second fox. This is the first report of Encephalitozoon infections in wildlife in Ireland.

Evaluation of serological tests for the diagnosis of Neospora caninum infection in dogs: Optimization of cut off titers and inhibition studies of cross-reactivity with Toxoplasma gondii

Diagnosis of Neospora caninum infection in dogs is based on serological assays such as the indirect fluorescent antibody test (IFAT) and enzyme-linked immunosorbent assays (ELISA). This study evaluated two serological tests (IFAT and ELISA) for the detection of IgG antibodies to N. caninum in 300 serum samples of dogs through the optimization of cut off titers by using the two-graph receiver-operating characteristic (TG-ROC) curve. In addition, the identification of major cross-reactive antigens with Toxoplasma gondii was investigated by inhibition ELISA and immunoblotting (IB) assays. IFAT and ELISA results showed 74% agreement, with a good negative concordance (P(neg)=0.83), but a poor positive concordance (P(pos)=0.42). The great majority (86%) of sera with positive concordant results (IFAT+/ELISA+) recognized at least two out of three N. caninum immunodominant antigens, particularly the 29-32 and 35-37 kDa bands. Optimization of cut off titers in IFAT and ELISA was performed considering the reactivity to at least two out of three N. caninum immunodominant antigens as infection markers, obtaining a titer of 50 for IFAT and 200 for ELISA. Seropositivity to N. caninum was significantly associated with T. gondii-seropositive samples, particularly in ELISA (55.4%). Inhibition ELISA curves for N. caninum showed a partial heterologous inhibition, indicating some degree of cross-reactivity between N. caninum and T. gondii antigens. Inhibition IB assays showed a moderate heterologous inhibition for N. caninum antigens above 45-50 kDa. These results indicate that ELISA should be used critically when crude tachyzoite antigen preparations are employed, due to possible cross-reactivity with other related parasites as T. gondii. Also, the cut off dilution of 1:50 in IFAT showed to be the most appropriated for N. caninum serology in dogs. Therefore, we suggest that N. caninum immunodominant antigens, specially the 17 and 29-32 kDa proteins, should be selected markers in serological assays for canine neosporosis.

Natural killer cells act as early responders in an experimental infection with Neospora caninum in calves

The intracellular protozoan parasite Neospora caninum is a cause of abortion and congenital disease in cattle worldwide. We have previously shown that natural killer (NK) cells produce IFN-gamma in response to N. caninum tachyzoites in vitro. This study aimed to investigate the role of NK cells and other cellular immune responses in an experimental N. caninum infection model in calves. Phenotyping of peripheral blood lymphocytes showed a drop in the percentage of NK cells at days 4-6 after i.v. inoculation, followed by an increase in the percentage of both NK cells and CD8+ T cells which peaked at days 11-15. A whole blood flow cytometric assay showed that CD4+ T cells were the major IFN-gamma producing cells, but in the early stages of the infection both NK cells and CD8+ T cells contributed to IFN-gamma production. We also compared the ability of two different N. caninum antigen preparations--sonicated soluble antigens and intact heat-inactivated parasites--to induce proliferation and IFN-gamma production in various cell types. Heat-inactivated tachyzoites induced a 3.7 times greater increase in the number of IFN-gamma producing NK cells compared with sonicated soluble antigens. This indicated the presence of some NK cell-stimulating antigens in the intact tachyzoite that were absent from the sonicated soluble antigens. The heat-inactivated whole tachyzoites also inhibited gammadelta T cell proliferation while the soluble antigens from N. caninum did not. We believe this is the first time NK cells have been demonstrated to be early responders in N. caninum infection in calves.

Prevalence of antibodies against Toxoplasma gondii and Neospora caninum in Hungarian red foxes (Vulpes vulpes)

In the present study we have investigated the seroprevalence to the protozoan parasites Toxoplasma gondii and Neospora caninum in 337 red foxes (Vulpes vulpes) from 16 out of 19 counties in Hungary. The foxes were originally collected within a National vaccination program against rabies. Antibodies to T. gondii were detected in as many as 228 (68%) of the foxes using a commercial direct agglutination test (DAT). In an indirect iscom ELISA, five foxes (1.5%) were positive for antibodies against N. caninum. The high prevalence of foxes positive for T. gondii might be explained by the widespread occurrence of the parasite in the diet of foxes. As a contrast, latent infections of N. caninum among red foxes in Hungary are much less common.

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.

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.

Immunodiagnosis of Besnoitia besnoiti infection by ELISA and Western blot

Besnoitia besnoiti, an obligate intracellular apicomplexan protozoan parasite, is the causative agent of bovine besnoitiosis. This infection may dramatically affect body condition and lead to irreversible infertility in males, resulting in important economical losses in livestock production. Identification of serologically positive animals is of major relevance to elaborate appropriate measures of control. While identification of clinical cases is relatively easy to carry out, the finding of subclinical forms of infection is more difficult, thus serology is considered as an appropriate diagnostic tool. In view to improve and validate immunodiagnosis, we evaluated an enzyme-linked immunosorbent assay (ELISA), complemented with a Western blot (both using a somatic B. besnoiti-tachyzoite antigen) to detect anti-B. besnoiti antibodies in bovine sera. The comparative evaluation of the 2 methods, using 13 sera from animals affected by the chronic phase of besnoitiosis and 10 asymptomatic carriers, yielded a diagnostic sensitivity of 87% for ELISA and 91% for Western blot analyses. Specificity was tested with sera from animals with confirmed Toxoplasma gondii (n=5) and Neospora caninum (n=12) infection, and with 64 negative sera from either an endemic or a non-endemic area. The ELISA specificity ranged between 96.4% and 98%, the Western blot specificity between 96.4% and 100%. The present study demonstrated that ELISA and Western blot, using in vitro generated somatic B. besnoiti antigen, is a useful tool combination to reliably detect animals that have been exposed to B. besnoiti infection, including both asymptomatic and symptomatic courses of disease.

Detection of immunoglobulin G antibodies to Neospora caninum in humans: high seropositivity rates in patients who are infected by human immunodeficiency virus or have neurological disorders

Considering that little is known about the epidemiology of Neospora caninum infection in humans, particularly in populations with high Toxoplasma gondii infection rates, the present study aimed to investigate the presence of antibodies to N. caninum in T. gondii-seropositive and -seronegative individuals. A total of 256 serum samples divided into four groups (61 samples from human immunodeficiency virus [HIV]-positive patients, 50 samples from patients with neurological disorders, 91 samples from newborns, and 54 samples from healthy subjects) were assessed for N. caninum and T. gondii serologies by indirect fluorescent-antibody test, enzyme-linked immunosorbent assay, and immunoblotting (IB). Immunoglobulin G antibodies to N. caninum were predominantly detected in HIV-infected patients (38%) and patients with neurological disorders (18%), while newborns and healthy subjects showed lower seropositivity rates (5% and 6%, respectively). Seropositivity to N. caninum was significantly associated with seropositivity to T. gondii in both HIV-infected patients and patients with neurological disorders. Seroreactivity to N. caninum was confirmed by IB, with positive sera predominantly recognizing the 29-kDa antigen of N. caninum. The results of this study indicate the presence of N. caninum infection or exposure in humans, particularly in HIV-infected patients or patients with neurological disorders, who could have opportunistic and concurrent infections with T. gondii. These findings may bring a new concern for the unstable clinical health of HIV-infected patients and the actual role of N. caninum infection in immunocompromised patients.

In vitro isolation and characterisation of the first canine Neospora caninum isolate in Australia

Neospora caninum was isolated and established in vitro from the skin lesion of a naturally infected dog. The identity of the parasite was evaluated by immunofluorescent antibody test (IFAT), microscopy, Western blotting and polymerase chain reaction (PCR). N. caninum DNA was detected in the whole blood, serum, skin lesion, rectal scrapings and faeces of the infected dog utilising a nested PCR targeting the Nc-5 gene of N. caninum. Antigenic and genetic characterisation of the isolate, designated WA-K9, at a number of loci including the Nc-5 gene, heat shock protein 70 (HSP-70) gene, alpha-tubulin and beta-tubulin genes revealed no variation between this isolate and two N. caninum isolates from different geographic areas. Clinical aspects of this case, which included cutaneous and neurological disease, are also discussed.

Seroprevalences of Toxoplasma gondii and Neospora sp. infections in Swedish horses

Sera from 414 Swedish horses were investigated for the presence of antibodies to Toxoplasma gondii and Neospora sp. by the T. gondii direct agglutination test (DAT), and an Neospora caninum iscom-ELISA. Five sera (1%) had a titre >1:40 in DAT, but when analysed by immunoblotting against T. gondii antigens only two of them were positive, giving a seroprevalence of 0.5%. Since the Neospora iscom ELISA had not been validated for equine sera it was used for an initial screening, and all sera with an optical density exceeding 0.200 absorbance units were selected for further investigation by immunoblot analysis. Of the 39 sera tested by immunoblotting, four reacted with at least two of the immunodominant Neospora antigens recognized by the positive control sera and were judged as positive, resulting in a seroprevalence of 1%. This is the first evidence of Neospora infection in Swedish horses. The study illustrates the necessity of critically evaluating results of serological analyses performed by methods that are not validated for the animal species under investigation.

The protozoan Neospora caninum directly triggers bovine NK cells to produce gamma interferon and to kill infected fibroblasts

Natural killer (NK) cells are considered to be key players in the early innate responses to protozoan infections, primarily indirectly by producing gamma interferon (IFN-gamma) in response to cytokines, like interleukin 12 (IL-12). We demonstrate that live, as well as heat-inactivated, tachyzoites of Neospora caninum, a Toxoplasma-like protozoan, directly trigger production of IFN-gamma from purified, IL-2-activated bovine NK cells. This response occurred independently of IL-12 but was increased by the addition of the cytokine. A similar IFN-gamma response was measured in cocultures of NK cells and N. caninum-infected autologous fibroblasts. However, no NK cell-derived IFN-gamma response was detected when cells were cultured with soluble antigens from the organism, indicating that intact tachyzoites or nonsoluble components are necessary for NK cell triggering. Furthermore, N. caninum-infected autologous fibroblasts had increased susceptibility to NK cell cytotoxicity compared to uninfected fibroblasts. This cytotoxicity was largely mediated by a perforin-mediated mechanism. The activating receptor NKp46 was involved in cytotoxicity against fibroblasts but could not explain the increased cytotoxicity against infected targets. Interestingly, N. caninum tachyzoites were able to infect cultured NK cells, in which tachyzoites proliferated inside parasitophorous vacuoles. Together, these findings underscore the role of NK cells as primary responders during a protozoan infection, describe intracellular protozoan infection of NK cells in vitro for the first time, and represent the first functional study of purified bovine NK cells in response to infection.

Evaluation of an iscom ELISA used for detection of antibodies to Neospora caninum in bulk milk

The intracellular parasite Neospora caninum is increasingly recognized as an important cause of abortion and stillbirth in cattle. Presence of specific antibodies indicates infection, and the immunostimulating complex (iscom) enzyme-linked immunoassay (ELISA) has previously been evaluated for use on individual milk and sera. In the present study, this test is investigated for use on bulk milk. In this study, 124 herds were used to analyse the relationship between within-herd prevalences based on individual sera and bulk milk optical densities. The individual test results were translated into a herd-level result, which enabled comparison of the bulk milk test result to the aggregate of individual serum results. The relative contribution of milk from cows with different milk yield and antibody status to the tank, i.e. its composition, was expected to influence the outcome of the bulk milk test. Therefore, sensitivity and specificity were calculated at different cut-off levels, not only using a standard cross-tabulation technique, but also a logistic regression model. By using the latter method, the sensitivity and specificity could be estimated adjusting for milk yield covariates. Specificity was estimated to be high ( approximately 98%) at the 0.20 cut-off, which can be used as a decision threshold to rule in infection. With more equal emphasis on sensitivity and specificity, a lower cut-off should be used. Although infection cannot be completely ruled out, herds with test results below 0.05 are highly likely to be non-infected. The within-herd prevalence of false negative herds is probably less than 10-15% at this level. From what is known about test performance at the individual level and the prevalence of infection, the estimate of the specificity of the bulk milk test should be quite accurate while the sensitivity is likely to be underestimated. We confirmed that the performance of the bulk milk test depends on the milk tank composition. In particular the milk yield of cows with high antibody levels affects the probability of a positive outcome of the bulk milk test.

Neospora caninum: adoptive transfer of immune lymphocytes precipitates disease in BALB/c mice

Neospora caninum is a recently described apicomplexan parasite first isolated from a dog in 1988 and has subsequently been shown to infect a wide range of mammals. In mice, Neospora can cause primary pneumonia, myositis, encephalitis, radiculoneuritis, and pancreatitis. Whereas, certain aspects of the host immune response to Toxoplasma gondii have been well studied, not as much is known about the full immune response to Neospora. This paper examines whether or not immune splenocytes are able to adoptively transfer protection against N. caninum infection in BALB/c mice. Mice receiving immune enriched CD8+ cells had severe neurological signs by 19 days post infection. Mice receiving immune enriched CD4+ cells had mild neurological signs on day 22 post infection. It would appear that additional immune cells can precipitate disease in the presence of circulating lymphocytes.

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.

Prevalence of antibodies to Toxoplasmagondii and Neosporacaninum in red foxes (Vulpesvulpes) from around the UK

The purpose of this study was to establish the prevalence of antibodies to Toxoplasma gondii and Neospora caninum in a random sample of red foxes from around the UK. Lung fluid from over 500 foxes was examined using an indirect fluorescent antibody test. Reciprocal titres of specific antibodies to T. gondii or N. caninum ranged from < 1:16 to 1:1024. A titre of 1:128 or greater was deemed indicative of exposure to the parasite. One hundred and eleven (20%) of the 549 foxes tested were seropositive to T. gondii, and only five (0.9%) were seropositive to N. caninum. No correlation could be made between positive samples and geographical distribution, as sample numbers varied greatly between regions. The results of this study indicate that red foxes of the UK have more exposure to T. gondii than to N. caninum in their environment.

Prevalence and transmission of Neospora caninum within infected Swedish dairy herds

In this long-term study, the changes in within-herd Neospora caninum seroprevalences and the relative importance of horizontal and vertical parasite transmission in Swedish dairy herds were investigated. The within-herd prevalences varied between 5.8% and 65.0% when the herds were first sampled. Comparing the prevalences of year 2000 with those found 2-3 years later, nine out of 14 investigated herds had a similar or lower within-herd prevalence while five herds had an increased portion of seropositive individuals. Three herds were free or almost free from infection at their last sampling. Changes in prevalence were not related to the level of prevalence that each herd had when first sampled. Antibody avidity measurements revealed that the majority of seropositive individuals in all herds were chronically infected. Dam-calf pair investigations and inspection of genealogic trees supplemented with antibody test results showed that vertical transmission was by far the dominant transmission route in all herds. Taken together, these results indicate that the prevalence of N. caninum infection in Swedish dairy cattle can be successfully reduced if actions to eliminate infection in a herd are combined with preventive measures to avoid re-infection.

Antibodies to Neospora caninum in the blood of European bison (Bison bonasus bonasus L.) living in Poland

The prevalence of antibodies to Neospora caninum was examined in European bison (Bison bonasus bonasus L.) living in free and fenced areas in Poland. Sera of 320 European bison, different ages and sexes, from breeding areas in Poland were tested for N. caninum antibodies using ELISA test. Positive antibody responses were found in 23 bison (prevalence 7.3%). Additionally, all positive sera were tested by Western blot to verify the ELISA results. The Western blot results confirmed the presence of antibodies to Neospora tachyzoites antigens in all 23 sera tested. The antibodies were detected against a wide range of NC-1 tachyzoite antigens. The antibody responses were directed against proteins at: 9.5, 17, 21, 27, 31, 36.5, 38, 40, 43, 47, 48.5, 53.5 and 58 kDa. The most heavily stained bands had molecular weights of 9.5, 17, 27 and 58 kDa. The most important is that antibody to N. caninum was detected for the first time in sera from bison cow shot in 1988. It is the year of recognition of this protozoan parasite. Our results indicate strongly the presence of N. caninum in European bison in Poland and suggest that a sylvatic cycle of N. caninum can exist. However, further studies are needed to evaluate the existence of a sylvatic cycle of N. caninum. The study on the effect of the infection on the health status and conservation of European bison should be taken under consideration too.

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

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

Neospora caninum 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.

Recognition patterns of Neospora caninum tachyzoite antigens by bovine IgG at different IFAT titres

This study describes qualitative and quantitative antibody response in cows naturally infected with Neospora caninum. The study was carried out with 269 serum samples obtained from 24 cows over a period of 15 weeks. Prior to sample collection, the cows were tested with ELISA. The 269 samples were screened with IFAT and categorized into seven IFAT titre groups (< 1 : 80, 1 : 80, 1 : 200, 1 : 600, 1 : 1000, 1 : 2000, > 1 : 2000). The samples were finally analysed by Western blotting. Seven immunodominant antigens (approximately 18-, approximately 25-, approximately 33-, approximately 35-36-, approximately 45-46-, approximately 47-, approximately 60-62 kDa) and five minor antigens (approximately 25, approximately 51, approximately 64, approximately 77, approximately 116 kDa) were recognized by cow sera. The recognition of approximately 46 kDa antigen by cow sera was common to samples with IFAT titre 1 : 80 and above. Another common antigen was the approximately 18 kDa antigen, which was recognized by samples with IFAT titre 1 : 200 and above. The most remarkable observation was the presence of the 45-46 kDa, the 77 kDa, and absence of the 18 kDa antigenic bands in samples with IFAT titre 1 : 80. This observation was consistent even in the face of fluctuating antibody titre where serum antibody titres from an animal exceeded then failed to reach 1 : 80. Antibody fluctuation was observed across all cows (pregnant and aborted) with no discernible fluctuation pattern. However, the fluctuation in antibody titre observed appeared to be most remarkable in initially ELISA-negative pregnant cows, and to a lesser extent in ELISA-positive pregnant cows, and ELISA-positive aborted cows. Although there was fluctuation in antibody titre, the banding patterns of N. caninum tachyzoite antigens by cows within the same IFAT titre group remained similar.

A long-term study of Neospora caninum infection in a Swedish dairy herd

A longitudinal study was performed in a Swedish dairy herd where Neospora caninum had been isolated from a stillborn calf. Starting in autumn 1994, blood samples from all female animals in the herd were collected once yearly until 1999. The sera were analysed for presence of IgG1 antibodies to N. caninum by the iscom ELISA, and by an avidity ELISA to establish the timing of infection. In addition, data on reproductive performance were compiled. During the study the percentage of seropositive female animals increased from 63% to 87%. In 1994 a large number of young animals tested seropositive although their dams were seronegative, indicating that a transmission of the parasite other than the vertical had recently occurred. Low avidity values supported this assumption. The annual abortion rate increased from a mean of 2% before the initiation of the study to 9% in 1994-1998. During the same time, as judged by the avidity data, a large proportion of the animals shifted from being recently to being chronically infected. The source of the external infection in the herd could not be identified.

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

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

Qualitative evaluation of selective tests for detection of Neospora hughesi antibodies in serum and cerebrospinal fluid of experimentally infected horses

Neospora hughesi is a newly recognized protozoan pathogen in horses that causes a myeloencephalitis similar to Sarcocystis neurona. There are no validated serologic tests using the gold standard sera that are currently available to detect specific N. hughesi antibodies and, thus, no tests available to detect antemortem exposure or estimate seroprevalence in the horse. The objectives of the present study were to establish a bank of gold standard equine sera through experimental infections with N. hughesi and to assess several serologic tests for the detection of related protozoan antibodies. Seven horses were inoculated with N. hughesi tachyzoites, and 7 horses received uninfected cell culture material. The horses were monitored, and blood and cerebrospinal fluid were collected repeatedly over a 4-mo period. With the sera, 4 different serologic techniques were evaluated. including a whole-parasite lysate enzyme-linked immunosorbent assay (ELISA), a recombinant protein ELISA, a modified direct agglutination test, and an indirect fluorescent antibody test. Qualitative and quantitative evaluation of the results showed that the N. hughesi indirect fluorescent antibody test (IFAT) consistently discriminated between experimentally infected and noninfected horses, using a cutoff of 1:640. Sera from 3 naturally infected horses had titers >1:640. Cerebrospinal fluid in all but I infected horse had very low N. hughesi IFAT titers (<1:160), starting at postinoculation day 30.

Seroprevalence of antibodies to Neospora caninum in dogs from Spain

The prevalence of Neospora caninum antibodies was determined in sera of 139 dogs from Catalonia (northeastern Spain) using the indirect immunofluorescence antibody test (IFAT). Antibodies in the IFAT were found in 17 of 139 dogs (12.2%) with titers ranging from 1:50 to 1: 1,600. Seroprevalence was higher in dogs over 1 yr old compared with dogs younger than 1 yr (P < 0.05). No statistical difference was observed when sex, breed, purpose, or modus vivendi was compared with seropositivity. Most dogs had low antibody titers, which indicated subclinical infection in the area studied. No neosporosis-related disease was reported from any dog, although a German shepherd with an antibody titer of 1:800 showed pododermatitis. All sera were also screened using a commercial direct agglutination test (DAT). The DAT showed a similar specificity but a lower sensitivity when compared with IFAT as a reference technique.

Production and characterization of monoclonal antibodies against dog immunoglobulin isotypes

A panel of six monoclonal antibodies (mAbs) recognizing antigenic determinants on canine immunoglobulin (Ig) heavy or light chains was produced and characterized. All monoclonals recognized the IgG(2) subclass, although only two were subclass-specific (CA3H1 and CA4F1). The CA3B8 mAb was found to be specific for an epitope on canine immunoglobulin G heavy chain, (IgG(1) and IgG(2) subclasses). Two mAbs (CA2E9 and CA5B2) reacted with an epitope on the heavy chain of canine IgG and IgM and another, CA4E7, bound to canine IgA, IgG and IgM isotypes; CA4E7 recognized an epitope on canine immunoglobulin light chain. CA4E7, CA4F1 and CA5B2 recognized an epitope in the Fab region. Three mAbs, CA3B8, CA4E7 and CA5B2, showed much lower reactivity with canine IgG by ELISA when IgG was periodate-treated, suggesting that they recognized a carbohydrate determinant. Cross-reactivity analysis of these mAbs with sera from horse, goat, cow, sheep, pig, cat, rabbit, hamster, rat, mouse and human indicated that two mAbs, CA3B8 and CA5B2, recognized a canine IgG-specific epitope; two others, CA3H1 and CA4E7, recognized an epitope also present in rabbit and sheep immunoglobulin respectively; and the remaining two (CA2E9 and CA4F1) recognized an epitope broadly present on the Igs of the species analyzed. This panel of antibodies will be a useful tool for future canine immunodiagnosis tests. With the exception of CA2E9, all mAbs were able to recognize plasma cells on paraffin-embedded tissues, and will thus be useful for immunohistochemical assays.

Pattern of recognition of Neospora caninum tachyzoite antigens by naturally infected pregnant cattle and aborted foetuses

Different aspects of Neospora tachyzoite antigen recognition by Neospora-infected heifers and cows and aborted foetuses were studied. The pattern of antigen recognition and the relationship between IFAT titres and number of Neospora antigens detected, were evaluated. In addition, the tachyzoite antigens involved in the humoral immune response developed against infection in normal cows and cows that aborted were also characterised throughout pregnancy. Comparison of tachyzoite antigen recognition was carried out in 13 thoracic and/or abdominal fluids from Neospora aborted foetuses and 33 sera from Neospora infected cows that had aborted. The kinetics of Neospora-antigen recognition was studied in Neospora-infected heifers and cows that had aborted foetuses (7) or not (14) during pregnancy. Based on the frequency and intensity of recognition, four IDAs-17-18, 34-35, 37 and 60-62kDa antigens-have been described. Moreover, a correlation was found between Western blot results and IFAT titres in both age groups. In relation to antigen recognition throughout pregnancy by seropositive cows that had aborted or not, the antibody fluctuations throughout pregnancy described in the literature could be due to differences in the intensity and frequency of recognition of particular antigens, especially the 17-18kDa antigen. We emphasize the important role that the 17-18kDa antigen could play in the serological diagnosis of Neospora infection in cattle as this was intensely detected in 100% of the animals.

Immunisation of mice against neosporosis

In the present study a murine encephalitis model was used to investigate if protection against neosporosis could be achieved by immunisation. Groups of 10 mice were immunised with a sublethal dose of live Neospora caninum tachyzoites, N. caninum antigens incorporated into iscoms, N. caninum lysate mixed with Quil A, or N. caninum lysate in PBS. Control mice were given Quil A only. Challenge infection with 2.5x10(6) N. caninum tachyzoites resulted in clinical symptoms that remained until the end of the experiment in the controls. In contrast, mice immunised with live parasites or parasite lysate in Quil A only showed mild and transient symptoms. Of nine mice immunised with N. caninum iscoms, seven recovered while two died. Most severely affected were the mice immunised with parasite lysate only; all of them died within 28 days post-infection. Histological examination and scoring of brain lesions gave a significantly lower (P<0.0001) lesion score in mice immunised with live parasites than in controls. The groups immunised with iscoms or lysate and Quil A also had reduced lesion scores (P<0.04 and 0.07, respectively) but not the group given parasite lysate alone. The lesions seen in the latter group differed from those in the other groups. There was less cellular reaction and more tachyzoites indicating an active infection. The N. caninum specific antibody responses and cytokine production (IFN-gamma, IL-4 and IL-5) of splenocytes were analysed at the time of challenge infection. The results suggest a correlation between protection and high levels of IFN-gamma. Also, the immune responses recorded in mice immunised with parasite lysate without adjuvant were relatively weak and more towards the Th2 type, when compared with the other immunisation schedules. This is consistent with the weaker inflammatory response observed in the brains of these mice.

Companion animal parasitology: a clinical perspective

In recent years there have been many changes to the ways that clinical veterinary science is conducted and nowhere is this more evident than in companion animal practice. Veterinarians working with pet dogs and cats are facing new challenges associated with the emergence and re-emergence of parasitic diseases. Some, such as Neospora caninum, have been recently recognised; others like Giardia and Cryptosporidium have been reported with increasing frequency, in part as a result of laboratory tests with improved sensitivity and specificity. In many regions, the emergence of parasitic diseases has been a consequence of pet travel and exotic diseases pose a unique diagnostic challenge for the veterinarian, as the index of suspicion for these conditions may be absent. The ranges of certain vector-borne diseases such as babesiosis, hepatozoonosis, ehrlichiosis, leishmaniasis and dirofilariasis are extending due to ecological and climatic changes and enhanced by animals with subclinical infection returning home from endemic areas. In companion animal practice, veterinarians have the additional responsibility of providing accurate information about the zoonotic transmission of parasite infections from pets, especially to those most vulnerable such as children, the elderly and the immunocompromised. Effective education is vital to allay public concerns and promote responsible pet ownership.

Diagnosis and seroepidemiology of Neospora caninum-associated bovine abortion

A round table was conducted at the VIIIth International Coccidiosis Conference on Neospora diagnosis with particular emphasis on strategies to diagnose bovine abortion. The strength and weakness of different assays for Neospora caninum infection and whether these methods have resulted in the overdiagnosis of neosporosis was discussed. It was evident that each diagnostic method, namely histology, immunohistochemistry, molecular detection and serological assays were, under certain circumstances, valuable in assessing the role N. caninum in abortion. Histological, immunohistochemical and molecular detection assays are of outstanding importance for the examination of tissues of aborted foetuses. While histology and immunohistochemistry allow direct assessment of pathomorphological changes caused by infection, molecular detection assays such as PCR are superior because of higher sensitivity and specificity in identifying N. caninum in foetal tissues. Serological tests, such as ELISA, are useful in determining whether an animal has been infected with N. caninum. Seroepidemiological approaches allow one to assess an abortion problem at a herd level and when used in conjunction with certain statistical methods are able to confirm a suspected N. caninum-associated abortion.

Seroprevalences of Toxoplasma gondii and Neospora caninum in Swedish red foxes (Vulpes vulpes)

The prevalences of antibodies to the protozoan parasites Toxoplasma gondii and Neospora caninum were investigated by the direct agglutination test (DAT) and ELISA, respectively, in 221 red foxes (Vulpes vulpes) from different parts of Sweden. A total of 84 (38%) of the analysed sera had antibodies to T. gondii, but none of the foxes had antibodies to N. caninum. The results indicate that T. gondii infection is fairly common in Swedish red foxes and that the infection is present in most parts of the country. They also show that N. caninum is not widespread as a latent infection among red foxes in Sweden.

Characterization of Neospora caninum surface protein NcSRS2 based on baculovirus expression system and its application for serodiagnosis of Neospora infection

The baculovirus expression system has proved to be a useful tool for the production of recombinant proteins. Here we have characterized the Neospora caninum surface protein NcSRS2 produced by two types of the recombinant virus and also have developed an enzyme-linked immunosorbent assay (ELISA) using recombinant NcSRS2 for the serologic diagnosis of Neospora infection. Western blot analysis showed two major protein bands that were detectable in insect cells infected with each recombinant baculovirus, and a lower-molecular-weight protein was detected in culture supernatants from a cell infected with the recombinant virus lacking the hydrophobic C-terminal tail. Analysis of the N-terminal amino acids showed that the secreted NcSRS2 lacked 6 kDa of the N-terminal signal peptide. Moreover, the detergent-soluble protein of insect cells infected with the recombinant baculovirus expressing the full-length NcSRS2 gene was used to develop an ELISA system based on specificity and reactivity to antisera against Toxoplasma gondii, Hammondia heydorni, or N. caninum. Anti-N. caninum mouse, dog, and bovine sera recognized the recombinant NcSRS2 on Western blots. Furthermore, we have shown that the developed ELISA system consistently discriminates indirect fluorescent-antibody test (IFAT)-positive bovine sera against N. caninum from IFAT-negative sera. These results indicate that the ELISA using baculovirus-expressed NcSRS2 can be useful for effective and reliable serodiagnosis of N. caninum infection.

Prevalence of Neospora caninum infection in dogs from beef-cattle farms, dairy farms, and from urban areas of Argentina

Prevalence of anti-Neospora caninum antibodies was determined in sera of 320 dogs from Argentina using the indirect fluorescent antibody test (IFAT). Antibodies to N. caninum were found in 121 of 320 (37.8%) sera with titers of 1:50 (21 dogs), 1:100 (23 dogs), 1:200 (23 dogs), 1:400 (17 dogs), 1:800 (23 dogs), and > or = 1:1.600 (14 dogs). The seropositivity (IFAT, > or = 1:50) was higher in dogs from dairy (48% of 125) and beef (54.2% of 35) farms than in dogs from urban areas (26.2% of 160). Prevalence of anti-N. caninum antibodies was higher in dogs more than 12 mo of age (47.7%, 105 of 222) versus in 12-mo-old or younger dogs (12.7% of 86), suggesting postnatal exposure of N. caninum infection in dogs.

A random amplified polymorphic DNA polymerase chain reaction technique that differentiates between Neospora species

Neospora caninum is a recently described coccidial parasite that was first isolated from a dog in 1988 and has subsequently been shown to infect a wide range of mammals. Neospora hughesi, a new species of this genus, has recently been isolated from the spinal cord of horses showing clinical signs of equine protozoal myeloencephalitis. The random amplified polymorphic DNA polymerase chain reaction technique is capable of differentiating between N. caninum and N. hughesi.

A European perspective on Neospora caninum

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

Progress in the serodiagnosis of Neospora caninum infections of cattle

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