Neospora caninum in cattle: experimental infection with oocysts can result in exogenous transplacental infection, but not endogenous transplacental infection in the subsequent pregnancy

Whilst it is presumed that infection of pregnant cattle with Neospora caninum oocysts can provoke abortion and is the likely cause of epidemic abortion outbreaks, only two previous experiments have involved inoculation of pregnant cows with oocysts (and only one abortion was provoked in 22 pregnancies). Here, we describe the oral oocyst challenge of 18 cows synchronously bred and inoculated precisely at 70 (n=6), 120 (n=6) and 210 (n=6) days in pregnancy with a nominal dose of 40,000 oocysts. Only one abortion occurred (at the 120 days challenge) which could be definitively ascribed to N. caninum and no transplacental infection (TPI) was detected in any of the other 11 calves born in the 70 and 120 day challenge groups. In contrast, 4/5 live calves born to cattle challenged at 210 days were transplacentally infected. When cows which had transplacentally infected their calves in the first pregnancy were rebred, no TPI occurred. The results show that the timing of challenge influences clinical and parasitological outcomes and that cattle in late pregnancy are exquisitely sensitive to oocyst challenge leading to exogenous TPI and congenitally infected calves. However, cattle which were indisputably systemically infected in their first pregnancy did not induce endogenous TPI in their subsequent pregnancy. This confirms previous results with experimental tachyzoite challenge and suggests that post-natal infection does not lead to persisting infections which can recrudesce in pregnancy.

Identification of ribosomal phosphoprotein P0 of Neospora caninum as a potential common vaccine candidate for the control of both neosporosis and toxoplasmosis☆

The characterization of the cross-reactive antigens of two closely related apicomplexan parasites, Neospora caninum and Toxoplasma gondii, is important to elucidate the common mechanisms of parasite-host interactions. In this context, a gene encoding N. caninum ribosomal phosphoprotein P0 (NcP0) was identified by immunoscreening of a N. caninum tachyzoite cDNA expression library with antisera from mice immunized with T. gondii tachyzoites. The NcP0 was encoded by a gene with open reading frame of 936 bp, which encoded a protein of 311 amino acids. The NcP0 gene existed as a single copy in the genome and was interrupted by a 432 bp intron. The NcP0 showed 94.5% amino acid identity to T. gondii P0 (TgP0). Anti-recombinant NcP0 (rNcP0) sera recognized a native parasite protein with a molecular mass of 34 kDa in Western blot analysis. Immunofluorescence analysis showed that the NcP0 was localized to the surface of N. caninum tachyzoites. A purified anti-rNcP0 IgG antibody inhibited the growth of N. caninum and T. gondii in vitro in a concentration-dependent manner. These results indicate that P0 is a cross-reactive antigen between N. caninum and T. gondii and a potential common vaccine candidate to control both parasites.

Prevention of lethal experimental infection of C57BL/6 mice by vaccination with Brucella abortus strain RB51 expressing Neospora caninum antigens

Bovine abortions caused by the intracellular protozoal parasite Neospora caninum are a major concern to cattle industries worldwide. A strong Th1 immune response is required for protection against N. caninum. Brucella abortus strain RB51 is currently used as a live, attenuated vaccine against bovine brucellosis. Strain RB51 can also be used as an expression vector for heterologous protein expression. In this study, putative protective antigens of N. caninum MIC1, MIC3, GRA2, GRA6 and SRS2, were expressed individually in B. abortus strain RB51. The ability of each of the recombinant RB51 strains to induce N. caninum-specific immunity was assessed in C57BL/6 mice. Mice were immunised by two i.p. inoculations, 4 weeks apart. Five weeks after the second immunisation, spleen cells from the vaccinated mice secreted high levels of IFN-gamma and IL-10 upon in vitro stimulation with N. caninum whole cell lysate antigens. N. caninum-specific antibodies of both IgG1 and IgG2a subtypes were detected in the serum of the vaccinated mice. Mice in the vaccinated and control groups were challenged with 2 x 10(7)N. caninum tachyzoites i.p. and observed for 28 days after vaccination. All unvaccinated control mice died within 7 days. Mice in the MIC1 and GRA6 vaccine groups were completely protected while the mice in the SRS2, GRA2 and MIC3 vaccinated groups were partially protected and experienced 10-50% mortality. The non-recombinant RB51 vector control group experienced an average protection of 69%. These results suggest that expression of protective antigens of N. caninum in B. abortus strain RB51 is a novel approach towards the development of a multivalent vaccine against brucellosis and neosporosis.

Production effects of pathogens causing bovine leukosis, bovine viral diarrhea, paratuberculosis, and neosporosis

The primary purpose of this research was to determine associations among seropositivity for bovine leukemia virus (BLV), bovine viral diarrhea virus (BVDV), Mycobacterium avium ssp. paratuberculosis (MAP), and Neospora caninum (NC) and each of 3 outcome variables (305-d milk, fat, and protein production) in Canadian dairy cattle. Serum samples from up to 30 randomly selected cows from 342 herds on monthly milk testing were tested for antibodies against BLV (IDEXX ELISA; IDEXX Corporation, Westbrook, ME), MAP (IDEXX or Biocor ELISA; Biocor Animal Health, Inc., Omaha, NE), and NC (IDEXX or Biovet ELISA; Biovet Inc., St. Hyacinthe, Quebec, Canada). Up to 5 unvaccinated cattle over 6 mo of age were tested for virus-neutralizing antibodies to the Singer strain of type 1 BVDV. Dairy Herd Improvement records were obtained electronically for all sampled cows. Linear mixed models with herd and cow as random variables were fit, with significant restricted maximum likelihood estimates of outcome effects being obtained, while controlling for potential confounding variables. Bovine leukemia virus seropositivity was not associated with 305-d milk, 305-d fat, or 305-d protein production. Cows in BVDV-seropositive herds (at least one unvaccinated animal with a titer > or =1:64) had reductions in 305-d milk, fat, and protein of 368, 10.2, and 9.5 kg, respectively, compared with cows in BVDV-seronegative herds. Mycobacterium avium ssp. paratuberculosis seropositivity was associated with lower 305-d milk of 212 kg in 4+-lactation cows compared with MAP-seronegative 4+-lactation cows. Neospora caninum seropositivity in primiparous cows was associated with lower 305-d milk, fat, and protein of 158, 5.5, and 3.3 kg, respectively, compared with NC-seronegative primiparous cows. There were no interactions among seropositivity for any of the pathogens and their effects on any of the outcomes examined, although the low MAP seroprevalence limited this analysis. Results from this research will contribute to understanding the economic impacts of these pathogens and justify their control.

Immunogenicity and protective effect against murine cerebral neosporosis of recombinant NcSRS2 in different iscom formulations

Recombinant NcSRS2, a major immunodominant surface antigen of the intracellular protozoan parasite Neospora caninum, was used as a model antigen to compare the immunogenicity of iscoms prepared according to three different methods. Two NcSRS2 fusion proteins were used, one that was biotinylated upon expression in Escherichia coli and linked to Ni2+-loaded iscom matrix (iscom without any protein) via a hexahistidyl (His6)-tagged streptavidin fusion protein, and another that contained both a His6-tag and streptavidin (His6-SA-SRS2') and was coupled to either Ni2+-loaded or biotinylated matrix. While all three iscom preparations induced N. caninum specific antibodies at similar levels, His6-SA-SRS2' coupled to biotinylated matrix generated the strongest cellular responses measured as in vitro proliferation and production of interferon-gamma and interleukin-4 after antigen stimulation of spleen cells. However, the relationship between the levels of these cytokines as well as between IgG1 and IgG2a titres in serum induced by the three iscom preparations were similar, indicating that the balance between Th1 and Th2 responses did not differ. After challenge infection, mice immunised with His6-SA-SRS2' coupled to biotinylated matrix had significantly lower amounts of parasite DNA in their brains compared to the other immunised groups. Possible reasons for the performance of the different iscom formulations are discussed.

Seroprevalence of Antibodies to Neospora caninum in Urban and Rural Dogs in north-west Italy

Sera were collected from 490 dogs from north-west Italy. One hundred and eighty-eight dogs were urban, while 302 dogs were rural. Among the latter, 190 were shepherd dogs and 112 were cattle farm dogs. Sera were tested for the presence of antibodies against Neospora caninum using the Neospora agglutination test. Seroprevalence at 1/40, 1/80, 1/160 dilution titres was significantly higher in rural (36.4%, 19.5%, 9.9% respectively) than in urban dogs (20.2%, 10.6%, 4.8% respectively). Seroprevalence did not differ significantly in males and females. In shepherd dogs, prevalence increased according to dogs' age, thus suggesting a post-natal exposure by horizontal transmission. The observed higher seroprevalence in rural dogs suggests the importance of lifestyle and alimentary habits (i.e. aborted foetuses, placentas and small mammals) in the acquisition of N. caninum infection. Our results confirm that dogs are exposed to N. caninum and play an important role in the epidemiology of N. caninum.

Use of an enzyme-linked immunosorbent assay in bulk milk to estimate the prevalence of Neospora caninum on dairy farms in Prince Edward Island, Canada

This study evaluated the use of bulk milk as a diagnostic tool for estimation of herd-level Neospora caninum exposure in Atlantic Canada; it was used to estimate the prevalence of dairy farms with a within-herd N. caninum-seroprevalence > or = 15% in Prince Edward Island (PEI). The variation over time of N. caninum antibodies in bulk milk is also reported. Skimmed bulk milk and individual serum samples were analyzed for N. caninum antibodies by using an enzyme-linked immunosorbent assay (ELISA). Bulk milk samples were collected in May 2004 (n = 235), May 2005 (n = 189), and June 2005 (n = 235). The prevalence of dairy farms with a within-herd seroprevalence > or = 15% on PEI was 6.4% in May 2004. In May and June 2005, respectively, 10.1% and 10.2% of farms had a > or = 15% within-herd seroprevalence. In 11 farms that were considered positive based on bulk milk samples, blood samples were collected from all adult cows in September 2005, in conjunction with a 4th bulk milk sample on the same day. The correlation coefficient between serology and bulk milk ELISA was 0.87. The results of this study demonstrate that the prevalence of N. caninum in dairy farms can be estimated by using a bulk milk ELISA.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Optimization of the use of C57BL/6 mice as a laboratory animal model for Neospora caninum vaccine studies

The development and testing of vaccines for Neospora caninum in mice require challenge studies to demonstrate a reduction in clinical signs or prevention of vertical transmission of the parasite after vaccination. Genetic susceptibility to N. caninum varies with the strain of mice. In this study, C57BL/6 mice were evaluated as a model for Neospora vaccine studies. A lethal challenge model was developed and the LD(50) was determined to be 1.5 x 10(7)N. caninum tachyzoites/mouse, delivered intraperitoneally. Brain lesions encountered in sections from sub-lethally challenged mice were scored on the basis of severity and total number of lesions to develop a histopathological scoring system for vaccine efficacy. A vertical transmission model for N. caninum vaccine studies was developed by studying mice that were infected either 2 weeks prior to mating or between days 12 and 14 of pregnancy. It was found that infection prior to mating reduced the average number of pups per litter. DNA extracted from fetal tissue was examined by a N. caninum specific polymerase chain reaction (PCR). The rate of vertical transmission was 0, 100 and 90.5% for the uninfected controls, mice infected during pregnancy and mice infected before mating, respectively. This study demonstrates that the C57BL/6 strain of mice is a good model for N. caninum vaccine studies because it is possible to establish a clear-cut lethal challenge model in C57BL/6 mice and they transmit the disease to their offspring efficiently.

Seroprevalence of and agroecological risk factors for Mycobacterium avium subspecies paratuberculosis and neospora caninum infection among adult beef cattle in cow-calf herds in Alberta, Canada

A province-wide cross-sectional seroprevalence and agroecological risk factor study of Mycobacterium avium subspecies paratuberculosis (MAP) and Neospora caninum (NC) infection among cattle in 100 cow-calf herds in Alberta was conducted. The seroprevalence of MAP in adult cattle was 1.5% across all herds. Using a widely accepted herd test cutpoint of 2 or more seropositive cows out of 30 animals tested, 7.9% of herds were estimated to be infected (95% confidence interval (CI): 2.3-23.4%). Seroprevalence of MAP differed by agroecological region; specifically, cattle and herds in areas with high soil pH (> 7.0), southern latitudes, and arid climates had a moderately reduced risk of infection (P < 0.10). Seroprevalence of NC infection was 9.7% among adult beef cattle province-wide--these levels also varied by agroecological region--with 91.0% of herds infected overall.

Cloning and expression of an antigenic domain of a major surface protein (Nc-p43) of Neospora caninum

Neospora caninum is an obligate intracellular protozoan that can infect domestic and wild canids, as well as ruminants and equines. It was described in 1988 as causing neuromuscular alterations and death in dogs. Recently, N. caninum has been the focus of considerable attention for its large impact on the dairy industry, given the economic losses related to breeding failures and to a decrease in productivity. ELISA diagnosis of neosporosis has not been widely used in Brazil, mostly because of the assay's cost, and thus the distribution of the disease in the country is not well known. In order to evaluate its ability to react with sera from infected animals from the state of Mato Grosso do Sul, an antigenic determinant domain of a major surface protein (Nc-p43) was produced. The antigenic domain, located in the distal 2/3 region of the C-terminus, was amplified by polymerase chain reaction. The DNA fragments were cloned into pet100/D-TOPO vectors. The recombinant plasmids were transformed into Escherichia coli of the BL21 Star (DE3) strain and induced to express the fused fragment of Nc-p43 as a 29-kDa protein that, when assayed with bovine Neospora-positive serum from a regional sample, was sensitive for identification by immunoblotting. This Nc-p43 fragment may be of use in additional studies targeted at diagnosing N. caninum infection and at evaluating the immunoprotection conferred by the protein fragment to animal hosts.

Prevalence ofNeospora caninumand persistent infection with bovine viral diarrhea virus in dairy-breed steers in a feedlot

OBJECTIVE

To determine the prevalence and effect of Neospora caninum infection and persistent infection (PI) with bovine viral diarrhea virus (BVDV) on weight gain, morbidity, and mortality rate in dairy-breed steer calves located on a feedlot in California.

DESIGN

Prospective cohort observational study.

ANIMALS

900 dairy-breed steer calves in 2 pens.

PROCEDURES

The 3- to 4-month-old calves were evaluated for serum antibodies against N caninum and infection with BVDV at entry to the feedlot. Five months later, sera were again analyzed for anti-N caninum antibodies; calves that were determined to have BVDV infection initially were retested to evaluate PI status. Average daily gain, morbidity, and deaths were recorded for all calves.

RESULTS

Among 900 calves, prevalence of N caninum infection was 16.7% (95% confidence interval, 14.3% to 19.3%); prevalence of BVDV-associated PI was 0.2% (95% confidence interval, 0.03% to 0.9%). Morbidity rate and time to first illness were not significantly different between calves that were seropositive or seronegative for N caninum. At the second sample collection, weight and average daily gain of calves that were seropositive for N caninum was less than that of seronegative steers in 1 pen, whereas these measures did not differ between groups in the other pen. Statistical power was insufficient to evaluate the effect of BVDV PI on any outcome measurement.

CONCLUSIONS AND CLINICAL RELEVANCE

Although N caninum serostatus had no significant effect on morbidity rate, some seropositive calves had reduced growth, compared with seronegative calves, 5 months after entry to the feedlot.

Analysis of the immune response to Neospora caninum in a model of intragastric infection in mice

To study experimental Neospora caninum infection initiated at the gastrointestinal tract, Toll-like Receptor 4- and functional IL-12Rbeta2 chain-deficient C57BL/10 ScCr mice were challenged intragastrically with 5 x 10(6) N. caninum tachyzoites. All parasite-inoculated mice eventually died with disseminated infection. In contrast, immunocompetent BALB/c mice challenged with 1 x 10(7) N. caninum tachyzoites by the intragastric (i.g.) or the intraperitoneal (i.p.) route remained alive for at least 6 months. Expansion of splenic B- and T-cells, the latter displaying both activated and regulatory phenotypes, and increased levels of IFN-gamma and IL-10 mRNA were detected in both groups of infected BALB/c mice compared with non-infected controls, whereas in the Peyer's patches only IFN-gamma mRNA levels were found to be increased. Parasite-specific IgG1, IgG2a and IgA antibody levels were elevated in the sera of all infected mice, whereas increased N. caninum-specific IgA levels were detected in intestinal lavage fluids of i.g. challenged mice only. These results show that N. caninum infection can be successfully established in mice by i.g. administration of tachyzoites. They also show that the immune response elicited in i.g. or i.p. infected BALB/c mice, although conferring some degree of protection, was not sufficient for complete parasite clearance.

Investigation for presence of Neospora caninum, Toxoplasma gondii and Brucella-species infection in killer whales (Orcinus orca) mass-stranded on the coast of Shiretoko, Hokkaido, Japan

Twelve killer whale (Orcinus orca) were hemmed in by ice floes, and nine died on the Aidomari coast in the Nemuro Strait in Rausu, Shiretoko, Hokkaido, Japan on 8 February 2005. Tissue samples collected from 8 whales were tested for Neospora caninum, Toxoplasma gondii, and Brucella species DNA by polymerase chain reaction (PCR) assay. Gamma-globulin isolated from blood samples by ammonium sulfate precipitation was tested for antibodies to these pathogens by means of agglutination tests and immunoblotting. None of the 8 tissue samples had antibodies to the pathogens, when subjected to agglutination tests. In immunoblotting, one sample (sample No.5) showed antibody binding to N. caninum antigens. In the PCR assay, none of the samples was positive. Further study is necessary to examine the prevalence of the pathogens in marine mammals inhabiting this area.

Monoclonal antibody directed against Neospora caninum tachyzoite carbohydrate epitope reacts specifically with apical complex-associated sialylated beta tubulin

Monoclonal antibodies (mabs) were generated against whole sonicated Neospora caninum tachyzoites as immunogen. Initial ELISA screening of the reactivity of hybridoma culture supernatants using the same antigen and antigen treated with sodium periodate prior to antibody binding resulted in the identification of 8 supernatants with reactivity against putative carbohydrate epitopes. Following immunoblotting, mab6D12 (IgG1), binding a 52/48-kDa doublet, and mab6C6 (IgM), binding a 190/180-kDa doublet, were selected for further studies. Immunofluorescence of tachyzoite-infected cultures localized the corresponding epitopes not to the surface, but to interior epitopes at the apical part of N. caninum tachyzoites. During in vitro tachyzoite to bradyzoite stage conversion, mab6C6 labeling translocated toward the cyst periphery, while for mab6D12 no changes in localization were noted. Upon extraction of tachyzoites with the nonionic detergent Triton-X-100, the 52-kDa band recognized by mab6D12 was present exclusively in the insoluble, cytoskeletal fraction of both N. caninum and Toxoplasma gondii tachyzoites. Tandem mass spectrometry analysis identified this protein as N. caninum beta tubulin. The 48-kDa band labeled by mab6D12 was a Vero cell protein contamination. The protein(s) reacting with mab6C6 could not be conclusively identified by mass spectrometry. Immunofluorescence consistently failed to label T. gondii tachyzoites, indicating that beta tubulin in T. gondii and N. caninum could be differentially modified or that the reactive epitope in T. gondii is masked. Immunogold TEM of isolated apical cytoskeletal preparations and dual immunofluorescence with antibody to tubulin confirmed that mab6D12 binds to the anterior part of apical complex-associated microtubules. The sodium periodate sensitivity of the beta tubulin associated epitope was confirmed by immunoblotting and ELISA, and treatment of N. caninum cytoskeletal proteins with sialidase prior to mab6D12 labeling resulted in a profound loss of antibody binding, suggesting that mab6D12 reacts with sialylated beta tubulin.

Neospora caninum-like oocysts observed in feces of free-ranging red foxes (Vulpes vulpes) and coyotes (Canis latrans)

The aim of this study was to examine the feces of free-ranging foxes and coyotes for the presence of Neospora caninum oocysts. Feces were collected from 271 foxes and 185 coyotes in the Canadian province of Prince Edward Island, processed by sucrose flotation, and examined by light microscopy for the presence of coccidian oocysts. In 2 fox and 2 coyote samples, oocysts morphologically and morphometrically similar to oocysts of N. caninum were observed. DNA was extracted from these samples and subjected to nested polymerase chain reaction (PCR) using primers to the N. caninum-specific Nc5 genomic sequence. Through DNA sequencing, alignment of the sequences of at least 3 clones from each isolate to sequences deposited in GenBank revealed 95-99% similarity to the Nc5 sequence of N. caninum. PCR using primers specific for Hammondia heydorni failed to yield an amplification product from these DNA samples.

First report of Neospora caninum abortion in a beef cow-calf herd from Andorra, Europe

Neospora caninum-associated abortion was diagnosed in a 7-mo gestational age beef cow fetus from Andorra. The fetus had a multifocal necrotizing encephalitis and nonpurulent multifocal myocarditis. The diagnosis was confirmed by demonstration of N. caninum DNA by polymerase chain reaction and tachyzoites by specific staining with N. caninum polyclonal antibodies in the fetal brain. The dam of the aborted fetus had serum N. caninum antibodies at the time of abortion but not 2 mo before abortion took place. This is the first report of N. caninum abortion in Andorra and the first confirmed N. caninum abortion in an acutely infected cow.

Vaccination as a control strategy against the coccidial parasitesEimeria,ToxoplasmaandNeospora

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

Serodiagnosis of Neospora caninum infection in cattle using a recombinant tNcSRS2 protein-based ELISA

The truncated NcSRS2 gene (tNcSRS2) by removal of the N-terminal hydrophobic sequence was cloned into the pGEX-6p-1 plasmid and subsequently expressed as a glutathione-S-transferase (GST) fusion protein. The purified recombinant tNcSRS2 protein was specific to Neospora caninum and was used in an ELISA for the diagnosis of neosporosis. There was a good agreement between tNctSRS2-based ELISA and three commercially available diagnostic kits (IDEXX ELISA, HIPRA ELISA and VMRD IFAT). Three hundred dairy cattle serum samples from 9 regions were tested by our ELISA. The herd prevalence was 100% and the overall prevalence was 20.3%. There was a statistically significant difference in seroprevalence between regions (P<0.01) and an association between abortion history and N. caninum seropositivity. Our study showed that neosporosis in dairy cattle is widespread in China.

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.

Seroprevalence of Neospora caninum in non-carnivorous wildlife from Spain

Serum samples from 1034 non-carnivorous wildlife from Spain were tested for antibodies to Neospora caninum by competitive screening enzyme linked immunosorbent assay (ELISA) and confirmed by an indirect fluorescent antibody test (IFAT). High agreement was observed between results in both techniques (kappa value higher than 0.9). Prevalences of N. caninum antibodies positive by both techniques were 11.8% of 237 red deer (Cervus elaphus), 7.7% of 13 barbary sheep (Ammotragus lervia), 6.1% of 33 roe deer (Capreolus capreolus) and 0.3% of 298 wild boar (Sus scrofa). In one of 53 hares (Lepus granatensis), antibodies were found in the ELISA but could not be confirmed by IFAT due to lack of sample. Antibodies to N. caninum were not found in any of 251 wild rabbits (Oryctolagus cuniculus), 79 fallow deer (Dama dama), 27 mouflon (Ovis ammon), 40 chamois (Rupicapra pyrenaica) and three Spanish ibex (Capra pyrenaica). Statistically significant differences were observed between N. caninum seroprevalence in red deer and management of hunting estates (open versus fenced) with higher prevalence in fenced estates, and among sampling sites. Seroprevalence was particularly high in some areas (MO estate in South-Central Spain or some estates of Catalonia, North-East Spain), while no contact with N. caninum was observed in others. Results indicate that in certain areas of Spain, N. caninum is present in wildlife, especially in red deer. These results have important implications in both sylvatic cycles and may influence the prevalence of infection in cattle farms in those areas. To our knowledge, this is the first report of antibodies to N. caninum in wildlife from Spain and the first report of N. caninum antibodies in barbary sheep and wild boar.

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

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

Neospora caninum antibodies detected in Midwestern white-tailed deer (Odocoileus virginianus) by Western blot and ELISA

White-tailed deer (Odocoileus virginianus) serve to maintain the Neospora caninum life cycle in the wild. Sera from white-tailed deer from south central Wisconsin and southeastern Missouri, USA were tested for antibodies to N. caninum by Western blot analyses and two indirect ELISAs. Seroreactivity against N. caninum surface antigens was observed in 30 of 147 (20%) of WI deer and 11 of 23 (48%) of MO deer using Western blot analysis. Compared to Western blot, the two indirect ELISAs were found to be uninformative due to degradation of the field-collected samples. The results indicate the existence of N. caninum antibodies in MO and WI deer, and that Western blot is superior to ELISA for serologic testing when using degraded blood samples collected from deer carcasses.

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.

Characterization of the immune response in the placenta of cattle experimentally infected with Neospora caninum in early gestation

A serial examination of three groups of cattle infected intravenously (iv) (Group 1, n=8) or subcutaneously (sc) (Group 2, n=8) with live Neospora caninum tachyzoites or with VERO cells (Group 3, n=8) at 70 days' gestation was carried out and the nature of the inflammatory responses in the placenta and the presence of parasite antigen were analysed. Immune cells expressing CD3, CD4, CD8, gamma delta (gammadelta) T-cell receptors (TCR), CD79alpha cytoplasmic (cy) (B cells) and NKp46 [natural killer (NK) cells] antigens were identified immunohistochemically and cells expressing mRNA for interferon-gamma (IFN-gamma) were labelled by in-situ hybridization. Intravenous inoculation caused mortality in all fetuses from 28 days post-inoculation (dpi) onwards. Subcutaneous inoculation caused mortality in 50% of the animals by 28dpi. Pathological changes in the placenta consisted of necrosis of fetal placental villi, necrosis and inflammation in adjacent areas of the maternal septum and inflammation at the base of the maternal caruncle. The inflammatory infiltrate consisted mainly of CD3(+) lymphocytes, dominated by CD4(+) and gammadelta TCR(+) cells, with CD8(+) cells present to a lesser extent. The results from the control group indicated fewer NK cells than those occurring in the placenta of human beings or mice. Infiltration of CD4(+) cells and NKp46(+) cells was observed in the caruncular base and septa 14 days after infection, whereas infiltration of gammadelta TCR(+) cells was observed from 28 dpi onwards. To our knowledge this is the first report on the presence and distribution of NK cells in the bovine placenta. Maternal inflammatory cells expressing mRNA for IFN-gamma were identified in animals inoculated with parasites iv or sc at 14 and 28 dpi, respectively. In the sc-inoculated dams with live fetuses at 28, 42 and 56dpi, there was no evidence of parasite antigen, infiltration of immune cells or production of IFN-gamma, suggesting that the parasite had not reached the placenta. The exact cause of fetal death was not established. Tissue destruction by the parasite may have occurred; in addition, there may have been a T helper 1 (Th-1) immune response to the neospora infection at the materno-fetal interface, resulting in infiltrations of CD4T cells, gammadelta T cells and NK cells and the subsequent production of IFN-gamma. It is possible that a pro-inflammatory Th-1 response early in gestation protects the dam by eliminating the parasite; however, it may lead to destruction of the placental tissues themselves and thus be incompatible with fetal survival.