A POLYGEN-adjuvanted killed Neospora caninum tachyzoite preparation failed to prevent foetal infection in pregnant cattle following i.v./i.m. experimental tachyzoite challenge

Advancement in the Antigenic Epitopes and Vaccine Adjuvants of African Swine Fever Virus

African swine fever virus (ASFV), a highly virulent double-stranded DNA virus, poses a significant threat to global pig farming, with mortality rates in domestic pigs reaching up to 100%. Originating in Kenya in 1921, ASFV has since proliferated to Western Europe, Latin America, Eastern Europe, and most recently China in 2018, resulting in substantial global agricultural losses. Antigenic epitopes, recognized by the immune system's T cells and B cells, are pivotal in antiviral immune responses. The identification and characterization of these antigenic epitopes can offer invaluable insights into the immune response against ASFV and aid in the development of innovative immunotherapeutic strategies. Vaccine adjuvants, substances that amplify the body's specific immune response to antigens, also play a crucial role. This review provides an overview of the progress in studying T/B-cell epitopes in ASFV proteins and ASFV vaccine adjuvants, highlighting their role in the immune response and potential use in new vaccine development.

Vaccination With a Gamma Irradiation-Inactivated African Swine Fever Virus Is Safe But Does Not Protect Against a Challenge

African swine fever (ASF) is among the most devastating viral diseases of pigs and wild boar worldwide. In recent years, the disease has spread alarmingly. Despite intensive research activities, a commercialized vaccine is still not available, and efficacious live attenuated vaccine candidates raise safety concerns. From a safety perspective, inactivated preparations would be most favourable. However, both historical and more recent trials with chemical inactivation did not show an appreciable protective effect. Under the assumption that the integrity of viral particles could enhance presentation of antigens, we used gamma irradiation for inactivation. To this means, gamma irradiated ASFV “Estonia 2014” was adjuvanted with either Polygen™ or Montanide™ ISA 201 VG, respectively. Subsequently, five weaner pigs per preparation were immunized twice with a three-week interval. Six weeks after the first immunization, all animals were challenged with the highly virulent ASFV strain “Armenia 2008”. Although ASFV p72-specific IgG antibodies were detectable in all vaccinated animals prior challenge, no protection could be observed. All animals developed an acute lethal course of ASF and had to be euthanized at a moderate humane endpoint within six days. Indeed, the vaccinated pigs showed even higher clinical scores and a higher inner body temperature than the control group. However, significantly lower viral loads were detectable in spleen and liver of immunized animals at the time point of euthanasia. This phenomenon suggests an immune mediated disease enhancement that needs further investigation.

Canine neosporosis: perspectives on pathogenesis and management

Canine neosporosis is a worldwide disease caused by the obligate intracellular parasite protozoan Neospora caninum, manifesting mainly neurological symptoms. N. caninum has a heteroxenous life cycle and affects a wide range of warm-blooded animals. The domestic and wild canids are the definitive host of the parasite. They shed oocysts after ingestion of tissue cysts from infected intermediate hosts (ovine, equine, bovine, canine, and many other species), containing bradyzoites, or oocyst-contaminated water and food. The presence of dogs in farms is considered a risk factor for production animals. A wide range of diagnostic methods are currently available, but the most used is serology, ie, indirect fluorescent antibody test specific to the antibody detection in blood serum samples. No vaccine is available, but control strategies should be focused on the vertical and horizontal transmission of the parasite, ie, avoid feeding dogs with raw or undercooked meat, and taking care with water for human and animal consumption. No medicines to control the transplacental transmission are available yet.

Cell mediated immune responses in the placenta following challenge of vaccinated pregnant heifers with Neospora caninum

The aim of the present study was to investigate and correlate the cell-mediated immune response and pathological changes at the maternal-fetal interface of Neospora-challenged pregnant cattle previously immunized with live and inactivated experimental vaccines. Pregnant heifers naïve to Neospora caninum were divided in 5 groups of 4 animals, each one immunized before mating: Group A heifers were intravenously (iv) immunized with 6.25 × 10(7) live tachyzoites of the NC-6 strain; group B heifers were immunized twice subcutaneously (sc) 3 weeks apart with native antigen extract of the NC-6 strain formulated with ISCOMs; group C heifers were sc immunized twice 3 weeks apart with three recombinant proteins (rNcSAG1, rNcHSP20, rNcGRA7) of the NC-1 strain formulated with ISCOMs; group D heifers were sc injected with sterile phosphate-buffered saline (PBS) and group E heifers received sc ISCOM-matrix (ISCOMs without antigen). All groups were iv-challenged with 4.7 × 10(7) NC-1 tachyzoites at 70 days of gestation. Heifers were culled at day 104 of gestation and placentomes were examined to evaluate lesions and local cellular immune responses using histopathology, immunohistochemistry and real time-PCR. Immunohistochemistry was performed using bovine leucocyte specific antibodies. Cytokine expression and levels (IFN-γ, IL-4, IL-10, IL-12 and TNF-α) were measured using real-time reverse transcription-PCR and ELISA, respectively. Minimal inflammation was observed in group A placentomes; while placentomes from group B, C, D and E had moderate to severe infiltration with CD3(+), CD4(+), γδ-T cells, CD8(+) cells and macrophages being more numerous in groups B and E placentomes, when compared with groups C and D (P<0.001). Cytokine levels were significantly increased in the caruncles of animals of groups B and C in comparison with the other animal groups (P < 0.001). The results from this study showed that the strongest cellular immune responses were observed in the placentomes of animals that were immunized with inactivated vaccines (groups B and C) and in the placentomes of animals that were sc-sham-inoculated (groups D and E). On the other hand, animals that were immunized with live tachyzoites showed a milder immune cell infiltration to the placenta possibly due to the existence of a protective systemic maternal immune response that helped to minimize N. caninum infection at the maternal-fetal interface.

Safety and immunogenicity of a soluble native Neospora caninum tachyzoite-extract vaccine formulated with a soy lecithin/β-glucan adjuvant in pregnant cattle

The global economic impact of Neospora caninum infection in cattle herds has promoted the development of vaccines that can be safely used during pregnancy. The aim of this study was to evaluate the safety and immunogenicity of a vaccine formulated with the soluble fraction of tachyzoite's lysate and a soy-based aqueous adjuvant (sNcAg/AVEC), which was protective in the mouse model and induced strong IFN-γ responses and high avidity antibodies in non-pregnant cattle. Ten pregnant heifers were vaccinated twice during the first trimester of gestation and 8 remained unvaccinated. Anti-N. caninum immune responses were efficiently primed by vaccination, evidenced by a quick induction of IgM serum titers (7dpv) and a prompt switch to high avidity IgG shortly after infection (performed at 78 or 225 days of gestation; n=5 each); while naïve cattle elicited lower IgG titers, with a delayed kinetics. High systemic IFN-γ levels were induced after infection which did not interfere with pregnancy. No local or systemic adverse effects were recorded along the study. Calves were born in term and in good health conditions, showing that the sNcAg/AVEC vaccine was safe when applied to healthy heifers during the first trimester of gestation.

A Neospora caninum vaccine using recombinant proteins fails to prevent foetal infection in pregnant cattle after experimental intravenous challenge

The aim of the present study was to evaluate the immunogenicity and protective efficacy of rNcSAG1, rNcHSP20 and rNcGRA7 recombinant proteins formulated with immune stimulating complexes (ISCOMs) in pregnant heifers against vertical transmission of Neospora caninum. Twelve pregnant heifers were divided into 3 groups of 4 heifers each, receiving different formulations before mating. Immunogens were administered twice subcutaneously: group A animals were inoculated with three recombinant proteins (rNcSAG1, rNcHSP20, rNcGRA7) formulated with ISCOMs; group B animals received ISCOM-MATRIX (without antigen) and group C received sterile phosphate-buffered saline (PBS) only. The recombinant proteins were expressed in Escherichia coli and purified nickel resin. All groups were intravenously challenged with the NC-1 strain of N. caninum at Day 70 of gestation and dams slaughtered at week 17 of the experiment. Heifers from group A developed specific antibodies against rNcSAG1, rNcHSP20 and rNcGRA7 prior to the challenge. Following immunization, an statistically significant increase of antibodies against rNcSAG1 and rNcHSP20 in all animals of group A was detected compared to animals in groups B and C at weeks 5, 13 and 16 (P<0.001). Levels of antibodies against rNcGRA7 were statistical higher in group A animals when compared with groups B and C at weeks 5 and 16 (P>0.001). There were no differences in IFN-γ production among the experimental groups at any time point (P>0.05). Transplacental transmission was determined in all foetuses of groups A, B and C by Western blot, immunohistochemistry and nested PCR. This work showed that rNcSAG1, rNcHSP20 and rNcGRA7 proteins while immunogenic in cattle failed to prevent the foetal infection in pregnant cattle challenged at Day 70 of gestation.

Two distinct populations of bovine IL-17⁺ T-cells can be induced and WC1⁺IL-17⁺γδ T-cells are effective killers of protozoan parasites

IL-17 has emerged as a key player in the immune system, exhibiting roles in protection from infectious diseases and promoting inflammation in autoimmunity. Initially thought to be CD4 T-cell-derived, the sources of IL-17 are now known to be varied and belong to both the innate and adaptive arms of the immune system. Mechanisms for inducing IL-17 production in lymphoid cells are thought to rely on appropriate antigenic stimulation in the context of TGF-β1, IL-6 and/or IL-1β. Using culture protocols adapted from human studies, we have effectively induced both bovine CD4(+) and WC1(+) γδ T-cells to produce IL-17 termed Th17 and γδ17 cells, respectively. The negative regulatory effect of IFN-γ on mouse and human IL-17 production can be extended to the bovine model, as addition of IFN-γ decreases IL-17 production in both cell types. Furthermore we show that infection with the protozoan Neospora caninum will induce fibroblasts to secrete pro-IL-17 factors thereby inducing a γδ17 phenotype that preferentially kills infected target cells. Our study identifies two T-cell sources of IL-17, and is the first to demonstrate a protective effect of IL-17(+) T-cells in ruminants. Our findings offer further opportunities for future adjuvants or vaccines which could benefit from inducing these responses.

Experimental ruminant models for bovine neosporosis: what is known and what is needed

At present, bovine neosporosis is an important worldwide concern because of its wide geographic distribution and economic impact. Abortion is the main clinical sign of bovine neosporosis in both dairy and beef cattle. Ruminant challenge models are critical to evaluate potential vaccine candidates to help tackle bovine neosporosis and to study pathogenesis and host responses to infection. Several research groups have developed ruminant models of Neospora caninum infection independently of others, resulting in a high degree of variability due to the use of different species of animals, breeds, strains/isolates of N. caninum, doses, routes and times of inoculation. Standardization is greatly needed to advance research in a more collaborative, timely and efficient manner. In the absence of widely accepted international guidelines, this manuscript serves to summarize and discuss the different models and parameters currently in use. Parameters essential for the development of non-pregnant and pregnant ruminant models are outlined and the main knowledge gaps are identified. This information could act as the basis to develop a consensus for international standard guidelines for ruminant models of neosporosis that would be helpful for researchers in this field worldwide.

Protective effect of intranasal immunization with Neospora caninum membrane antigens against murine neosporosis established through the gastrointestinal tract

Neospora caninum is an Apicomplexa parasite that in the last two decades was acknowledged as the main pathogenic agent responsible for economic losses in the cattle industry. In the present study, the effectiveness of intranasal immunization with N. caninum membrane antigens plus CpG adjuvant was assessed in a murine model of intragastrically established neosporosis. Immunized mice presented a lower parasitic burden in the brain on infection with 5 × 10(7) tachyzoites, showing that significant protection was achieved by this immunization strategy. Intestinal IgA antibodies raised by immunization markedly agglutinated live N. caninum tachyzoites whereas previous opsonization with IgG antibodies purified from immunized mice sera reduced parasite survival within macrophage cells. Although an IgG1 : IgG2a ratio < 1 was detected in the immunized mice before and after infection, indicative of a predominant T helper type 1 immune response, no increased production of interferon-γ was detected in the spleen or mesenteric lymph nodes of the immunized mice. Altogether, these results show that mucosal immunization with N. caninum membrane proteins plus CpG adjuvant protect against intragastrically established neosporosis and indicate that parasite-specific mucosal and circulating antibodies have a protective role against this parasitic infection.

Vaccines against neosporosis: what can we learn from the past studies?

Neospora caninum is an intracellular apicomplexan parasite, which is a leading cause of abortion in cattle; thus neosporosis represents an important veterinary health problem and is of high economic significance. The parasite can infect cattle via trans-placental transmission from an infected cow to its fetus (vertical transmission), or through the oral route via ingestion of food or water contaminated with oocysts that were previously shed with the feces of a canid definitive host (horizontal transmission). Although vaccination was considered a rational strategy to prevent bovine neosporosis, the only commercialized vaccine (Neoguard®) produced ambiguous results with relatively low efficacy, and was recently removed from the market. Therefore, there is a need to develop an efficient vaccine capable of preventing both, the horizontal transmission through infected food or water to a naïve animal as well as the vertical transmission from infected but clinically asymptomatic dams to the fetus. Different vaccine strategies have been investigated, including the use of live attenuated vaccines, killed parasite lysates, total antigens or antigen fractions from killed parasites, and subunit vaccines. The vast majority of experimental studies were performed in mice, and to a certain extent in gerbils, but there is also a large number of investigations that were conducted in cattle and sheep. However, it is difficult to directly compare these studies due to the high variability of the parameters employed. In this review, we will summarize the recent advances made in vaccine development against N. caninum in cattle and in mice and highlight the most important factors, which are likely to influence the degree of protection mediated by vaccination.

Oligomannose-coated liposome-entrapped dense granule protein 7 induces protective immune response to Neospora caninum in cattle

Neospora caninum is an intracellular protozoan parasite that causes abortion in cows. Vaccination is an important strategy for control of neosporosis, and a safe and effective vaccine suitable for cattle is required. Dense granule protein 7 of N. caninum (NcGRA7) is a secretory protein with high antigenicity in hosts. We demonstrated previously that NcGRA7 entrapped in liposomes coated with mannotriose (M3-NcGRA7) could induce a parasite-specific T-helper type 1 immune response and produce humoral antibodies that resulted in increased offspring survival and decreased infection in the brains of mice dams. In the present study, the efficacy of M3-NcGRA7 as a vaccine candidate against N. caninum has been evaluated in cattle (n=12). Cattle were immunized with M3-NcGRA7 containing 50 μg (n=4) or 200 μg NcGRA7 (n=4) subcutaneously twice with a 4-week interval and all cattle including the non-immunized controls (n=4) were inoculated with 10(7) tachyzoites of Nc-1 strain 27 days after the second immunization and euthanized at 85-87 days post infection (dpi). In immunized cattle, NcGRA7-specific antibody production and IFN-γ production in PBMC was induced before challenge. At 3 dpi, body temperature and concentration of serum IFN-γ tended to be higher in control cattle than in the immunized cattle. Furthermore, the parasite load in the brain significantly decreased in cattle immunized with 50 μg M3-NcGRA7 compared with controls. These results suggest that M3-NcGRA7 can induce protective immune responses to N. caninum tachyzoites in cattle, which could lead to practical application of safe and effective subunit vaccines.

Parasite limiting macrophages promote IL-17 secretion in naive bovine CD4⁺ T-cells during Neospora caninum infection

Neospora caninum infects bovine hosts giving rise to pro-inflammatory immune responses that can result in foetal death or spontaneous abortion, this appears to be mediated by the actions of IFN-γ on cell activation and migration/trafficking. Yet successful vaccination or natural immunity is also strongly correlated with IFN-γ production. We utilised in vitro infection of bovine macrophages to prime naive T-cell responses. Naive T-cells in contact with infected macrophages produce both IFN-γ and IL-17 in a pattern that is dependent on whether the priming macrophage was protected or non-protected. Our results may explain the apparent dual role of IFN-γ during infection if a second major pro-inflammatory cytokine, IL-17, is produced simultaneously.

Comparative efficacy of immunization with inactivated whole tachyzoites versus a tachyzoite-bradyzoite mixture against neosporosis in mice

The worldwide economic impact ofNeospora caninuminfection has caused the development of effective vaccines to become one of the main goals in the field of neosporosis research. In this study, the protection conferred by antigens from inactivated whole tachyzoites (TZ) and a tachyzoite-bradyzoite mixture (TZ-BZ) ofN. caninum(Nc-Spain7 isolate) incorporated into a water-in-oil emulsion (W/O) and aluminium hydroxide-ginseng extract (Al/G) was evaluated in mouse models of congenital and cerebralN. caninuminfection. Immunization with TZ-BZ induced congenital and cerebral neosporosis exacerbation that was mainly characterized by reduced neonatal median survival time and increased parasite presence in adult mouse brains. The immune response of mice immunized with TZ-BZ was characterized by an increase in IFN-γexpression prior to challenge and an increase in IL-4 expression accompanied with significantly higher levels of antibodies against 2 recombinant bradyzoite-specific proteins (rNcSAG4 and rNcBSR4) after challenge. Immunization with TZ in W/O significantly reduced neonatal mortality, vertical transmission as well as parasite presence in adult mouse brains and induced a strong humoral immune response. The current study demonstrates the critical role of stage-specific antigens and adjuvants on the development of effective inactivated vaccines for the prevention ofN. caninuminfection.

Immunization of female BALB/c mice with Neospora cyclophilin and/or NcSRS2 elicits specific antibody response and prevents against challenge infection by Neospora caninum

Neospora caninum is the causal agent of bovine neosporosis which results in high levels of abortion. The present study determined the protective efficacy of two Neospora antigens--Neospora cyclophilin (NcCyP) and NcSRS2. The ability of native NcCyP to upregulate mouse IFN-γ was also confirmed in this study. Recombinant NcCyP or NcSRS2 were tested either alone or in combination and formulated with adjuvant ImmuMax-SR and CpG. Female BALB/c mice (n=15) of 10-12 weeks of age were immunized s.c. twice over a 2-week interval with vaccines containing either NcCyP (20 μg/dose) alone, NcSRS2 (20 μg/dose) alone, NcCyP plus NcSRS2, or non-recombinant bacterial antigen (NR) in 2 separate trials. All mice were challenge-infected 3 weeks following the booster immunization and necropsied 3 weeks after the challenge infection. Brain and serum were collected and Nc-specific DNA sequence in brain tissue and antibodies in serum were analyzed by PCR or ELISA/Western blotting. Results showed that mice vaccinated with rNcCyP, rNcSRS2, or both rNcCyP and rNcSRS2 responded with high levels of NcCyP or NcSRS2 specific antibodies. Overall, mice received vaccines formulated with either rNcCyP or rNcCyP and rNcSRS2 had a higher (p<0.01) percent protection when compared to the mock- or non-vaccinated mice. The group immunized with rNcSRS2 alone exhibited slightly lower levels of protection, which was higher (p<0.05) than that of the non-vaccinated group but did not differ (p=0.06) from that of the mock-vaccinated group. The results of the present study indicate that NcCyP is a highly efficacious vaccine candidate which may be useful in protection against Neospora infection.

Failure of a vaccine using immunogenic recombinant proteins rNcSAG4 and rNcGRA7 against neosporosis in mice

The development of an effective vaccine against Neospora caninum infection in cattle is an important issue due to the significant economic impact of this parasitic disease worldwide. In this work, the immune response, safety and efficacy of different vaccine formulations using the N. caninum recombinant proteins rNcSAG4 (the first bradyzoite-specific protein assayed as a vaccine) and rNcGRA7 were evaluated in mouse models. The survival curves of pups from all vaccinated groups showed a slight delay in time to death compared to control groups; this difference was statistically significant for rNcSAG4+adjuvant group. Immune response of mice vaccinated with rNcSAG4 was characterized by reduced specific IgG and cytokine levels with an equilibrated IFN-gamma/IL-10 balance. Regarding mice vaccinated with rNcGRA7, a very strong humoral and cellular immune response was generated characterized by a hyper-production of IFN-gamma. This response was not accompanied by significant protection. Vaccination with a mixture of both recombinant proteins reduced infection in lung and brain during acute and chronic infection, respectively, although it was not statistically significant. In summary, no significant protection was obtained with these vaccine formulations in the present mouse models. However, the study reveals some positive results on immune response and efficacy for both recombinant proteins; these results are being discussed in order to suggest new approaches with new chronic infection mouse models and adjuvants.

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

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

Immunogenicity of a DNA vaccine expressing the Neospora caninum surface protein NcSRS2 in mice

The immunogenicity of a DNA vaccine expressing the surface protein NcSRS2 of Neospora caninum was studied in BALB/c mice. The NcSRS2-encoding DNA was obtained by PCR amplification of the NcSRS2 ORF gene from the p43 plasmid encoding the N. caninum surface protein NcSRS2, ligated to the mammalian expression vector pcDNA3.1/Zeo(+) and propagated in E. coli DH5alpha to produce the N. caninum NcSRS2 DNA vaccine. BALB/c mice were immunised by two intramuscular injections of the DNA vaccine with or without complete Freund's adjuvant (CFA). Serum antibody titres and nitric oxide (NO) concentrations, and splenocyte proliferation and cytokine expression were measured after immunisation. The DNA vaccine induced T-cell-mediated immunity as shown by significantly increased NO concentrations, cytokine gene (IL-2 and IFN-gamma) expression, and NcSRS2 protein-stimulated lymphocyte proliferation in mice immunised with the DNA vaccine. The vaccine also induced weak humoral immunity. The immunogenicity of the DNA vaccine was slightly enhanced by CFA. The immune response was specific to NcSRS2. No immune response was observed in mice immunised with the pcDNA3.1/Zeo(+) vector alone.

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

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

NcGRA2as a molecular target to assess the parasiticidal activity of toltrazuril againstNeospora caninum

The treatment ofNeospora caninuminfection in the bovine host is still at an experimental stage. In contrast to thein vivosituation, a wide range of compounds have been intensively investigated in cell-culture-based assays. Tools to demonstrate efficacy of treatment have remained conventional including morphological and cell biological criteria. In this work, we present a molecular assay that allows the distinction between live and dead parasites. Live parasites can be detected by measuring the mRNA level of specific genes, making use of the specific mRNA available in live cells. TheNcGra2gene ofN. caninum, which is known to be expressed in both tachyzoites and bradyzoites, was used to establish a quantitative real-time RT-PCR, for monitoring parasite viability. Validation of the systemin vitrowas achieved usingNeospora-infected cells that had been treated for 2–20 days with 30 μg/ml toltrazuril.NcGRA2-RT-real time PCR demonstrated that a 10-day toltrazuril-treatment exerted parasitostatic activity, as assessed by the presence ofNcGRA2-transcripts, whereas after a 14-day treatment period noNcGRA2-transcripts were detected, showing that the parasites were no longer viable. Concurrently, extended culture for a period of 4 weeks in the absence of the drug following the 14-day toltrazuril treatment did not lead to further parasite proliferation, confirming the parasiticidal effect of the treatment. This assay has the potential to be widely used in the development of novel drugs againstN. caninum, with a view to distinguishing between parasiticidal and parasitostatic efficacy of given compounds.

Humoral immune response in pregnant heifers inoculated with Neospora caninum tachyzoites by conjunctival route

The aim of this study was to compare systemic humoral immune responses in pregnant heifers inoculated with Neospora caninum tachyzoites by conjunctival and intravenous routes. Twenty nine heifers separated in three experimental groups were studied: Group 1 (n=10 animals) and Group 2 (n=9 animals) were inoculated with 10(8) of N. caninum tachyzoites by conjunctival and intravenous routes at 5th month of gestation, respectively; Group 3 (n=10 animals) were non-inoculated control animals. An indirect fluorescent antibody test (IFAT) and western immunoblotting (IB) were used to analyze the humoral immune response. All animals from Group 1 developed N. caninum specific antibody responses after conjunctival inoculation recording the highest antibody titer (mean+/-SE: 160+/-49.9) at 6th month of gestation. There were statistical differences between humoral immune responses found in Group 1 and 2 being higher in the second one at 6.5th, 8.5th and 9th months of gestation (P<0.05). Interestingly, all heifers from Group 1 reverted to seronegative status at the end of gestation. No increase in antibody was detected in the uninfected control group. Same pattern of N. caninum antigens was recognized by sera from heifers inoculated by conjunctival route and heifers inoculated by intravenous route. Recognized antigens were 116, 92, 84, 77, 45, 40, 25-26 and 17-18 kDa. The conjunctival instillation of N. caninum tachyzoites in pregnant heifers induces specific systemic antibodies. Further work is needed in order to clarify the consequences of this novel experimental route of infection not only on the fetus but also on the dam.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Epidemiology and control of neosporosis and Neospora caninum

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

Immunization of cattle with live tachyzoites of Neospora caninum confers protection against fetal death

Neospora caninum is an obligate intracellular protozoan parasite that causes abortion in cattle. It is normally found as a latent infection controlled by a T-helper-cell type 1 response involving CD4(+) cytotoxic T cells and gamma interferon. Cattle may be infected by two different routes: transplacentally as a result of activation of the latent infection in the mother causing congenital infection or abortion and by ingestion of oocysts, which, if it occurs during gestation, can also result in abortion. Here, for the first time, we establish proof that live vaccination protects against fetal death, whereas immunization using whole-tachyzoite lysate in different adjuvants fails to protect against fetal death. Strong antibody responses were induced in all the vaccinated groups, and the quality and magnitude of these responses were similar in the live- and the lysate-vaccinated groups. In contrast, only the group immunized with live tachyzoites had strong cellular and gamma interferon responses prior to challenge, and these responses correlated with protection against fetopathy. These results suggest that a cellular immune response may be important in the mechanisms involved in protection against N. caninum-associated abortions.

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

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

Vaccination with gamma-irradiated Neospora caninum tachyzoites protects mice against acute challenge with N. caninum

Neospora caninum, an apicomplexan parasite, is a leading cause of bovine abortions worldwide. The efficacy of gamma-irradiated N. caninum strain NC-1 tachyzoites as a vaccine for neosporosis was assessed in C57BL6 mice. A dose of 528 Gy of gamma irradiation was sufficient to arrest replication but not host cell penetration by tachyzoites. Female C57BL6 mice were vaccinated with two intraperitoneal inoculations of 1 x 10(6) irradiated tachyzoites at 4-wk intervals. When stimulated with N. caninum tachyzoite lysates, splenocytes of vaccinated mice, cultured 5 and 10 wk after vaccination, secreted significant (P<0.05) levels of interferon gamma, interleukin (IL)-10, and small amounts of IL-4. Antibody isotype-specific ELISA of sera from vaccinated mice exhibited both IgG1 and IgG2a isotypes of antibodies. Vaccinated mice were challenged intraperitoneally with 2 x 10(7)N. caninum tachyzoites. All vaccinated mice remained healthy and showed no obvious signs of neosporosis up to the 25th day post-challenge when the study was terminated. All unvaccinated control mice died within 1 wk of infection. Gamma-irradiated N. caninum tachyzoites can serve as an effective, attenuated vaccine for N. caninum.

Pathogenesis of bovine neosporosis

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

Humoral immune reaction of newborn calves congenitally infected with Neospora caninum and experimentally treated with toltrazuril

Neospora caninum is widely recognized as one of the most important infectious organisms causing abortion and stillbirth in cattle. This parasite causes severe economical losses worldwide. Infection is mostly passed vertically from mother to calf during pregnancy. Under certain circumstances, an infection can lead to abortion, but in most cases it results in a chronically infected calf, which itself will represent the next endogenously infectious generation. So far, no reliable therapeutic or metaphylactic tool has been developed. One possibility to control the problem may consist of treating newborn calves that became vertically infected by a persistently infected mother. This may allow parasite-free offspring. The aim of the present study was to address the questions: (1) can serology be used to assess efficiency of treatment in toltrazuril-medicated animals? and (2) is a strategic prevention measure possible by means of producing N. caninum-free calves from positive cows? Calves from Neospora-seropositive cows and heifers were randomly split into two different medication groups: 36 calves were medicated with toltrazuril and 36 calves obtained a placebo. Medication (20 mg toltrazuril per kg bw) was administered three times, every second day, within the 7 days post natum. Three months after medication, there was no difference in antibody reactivity between the two groups. At later time points (4-6 months), however, significant differences were found, as explained by a strong humoral immunity after chemotherapeutical affection of parasites, while the placebo-treated animals only responded weakly to the persistent infection. In summary, we concluded that (1) serology was not an entirely appropriate tool to answer our initial question and (2) toltrazuril has the potential to eliminate N. caninum in newborn calves. As a consequence, we plan to follow up toltrazuril-medicated calves clinically and serologically over a longer period and investigate if they give birth to Neospora-free calves.

Precolostral serology in calves born from Neospora-seropositive mothers

The present study was designed to exploratively determine (a) how many healthy calves, born from seropositive mothers, were also precolostrally seropositive; (b) how many precolostrally negative calves became postcolostrally positive; and (c) in these calves, how the IgG1/IgG2 situation developed pre- and postcolostrally. All calves were born from mothers that were determined to be seropositive in a conventional Neospora caninum-ELISA and by immunoblotting. When the diagnostic performance of the conventional ELISA was compared with that of immunoblotting and an IgG1/IgG2-ELISA in the calves, the latter two exhibited a higher sensitivity: From a total of 15 precolostral calf sera, 7 were positive in the conventional ELISA (diagnostic sensitivity 47%) compared to 15 that were positive by immunoblotting (diagnostic sensitivity 100%) and 12 that were positive by the IgG1/IgG2-ELISA (diagnostic sensitivity 80%). With regard to IgG1/IgG2 findings in the dams, IgG2 appeared as the dominant subclass in the humoral immune response of adult cattle, while in calves, IgG1 appeared as the main prenatally/precolostrally reactive antibody isotype. Provided that precolostral seropositivity reflects postnatal persistent infection with N. caninum, we then postulate that, basically, all of our study calves born form N. caninum-seropositive mothers were prenatally infected with the parasite, and may, thus, all become members of the next transmitting generation.

Review Article. Protecting babies: vaccine strategies to prevent foetopathy in Neospora caninum-infected cattle

Neospora caninum is an apicomplexan protozoan parasite that is a significant infectious abortifacient agent in cattle. Despite the fact that it is a member of a well described taxonomic group, it is a relatively newly discovered parasite and its biology is not yet fully understood. Cattle become infected either congenitally via transplacental transmission or post-natally by ingesting oocysts derived from the definitive host; dogs and coyotes are the only definitive hosts that have been described to date. It is not known which of these two forms of transmission occurs most frequently and which is the most likely to result in abortion; there are no drugs available to treat infected cattle, so current control strategies rely on prevention of infection by management methods and strict hygiene; an effective vaccine would be a great advantage in its control. Neospora caninum is an economically important veterinary pathogen, but we can also draw analogies between its foetopathic effects and those of human pathogens such as Toxoplasma gondii, Chlamydophila abortus and Plasmodium falciparum. Understanding the immune response and the materno-foetal relationship in N. caninum-infected cattle may help us to design vaccination strategies, not only for neosporosis but also for other foetopathic agents.

Immunization with native surface protein NcSRS2 induces a Th2 immune response and reduces congenital Neospora caninum transmission in mice

NcSRS2, a tachyzoite surface protein of Neospora caninum, is an immunodominant protein with respect to induction of antibody production and has a role in attachment and invasion of host cells. Native NcSRS2 was isolated from whole tachyzoite lysate antigen by affinity chromatography using NcSRS2 specific monoclonal antibody and used to immunize BALB/c mice in a congenital transmission study. NcSRS2 was a highly conserved protein as indicated by comparison of deduced amino acid sequence obtained from NcSRS2 gene sequences of 10 geographically distinct N. caninum isolates. Mice immunized with purified native NcSRS2 produced antigen-specific antibody, primarily of IgG 1 subtype. Following challenge during gestation with 10(7) tachyzoites, immunized mice had a statistically significant decreased frequency of congenital transmission compared to non-immunized mice (P<or=0.05) or mice inoculated with adjuvant alone (P<or=0.01). Decreased congenital transmission among immunized mice correlated with a predominately Th2 immune response compared to non-immunized mice as indicated by an increased ratio of interleukin 4 (IL-4) to interferon gamma (IFN-gamma) secretion from antigen-stimulated splenocytes. The results provide a rationale for NcSRS2 as a candidate subunit vaccine antigen for reduction of N. caninum congenital transmission. Furthermore, the studies suggest that a Th2 immune response, if directed against an appropriate antigen, may induce protection against N. caninum congenital infection in mice.

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

A prospective study was designed to investigate the presence of Neospora caninum in semen and blood of eight bulls seropositive to N. caninum using nested-PCR procedures. Positive semen and blood samples were bioassayed in a BALB/c nu/nu mouse model. Specific anti-N. caninum serological and interferon-gamma (IFN-gamma) responses were also studied. In parallel, five seronegative bulls acted as non-infected controls. All bulls were located in a collaborating AI centre and monitored for 22 weeks. Six of eight seropositive bulls showed N. caninum DNA in their semen and/or blood samples at some time during the course of the study. In all positive semen samples, we consistently found Neospora-DNA in the cell fraction and not in seminal plasma. Parasite load, as determined by a real-time PCR in nested-PCR positive semen samples, ranged from 1 to 10 parasites/ml. We found no association between the presence of N. caninum DNA in semen and blood. N. caninum could not be detected in the BALB/c nu/nu mice inoculated with PCR-positive semen or blood samples. Specific IgG antibody levels in seropositive bulls fluctuated over time, at times falling below cut-off level. The response was predominantly IgG2, with significant differences compared to control bulls (P < 0.05). The overall mean specific IFN-gamma response in seropositive bulls was also higher than those observed in the control group (P < 0.05), although extensive variation in individual responses was observed among bulls and over time. No significant association was found between bulls showing Neospora DNA in semen, blood, or both, and specific IgG, IgG1, IgG2, IgM and IgA levels or IFN-gamma response. This study is the first to report the presence of Neospora DNA in semen and blood of naturally-infected bulls. Our observations indicate intermittent presence of N. caninum in blood and semen and shedding in semen in low numbers.

Immune response to Neospora caninum in naturally infected heifers and heifers vaccinated with inactivated antigen during the second trimester of gestation

The objective of this study was to compare the immune response to Neospora caninum in naturally infected heifers and heifers inoculated with a killed whole N. caninum tachyzoite preparation during the second trimester of gestation. Nine Holstein heifers were used in this study; three naturally infected heifers were born from seropositive dams, and six seronegative heifers were born from seronegative dams. Four seronegative heifers were subcutaneously vaccinated with a killed whole N. caninum tachyzoite preparation at weeks 13, 15 and 17 of gestation. A killed whole N. caninum tachyzoite preparation containing 45 mg of protein/5 ml dose was formulated with 70% of mineral oil adjuvant (13% consisting of Arlacel C, 85% Marcol 52 and 2% Tween-80). Similarly, two seronegative heifers (negative controls) were inoculated with mock-infected bovine monocytes in oil adjuvant. Humoral immune responses were tested by using an indirect fluorescent antibody test (IFAT) and an indirect enzyme-linked immunosorbent assay (ELISA) for detecting isotype specific antibodies. Cellular immune responses were assessed by lymphocyte proliferation test (LPT) and IFN-gamma production. N. caninum-specific antibody responses increased in immunized cattle by week 15 of gestation (mean reciprocal antibody titers 450+/-252), peaked at week 23 (mean 16,000+/-6400). Maximum antibody response in naturally infected heifers was observed at week 19 of gestation (mean: 3467+/-2810). Mean serum IFAT titers were significantly higher in immunized heifers compared with those in naturally infected heifers from weeks 17 to 25 (P < 0.05). Analysis of isotype specific antibodies in naturally infected heifers revealed a predominant IgG1 response in one heifer and a predominant IgG2 response in the other two. Similar titers of IgG1 and IgG2 occurred in immunized heifers. Control heifers remained seronegative throughout the study by IFAT and ELISA. Significant antigen-specific proliferation responses were only detected in naturally infected heifers in week 19 of gestation. Peripheral mononuclear blood cells (PMBC) from immunized animals produced IFN-gamma in similar concentrations to those of infected animals (P > 0.05). No abortion was seen in any experimental group; however, one calf from a vaccinated heifer died due to dystocia. All calves from vaccinated and control heifers were seronegative by IFAT at 6 months of age; in contrast, calves born from naturally infected heifers remained seropositive with titers > or = 200. Killed vaccine induced similar immune responses to those found in chronically, naturally infected cattle which did not abort; however, different immune pathways may be followed in vaccinated and natural infected heifers with differences in degree of protective immunity.

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.

Identification of vaccine candidate peptides in the NcSRS2 surface protein of Neospora caninum by using CD4+ cytotoxic T lymphocytes and gamma interferon-secreting T lymphocytes of infected holstein cattle

Previously, our laboratory showed that Holstein cattle experimentally infected with Neospora caninum develop parasite-specific CD4+ cytotoxic T lymphocytes (CTL) that lyse infected, autologous target cells through a perforin-granzyme pathway. To identify specific parasite antigens inducing bovine CTL and helper T-lymphocyte responses for vaccine development against bovine neosporosis, the tachyzoite major surface proteins NcSAG1 and NcSRS2 were targeted. In whole tachyzoite antigen-expanded bovine T-lymphocyte lines, recombinant NcSRS2 induced potent memory CD4+- and CD8+-T-lymphocyte activation, as indicated by proliferation and gamma interferon (IFN-gamma) secretion, while recombinant NcSAG1 induced a minimal memory response. Subsequently, T-lymphocyte epitope-bearing peptides of NcSRS2 were mapped by using overlapping peptides covering the entire NcSRS2 sequence. Four experimentally infected cattle with six different major histocompatibility complex (MHC) class II haplotypes were the source of immune cells used to identify NcSRS2 peptides presented by Holstein MHC haplotypes. NcSRS2 peptides were mapped by using IFN-gamma secretion by rNcSRS2-stimulated, short-term T-lymphocyte cell lines, IFN-gamma enzyme-linked immunospot (ELISPOT) assay with peripheral blood mononuclear cells, and 51Cr release cytotoxicity assay of rNcSRS2-stimulated effector cells. Four N. caninum-infected Holstein cattle developed NcSRS2 peptide-specific T lymphocytes detected ex vivo in peripheral blood by IFN-gamma ELISPOT and in vitro by measuring T-lymphocyte IFN-gamma production and cytotoxicity. An immunodominant region of NcSRS2 spanning amino acids 133 to 155 was recognized by CD4+ T lymphocytes from the four cattle. These findings support investigation of subunit N. caninum vaccines incorporating NcSRS2 gene sequences or peptides for induction of NcSRS2 peptide-specific CTL and IFN-gamma-secreting T lymphocytes in cattle with varied MHC genotypes.

Toltrazuril treatment to control diaplacental Neospora caninum transmission in experimentally infected pregnant mice

We addressed the question whether diaplacental transmission of Neospora caninum can be controlled by metaphylactic chemotherapy using toltrazuril or enrofloxacin. Female C57/BL6 mice, infected on day 10 of pregnancy, were medicated for 6 consecutive days p.i. with 52.5 mg toltrazuril or - as an out-group control medication--16.7 mg enrofloxacin per kg body weight per day. Other control groups received either infection but no medication or vice versa. Toltrazuril treatment significantly reduced pre- and perinatal losses (10 deliveries of healthy newborns, versus 1 abortion and 4 failures) when compared to control-enrofloxacin (2 deliveries, versus 1 abortion, 7 failures and 2 pre-parturient deaths of dams) and non-treated animals (3 deliveries, versus 6 abortions, 8 failures and 4 pre-parturient deaths). Simultaneously, PCR-based parasite detection in the brain of mothers, histopathological findings as well as clinical fatality were significantly less frequent in toltrazuril-treated dams. The overall toltrazuril treatment efficacy was determined as 87 %, that of enrofloxacin-treatment as 17 %. The progenies of toltrazuril-treated dams also exhibited a very low rate of PCR-positivity in their brain (3 out of 39), whereas untreated dams delivered litters with mostly PCR-positive brains (12 out of 14) and a relatively high death rate post-partum (5 out of 19 newborns died). Mice subjected to a second mating delivered newborns all negative by N. caninum-PCR, indicating that diaplacental tachyzoite passage does not occur in a later, repeated pregnancy. Overall, our experiments showed that toltrazuril-treatment of an acute N. caninum-infection--induced during pregnancy--results in a clear reduction of fetal losses and a marked reduction of diaplacental passage of the parasite to the fetal brain, whereas enrofloxacin, as an out-group control substance, failed to show the same effect.

Immune responses during pregnancy in heifers naturally infected with Neospora caninum with and without immunization

This study was designed to identify changes in parasite-specific immune responses that occur during vertical transmission of Neospora caninum and can be used as indicators of parasite reactivation in naturally infected heifers. Ten heifers were unimmunized and 11 immunized with killed tachyzoites. One unimmunized heifer, which aborted at week 19 of gestation, had an increase in parasite-specific antibodies, mainly IgG(2), from week 15 to week 19 and a concomitant decline in parasite-specific cell-mediated immune (CMI) responses. Eight unimmunized heifers, which had live full-term congenitally infected calves, had an increase in antibodies, mainly IgG(2), from week 21 onwards. All immunized heifers delivered live full-term congenitally infected calves, and had a bimodal increase in antibodies; primarily IgG(1) following immunization and predominantly IgG(2) from week 17 onwards. Immunized heifers had significantly greater overall mean humoral and CMI responses than unimmunized heifers. Nine uninfected control heifers and their calves were seronegative. These results indicate that reactivation of a latent infection occurred in the naturally infected heifers, regardless of their immunization status, and was associated with increased parasite-specific antibodies, mainly IgG(2).

Evaluation of vaccination with Neospora caninum protein for prevention of fetal loss associated with experimentally induced neosporosis in sheep

OBJECTIVE

To evaluate the immunologic response of a killed tachyzoite vaccine against Neospora caninum and its effectiveness in preventing fetal loss associated with experimentally induced neosporosis in sheep.

ANIMALS

30 Dorset ewes.

PROCEDURE

Ewes were randomly allocated to receive vaccination on days 1 and 60 of the study with a killed N caninum tachyzoite preparation in a commercially available adjuvant or a saline-adjuvant mixture. A ram was placed on pasture with the ewes from days 15 to 60. Blood was collected from ewes before primary and booster vaccinations and prior to experimental challenge with N caninum tachyzoite performed on day 90; sera were assessed via Neospora agglutination (NA) and immunofluorescence antibody (IFA) assays. Blood was collected from lambs before they suckled, and sera were tested for antibodies against N caninum.

RESULTS

Of the 14 vaccinated ewes that became pregnant, 12 gave birth to live-born lambs; in contrast, 5 of 11 pregnant control ewes gave birth to live-born lambs. Whereas vaccination improved fetal survival in pregnant ewes challenged with N caninum tachyzoites, it did not appear to have any appreciable effect on transmission of N caninum to offspring, as indicated by results of NA and IFA assays.

CONCLUSIONS AND CLINICAL RELEVANCE

The N caninum tachyzoite vaccine used in this study appeared to provide protection against fetal loss associated with experimentally induced neosporosis in a high proportion of pregnant ewes.

Effect of a killed whole Neospora caninum tachyzoite vaccine on the crude abortion rate of Costa Rican dairy cows under field conditions

A standard field trial was carried out to assess the effect of a commercial Neospora-vaccine based on whole killed tachyzoites (Bovilis-Neoguard, Intervet) on the abortion rate. Eight hundred and seventy-six cows, over 2.5 months pregnant, belonging to 25 Costa Rican dairy herds, were used in the analysis. For each cow vaccinated, a cow of the same herd, breed and age category, was selected as control. The period of administration of treatments extended from June to November of 2000. The treatments were administered in two, 5-ml doses 1 month apart, the first dose given between day 75 and 90 of gestation. The incidence of abortion among all treated cows was of 16.0% (140/876). The treatment specific incidence was 11.2% (49/438) and 20.8% (91/438) for the vaccinated and the placebo group, respectively. The prevented fraction by vaccination amounted to 0.46 (95% CI: 0.26, 0.61), and the cumulative incidence ratio for the vaccinated group was 0.54. The Cox hazard ratio was 0.51(95% CI: 0.37, 0.72), meaning that the force of abortion is reduced twice in the vaccinated group. The results of this study, the first one following this type of design, shows that the killed whole Neospora caninum tachyzoite preparation had a reasonable effect on the abortion rate in Costa Rican dairy cattle.

Inclusion of CpG adjuvant with plasmid DNA coding for NcGRA7 improves protection against congenital neosporosis

The present study showed that incorporation of CpG adjuvant into plasmid DNA coding for NcGRA7 antigen resulted in a twofold increase in the level of protection against congenital transfer of Neospora caninum. The level of protection was considerably higher than that observed in pups born from dams immunized with nonrecombinant plasmid.

Development of vaccines to control bovine tuberculosis in cattle and relationship to vaccine development for other intracellular pathogens

Vaccination of cattle against bovine tuberculosis could be an important strategy for the control of disease either where there is a wildlife reservoir of Mycobacterium bovis infection or in developing countries where it is not economically feasible to implement a 'test and slaughter' control program. Advances in the understanding of protective immune responses to M. bovis infection in cattle and the advent of new molecular biological techniques, coupled with the sequencing of the M. bovis genome have provided opportunities for the rational development of improved tuberculosis vaccines. A number of new tuberculosis vaccines including attenuated M. bovis strains, killed mycobacteria, protein and DNA vaccines are under development and many are being assessed in cattle. Recent results have revealed several promising vaccine candidates and vaccination strategies. Ways of distinguishing between vaccinated and infected cattle are becoming available and the possibility of new approaches to the eradication of tuberculosis from domestic livestock is discussed. Similarities between the mechanisms of protective immunity against M. bovis and against other intracellular parasites continue to be found and discoveries from vaccine studies on bovine tuberculosis may provide helpful insights into requirements for vaccines against other intracellular pathogens.

Vaccination of ewes for prevention of vertical transmission of Neospora caninum

OBJECTIVE

To evaluate the immunologic response of a killed tachyzoite vaccine against Neospora caninum and its effectiveness in preventing vertical transmission of N caninum in sheep.

ANIMALS

40 Dorset ewes seronegative for N caninum.

PROCEDURE

Group-A ewes (n = 20) were vaccinated on days 1 and 126 with a killed N caninum tachyzoite preparation in a commercially available adjuvant. Group-B ewes (n = 20) were sham vaccinated. Blood samples were collected from ewes every 2 weeks and a recombinant ELISA (rELISA) was used to determine serum antibody titers against N caninum. During pregnancy, ewes were challenged with live N caninum tachyzoites. Precolostral serum was collected from lambs and tested for antibodies against N caninum by use of an indirect fluorescence antibody test and the rELISA. Tissue specimens from stillborn lambs or lambs that died within 2 weeks of birth were collected and examined for N caninum antigen and DNA by use of immunohistochemistry and polymerase chain reaction assay, respectively.

RESULTS

Serum antibody titers against N caninum were significantly higher in group-A ewes, compared with group B ewes, following vaccination. Serum antibodies against N caninum were detected in 100% (33/33) of group-B lambs and 75% (18/24) of group-A lambs. In tissue specimens, N caninum DNA was detected in 9 of 11 group-B lambs and 0 of 10 group-A lambs. Histologically, N caninum tachyzoites were observed in 4 group-A lambs and 3 group-B lambs.

CONCLUSIONS AND CLINICAL RELEVANCE

The killed tachyzoite vaccine against N caninum stimulated a humoral immune response in sheep and provided partial protection against vertical transmission.

Immune responses to Neospora caninum and prospects for vaccination

Developing an effective vaccine against neosporosis presents several interesting challenges. The parasite is spread efficiently from mother to foetus over several generations, and naturally infected cattle do not appear to develop adequate protective immunity. Modulation of the immune response during pregnancy favours parasite survival and multiplication. However, induction of pro-inflammatory responses that are thought to be protective against Neospora caninum would be detrimental to the pregnancy. So, is vaccination a feasible option to control the disease? This article discusses some of these issues and reports on the progress towards a vaccine for neosporosis.