Vaccines against veterinary helminths

Immunization with EmCRT-Induced Protective Immunity against Echinococcus multilocularis Infection in BALB/c Mice

Alveolar echinococcosis (AE) is a severe parasitic zoonosis caused by the larval stage of Echinococcus multilocularis. The identification of the antigens eliciting acquired immunity during infection is important for vaccine development against Echinococcus infection. Here, we identified that E. multilocularis calreticulin (EmCRT), a ubiquitous protein with a Ca²⁺-binding ability, could be recognized by the sera of mice infected with E. multilocularis. The native EmCRT was expressed on the surface of E. multilocularis larvae as well as in the secreted products of metacestode vesicles and protoscoleces (PSCs). The coding DNA for EmCRT was cloned from the mRNA of the E. multilocularis metacestode vesicles and a recombinant EmCRT protein (rEmCRT) was expressed in E. coli. Mice immunized with soluble rEmCRT formulated with Freund’s adjuvant (FA) produced a 43.16% larval vesicle weight reduction against the challenge of E. multilocularis PSCs compared to those that received the PBS control associated with a high titer of IgG, IgG1 and IgG2a antibody responses as well as high levels of Th1 cytokines (IFN-γ and IL-2) and Th2 cytokines (IL-4, IL-5 and IL-10), produced by splenocytes. Our results suggest that EmCRT is an immunodominant protein secreted by E. multilocularis larvae and a vaccine candidate that induces partial protective immunity in vaccinated mice against Echinococcus infection.

Worm control practices on free-range egg farms in Australia and anthelmintic efficacy against nematodes in naturally infected layer chickens

This study investigated worm control practices by free-range egg farmers and the efficacy of the commercial anthelmintics levamisole (LEV), piperazine (PIP), flubendazole (FLBZ) and fenbendazole (FBZ) against gastrointestinal nematodes on two free-range layer farms in Australia. An online survey comprising 36 questions was designed and implemented using SurveyMonkey. The survey contained questions about participant demographics, farm and flock characteristics, perceived intestinal worm importance, infection monitoring, deworming and other worm control practices. A link for the survey was emailed to free range egg producers from their industry body in December 2019. The anthelmintic efficacy trial was conducted in a total of 229 layers naturally infected with Ascaridia galli, Hetarakis gallinarum, Capillaria spp. and/or tape worms. Chickens received a single oral dose of LEV (28 mg/kg), PIP (100 mg/kg), FBZ (10 mg/kg) or LEV-PIP co-administered at their full individual doses, and FLBZ (Flubenol®), 30 ppm or 60 ppm) in the feed over 7 days. Anthelmintic efficacies were estimated by both worm count reduction (WCR %) and excreta egg count reduction (EECR %) tests 10 days after start of treatment. The survey with a response rate of 16/203, revealed that worm infection was of moderate concern to the producers and the majority (68%) felt that the current anthelmintics work effectively. The level of understanding of worms, monitoring and control practices did not reveal any major deficiencies of concern. The most commonly used anthelmintic was LEV (73%) followed by PIP (45%). Based on a standard cut-off value (≥90%), LEV, LEV-PIP, and FBZ attained the desired efficacy but PIP exhibited reduced efficacy against immature A. galli (61-85%), all stages of H. gallinarum (42-77%) and Capillaria spp. (25-44%). FLBZ was highly effective against all stages of roundworms and tapeworm infections. Even though there was some association between the efficacies estimated by WCR % and EECR % the latter was poorly associated in the natural infection model and hence does not provide a reasonable alternative for assessing anthelmintic efficacy when immature stages of the lifecycle are included. These results show no evidence of loss of susceptibility to the tested anthelmintics on these farms supporting the perception of producers that participated in the survey that current treatments work effectively. The reduced efficacy of PIP against some species and immature stages is related to its spectrum of activity rather than providing evidence of emerging resistance.

Immunomodulation and Immune Escape Strategies of Gastrointestinal Helminths and Schistosomes

Parasitic worms (helminths) developed various immunoregulatory mechanisms to counteract the immune system of their host. The increasing identification and characterization of helminth-derived factors with strong immune modulatory activity provides novel insights into immune escape strategies of helminths. Such factors might be good targets to enhance anti-helminthic immune responses. In addition, immunosuppressive helminth-derived factors could be useful to develop new therapeutic strategies for treatment of chronic inflammatory conditions. This review will take an in depth look at the effects of immunomodulatory molecules produced by different helminths with a focus on schistosomes and mouse models of hookworm infections.

Prevalence of gastrointestinal helminth infections in free-range laying hens under mountain farming production conditions

1. A cross-sectional study was conducted from September 2015 to July 2016 in South Tyrol, Northern Italy to examine the prevalence of gastrointestinal helminths in free-range laying hens under mountain farming production conditions. 2. A total of 280 laying hens from 14 free-range mountain farms (4 organic, 10 conventional) were randomly collected at the end of the laying period. Faecal samples were taken to analyse faecal egg counts (FEC) and faecal oocyst counts (FOC). The gastrointestinal tracts were removed post mortem and examined for the presence of helminths. 3. In faeces, FEC values averaged 258 eggs per g of faeces, which were dominated by Ascaridia galli and Heterakis gallinarum. Mean FOC was 80 oocysts/g. In the gastrointestinal tract, at least one nematode species was found in 99.3% of the examined hens. H. gallinarum was the most prevalent nematode (95.7%), followed by Capillaria spp. (66.8%) and A. galli (63.6%). Thirty per cent of the chickens were infected with cestodes (tapeworms). Correlation coefficients between worm counts of H. gallinarum, Capillaria spp. and A. galli ranged from 0.41 to 0.51. 5. The helminth prevalence did not differ between conventional and organic farms, whereas total worm burden was higher in organic compared with conventional farms (318.9 vs. 112.0). Prevalence and infection intensity did not differ between farms that used anthelmintic treatments and those that did not. 6. In conclusion, free-range laying hens under the studied mountain farming conditions are at high risk of nematode infection, especially in organic systems. The vast majority of hens are subclinical infected with at least one helminth species.

Progress in the development of subunit vaccines for gastrointestinal nematodes of ruminants

The global increase in anthelmintic resistant nematodes of ruminants, together with consumer concerns about chemicals in food, necessitates the development of alternative methods of control for these pathogens. Subunit recombinant vaccines are ideally placed to fill this gap. Indeed, they are probably the only valid option for the long-term control of ruminant parasitic nematodes given the increasing ubiquity of multidrug resistance in a range of worm species across the world. The development of a subunit multicellular parasite vaccine to the point of practical application would be a groundbreaking step in the control of these important endemic infections of livestock. This review summarizes the current status of subunit vaccine development for a number of important gastrointestinal nematodes of cattle and sheep, with a focus on the limitations and problems encountered thus far, and suggestions as to how these hurdles might be overcome.

Partially protective immunity induced by the 14-3-3 protein from Trichinella spiralis

Trichinellosis, a widespread zoonosis, is considered to be an emerging or re-emerging infectious parasitic disease. The development of vaccines to prevent Trichinella infection in domestic animals and humans is important for disease control. In a previous study, we identified Ts14-3-3 as an immunodominant protein from Trichinella spiralis (T. spiralis) adult worms recognized by early infection sera from pigs and mice. In this study, we further confirmed that Ts14-3-3 mRNA is expressed in both adult worms and in the larval stages of T. spiralis. Immunostaining with anti-Ts14-3-3 mouse sera further confirmed that native Ts14-3-3 is highly expressed on the surface of T. spiralis muscle larvae. The immune recognition by infected sera, its expression in both adult and larval stages and its exposure on the surface of the parasite led us to explore Ts14-3-3 as a vaccine antigen. Recombinant Ts14-3-3 formulated with an ISA50v2 adjuvant produced strong total IgG and balanced IgG1 and IgG2a responses in vaccinated mice and stimulated mouse splenocytes to produce high levels of Th1 (INF-γ, IL-2) and Th2 (IL4, IL5) cytokines. These results indicate that Ts14-3-3 is highly immunogenic and is able to induce balanced Th1/Th2 immune responses. These vaccine-induced immune responses resulted in a reduction in muscle larvae of up to 46.2% in vaccinated mice upon subsequent larval challenge relative to the number of larvae in mice received PBS control. The significant reduction in muscle larvae in vaccinated mice suggests that Ts14-3-3 is a promising vaccine target for potential use in domestic pigs to prevent trichinellosis transmission.

Vaccination with recombinant protein (r22C03), a putative attachment factor of Neoparamoeba perurans, against AGD in Atlantic salmon (Salmo salar) and implications of a co-infection with Yersinia ruckeri

Amoebic gill disease (AGD) affects salmonids during the marine grow-out phase in the Tasmanian industry and in other major salmonid producing countries. During the period post-transfer to seawater, the bacterial condition yersiniosis can also cause high levels of mortality in Atlantic salmon grown in Tasmania, in addition to the hatchery outbreaks. The recombinant protein r22C03, a mannose-binding protein-like (MBP-like) similar to attachment factors of other amoebae, was tested as a vaccine candidate against AGD in a large scale challenge trial. Fish were immunised with r22C03 combined with FCA via intraperitoneal (i.p.) injection, and given a booster five weeks later by either i.p. injection (RP group) or by a dip-immersion (mRP). Fish were then challenged twice with Neoparamoeba perurans: the initial challenge 16 weeks after primary immunisation was terminated due to presence of ulcerative lesions in the skin of salmon; the second challenge was carried out after five weeks of treatment with oxytetracycline. These skin lesions might have been associated with a concurrent infection with Yersinia ruckeri, which was detected by real-time qPCR in serum of a large proportion of moribund and survivor fish after the AGD challenge. Before and during the N. perurans infection, levels of antibodies against r22C03 were measured by ELISA in serum, skin mucus and supernatant from skin and gill explants. For the second challenge, the average size of AGD lesions was recorded from histology sections and survival curves were obtained. Before AGD challenge, r22C03 induced antibody responses in serum and explants with both vaccination strategies. At the end of the challenge, levels of antibodies were lower than before challenge irrespective of treatment. Both vaccinated groups presented increased serum antibody responses, while only mRP presented antibody responses in skin mucus, and no significant antibody responses were measured in the explants. Antibodies did not confer protection to N. perurans infection, as no difference was observed in the survival curves of the vaccinated and control groups, and there was no effect on the gill lesion size. The concurrent yersiniosis infection probably represented more closely infection patterns observed in commercial settings. However, it could have interfered with the survival results and with the ability of the fish to respond to the amoebae infection.

Two types of galactosylated fucose motifs are present on N-glycans of Haemonchus contortus

N-Glycans from the nematode Haemonchus contortus (barber pole worm), a parasite of sheep and cattle, were the first to be described to possess up to three fucose residues associated with the N,N'-diacetylchitobiosyl core, two being on the reducing-terminal proximal GlcNAc and one on the distal core GlcNAc residue. The assumption was that truncated glycans from this organism with three hexose residues have the composition Man3GlcNAc2Fuc1-3. In this study, we have performed HPLC and MALDI-TOF MS/MS in combination with selected digestions of N-glycans from Haemonchus. A dominant trifucosylated Hex3HexNAc2Fuc3 glycan was modified not only with α1,6-fucose but also with a proximal core α1,3-fucose and a galactosylated distal α1,3-fucose; thereby, only two of the hexose residues were mannose. Other N-glycans displayed galactosylation of the core α1,6-fucose, antennal fucosylation or modification with phosphorylcholine. Thus, the N-glycans of Haemonchus contain a number of potentially immunogenic glycan epitopes also found in other parasites and our proposed structures are in line with the previously defined specificity of nematode glycosyltransferases as we show that distal fucosylation and the presence of an α1,6-mannose are apparently mutually exclusive. These data are thereby of importance for engineering cell lines capable of mimicking Haemonchus-type N-glycans in the preparation of recombinant proteins as vaccine candidates.

LPS and inactivated Propionibacterium acnes elicit a partially protective response in primary infections of Heligmosomoides polygyrus

Intestinal helminth infections are common and of paramount economic importance in domestic animals. Available chemotherapy is limited and anthelmintic resistance is widespread in some hosts. This scenario favors the exploration of alternative methods of control, among them immune modulators. The effect of Escherichia coli LPS+Propionibacterium acnes on a primary infection of Heligmosomoides polygyrus (Trichostongyloidea) in mice has been tested. Nematode infection induced a rise of specific IgG1, both serum and intestinal, and a significant reduction in the unspecific (ConA) lymphoproliferative response. Treatment with the immune modulator (days -2, 0, 7 and 14 post infection) elicited an apparent delay of larval intramucosal development. Moreover cumulative nematode egg shedding in treated mice was significantly lower (p=0.0041). Preliminary results point toward the interest of immune modulators to control intestinal helminths.

An antigenic recombinant serine protease from Trichinella spiralis induces protective immunity in BALB/c mice

In this study, we report the cloning and characterization of a cDNA encoding a Trichinella serine protease gene (TspSP-1.3) from GenBank. The recombinant TspSP-1.3 protein (rTspSP-1.3) was expressed in an Escherichia coli expression system and purified with Ni-affinity chromatography. Real-time quantitative PCR analysis revealed that TspSP-1.3 was expressed at significantly higher levels in muscle larvae and adult worms than in newborn larvae. TspSP-1.3 was detected in excretory-secretory proteins of Trichinella spiralis with western blotting. Immunization with the rTspSP-1.3 antigen induced humoral immune responses, which manifested as elevated specific anti-rTspSP-1.3 IgG and IgE antibodies and a mixed Th1/Th2 response. To determine whether purified rTspSP-1.3 had good antigenicity and could be a vaccine candidate for the control of T. spiralis infection, we immunized BALB/c mice with rTspSP-1.3 and subsequently challenged the mice with T. spiralis larvae. The results showed that mice vaccinated with rTspSP-1.3 exhibited an average reduction in the muscle larvae burden of 39 % relative to the control group. These results suggest that TspSP-1.3 could be a novel vaccine candidate for controlling Trichinella infection.

Array-assisted characterization of a fucosyltransferase required for the biosynthesis of complex core modifications of nematode N-glycans

Fucose is a common monosaccharide component of cell surfaces and is involved in many biological recognition events. Therefore, definition and exploitation of the specificity of the enzymes (fucosyltransferases) involved in fucosylation is a recurrent theme in modern glycosciences. Despite various studies, the specificities of many fucosyltransferases are still unknown, so new approaches are required to study these. The model nematode Caenorhabditis elegans expresses a wide range of fucosylated glycans, including N-linked oligosaccharides with unusual complex core modifications. Up to three fucose residues can be present on the standard N,N'-diacetylchitobiose unit of these N-glycans, but only the fucosyltransferases responsible for transfer of two of these (the core α1,3-fucosyltransferase FUT-1 and the core α1,6-fucosyltransferase FUT-8) were previously characterized. By use of a glycan library in both array and solution formats, we were able to reveal that FUT-6, another C. elegans α1,3-fucosyltransferase, modifies nematode glycan cores, specifically the distal N-acetylglucosamine residue; this result is in accordance with glycomic analysis of fut-6 mutant worms. This core-modifying activity of FUT-6 in vitro and in vivo is in addition to its previously determined ability to synthesize Lewis X epitopes in vitro. A larger scale synthesis of a nematode N-glycan core in vitro using all three fucosyltransferases was performed, and the nature of the glycosidic linkages was determined by NMR. FUT-6 is probably the first eukaryotic glycosyltransferase whose specificity has been redefined with the aid of glycan microarrays and so is a paradigm for the study of other unusual glycosidic linkages in model and parasitic organisms.

Granule exocytosis of granulysin and granzyme B as a potential key mechanism in vaccine-induced immunity in cattle against the nematode Ostertagia ostertagi

Ostertagia ostertagi is considered one of the most economically important bovine parasites. As an alternative to anthelmintic treatment, an experimental host-protective vaccine was previously developed on the basis of ASP proteins derived from adult worms. Intramuscular injection of this vaccine, combined with QuilA as an adjuvant, significantly reduced fecal egg counts by 59%. However, the immunological mechanisms triggered by the vaccine are still unclear. Therefore, in this study, the differences in immune responses at the site of infection, i.e., the abomasal mucosa, between ASP-QuilA-vaccinated animals and QuilA-vaccinated control animals were investigated on a transcriptomic level by using a whole-genome bovine microarray combined with histological analysis. Sixty-nine genes were significantly impacted in animals protected by the vaccine, 48 of which were upregulated. A correlation study between the parasitological parameters and gene transcription levels showed that the transcription levels of two of the upregulated genes, those for granulysin (GNLY) and granzyme B (GZMB), were negatively correlated with cumulative fecal egg counts and total worm counts, respectively. Both genes were also positively correlated with each other and with another upregulated gene, that for the IgE receptor subunit (FCER1A). Surprisingly, these three genes were also correlated significantly with CMA1, which encodes a mast cell marker, and with counts of mast cells and cells previously described as globule leukocytes. Furthermore, immunohistochemical data showed that GNLY was present in the granules of globule leukocytes and that it was secreted in mucus. Overall, the results suggest a potential role for granule exocytosis by globule leukocytes, potentially IgE mediated, in vaccine-induced protection against O. ostertagi.

Cloning and characterization of the fatty acid-binding protein gene from the protoscolex of Taenia multiceps

Taenia multiceps (Cestoda: Taeniidae), a worldwide cestode parasite, is emerging as an important helminthic zoonosis due to serious or fatal central nervous system disease commonly known as coenurosis in domestic and wild ruminants including humans. Herein, a fatty acid-binding protein (FABP) gene was identified from transcriptomic data in T. multiceps. This gene, which contains a complete coding sequence, was amplified by reverse-transcriptase polymerase chain reaction. The corresponding protein, which was named TmFABP, had a molecular weight of 14 kDa, and subsequently was recombinantly expressed in Escherichia coli. The fusion protein was purified on Ni-NTA beads (Bio-Rad). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyses showed that the purified recombinant protein caused immunogenicity. Immunohistochemical studies showed that TmFABP was expressed at the tegumental level in the protoscolices and in the cells between the body wall and parenchyma layer of the cestode. In sections from gravid proglottids, intense staining was detected in the uterus and eggs. Based on this, TmFABP could be switched on during differentiation of germinative layers to protoscoleces and from metacestodes to adult worms. Taken together, our results already reported for T. multiceps suggest the possibility of TmFABP developing a vaccine to control and prevent coenurosis.

The role of nuclear technologies in the diagnosis and control of livestock diseases--a review

Nuclear and nuclear-related technologies have played an important role in animal health, particularly in relation to disease diagnosis and characterization of pathogenic organisms. This review focuses primarily on how and where nuclear technologies, both non-isotopic and isotopic methods, have made their impact in the past and where it might be expected they could have an impact in the future. The review outlines the extensive use of radiation attenuation in attempts to create vaccines for a multiplicity of pathogenic organisms and how the technology is being re-examined in the light of recent advances in irradiation techniques and cryopreservation/lyophilization that might obviate some of the problems of maintenance of viable, attenuate vaccines and their transport and use in the field. This approach could be used for a number of parasitic diseases where vaccination has been problematic and where investigations into the development of molecular vaccines have still failed to deliver satisfactory candidates for generating protective immune responses. Irradiation of antigens or serum samples also has its uses in diagnosis, especially when the samples need to be transported across international boundaries, or when handling the pathogens in question when carrying out a test presents serious health hazards to laboratory personnel. The present-day extensive use of enzyme immunoassays and molecular methods (e.g., polymerase chain reaction) for diagnosis and characterization of animal pathogens has its origins in the use of isotope-labeled antigens and antibodies. These isotopic techniques that included the use of 75Se, 32P, 125I, and 35S isotopes enabled a level of sensitivity and specificity that was hitherto unrealized, and it is prescient to remind ourselves of just how successful these technologies were, in spite of their infrequent use nowadays. Finally, the review looks at the potential for stable isotope analysis for a variety of applications--in the tracking of animal migrations, where the migrant are potential carriers of transboundary animal diseases, and where it would be useful to determine the origins of the carrier, e.g., Highly Pathogenic Avian Influenza and its dissemination by wild water fowl. Other applications could be in monitoring sequestered microbial culture (e.g., rinderpest virus) where in the case of accidental or deliberate release of infective culture it would be possible to identify the laboratory from which the isolate originated.

Vaccination of mice with an antigenic serine protease-like protein elicits a protective immune response against Trichinella spiralis infection

Trichinellosis has major economic impacts on animal husbandry and food safety, and the control and elimination of trichinellosis is a major objective of veterinary medicine. A gene encoding serine protease of Trichinella spiralis (Ts-Adsp) was identified by immunoscreening an adult T. spiralis cDNA library. In this study, the recombinant Ts-Adsp protein (rTs-Adsp) was cloned and expressed in a prokaryotic expression system and purified by Ni-affinity chromatography. To determine whether the purified rTs-Adsp is a potential vaccine candidate for the control of T. spiralis infection, we immunized BALB/c mice with this protein in combination with an alum adjuvant and subsequently challenged with T. spiralis larvae. The results showed that mice vaccinated with rTs-Adsp exhibited an average reduction in the muscle larvae burden of 46.5% relative to the control group. Immunization with the rTs-Adsp antigen induced both humoral and cellular immune responses, which manifested as elevated specific anti-rTs-Adsp IgG and IgE antibodies and a mixed Th1-Th2 response, as determined by Th1 (IFN-γ and IL-2) and Th2 (IL-4, IL-10, and IL-13) cytokine profiling, with the Th2 predominant. Thus, purified rTs-Adsp is able to limit the invasion of T. spiralis , and this protein could be an effective vaccine candidate for trichinellosis.

Phage-display library biopanning as a novel approach to identifying nematode vaccine antigens

Infections with parasitic nematodes are of significant welfare and economic importance worldwide, and because of the emergence of anthelmintic resistance, this has lead to alternative methods of parasite control being required. Vaccination offers a feasible alternative control, and the majority of research has focused on the production of recombinant versions of native antigens previously identified as protective in vaccinated animals. Attempts at the production of protective recombinant subunit vaccines have been hindered, however, as these antigens have invariably failed to replicate the same level of protective immune response as seen with the native versions. It has been proposed that these failures are owing to the fact that the recombinant proteins do not contain the appropriate post-translational modifications to retain the protective capacity of the native molecules. In this review, we discuss a novel approach to vaccine antigen identification through the application of random peptide phage-display libraries and their use to identify peptide sequences that potentially mimic the structure(s) of antigenic epitopes. This area of research is still relatively novel with respect to parasites, and the current state of the art will be discussed here.

Update on trematode infections in sheep

Trematode parasites live in the liver, fore stomachs or blood vessels of a wide range of animals and humans. Most of them have a special economic and veterinary significance. Liver fluke disease of sheep and other animal species is caused by the common liver fluke Fasciola hepatica. Hepatic fasciolosis occurs throughout the world, where climatic conditions are suitable for the survival of aquatic intermediate host snails. Also of importance for ruminants, in some parts of the world, are Fasciola gigantica and Fascioloides magna. Other trematodes infecting ruminants include Dicrocoelium dendriticum; Eurytrema pancreaticum and Eurytrema coelomaticum. Among the Paramphistomidae, some species can infect sheep and other ruminants. Finally, Schistosoma spp. are found in the blood vessels of ruminants and are of minor importance in temperate regions. The manuscript concentrates on trematode species of veterinary importance for domestic sheep.

A mechanistic model of developing immunity to Teladorsagia circumcincta infection in lambs

Acquired immunity influences the severity of parasitic disease, but modelling the effects of acquired immunity in helminth infections has proved challenging. This may be due to a lack of suitable immunological data, or to the perceived complexity of modelling the immune response. We have developed a model of T. circumcincta infection in domestic sheep that incorporates the effects of acquired immunity on parasite establishment and fecundity. A large data set from commercially managed populations of Scottish Blackface sheep was used, which included relationships between IgA activity and worm length, and between worm length and fecundity. Use was also made of a recently published meta-analysis of parasite establishment rates. This realistic but simple model of nematode infection emulates observed patterns of faecal egg counts. The end-of-season faecal egg counts are remarkably robust to perturbations in the majority of the parameters, possibly because of priming of the immune system early in the season, reducing parasite establishment and growth and, therefore, faecal egg counts. Lowering the amount of early infection leads to higher end-of-season egg counts. The periparturient rise in egg counts in ewes appears to have an important role in supplying infection for the priming of the immune response. This feedback in the immune priming suggests that nematode infections may be difficult to eliminate.

Adult Brugia malayi approximately 34 kDa (BMT-5) antigen offers Th1 mediated significant protection against infective larval challenge in Mastomys coucha

We earlier reported a sizeable protection conferred by 'mitochondria rich' (MT) fraction of adult B. malayi and the present study was planned to locate the candidate protective molecule/s in the active fraction. The MT fraction was subjected to sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and the antigen bands showing strong immune-reactivity with the resistant mastomys sera were assayed for their lymphoproliferative response using splenocytes of protected animals. Of the eight such protein bands, one sub fraction with a molecular weight of approximately 34 kDa (BMT-5) produced utmost cellular proliferation and was therefore exploited for vaccination study. BMT-5 emulsified in Freund's adjuvant produced discernible protection causing 69 and 67% reductions in microfilaraemia and adult worm burden respectively along with sterilization of 68% of the recovered female parasites. Significant levels of filaria-specific and non-specific lymphoproliferation along with enhanced release of Th1 cytokines (TNF-alpha, IFN-gamma and IL-2) by splenocytes were observed in the vaccinated mastomys in addition to elevated levels of antigen-specific IgG, IgG2a, IgG2b and IgA. The peritoneal macrophages of immunized animals also revealed enhanced nitric oxide production in the presence of BMT-5. The findings suggest that approximately 34 kDa (BMT-5) molecules present in the MT fraction of adult B. malayi provided sizeable protection against infective larval challenge by generating a Th1 biased milieu in the host.

Proteomic analysis of excretory/secretory products released by Teladorsagia circumcincta larvae early post-infection

Teladorsagia circumcincta is an important parasitic nematode of domestic small ruminants. Drug resistance in this species is common so alternative methods of control are required. As animals develop immunity to T. circumcincta, vaccination is a valid option. Little is known about the antigens that play a role in stimulating immunity at this host/parasite interface. As responses generated between 1 and 5 dpi are known to affect development of these nematodes in their gastric niche, we focused on proteins released during the early stages of infection. To identify molecules potentially involved in immunity, we undertook a proteomics analysis of proteins released from larvae harvested at 1-, 3- and 5-days post-infection (dpi). This analysis produced peptide sequence data that was used to search information available in T. circumcincta expressed sequence tag (EST) databases and enabled identification of a number of excretory/secretory (ES) proteins. Immunoblots were performed to assess the relative molecular weight of ES antigens that were targets of local IgA responses in mucus from sheep rendered immune to infection. ELISA was performed to assess antigen-specific mucus IgA levels in individual sheep. These experiments provided preliminary evidence that the proteins identified in the larval secretome were subject to these antibody responses.

A study of the liver of goats immunized with a synthetic peptide of the Sm14 antigen and challenged with Fasciola hepatica

A synthetic peptide of the Sm14 antigen of Schistosoma mansoni was used to immunize goats against experimental challenge with Fasciola hepatica. The goats used consisted of: group 1 (unimmunized and uninfected [controls]); group 2 (unimmunized and infected); group 3 (immunized and infected). Compared with group 2, the animals of group 3 showed at necropsy a reduction in hepatic worm burden; however, because of variability in the two groups this reduction was not statistically significant. A gross morphometric study of the hepatic changes revealed a correlation between lesions and worm burdens in group 3. No significant differences in damaged areas were found between groups 2 and 3, except that group 2 had more severe bile duct hyperplasia. A striking hepatic inflammatory infiltration of CD3+ T lymphocytes and IgG+ plasma cells was found in both groups 2 and 3, especially the latter.

Experimental vaccines in animal models for schistosomiasis

Considerable morbidity and mortality results from the affliction of an estimated 200 million people worldwide by several species of schistosomes; 779 million are exposed to the disease in 74 different countries. Even though anti-parasitic drugs and other control measures, including public hygiene and snail control are available, the advent of an effective vaccine still remains the most potentially powerful means for the control of this disease. The putative vaccine could be administered to small children prior to the time when their contact with infected water is maximal, so as to prevent severe infection in the subsequent years. This review attempts to summarize the status of schistosome vaccine development with special emphasis on functionally important vaccine candidates. The importance of utilizing both murine and nonhuman primate models as a prerequisite for clinical trials is discussed.

Identification of immuno-reactive proteins from a sheep gastrointestinal nematode, Trichostrongylus colubriformis, using two-dimensional electrophoresis and mass spectrometry

Gastrointestinal nematode infections of livestock animals are prevalent and costly problems worldwide. Currently, infections are controlled by anthelmintic chemicals but increasing drug resistance has prompted research interest to shift towards alternative methods of control such as vaccine development and selection of worm-resistant animals. The present study analyses proteins from Trichostrongylus colubriformis infective L3s that are recognised by IgG of immune sheep. Following protein separation via two-dimensional electrophoresis and Western blot probing with plasma from sheep resistant to T. colubriformis, mass spectrometry-based proteomic analyses were used to identify immuno-reactive protein spots. We were able to identify 28 immune targets, including aspartyl protease inhibitor, enolase, chaperone proteins, galectin, glycolytic enzymes, kinase, phosphatase and structural muscle proteins such as myosin, paramyosin, calponin and DIM-1. The data suggest that immune responses to T. colubriformis are dispersed over a relatively large number of parasite antigens, including several cytoplasmically expressed proteins. The results have new implications for understanding the molecular mechanisms that underpin host-parasite interaction during gastrointestinal nematode infections.

Parasite vaccines: The new generation

Parasites cause some of the most devastating and prevalent diseases in humans and animals. Moreover, parasitic infections increase mortality rates of other serious non-parasitic infections caused by pathogens such as HIV-1. The impact of parasitic diseases in both industrialised and developing countries is further exacerbated by the resistance of some parasites to anti-parasitic drugs and the absence of efficacious parasite vaccines. Despite years of research, much remains to be done to develop effective vaccines against parasites. This review focuses on the more recent vaccine strategies such as DNA and viral vector-based vaccines that are currently being used to develop vaccines against parasites. Obstacles yet to be overcome and possible advantages and disadvantages of these vaccine modalities are also discussed.

Three surface antigens dominate the mucosal antibody response to gastrointestinal L3-stage strongylid nematodes in field immune sheep

Although gastrointestinal nematode parasites are a major human and veterinary health problem, little is known about how the host is sometimes able to mount an effective immune rejection response. In previous work, we identified a carbohydrate larval surface antigen (CarLA) as the target of mucosal antibodies that can elicit rejection of Trichostrongylus colubriformis L3s in sheep. Here we characterise the natural mucosal antibody responses to L3s from three major strongylid gastrointestinal parasites of sheep, Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia circumcincta. The mucosal antibody repertoire of naturally field-immune sheep was displayed on bacteriophage as single-chain antibodies (scFvs) and phage were selected for the ability to bind to the surface of living L3s of the three nematode species. All nematode-binding scFvs were found to recognize one of three different antigen classes that are each found in the three strongylid species. These three antigen classes appear to represent all of the major antigens recognized on Western blots by pooled mucosal antibodies from field-immune sheep. One of the antigen classes is a heterogeneous, high molecular weight molecule that is protease-sensitive. The scFvs recognizing this surface antigen also recognize a similar antigen in all strongylids tested. A second antigen class is a protease-insensitive, low molecular weight antigen found only in sheaths and scFvs recognizing this antigen cross-react with a similar molecule found in all strongylids tested. The third surface antigen class is CarLA and all of the anti-CarLA scFvs obtained from the field-immune sheep repertoire were specific to L3s of only one species and often recognized only a subset of the worms. Thus three different L3-stage surface antigens, two that lack a protein component, dominate the natural mucosal antibody response to L3-stage gastrointestinal strongylid nematodes in sheep.

DifferentialN-glycan- and protein-directed immune responses inDictyocaulus viviparus-infected and vaccinated calves

Calves with naturally acquiredDictyocaulus viviparusinfection mount an effective immune response. In the search for protection-inducing antigens, we found that severalD. viviparusthird-stage larval (L3) and adult ES products carry N-glycans. Deglycosylation of the worm antigens using PNGase F resulted in reduced IgA, IgE, IgG1 and IgG2 (but not IgM) reactivities in sera of primary infected animals, suggesting that the carbohydrate moieties contained immunodominant epitopes. Challenge infection resulted in increased specific serum antibody levels against ES and L3 in the re-infected and challenge control groups. Testing of sera by enzyme-linked immunosorbent assay (ELISA) demonstrated a significant increase in IgG1 and IgE (but not IgA or IgG2) reactivity against the deglycosylated antigens in the re-infected group compared with the challenge control group. Sera from calves vaccinated with irradiated larvae showed a strong anti-N-glycan response, but no booster response against the protein backbone after challenge infection, consistent with the absence of a memory response. Together, our results suggest thatD. viviparusproteins carry immunodominant N-glycan moieties that elicit a strong but short-lived immune response during infection and after vaccination, whereas the protein backbones effectively induce a memory response which results in a long-lasting, potentially protective immune response in re-infected, but not in vaccinated calves.