Vaccination of lambs against Haemonchus contortus infection with a somatic protein (Hc23) from adult helminths

Mucosal Immunity of Major Gastrointestinal Nematode Infections in Small Ruminants Can Be Harnessed to Develop New Prevention Strategies

Gastrointestinal parasitic nematode (GIN) infections are the cause of severe losses to farmers in countries where small ruminants such as sheep and goat are the mainstay of livestock holdings. There is a need to develop effective and easy-to-administer anti-parasite vaccines in areas where anthelmintic resistance is rapidly rising due to the inefficient use of drugs currently available. In this review, we describe the most prevalent and economically significant group of GIN infections that infect small ruminants and the immune responses that occur in the host during infection with an emphasis on mucosal immunity. Furthermore, we outline the different prevention strategies that exist with a focus on whole and purified native parasite antigens as vaccine candidates and their possible oral-nasal administration as a part of an integrated parasite control toolbox in areas where drug resistance is on the rise.

In silico analysis of two Haemonchus spp. serine protease peptides (S28) and their immunomodulatory activity in vitro

The aim of this study was to evaluate the in vitro immune modulation of two de novo peptides with hypothetical identity to the serine protease family (S28) from Haemonchus spp. Expression of mRNAs encoding these peptides was confirmed by RTqPCR in L₃ and adult stage parasites. Antibodies from serum samples collected from an H. contortus-infected lamb at 60 days post infection detected both peptides, as assessed by indirect ELISA. Lamb peripheral blood mononuclear cells (PBMCs) were exposed to each peptide, as well as to the peptide mixture, and cell proliferation assays were performed at 24, 48 and 72 h. The relative expression of the IL4, IL5, IL6, IL13, CXCL8 and FCεR1A genes was quantified by RTqPCR from lamb PBMCs exposed to the peptide mixture at 24 and 48 h. With respect to immune gene expression, 15- and 3-fold upregulation at 24 h was observed with IL5 and CXCL8, respectively, and 2-fold upregulation of CXCL8 at 48 h. In contrast, downregulation of IL5 was stimulated at 48 h. These data suggest that these peptides (pep-hsp and pep-pcx), which show high identity with intestinal and excretion/secretion serine proteases, can trigger immunogenic activity, and suggest that they may be useful as potential parasite vaccines.

Haemonchosis in Sheep and Goats, Control Strategies and Development of Vaccines against Haemonchus contortus

Simple Summary

Haemonchus contortus is the most pathogenic blood-feeding parasitic nematode in sheep and goats, threatening animal welfare and causing tremendous economic losses to the small ruminant industry. This comprehensive review article sums up current control strategies, worm-derived antigens and recent advances in anti-Haemonchus vaccine development. New insights into antigen engineering and general considerations for clinical trials are discussed here.

Abstract

The evolutionary success of parasitic worms causes significant economic losses and animal health problems, including in the small ruminant industry. The hematophagous nematode Haemonchus contortus is a common endoparasite that infects wild and domestic ruminants worldwide, especially in tropical and subtropical regions. To date, the most commonly applied control strategy is the administration of anthelminthic drugs. The main disadvantages of these chemicals are their ecotoxic effects, the necessary withdrawal period (especially important in dairy animals) and the increasing development of resistance. Vaccines offer an attractive alternative control strategy against Haemonchus infections. In previous years, several potential vaccine antigens prepared from H. contortus using the latest technologies have been assessed in clinical trials using different methods and strategies. This review highlights the current state of knowledge on anti-H. contortus vaccines (covering native, recombinant and DNA-based vaccines), including an evaluation, as well a discussion of the challenges and achievements in developing protective, efficient, and long-lasting vaccines to control H. contortus infection and haemonchosis in small ruminants. This paper also addresses novel developments tackling the challenge of glycosylation of putative candidates in recombinant form.

Immunization With Recombinant Haemonchus contortus Y75B8A.8 Partially Protects Local Crossbred Female Goats From Haemonchus contortus Infection

Haemonchus contortus Y75B8A.8 (Hc8) derived from H. contortus excretory–secretory (ES) products was identified as a functional inhibitor of goat interleukin 2 (IL-2). It may act as a vaccine candidate for the development of therapeutic strategies against H. contortus infection. In this research, recombinant Hc8 (rHc8) and goat anti-rHc8 polyclonal antibodies were employed to evaluate the protective capacities of Hc8 antigen against H. contortus infections via active and passive immunization trials, respectively. In both trials, local crossbred female goats aged 9–12 months old were randomly divided into three groups, five in each group, respectively. Parasitological examinations, including fecal egg counts (FEC), cumulative FEC (cFEC), and worm burdens, were performed. In addition, antibody levels in mucosal homogenate (MH) samples and hematological and immunological parameters were detected. In the passive trial, goats were intravenously immunized with 5 mg total IgG containing anti-rHc8 goat polyclonal antibodies. After twice immunization, compared with the challenged control group, cFEC was reduced by 39%. In addition, there was a 46% reduction of worm burdens compared with the challenged controls. In the active immunization trials, 500 μg of recombinant Hc8 protein was given subcutaneously twice to 9–12-month-old local crossbred female goats with a 2-week interval, resulting in the generation of high levels of antigen-specific circulating antibodies. Besides, cFEC and abomasal worm burden were reduced by 70 and 55%, respectively, compared with the challenged control group. In addition, immunized goats had higher mucosal homogenate IgA and hemoglobin levels than the challenged controls in both passive and active immunization trials. These preliminary results demonstrated the immunoprophylactic effects of Hc8 antigen and will inform new studies on ES proteins in developing subunit recombinant vaccines against H. contortus.

In vitro anthelmintic activity of Dennettia tripetala G. Baker (Annonaceae) Fruits against Haemonchus contortus

Helminthosis is one of the greatest causes of parasitic disease and loss in animal productivity. As such, the control of helminth parasites is of critical importance. This study was aimed to investigate the in vitro anthelmintic activity of Dennettia tripetala G. Baker (Annonaceae) fruits against Haemonchus contortus. Using in vitro techniques, the anthelmintic activity of extracts and fractions of D. tripetala G. Baker (Annonaceae) was evaluated for ovicidal (Egg hatch inhibition test) and larvicidal (larval mortality test) activity. Besides, the maximum tolerated dose was determined in adult albino rats administered, 300, 400, and 500 mg/kg body weight of the CME fraction, and observed over a period of 48 h for signs of toxicity and mortality. Phytochemical screening uncovered the occurrence of flavonoids, steroids/triterpenes, cardiac glycosides, saponins, tannins, carbohydrates, and alkaloids in the crude methanol extract (CME), the ethyl acetate fraction (EAF), and butanol fraction. The maximum tolerated dose of the CME of D. tripetala did not produce observable signs of toxicity or death in all the rats given up to 500 mg/kg. The CME and EAF of D. tripetala fruits produced a significant ( p < 0.05 ) reduction in the hatchability of H. contortus eggs in a concentration-dependent manner, while the CME at concentrations between 12.5 and 100 mg/ml completely inhibited the hatching of H. contortus eggs. Similarly, EAF at doses of 25, 50, and 100 mg/ml completely inhibited the hatching of H. contortus eggs. The CME and EAF of D. tripetala fruits produced significant ( p < 0.05 ) larvicidal activity against L₃ of H. contortus in a concentration-dependent manner while the CME at concentrations between 6.25 and 100 mg/ml caused larval mortality of H. contortus L₃ larvae completely. This study suggests that methanol extract and fractions of D. tripetala fruits possess beneficial anthelmintic (ovicidal and larvicidal) activity against H. contortus, and may be a suitable alternative anthelmintic candidate for the control of nematodes.

Anthelmintic activity of methanol extract of Dennettia tripetala G. Baker (Annonaceae) fruits against Haemonchus contortus in red Sokoto goats

Haemonchosis is a gastrointestinal parasitic disease of economic importance in ruminants especially sheep and goats. In view of the rising costs of conventional veterinary anthelmintics and the development of resistance by Haemonchus contortus, there is a need to develop alternative ethnoveterinary therapies for the treatment and management of Haemonchosis. This study investigated the anthelmintic activity of Dennettia tripetala G. Baker (Annonaceae) fruits against Haemonchus contortus in red Sokoto goats. The maximum tolerated dose was determined in adult albino rats administered, 3000, 4000, and 5000 mg/kg body weight of the crude methanol extract (CME) fraction, and observed over a period of 48 h for signs of toxicity and mortality. The in vivo anthelmintic activity was evaluated using 20 kids infected with H. contortus and randomly allocated into 5 groups (1, 2, 3, 4, and 5). Kids in groups 1, 2, and 3 were treated with CME at doses of 1250, 2500, and 5000 mg/kg respectively for 3 consecutive days per os. Groups 4 and 5 were treated with albendazole (7.5 mg/kg) once and distilled water (5 ml) respectively and served as treated and untreated controls. Blood samples were collected for haematology. The maximum tolerated dose of the CME of D. tripetala did not produce observable signs of toxicity or death in all the rats given up to 5000 mg/kg. There was significant (P < 0.05) reduction in faecal egg count by CME at doses of 1250 mg/kg (91.6%), 2500 mg/kg (98.5%), and 5000 mg/kg (100%) at day 14 post-treatment. The total plasma protein (TPP) and FAMACHA© scoring values were significantly improved (P < 0.05) in the treated groups. These results indicate that methanol extract and fractions of D. tripetala fruits possess beneficial anthelmintic activity against H. contortus and may be a suitable alternative anthelmintic candidate for the control of haemonchosis in goats.

A journey through 50 years of research relevant to the control of gastrointestinal nematodes in ruminant livestock and thoughts on future directions

This review article provides an historical perspective on some of the major research advances of relevance to ruminant livestock gastrointestinal nematode control over the last 50 years. Over this period, gastrointestinal nematode control has been dominated by the use of broad-spectrum anthelmintic drugs. Whilst this has provided unprecedented levels of successful control for many years, this approach has been gradually breaking down for more than two decades and is increasingly unsustainable which is due, at least in part, to the emergence of anthelmintic drug resistance and a number of other factors discussed in this article. We first cover the remarkable success story of the discovery and development of broad-spectrum anthelmintic drugs, the changing face of anthelmintic drug discovery research and the emergence of anthelmintic resistance. This is followed by a review of some of the major advances in the increasingly important area of non-pharmaceutical gastrointestinal nematode control including immunology and vaccine development, epidemiological modelling and some of the alternative control strategies such as breeding for host resistance, refugia-based methods and biological control. The last 50 years have witnessed remarkable innovation and success in research aiming to improve ruminant livestock gastrointestinal nematode control, particularly given the relatively small size of the research community and limited funding. In spite of this, the growing global demand for livestock products, together with the need to maximise production efficiencies, reduce environmental impacts and safeguard animal welfare - as well as specific challenges such as anthelmintic drug resistance and climate change- mean that gastrointestinal nematode researchers will need to be as innovative in the next 50 years as in the last.

Characteristics of Biotin lipoyl attachment and 2-oxoacid dehydrogenase acyltransferase of the parasitic nematode Haemonchus contortus and its modulatory functions on goat PBMCs in vitro

Biotin lipoyl attachment and 2-oxoacid dehydrogenase acyltransferase (BLAODA), as an essential excretion of Haemonchus contortus (HcESPs), was identified to have antigenic functions. T helper-9 (Th9) cells secrete interleukin (IL)-9, a signature cytokine associated with tumour immunology, allergy and autoimmunity. Nonetheless, the understanding of modulatory functions of BLAODA on Th9 and other immune cells is limited. In this study, the BLAODA gene was cloned, and the recombinant (r) protein of BLAODA (rHcBLAODA) was expressed and immunoblotting was performed. The results revealed that HcBLAODA gene was successfully cloned and rHcBLAODA protein was expressed. The localization of rHcBLAODA was confirmed on the surface of gut sections from adult H. contortus. The rHcBLAODA protein capability to react precisely with anti-H. contortus antibodies were confirmed by immunoblotting and immunofluorescence assay (IFA). Further functional analysis showed that interaction of rHcBLAODA with host cells significantly enhanced Th9 cells generation, IL-9 expression, nitric oxide production and cell apoptosis while suppressing the cells proliferation and cells migration depending on the concentration. Overall, these findings suggest that rHcBLAODA protein could modulate the host immune response by inducing Th9 cells to secrete IL-9 cytokine in vitro.

Advances in the Development of Anti-Haemonchus contortus Vaccines: Challenges, Opportunities, and Perspectives

The gastrointestinal nematode parasite Haemonchus contortus (H. contortus) is a resident of tropical and subtropical regions worldwide that imposes significant production losses, economic losses, and animal health issues in the small ruminant industry, particularly sheep and goats. Considerable efforts have been made to understand how immunity is elicited against H. contortus infection. Various potential vaccine antigens have been tested by different methods and strategies applied in animal models, and significant progress has been made in the development of vaccines against H. contortus. This review highlighted and shared the knowledge about the current understanding of host immune responses to H. contortus and ongoing challenges in the development of a protective, effective, and long-lasting vaccine against H. contortus infection. We have also pinpointed some achievements and failures in the development and testing of vaccines, which will establish a road map for future research directions to explore new effective vaccine candidates for controlling and preventing H. contortus infection.

Haemonchus contortus transthyretin domain - containing protein (HcTTR): A promising vaccine candidate against Haemonchus contortus infection

Haemonchus contortus transthyretin domain-containing protein (HcTTR) with 136 amino acids belongs to a transthyretin-like (TTL) family member. In our previous study, it was reported that HcTTR was a novel antagonist of the goat cytokine Interleukin 4 (IL-4), and was involved in the regulation of host immune responses, implying that it might be applied for therapeutic strategies or vaccine development against the infection of H. contortus. Thus, the protective capacities of HcTTR against H. contortus infections via active and passive immunization trials were examined. For the passive protection trials, H. contortus-infected goats were intravenously immunized twice with 5 mg of total IgG containing anti-rHcTTR goat polyclonal antibodies. The results showed that the significant rates of reduction in egg shedding and worm burden was 58.12% and 64.61%, respectively, as compared with the positive control group. For the active protection trials, local goats were vaccinated twice with 500 μg of recombinant HcTTR to generate antigen-specific circulating antibodies, resulting in 63.7% reduction in eggs shedding and 66.4% reduction in worm burdens after H. contortus challenge. In both passive and active trials, the immunized goats displayed higher mucosal IgA levels and less anaemic compared to the challenged positive controls. Pen trials indicated that HcTTR generated partial immune protective effects against H. contortus challenge and it could be a promising vaccine candidate for development of effective strategy to control H. contortus.

Adhesion-Regulating Molecule from Haemonchus contortus: Potential Antigen for Diagnosis of Early Infection in Goats

Haemonchus contortus, a blood-sucking nematode of ruminants, causes large economic losses worldwide. Diagnosis of infection mainly depends on the evaluation of clinical signs and fecal examination. However, this has limitations for the diagnosis of early or light infections, where serological diagnosis seems to be more accurate and reliable. In this study, the recombinant H. contortus adhesion-regulating molecule protein (rHCADRM) was expressed and purified, and its diagnostic potential was evaluated. Serum samples from goats experimentally infected with H. contortus (n = 5) were collected at 0 (before infection, negative control), 7, 14, 21, 35, 49, 63, 85, and 103 days post-infection (DPI). The reactions between rHcADRM and goat serum were tested using Western blot (WB) analysis. The results show that rHcADRM can be recognized in the serum as early as 14 DPI, and the antibody against rHcADRM in infected goat could be maintained for over 89 days. No reaction was found between rHcADRM and antibodies against Trichinella spiralis, Fasciola hepatica, or Toxoplasma gondii. An indirect enzyme-linked immune sorbent assay (ELISA) was developed based on rHcADRM. The optimal coating antigen (279 ng of rHcADRM/well) and serum dilutions (1:50) were determined by checkerboard titration. A total of 64 serum samples, including 32 from H. contortus infection goats and 32 from helminth-free goats, were used to determine the positive (0.362) and negative (0.306) cut-off values for the ELISA. The results show this serological diagnosis method is highly sensitive (90.6%) and specific (93.75%). The coefficient of variation within run and between runs was less than 11%. To apply this indirect ELISA during field examination, 51 serum samples were randomly collected from goat farms and tested using this method. The result showed that 19.6% (10/51) of goats were infected with H. contortus, which was 100% consistent with the necropsy result, higher than that of fecal examination (15.7%, 8/51). These results indicate that rHcADRM could be a potential antigen for diagnosis of H. contortus infection in goats.

Immunization with recombinant rHc23 partially protects lambs against trickle infections by Haemonchus contortus

Background

Haemonchosis is one of the most economically important parasitic diseases affecting small ruminants all over the world. Chemotherapeutic control has several shortcomings (limited anthelmintic arsenal, frequent resistance) and is hardly affordable by many farm economies. A recombinant antigen (rHc23) was shown to induce significant protection in vaccination trials with single dose challenges and different adjuvants.

Results

Lambs were vaccinated with 100 μg rHc23/dose + bacterial immunostimulant (BI) (LPS from Escherichia coli + Propionibacterium acnes extract) (days − 2, 0, 7 and 14) and subjected to a trickle infection with two dosages [6x, 1000 infective larvae (L3) or 6x, 2000 L3]. Vaccinated lambs showed a significant antibody response against rHc23 and Haemonchus contortus soluble extract as assessed by ELISA and Western blot (WB). Fecal egg counts (epg) along the experiment of vaccinated and BI treated lambs were significantly reduced. All vaccinated animals showed total egg output and abomasal helminth burdens (median, average) lower than those from unvaccinated or BI-treated animals lambs although differences were not statistically significant.

Conclusions

Vaccination with 100 μg rHc23/dose + BI against H.contortus trickle infections apparently induced lower epg values and helminth burdens at the end of the experiment. Intragroup individual variations did not allow to obtain conclusive results and more research is needed including adjuvants and larger groups of animals to validate the potential value of rHc23 as candidate to develop a recombinant vaccine for lambs haemonchosis.

Vaccination of lambs against Haemonchus contortus with the recombinant rHc23. Effect of adjuvant and antigen dose

Haemonchus contortus is the most pathogenic gastrointestinal helminth of small ruminants. Natural or experimental repeated infections and several native antigens confer a partially protective immune response but vaccination with subunit antigens has been elusive. Promising results have been obtained with a recombinant form of a somatic antigen (rHc23). In this paper we present the results obtained in vaccination trials in lambs using two dosages of rHc23 and standard adjuvants. Six-months old Manchego females lambs were vaccinated with rHc23 (50 or 200 μg/dose) adjuvanted with 1mL aluminum hydroxide on days -42, -28 and -14 or with 200 μg/dose rHc23 and 5 mg Quil A on days -49, -28 and -7. Control lambs were kept receiving only the adjuvants the same days or no treatment. Moreover one group did not receive any treatment or infection. On day 0 vaccinated lambs, untreated animals and those receiving the adjuvant were infected per os with a monospecific single infection of 4000 L3 of H. contortus. Infection was kept for 58 days and follow-up included the determination of serum specific antibody response (ELISA, WB), hematological parameters (eosinophil counts, hematocrit) and fecal egg counts (epg). Absence of hematocrit alterations, reduction of helminth's eggs output and abomasal parasite burden at the end of the experiment were the efficacy criteria of vaccination with the recombinant. Immunization with both adjuvants and antigen dosages elicited strong antibody responses particularly with Quil A. Vaccinated groups showed significant reduction of fecal egg excretion and abomasal helminth burdens. Highest protection of lambs against challenge was achieved with aluminum hydroxide and 200 μg/dose rHc23 with a reduction of over 70% of the abomasal burden and over 80% of fecal egg output. Results suggest that rHc23 could be a valuable recombinant candidate for vaccination against haemonchosis. No clear relationship was found between antibody levels and protection this pointing towards involvement of both humoral and cellular components in the protective response elicited by rHc23.

Mind the gaps in research on the control of gastrointestinal nematodes of farmed ruminants and pigs

Gastrointestinal (GI) nematode control has an important role to play in increasing livestock production from a limited natural resource base and to improve animal health and welfare. In this synthetic review, we identify key research priorities for GI nematode control in farmed ruminants and pigs, to support the development of roadmaps and strategic research agendas by governments, industry and policymakers. These priorities were derived from the DISCONTOOLS gap analysis for nematodes and follow-up discussions within the recently formed Livestock Helminth Research Alliance (LiHRA). In the face of ongoing spread of anthelmintic resistance (AR), we are increasingly faced with a failure of existing control methods against GI nematodes. Effective vaccines against GI nematodes are generally not available, and anthelmintic treatment will therefore remain a cornerstone for their effective control. At the same time, consumers and producers are increasingly concerned with environmental issues associated with chemical parasite control. To address current challenges in GI nematode control, it is crucial to deepen our insights into diverse aspects of epidemiology, AR, host immune mechanisms and the socio-psychological aspects of nematode control. This will enhance the development, and subsequent uptake, of the new diagnostics, vaccines, pharma-/nutraceuticals, control methods and decision support tools required to respond to the spread of AR and the shifting epidemiology of GI nematodes in response to climatic, land-use and farm husbandry changes. More emphasis needs to be placed on the upfront evaluation of the economic value of these innovations as well as the socio-psychological aspects to prioritize research and facilitate uptake of innovations in practice. Finally, targeted regulatory guidance is needed to create an innovation-supportive environment for industries and to accelerate the access to market of new control tools.

Evaluation of crude larval protein and recombinant somatic protein 26/23 (rHcp26/23) immunization against Haemonchuscontortus in sheep

Aim:

The aim of this study was to evaluate the potential possibility of crude larval and recombinant (rHcp26/23) antigens of Haemonchus contortus for immunization to control sheep hemonchosis.

Materials and Methods:

A total of 21 lambs were divided into five groups. Lambs were immunized with larval and recombinant (rHcp26/23) proteins at day 0 and day 14 and after that challenged with 5000 infective larvae of H. contortus on day 42. An unvaccinated positive control group was challenged with L3 in the meantime. An unvaccinated negative control group was not challenged.

Results:

Fecal egg count reduction taking after challenge for rHcp26/23 and larval antigens was 92.2% and 38.2%, respectively, compared with the positive control group. Vaccine incited protection in rHcp26/23 and larval immunization was reflected in significant (p<0.05) decreases in worm burden; 59.9% and 40.1%, respectively.

Conclusion:

Recombinant rHcp26/23 vaccine induced a partial immune response and had immune-protective effect against sheep hemonchosis.

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.

In vitro larvicidal and in vivo anthelmintic effects of Oxalis tetraphylla (Oxalidaceae) hydroalcoholic extract against Haemonchus contortus in lambs

The in vitro larvicidal and in vivo anthelmintic effects of Oxalis tetraphylla hydroalcoholic extract (HE), against Haemonchus contortus in experimentally infected lambs, were assessed. We used a microtitration plate method, comprising the following two stages. Stage 1: 20 μl of water containing 200 sheathed H. contortus infective larvae (ShHcl) were deposited in every well of three series; then, the series 2 and 3 wells were treated with 80 μl 1% ivermectin and O. tetraphylla HE at 20 mg/ml, respectively. Stage 2: the same procedure was performed replacing the ShHcl with exsheathed larvae (ExShHcl). Evaluations were performed after 24 and 48 h. The total numbers of dead and live larvae were counted. A second experiment evaluated the reduction in nematode egg populations in the faeces of lambs treated orally with the O. tetraphylla HE. The 27 lambs used were divided into Groups 1, 2 and 3 (n = 9), which were administered water (positive control), levamisole 1 m (7.5 mg/kg body weight (BW), as a unique dose) and O. tetraphylla HE (20 mg/kg BW), respectively. The plant HE was administered daily for 8 days. The in vitro assay showed 80.9% and 86.5% larval mortality of ShHcl after 24 and 48 h, respectively, while the corresponding mortality values for ExShHcl were 97 and 99%, respectively. The in vivo assay showed variability in the eggs/gram of faeces (epg) values; however, at the end of the trial, the average reduction in the epg values of the O. tetraphylla HE group was 45.6% (P < 0.05). Oxalis tetraphylla HE contains compounds that belong to the flavonol group with anthelmintic activity.

Efficacy of glutathione-S-transferase purified antigen of the gastro-intestinal nematode Haemonchus contortus in diagnosis of sheep haemonchosis

Haemonchus contortus is one of the most pathogenic and economically important parasites of sheep. Different H. contortus antigens; crude somatic antigen (CSA), excretory/secretory antigen (ESA), crude larval antigen (CLA), glutathione-S-transferase antigen (GST) and recombinant protein (rhcp 26/23) were prepared and characterized using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot. The antigens were immunologically evaluated through indirect enzyme linked immunosorbent assay (ELISA) for diagnosis of haemonchosis in experimentally and naturally infected sheep. Analysis of the resultant bands of SDS-PAGE demonstrated that 13, 6, 11, 2 and 1 protein bands from CSA, ESA, CLA, GST and rhcp 26/23, respectively and analysis of the resultant bands of western blot showed that 13, 6, 4 and 1 reactive bands detected from CSA, ESA, CLA and GST, respectively. The results of ELISA of different antigens revealed that sero-prevelance of CSA, ESA, CLA, GST and rhcp 26/23 were 78.51, 82.34, 85.319, 45.319 and 90.8% respectively, sensitivity were 100, 90, 100, 96.66 and 90%, respectively and specificity were 0, 70, 10, 70 and 6.66%, respectively with diagnostic potency were 50, 80, 55, 83.33 and 48.33%, respectively. Statistical analysis using Chi square test found that GST is the best one that can be used. The cross reactivity of GST antigen, crude Fasciola antigen and crude Moniezia antigen tested versus their homologous hyper immune sera at different dilutions using ELISA. The current study reported that GST antigen could be considered as a promising antigen for diagnosis of haemonchosis.

Self-adjuvanting C18 lipid vinil sulfone-PP2A vaccine: study of the induced immunomodulation against Trichuris muris infection

Despite the importance of the adjuvant in the immunization process, very few adjuvants merge with the antigens in vaccines. A synthetic self-adjuvant oleic-vinyl sulfone (OVS) linked to the catalytic region of recombinant serine/threonine phosphatase 2A from the nematode Angiostrongylus costaricensis (rPP2A) was used for intranasal immunization in mice previously infected with Trichuris muris. The animal intranasal immunization with rPP2A-OVS showed a reduction of 99.01% in the number of the nematode eggs and 97.90% in adult. The immunohistochemical analysis of the intestinal sections showed that in immunized animals with lipopeptide the mucus was significantly higher than in the other experimental groups. Also, these animals presented significantly different chemokine, CCL20 and CCL11, levels. However, although the number and size of Tuft cells did not vary between groups, the intensity of fluorescence per cell was significant in the group immunized with the rPP2A-OVS. The results of the present study suggest that mice immunized with the lipopeptide are capable of activating a combined Th17/Th9 response. This strategy of immunization may be of great applicability not only in immunotherapy and immunoprophylaxis to control diseases caused by nematodes but also in pathologies necessitating action at the level of the Th9 response in the intestinal mucosa.

Larvicidal activity of Bacillus circulans against the gastrointestinal nematode Haemonchus contortus in sheep

Efficient control of gastrointestinal parasites is necessary in sheep breeding. However, the available chemically based anthelmintics are becoming less effective due to the development of parasite resistance. An alternative to this problem is biological control. In the present study, we tested the larvicidal effect of Bacillus circulans by administering a spore suspension (2 × 109 colony forming units/ml) orally to lambs naturally infected with Haemonchus contortus. The number of faecal larvae was quantified daily and a significant reduction (~87%, P< 0.05) of larval development was observed after administration of B. circulans. Using a transformed B. circulans with green fluorescent protein, we were able to detect B. circulans in the faeces at 4 h post-administration and 72 h after cessation of its administration. These results suggest the use of B. circulans as a promising biological alternative for parasite control.

Immunity to Haemonchus contortus and Vaccine Development

Sheep are capable of developing protective immunity to Haemonchus contortus through repeated exposure to this parasite, although this immune protection is the result of a complex interaction among age, gender, physiological status, pregnancy, lactation, nutrition and innate and adaptive immunity in the host animal. There are multiple effectors of the protective immune response, which differ depending on the developmental stage of the parasite being targeted, and our understanding of the effector mechanisms has developed considerably in the 2000s. The rational design of vaccines based on 'natural' or 'exposed' antigens depends on an understanding of this exposure-induced immunity. However, the most effective current vaccines rely on protection via the induction of high circulating antibody levels to 'hidden' gut antigens of H. contortus. The success of this latter strategy has resulted in the launch of a vaccine, which is based on extracts of the parasite's gut, to aid in the control of Haemonchus in Australia. The development of recombinant subunit vaccines based on the components of the successful native vaccine has not yet been achieved and most of the recent successes with recombinant subunit vaccines have focussed on antigens unrelated to the gut antigens. The future integration of an understanding of the immunobiology of this parasite with advances in antigen identification, expression (or synthesis) and presentation is likely to be pivotal to the further development of these recombinant subunit vaccines. Recent progress in each of the components underpinning this integrated approach is summarized in this review.

The Identification of Haemonchus Species and Diagnosis of Haemonchosis

Diagnosis is often equated with identification or detection when discussing parasitic diseases. Unfortunately, these are not necessarily mutually exclusive activities; diseases and infections are generally diagnosed and organisms are identified. Diagnosis is commonly predicated upon some clinical signs; in an effort to determine the causative agent, identification of genera and species is subsequently performed. Both identification and diagnosis play critical roles in managing an infection, and involve the interplay of direct and indirect methods of detection, particularly in light of the complex and expanding problem of drug-resistance in parasites. Accurate and authoritative identification that is cost- and time-effective, based on structural and molecular attributes of specimens, provides a foundation for defining parasite diversity and changing patterns of geographical distribution, host association and emergence of disease. Most techniques developed thus far have been grounded in assumptions based on strict host associations between Haemonchus contortus and small ruminants, that is, sheep and goats, and between Haemonchus placei and bovids. Current research and increasing empirical evidence of natural infections in the field demonstrates that this assumption misrepresents the host associations for these species of Haemonchus. Furthermore, the capacity of H. contortus to utilize a considerably broad spectrum of ungulate hosts is reflected in our understanding of the role of anthropogenic forcing, the 'breakdown' of ecological isolation, global introduction and host switching as determinants of distribution. Nuanced insights about distribution, host association and epidemiology have emerged over the past 30years, coincidently with the development of increasingly robust means for parasite identification. In this review and for the sake of argument, we would like to delineate the diagnosis of haemonchosis from the identification of the specific pathogen. As a foundation for exploring host and parasite biology, we will examine the evolution of methods for distinguishing H. contortus from other common gastrointestinal nematodes of agriculturally significant and free-ranging wild ruminants using morphological, molecular and/or immunological methods for studies at the species and genus levels.

Vaccination of lambs with the recombinant protein rHc23 elicits significant protection against Haemonchus contortus challenge

Gene encoding a somatic protein of Haemonchus contortus (Hc23) known to confer significant protection against experimental haemonchosis has been cloned and expressed in a prokaryotic system. A cDNA library of H. contortus using the vector λ ZAP II was obtained. Full-length gene was amplified, cloned and expressed in Escherichia coli BL21. The recombinant protein was purified in Ni-NTA column. Recombinant protein (rHc23) had 203 aminoacids and a molecular mass of 24.15 kDa. Recombinant protein (100 μg/dose) with aluminum hydroxide as adjuvant was administered to 5-6 months age female Assaf lambs on days -42, -28 and -14. On day 0 animals were infected with 15,000 L3 of H. contortus. Vaccination with rHc23 elicited a significant protection against challenge, with >80% reductions in both fecal egg counts and average abomasal parasite burdens at the end of the experiment (45 days post challenge) besides lack of variations in packed cell volume. Results support the feasibility of vaccination against lamb haemonchosis with a recombinant product from an exposed antigen.

Vaccination of sheep and cattle against haemonchosis

Vaccines against gastrointestinal nematodes are one potential option for the control of parasitic gastroenteritis in ruminants. Excretory/secretory (E/S) and hidden antigens are being studied as candidates for vaccines against Haemonchus spp., which is a major parasite in cattle and small ruminants that are raised in warm climates. Protection has been observed after vaccination with some E/S proteases, particularly cysteine proteases and with some glycans that are abundant on the surfaces and in the secretory products of helminths. However, the most promising results are being obtained with glycoprotein antigens extracted from the microvillar surfaces of the Haemonchus contortus intestinal cells. These antigens are called 'hidden' because they are not exposed to the host's immune system during infection. Thus far, recombinant forms of these antigens have not been usefully protective. However, because only 5 μg of antigen is required per dose, production of a native antigen vaccine from adult parasites has been found to be practical and commercially viable. Trials indicate that a vaccine made from one particular isolate will cross-protect against geographically distant isolates.