Serum IgG response of Manchego lambs to infections with Haemonchus contortus and preliminary characterization of adult antigens

Reducing fecal egg count through selective breeding alters dorper lamb response to Haemonchus contortus in an artificial challenge trial

Infection by gastrointestinal nematodes (GIN), particularly Haemonchus contortus, can be detrimental to sheep health and performance. Genetic susceptibility to GIN varies between breeds, with those lacking high levels of natural resistance often requiring frequent anthelmintic treatment when facing parasitic challenge. Genetic technology can serve as a tool to decrease GIN susceptibility via selection for sheep with reduced fecal egg count (FEC) estimated breeding values (EBVs). However, the physiological changes that result from implementation of this strategy are not well described. Additionally, there is a need for comparison of animals from recent selective breeding against breeds with inherent GIN resistance. In this study we administered a challenge of H. contortus to Dorper x White Dorper (DWD; n = 92) lambs that have been genetically selected for either low (DWD-) or high (DWD+) FEC EBVs and Barbados Blackbelly x Mouflon (BBM; n = 19) lambs from a genetically resistant breed backgrounds. Lamb FEC, packed-cell volume (PCV) and serum IgG were measured at intermittent levels over 5 weeks. At day 21 and day 35, the selectively bred DWD- had a lower mean FEC compared to DWD+, but were higher than BBM. Reductions in both PCV and serum IgG from initial day 0 levels were observed in DWD lambs, but not in BBM. Furthermore, from a subset of lambs (n = 24) harvested at day 21, DWD- only tended (p = 0.056) to have lower mean worm counts than DWD+, with BBM having the lowest mean worm count. Differentially expressed genes (DEGs) identified via RNA-sequencing of abomasal tissue at day 21 indicate a more pronounced Th2 immune response and more rapid worm expulsion occurred in iBBM than iDWD- and iDWD+ lambs. However, gene expression in DWD- suggests an association between reduced FEC EBV and gastric acid secretion and the ability to limit worm fecundity. Ultimately, selection of Dorper sheep for low FEC EBV can reduce susceptibility to GIN, but it will likely require multiple generations with this trait as a breeding priority before presenting a similar resistance level to Caribbean breeds.

Immunoglobulins as Biomarkers for Gastrointestinal Nematodes Resistance in Small Ruminants: A systematic review

The rise of anthelmintic resistance worldwide has led to the development of alternative control strategies for gastrointestinal nematodes (GIN) infections, which are one of the main constraints on the health of grazing small ruminants. Presently, breeding schemes rely mainly on fecal egg count (FEC) measurements on infected animals which are time-consuming and requires expertise in parasitology. Identifying and understanding the role of immunoglobulins in the mechanisms of resistance could provide a more efficient and sustainable method of identifying nematode-resistant animals for selection. In this study we review the findings on immunoglobulin response to GIN in the literature published to date (june 2019) and discuss the potential to use immunoglobulins as biomarkers. The literature review revealed 41 studies which measured at least one immunoglobulin: 35 focused on lamb immune response (18 used non-naïve lambs) and 7 on yearlings. In this review we propose a conceptual model summarizing the role of immunoglobulins in resistance to GIN. We highlight the need for more carefully designed and documented studies to allow comparisons across different populations on the immunoglobulin response to GIN infection.

Early antibody response and clinical outcome in experimental canine leishmaniasis

Infected dogs are the main reservoir of zoonotic visceral leishmaniasis, a widespread parasitic disease caused by Leishmania infantum. Therefore, the control of canine infections is required to reduce the incidence of human cases. Disease outcome in dogs depends on the fine balance between parasite virulence and efficacy of the immune system. Thus, knowledge of early response could yield relevant information for diagnosis and follow-up. In our study, 20 Beagle dogs were intravenously infected with 10⁸ amastigotes of a fresh isolate of L. infantum and monitored along 16 weeks post inoculation. Specific antibody response and clinical evolution of infected animals were highly variable. Immunofluorescence antibody test (IFAT) and enzyme linked immunosorbent assay (ELISA) were useful to assess infection status, although only ELISA with promastigote-coated plates and, particularly, western blotting (WB) allowed an early diagnosis. Prominent antigens were identified by mass peptide fingerprinting. Chaperonin HSP60, 32 and 30 KDa antigens were recognized by all dogs on week 10 post infection. This suggests that these antigens may be valuable for early diagnosis. Advanced infection showed, in addition, reactivity to HSP83 and HSP70. Disease outcome did not show a clear relationship with ELISA or IFAT titers. Correlation between the clinical status and the combined reactivity to some antigens sustains their use for diagnosis and follow-up.

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.

Experimental mixed infection of Leishmania (Leishmania) amazonensis and Leishmania (L.) infantum in hamsters (Mesocricetus auratus)

In South America, visceral leishmaniasis is frequently caused by Leishmania infantum and, at an unknown frequency, by Leishmania amazonensis. Therefore, mixed infections with these organisms are possible. Mixed infections might affect the clinical course, immune response, diagnosis, treatment and epidemiology of the disease. Here we describe the clinical course of mixed infections with L. amazonensis and L. infantum in a hamster model. We show that mixed infections are associated with more severe clinical disease than infection with L. amazonensis or L. infantum alone. In spleens with mixed infections, L. infantum outcompeted L. amazonensis in the tissue, but not in culture from tissue. We found increased levels of IgG in animals infected with L. infantum. Although more than 30 bands were revealed in a Western blot, the highest immunogenicity was observed with proteins having molecular masses of 95 and 90 kDa, whereas proteins with molecular masses of lower than 50 kDa were reactive frequently with serum from hamsters infected with L. amazonensis, and proteins with molecular masses of 80 and 70 kDa were reactive only with serum from hamsters infected with L. infantum. This finding has important implications regarding the biology of Leishmania and humoral immune responses to infections with these organisms.

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.

Effect of condensed tannins supplementation through leaf meal mixture on voluntary feed intake, immune response and worm burden in Haemonchus contortus infected sheep

The study was carried out to assess the effect of condensed tannins (CT) supplementation through leaf meal mixture (LMM) on feed intake, humoral [Immunoglobulin G (IgG)], cell mediated immune response (CMI) and faecal egg counts in Haemonchus contortus infected sheep. Eighteen sheep were randomly divided into three groups (negative control-NC, infected control-C and Infected treatment-T) of six animals in each group in a completely randomized block design for a period of 90 days. Twelve H. contortus infected adult sheep were allocated into two equal groups C and T, supplemented with 0 and 1.5 % of CT, respectively. Six non-infected sheep of similar age and body weight of NC group were included in this study to compare their immune response with H. contortus C and CT supplemented T groups. Intake of dry matter and organic matter (g day(-1) and % live weight) was statistically similar (P < 0.05) among the three groups. The anti-Haemonchus IgG and CMI response was higher in T group as compared to C group. The mean faecal egg counts was significantly (P < 0.001) higher in C group as compared to T group. It may be concluded that dietary supplementation of CT (1.5 %) through LMM improved humoral and CMI immune response and decreased worm load in H. contortus infected sheep.

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.

Evaluation of miltefosine for the treatment of dogs naturally infected with L. infantum (=L. chagasi) in Brazil

Dogs naturally infected with Leishmania Infantum (=L. chagasi) were treated with miltefosine using different therapeutic regimens. The animals were evaluated for clinical evolution, biochemical parameters, parasite load (by real-time PCR), cytokine levels and humoral response. After treatment and during the following 24 months, there was progressive clinical improvement and complete recovery in 50% (7/14) of the treated animals. There was a decrease in the smear positivity of the bone marrow after treatment, and there was also a gradual and constant decrease in positive cultures at the end of the follow-up period. However, the PCR detection of parasite DNA remained positive. In general, all animals presented a significant increase in parasite load 6 months after treatment. The IFN-γ levels in all the groups tended to increase during follow-up period, regardless of the miltefosine dose administered. The IL-4 and IL-10 levels of the animals tended to decrease during follow-up, except after 300 days when only IL-10 increased. The serum antibodies identified antigens that ranged from 116 kDa to less than 29 kDa in the Western blot assay. Furthermore, 300 days after treatment, qualitative and quantitative differences in the antigen profiles were observed. Antigens of 97 and 46 kDa were the most intensely recognized. Higher levels of antigen-specific Leishmania IgG were detected before and 300 days after treatment in all groups. Taking together, the improvement in the clinical symptoms was not followed by parasitological clearance, suggesting that treatment with miltefosine is not recommended, especially in endemic areas like Brazil, where children are the major victims and dogs are involved in the maintenance of the parasite cycle.

Biological characterization and pathogenicity of three Haemonchus contortus isolates in primary infections in lambs

The biological characterization and differential pathogenicity of three isolates of Haemonchus contortus, one autochthonous (Aran 99) and two allochthonous (Moredun Research Institute, MRI, and Merck Sharp and Dohme, MSD) were studied by primary experimental infection of Manchego lambs. Thus, six female lambs (5.5 months old) were infected with 12,000 L3 larvae of each helminth isolate. Parasitological (pre-patent period, parasite egg shedding dynamics), biopathological (packed cell volume (PCV), haemoglobin concentration, plasma proteins, serum pepsinogen) and zootechnical parameters (live weight gain, thoracic perimeter) were measured throughout the study. After sacrifice (85 days post-infection (pi)), lamb carcasses were inspected for parasite burden and development (establishment rate, male/female ratio, degree of parasite development), and the average carcass weight of the experimental groups was compared. The autochthonous combination (Manchego lambs-Aran 99) had a longer pre-patent period (28 days) and a significantly different pattern of egg elimination (maximum elimination on day 80 pi). The establishment rate and parasite burden (average values of 8.18% and 988 adult helminths, respectively) were both low, with no significant differences between isolates. There were no significant differences in parasitic nematode development in terms of size and weight (1264.66 microm and 149.45 microg for male worms and 2093.33 microm and 411.46 microg for females, respectively), although Aran 99 females weighed less (p<0.05). All isolates induced a slight but significant reduction of PCV values from day 23 pi onwards. Inter-isolate differences were found, with the effects in the case of MSD being more pronounced. Variations of serum protein levels were minimal in all lamb groups. The live weight gain of MSD- and Aran 99-infected animals was significantly lower (p<0.05) than for MRI-infected lambs and uninfected control animals. Carcass yield from the lambs infected with the autochthonous isolate (Aran 99) was lower. The MSD isolate therefore showed a higher comparative pathogenicity.

Isolation and immunolocalization of a putative protective antigen (p26/23) from adult Haemonchus contortus

The putative protective antigen, p26/23, from adult Haemonchus contortus was isolated. A soluble extract from adult helminths obtained from the abomasa of hyperinfected (12,000 infective larvae) female Manchego lambs and treated with a mixture of protease inhibitors was subjected to affinity chromatography (hexylgluthatione) to eliminate the enzyme gluthatione S-transferase. The eluate was analyzed by electrophoresis under denaturing and reducing conditions (sodium dodecyl sulfate polyacrylamide gel electrophoresis), electrotransferred to nylon membranes, and assayed by Western blot with sera from immunized lambs. The bands recognized by the lambs' sera corresponding to proteins with a molecular weight of 23-26 kDa (p26/23) were excised, eluted, and separated by reverse-phase chromatography. This allowed the isolation of a single protein, which was expressed in both infective larvae (L3) and the adult stage of the parasite. The first 20 amino acids of the N-terminal end of the purified protein were determined. The partial amino acid sequence revealed a 100% identity with the N terminus of one of the peptides present in the p26/23 immunoprotective fraction previously tested by us against sheep haemonchosis. No significant homology with any reported sequence was found except for the deduced sequence of a hypothetic H.contortus protein (HCC00515). Immunolocalization studies showed that the protein was expressed in the hypodermic chords of the nematode.

Leishmania-specific lymphoproliferative responses and IgG1/IgG2 immunodetection patterns by Western blot in asymptomatic, symptomatic and treated dogs

Peripheral cell responses against Leishmania infantum and serology by IFAT and WB were determined in 87 untreated dogs from an endemic area (Madrid, Spain) and in 15 treated dogs (antimonials, allopurinol). All untreated symptomatic dogs (nine) did not show any lymphoproliferative response, whereas 21 out of 78 untreated asymptomatic dogs had a positive cellular response. Serum IgG(2) from dogs with clinical signs of patent leishmaniosis reacted with a variety of peptides (26, 29, 34-35.4, 42, 45, 50-57 and 67 kDa), but IgG(1) response was mainly directed against a 67-kDa peptide. Successfully treated dogs displayed a low immunoreactivity of both IgG(1) and IgG(2), particularly against 67 kDa, thus indicating the potential prognostic value of this region. Positive cellular response of dogs treated with good clinical progress was only observed up to 5-12 months post treatment. Untreated asymptomatic dogs with positive cell response showed a clear recognition by IgG(2) of approximately 67 and 45 kDa antigens, whereas IgG(1) did not recognise any antigen.

Immunization against ovine haemonchosis with three low molecular weight somatic antigens of adult Haemonchus contortus

Individual bands (15) from electroblotted soluble extracts of adult Haemonchus contortus were excised and three peptides of molecular weight ca. 56 (F4), 39 (F8) and 18.5 kDa (F14) used to vaccinate 4-4.5-months-old lambs against the nematode. Immunizing doses from each peptide were administered in 1 ml Freund complete adjuvant (first 50 microg injection) and 1 ml Freund incomplete adjuvant (second and third 50 microg injections) to six lambs. Two weeks after last immunization, animals were challenged with 300 L-3/kg live weight (LW). Lambs were slaughtered 34 days after challenge. Immunization induced a strong antibody response estimated by enzyme-linked immunosorbent assay, whereas no peripheral lymphoproliferative response was observed. Lambs in the F8-vaccinated group showed on average delayed pre-patent period, lower faecal egg counts and reduction of abomasal worm burdens, although the differences were not statistically significant.

Follow-up of Leishmania infantum naturally infected dogs treated with allopurinol: immunofluorescence antibody test, ELISA and Western blot

Fourteen dogs naturally infected with Leishmania infantum and treated with allopurinol were monitored clinically and serologically with immunofluorescent antibody test (IFAT, amastigotes and promastigotes), enzyme linked-immunosorbent-assay (ELISA, IgG1 and IgG2) and Western blotting (WB). In all dogs therapy lead to clinical improvement together with decreasing specific antibodies in IFAT, ELISA and WB, demonstrating the usefulness of serology for follow-up. Although IgG1 and IgG2 varied considerably between individual animals, IgG2 of all dogs was predominantly in both ELISA and WB. This suggests the value of monitoring the IgG2 response (especially against 29 and 67 kDa antigens) in the follow-up of treated dogs.

Vaccination of Manchego lambs against Haemonchus contortus with a somatic fraction (p26/23) of adult parasites

A low molecular weight fraction from adult Haemonchus contortus containing two peptides (p26/23) was used to vaccinate Manchego female lambs between 3.5 and 5 months of age. Immunizing injections were given three times on days 0, 14 and 28 of the experiment. On day 43, lambs were challenged with 400 third stage larvae/kg live weight. Vaccination induced a lengthening of prepatent periods, significant reduction (> 60%) in mean faecal egg counts and smaller variations in packed cell volume values. At necropsy, average worm burden in the vaccinated lambs was significantly lower (61.6%) than that found in unvaccinated challenged animals. A clear correlation was found between protection and serum antibody response in immunized lambs.

Serum antibody response of Castellana sheep to Haemonchus contortus infection and challenge: relationship to abomasal worm burdens

Primary and secondary serum antibody responses to Haemonchus contortus were studied in Castellana sheep. Ten-month-old sheep were infected (200 L3/kg live weight (lw)) and challenged (400 L3/kg lw) or uninfected and equally challenged with H. contortus. Primary infections induced a partially protective response upon challenge, characterized by higher serum protein levels, longer prepatent periods, lower fecal egg counts, and significant reduction in the establishment rate of the parasite and abomasal adult and L4 worm burdens. The resistant status of the infected and challenged sheep was not clearly related either to the serum specific antibody levels (IgG: IgG1, IgG2; IgM; IgA) estimated by ELISA or to immunodetection patterns in the Western blots.

Value of Western blotting in the clinical follow-up of canine leishmaniasis

Specific serum antibody levels in Leishmania infantum-infected dogs treated with a combination of glucantime and allopurinol were estimated by indirect immunofluorescence and Western blotting. The sensitivity of Western blot was greater than that obtained with immunofluorescence titration. In general, both diagnostic methods concurred with the post-treatment clinical status of the animals. Clinical improvement of successfully treated dogs was related to lower immunofluorescence titers and simpler and/or less reactive immunodetection patterns in Western blotting. The recognition, by infected dogs, of certain low molecular weight antigens, particularly one of approximately 26 kDa, was restricted to pretreatment samples and a single animal in relapse thus apparently constituting an active infection marker.

Infection-induced protection against Haemonchus contortus in merino and manchego sheep. Relationship to serum antibody response

Resistance to primary and secondary infections with Haemonchus contortus was studied in 10-month-old Manchego and Merino sheep. No notable interbreed differences were observed after primary infections in the parameters determined (prepatency period, faecal egg output, abomasal worm burden). Previously infected sheep (200 L-3/kg live weight (lw)) from both breeds showed notable protection after challenge (400 L-3/kg lw), evidenced by lower eggs/g faeces (epg) values and worm burdens. A protective response in the Manchego breed was associated with arrested development of fourth stage larvae in the abomasal mucosa, whereas in the Merino breed a more rapid expulsion mechanism seems to be involved. Serum antibody levels (IgG, IgA) were infective dose-dependent and protection from re-infection was not clearly related to the parasite-specific IgG response estimated by enzyme-linked immunosorbent assay (ELISA) and Western blotting.

Identification and partial purification of a 26 kilodalton antigen of adult Haemonchus contortus

Adult H. contortus soluble extracts were fractionated by means of gel filtration (S-200) and anion exchange chromatography (DEAE-Sephacel). Fractions from both analyses were checked by ELISA and western blotting (WB) with sera from lambs infected with H. contortus, monospecific heterologous sera (anti-Trichostrongylus colubriformis and anti-Teladorsagia circumcinta) and sera from naturally infected sheep with mixed trichostrongylid infections. High cross reactivity was seen between H. contortus and heterologous sera, particularly with the anti-T. colubriformis serum, when fractions from gel filtration were checked by ELISA. Individual fractions containing the highest positive/negative and positive/heterologous ratios were pooled and analysed by SDS-PAGE. One of the pools (A4) containing 2 regions around 48-55 and 25-27 kDa were strongly recognized by homologous sera in WB. Similar results were obtained with the first peak eluted in the DEAE-Sephacel chromatography with NaCl 0.1 M. The pooled fraction A4 from gel filtration was further fractionated by anion exchange chromatography and the peak obtained with the NaCl gradient contained a ca. 26 kDa antigen apparently specific for the diagnosis of H. contortus infections in lambs.

Comparison of two enzyme immunoassays for the detection of Haemonchus contortus infections in sheep

Two enzyme-linked immunosorbent assays (ELISA) using either excretory/secretory (ES) products or crude somatic antigens (CSA) of adult Haemonchus contortus were compared for their ability to detect antibodies against H. contortus in sheep. Serum samples obtained from a group of 32 H. contortus mono-infected sheep were tested in the two ELISAs and the obtained data were compared with the results of the faecal examinations of these sheep. The first sheep became patent 3 weeks post infection (p.i.) and all sheep had positive egg counts at week 5 p.i. The first antibodies against H. contortus were detected 1 week p.i. and all sheep were found positive by both ELISAs at week 4 p.i. Using sera from a large number of H. contortus-infected sheep a difference in sensitivity between the ES ELISA (97.7%) and the CSA ELISA (89.2%) was found. The specificity of each assay was determined by testing sera obtained from sheep with mono-infections of H. contortus, Trichostrongylus colubriformis, Trichostrongylus vitrinus, Ostertagia circumcincta, Nematodirus battus, Cooperia curticei, Fasciola hepatica, Taenia ovis or Eimeria spp. The specificity of the ES ELISA was 87.2%, whereas the specificity of the CSA ELISA was 82.7%.

Isotype-specific serum antibody responses of sheep to Haemonchus contortus antigens

In total, 19 8-month-old Texel sheep were used to study the isotype-specific serum antibody responses against infective larvae and adult worms of Haemonchus contortus. Group Group 1 sheep (n = 7) were infected with 20,000 L3 larvae (Week 0), treated with ivermectin 6 weeks post-infection and subsequently challenged at Week 10 of the experiment. This challenge consisted of a trickle infection of 10,000 L3 larvae per week for 5 weeks. Group 2 sheep (n = 7) received a single infection at Week 10 of the experiment, and Group 3 (n = 5) served as a non-infected control group throughout the entire experiment. Individual blood and faeces samples were collected at weekly intervals. The immune responses were monitored by ELISA and Western blotting. The secondary immune response coincided with a significant reduction of the Haemonchus egg output and reduction of worm counts. Both primary and challenge infections induced humoral immune responses, and ELISA revealed that the most dominant serum antibody responses belong to the IgG1 isotype and to a lesser extent to IgG2. IgM and IgA responses were less dominant. Western blotting experiments demonstrated that many antigens were commonly recognized by antibodies from both primary and challenge infected animals. However, sera of immune animals specifically reacted with low molecular weight proteins. In particular, a 24 kDa antigen present in adult worms appeared to be specifically recognized.

Cross antigenicity among ovine trichostrongyloidea. Preliminary report

A preliminary trial on the extent of cross-antigenicity among the sheep strongylids Haemonchus contortus, Trichostrongylus colubriformis, Teladorsagia circumcincta and Nematodirus battus in 2.5- to 4-month-old lambs has been carried out using ELISA and Western blotting (WB). Cross antigenicity was tested using soluble extracts from adult and third stage larvae (L3) of H. contortus as antigenic source probed with sera from lambs with monospecific heterologous infections. There was cross-antigenicity between L3 of H. contortus and Trichostrongylus colubriformis in ELISA and WB. Immunodetection results with adult H. contortus antigen showed a closer relationship to Teladorsagia circumcincta. Certain heterologous sera reacted with H. contortus antigens more strongly than the homologous one, but sera from the H. contortus-infected animals had reactivity around the 25 kDa region from adult antigens which could have potential diagnostic use.

Lamb serum recognition of infective larvae and adult Haemonchus contortus antigens

Sixteen- to eighteen-week-old lambs were infected with 2500 3rd stage larvae (L-3) of Haemonchus contortus or kept as uninfected controls. Two months later all animals were challenged with 5000 L-3 of this parasite. Soluble antigens of H. contortus L-3 and adult worms were analyzed by SDS-PAGE and Western blotting during experimental infection and challenge. Antigens from both sources, particularly of low molecular weight under reducing conditions, were recognised by the pooled sera of infected lambs. No single L-3 antigen was recognised by all infected lambs, whereas two peptides having around 25 and 26 kDa from adults were recognised by infected animals during the patency and could be of potential use in the diagnosis of lamb haemonchosis.