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

Secretory IgA as Biomarker for Gastrointestinal Nematodes Natural Infection in Different Breed Sheep

Specific IgA antibody has been shown to play an important role in resistance to gastrointestinal nematode (GIN) infections in sheep, particularly in Teladorsagia circumcincta parasitosis. In some breeds, negative associations have been shown between IgA levels and worm burden in experimentally infected sheep. In the present study, we have studied the relationship between IgA levels in naturally infected sheep (582 ewes in total; 193 younger than one year old and 389 older than one year old) and fecal egg count (FEC) in the Assaf, Castellana, and Churra breeds. ELISA assays were performed to measure IgA levels against the somatic antigen of T. circumcincta third larval stage (L₃) and a 203-amino-acid fragment of the protein disulfide isomerase from the same GIN species. A multilevel random intercept model was developed to predict the infection risk according to age or breed. Spearman's correlation rank was used for statistical analysis. The prediction model showed that breed was not an influential factor in this study, although the Assaf breed could be considered slightly more susceptible than the others. In addition, age affected the infection risk, with the young ewes more susceptible to infection than the adult groups, except for the Castellana breed, whose risk of infection was similar at all ages. The most significant positive association was found between FEC and IgA measured in the nasal secretions of young ewes using both antigens (Rho = 0.5; p = 0.00); the correlation of FEC with IgA in serum was moderately significant (Rho = 0.306; p = 0.00). Comparing both antigens, the protein disulfide isomerase antigen was less reactive than the somatic antigen from L₃. In conclusion, under natural conditions, specific IgA against GIN was positively associated with FEC in sheep, with nasal secretions from young animals being the sample where this association is stronger, which, therefore, could be used as a marker of infection in further studies.

Development and evaluation of an indirect ELISA for detection of Teladorsagia circumcincta infection in sheep

Background

The gastrointestinal helminth, Teladorsagia circumcincta, is one of the major health risks and production-limiting diseases in small ruminant populations, particularly in temperate regions. With the increasing importance of disease management and recruited anthelmintic resistant types, accurate approaches are needed for the diagnosis of the infection in the host. Due to uncertain results using faecal examinations, the ELISA method was indicated for the detection of nematode antigenic materials. Despite some promising results, problems were described in terms of test specificity and cross-reactions. Therefore, this study aimed to evaluate the IgG response to worm somatic and excretory/secretory (ES) products using western blot analysis and an indirect ELISA for the detection of T. circumcincta infection in sheep.

Results

Based on the immuno-reactivity analysis, immunogenic fractions with molecular weights (MWs) of approximately 60, 75 and 100 kDa were detected in somatic content and two antigens of about 63 and 75 kDa in ES material. Accordingly, a specific product at 75 kDa had the strongest reaction and appeared as the most common antigenic protein. In ELISA, all the sera from the infected sheep revealed the OD rates above the calculated cut-off value with about two-fold greater average. Negative control samples were also specifically recognized with the mean OD rate of about 1/3 of the estimated cut-off value. The cross-reaction test, using rabbit anti-T. circumcincta IgG, did not show reactivity with the ES antigens of other prevalent nematodes including Haemonchus contortus, Protostrongylus rufescens and Marshallagia marshalli. In contrast, a strong positive reaction was observed with the somatic antigens of M. marshalli.

Conclusions

The results of this study indicated that the indirect ELISA method using the ES content enables distinguishing the T. circumcincta infected sheep with high specificity. Those antigenic ES peptides with 63 and particularly 75 kDa MWs should be further investigated due to the potential for serological diagnostic methods and immunoprotective targets in the host.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03042-1.

Acyl-CoA oxidase ACOX-1 interacts with a peroxin PEX-5 to play roles in larval development of Haemonchus contortus

Hypobiosis (facultative developmental arrest) is the most important life-cycle adaptation ensuring survival of parasitic nematodes under adverse conditions. Little is known about such survival mechanisms, although ascarosides (ascarylose with fatty acid-derived side chains) have been reported to mediate the formation of dauer larvae in the free-living nematode Caenorhabditis elegans. Here, we investigated the role of a key gene acox-1, in the larval development of Haemonchus contortus, one of the most important parasitic nematodes that employ hypobiosis as a routine survival mechanism. In this parasite, acox-1 encodes three proteins (ACOXs) that all show a fatty acid oxidation activity in vitro and in vivo, and interact with a peroxin PEX-5 in peroxisomes. In particular, a peroxisomal targeting signal type1 (PTS1) sequence is required for ACOX-1 to be recognised by PEX-5. Analyses on developmental transcription and tissue expression show that acox-1 is predominantly expressed in the intestine and hypodermis of H. contortus, particularly in the early larval stages in the environment and the arrested fourth larval stage within host animals. Knockdown of acox-1 and pex-5 in parasitic H. contortus shows that these genes play essential roles in the post-embryonic larval development and likely in the facultative arrest of this species. A comprehensive understanding of these genes and the associated β-oxidation cycle of fatty acids should provide novel insights into the developmental regulation of parasitic nematodes, and into the discovery of novel interventions for species of socioeconomic importance.

Haemonchus contortus: siRNA mediated knockdown of matrix metalloproteinase 12A (MMP-12) results in reduction of infectivity

BACKGROUND

RNA interference (RNAi) is an important tool to determine the role of genes. RNAi has been widely used to downregulate target molecules, resulting in the reduction of mRNA for protein expression. Matrix metalloprotease 12A (MMP-12) is known to have important roles during embryonic development, organ morphogenesis and pathological processes in animals. However, MMP-12 from Haemonchus contortus has not been characterized.

METHODS

Haemonchus contortus MMP-12 gene was cloned and recombinant protein of MMP-12 (rHc-MMP-12) was expressed. Binding activities of rHc-MMP-12 to goat peripheral blood mononuclear cells (PBMCs) were assessed by immunofluorescence assay (IFA) and the immuno-regulatory effects of rHc-MMP-12 on cell proliferation and nitric oxide production were observed by co-incubation of rHc-MMP-12 with goat PBMCs. Furthermore, a soaking method was used to knockdown the expression of Hc-MMP12 gene using three siRNA, targeting different regions of the gene and infectivity of effective siRNA on the development of H. contortus was evaluated in goat.

RESULTS

rHc-MMP-12 was successfully expressed in an expression vector as well as the tissues of the cuticle of adult H. contortus worms and a successful binding with PBMCs surface were observed. Increased cellular proliferation and nitric oxide production by goat PBMCs was observed in a dose-dependent manner. Quantitative real time PCR (qRT-PCR) results confirmed the successful silencing of Hc-MMP-12 gene in siRNA of 1, 2 and 3 treated third-stage larvae (L3) of H. contortus in vitro. The most efficient qRT-PCR-identified siRNA template was siRNA-2, with a 69% suppression rate compared to the control groups. Moreover, in an in vivo study, silencing of the Hc-MMP-12 gene by siRNA-2 reduced the number of eggs (54.02%), hatchability (16.84%) and worm burden (51.47%) as compared to snRNA-treated control group. In addition, a shorter length of worms in siRNA-2-treated group was observed as compared to control groups.

CONCLUSIONS

Our results indicate that siRNA-mediated silencing of Hc-MMP-12 gene in H. contortus significantly reduce the egg counts, larval hatchability, and adult worm counts and sizes. The findings of the present study demonstrate important roles of Hc-MMP-12 in the development of H. contortus.

Recombinant cold shock domain containing protein is a potential antigen to detect specific antibody during early and late infections of Haemonchus contortus in goat

BACKGROUND

Haemonchus contortus (H. contortus) is one of the most important parasites that cause huge economic losses to small ruminant industry worldwide. Effective prognosis and treatment depend upon the early diagnosis of H. contortus infection. To date, no widely-approved methods for the identification of prepatent H. contortus infection are available to identify prepatent H. contortus infection properly. The aim of this study was to evaluate the diagnostic potential of recombinant cold shock H. contortus protein (rHc-CS) during early and late infections of H. contortus in goat.

RESULTS

Purified rHc-CS exhibited a clear band, with a molecular weight about 38 kDa. H. contortus eggs were not detected by fecal egg count technique from feces collected at 0 to 14 days post infection (D.P.I). However, eggs were detected at 21, 28 and 35 D.P.I. Hence, results of immunoblotting assay showed specific anti rHc-CS antibody detection in all goat sera collected at early stage (14 D.P.I) and late stage (21-103 D.P.I) of H. contortus infection. Furthermore, no cross reactivity was observed against Trichinella spiralis, Fasciola hepatica and Toxoplasma gondii or uninfected goats. Among several evaluated rHc-CS indirect-ELISA format variables, favorable antigen coating concentration was found 0.28 μg/well at 37 °C 1 h and overnight at 4 °C. Moreover, optimum dilution ratio of serum and rabbit anti-goat IgG was recorded as 1:100 and 1:4000, respectively. The best blocking buffer was 5% Bovine Serum Albumin (BSA) while the best time for blocking, serum incubation and TMB reaction were recorded as 60, 120 and 10 min, respectively. The cut-off value for positive and negative interpretation was determined as 0.352 (OD450). The diagnostic specificity and sensitivity of the rHc-CS, both were recorded as 100%.

CONCLUSION

These results validated that rHc-CS is a potential immunodiagnostic antigen to detect the specific antibodies during early and late H. contortus infections in goat.

Development and Potential Application of Ras Domain Containing Protein from Haemonchus contortus for Diagnosis of Goat Infection

Haemonchus contortus is an important gastrointestinal nematode of small ruminants that causes significant mortality in goats worldwide. Diagnosis of this infection mainly depends on the evaluation of clinical signs and fecal examination. However, limitations often occur in early or mild infections. For this purpose, serological diagnosis seems to be more accurate and reliable. Ras domain-containing protein (Ras) is one of H. contortus's excretory and secretory products (ESPs) that can be isolated from different larval stages of the nematode. In this study, the recombinant H. contortus Ras domain-containing protein (rHcRas) was expressed and purified and its diagnostic potential was evaluated. Reactions between rHcRas and goat sera were tested using Western blotting (WB). The results showed that rHcRas could be recognized by sera as early as 14 days post infection (DPI), and antibodies against rHcRas in infected goats could be maintained for over 89 days. No reaction was found between rHcRas and antibodies against Trichinella spiralis, Fasciola hepatica, or Toxoplasma gondii. An indirect enzyme-linked immunosorbent assay (ELISA) was produced based on rHcRas. The optimal coating antigen (157 ng of rHcRas/well) and serum dilutions (1:50) were determined via checkerboard titration. Indirect ELISA based on rHcRas showed 87.5% sensitivity and 90.6% specificity. The cut-off values for this experiment were determined to be 0.324 (positive) and 0.273 (negative), respectively, and the variation coefficient (CV) was less than 15%. The results of the indirect ELISA in-field examination showed that 17.6% (9/51) of the goats were infected with H. contortus, higher than the fecal examination results (15.7%, 8/51). When compared the results of the indirect ELISA and necropsy testing, 98.0% (50/51) consistency was found. These results indicated that rHcRas was a potential antigen for the diagnosis of H. contortus infection in goats.

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.

Immunodiagnostic potential of recombinant tropomyosin during prepatent Haemonchus contortus infection in goat

Excretory and secretory products (ESPs) are released by the parasites during Haemonchus contortus (H. contortus) infection. In this study, Tropomyosin (TpMy), one of these ESPs was used to develop western blotting and optimized Enzyme Linked immunosorbent assay (ELISA) for detection of H. contortus during early infection in goat. Microscopic examination was performed parallel for comparison. Recombinant tropomyosin protein was purified successfully. Western blotting results revealed that anti-recombinant H. contortus Tropomyosin (rHc-TpMy) antibodies could recognize the natural proteinand rHc-TpMy antigen did not show any cross-reaction with goat anti-sera of Fasciola hepatica, Trichinella spiralis, and Toxoplasma gondii. Moreover, initial antibodies were detected by both western blotting and indirect ELISA at 14 days post infection (DPI) and persisted till 30 DPI but fecal eggs count couldn't detect the eggs in feces at early stage (7 and 14 DPI). The optimized antigen coating concentration was calculated as 10 μg/ml (P/N Optimum Density₄₅₀ = 4.165) with optimized dilution of serum (1:50) and secondary antibody (1:2500). Positive and negative cutoff value of the indirect-ELISA assay was calculated as 0.392 and 0.344, respectively. Receiver operating characteristic curve analysis validated the cutoff value (0.392) based on a high specificity and sensitivity. Indirect ELISA showed 90% diagnostic sensitivity and 100% diagnostic specificity. In comparison of serological and conventional method, rHc-TpMy based indirect ELISA showed more positive results (30%; 9/30) than microscopic examination (20%; 6/30). These results demonstrated that rHc-TpMy is a potential immunodiagnostic antigen to detect specific antibodies at early stage of infection in goat and serological methods are more reliable as compared to microscopic examination.

Assessment of Haemonchus contortus larval and adult somatic antigens in sero-diagnosis of haemonchosis in naturally infected sheep and goats

The current work was carried out to evaluate the potency of larval and adult somatic Haemonchus contortus (H. contortus) antigens in detection of haemonchosis among sheep and goats using ELISA. Two hundred and forty-three fecal and blood samples were randomly collected from small ruminants (107 sheep and 136 goats) in Beni-Suef Governorate, Egypt, during the period from June to August 2018. The fecal analysis exhibited that 26.33% of the small ruminants were infected with gastrointestinal nematodes. The overall prevalence of H. contortus was reached 22.22% whereas it was 27.10% and 18.38% among sheep and goats, respectively. The current study elucidated that the larval antigen has claimed more superior diagnostic results compared to the adult somatic H. contortus antigen. The apparent overall sero-prevalence among small ruminants was reached 51.85%. Separately, it was 64.48% in sheep and 41.91% in goats. The larval antigen had proved 96.55% sensitivity and 47.43% specificity, for sheep serum samples. Meanwhile, sensitivity and specificity for goats' sera were 100% and 71.17%, respectively. Diagnostic efficacy of ELISA was recorded 60.74% in sheep and 76.47% in goats. This study deduced that the larval antigen has proved the priority and the potency for diagnosis of H. contortus infection. Moreover, haemonchosis is a prevalent disease among the examined sheep and goats.

Immunodiagnosis of Haemonchus contortus infection in sheep by counter immuno-electrophoresis using somatic antigen

The present study was undertaken for the immuno-diagnosis of Haemonchus contortus infection in sheep by counter immuno-electrophoresis (CIEP) using crude somatic antigen. Adult worms of H. contortus were found in 57 out of 100 abomasums screened. A total of 250 serum samples which includes, 100 serum from local abattoir in and around Shimoga region from the sheep from which the abomasums were collected for H. contortus worms and 150 serum from the migratory sheep were collected to detect the circulating antibody of H. contortus by CIEP using crude whole worm somatic antigen. Out of 100 abomasums screened, 18 were heavily infected with adult worms of H. contortus and their serum samples showed positive reaction with clear thick precipitin line with crude somatic antigen of H. contortus by CIEP and 39 samples showed light precipitin line, which were moderately infected with adult worms of H. contortus during necropsy. However, the 12 serum samples showed positive reaction with clear precipitin line, but their abomasums did not show H. contortus and the remaining 31 were not harbouring any adult worms of H. contortus and no precipitin line observed by CIEP. The sensitivity and specificity of CIEP was found 100 and 72.09 %, respectively. In the present study, 62 % sero-prevalence was observed with CIEP among 150 serum samples from migratory sheep screened for antibodies of H. contortus using crude whole worm somatic antigen of H. contortus.

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.

Evaluation of different Haemonchus contortus antigens for diagnosis of sheep haemonchosis by ELISA and their cross reactivity with other helminthes

Haemonchus contortus (H. contortus) remains important nematode that infecting sheep all over the world. Truthful diagnosis of haemonchosis needs reliable Enzyme linked immune sorbent assay test as well as the immuno-reactive protein profile of different prepared H. contortus antigens; larval (L), excretory secretory product (ESP) and adult somatic H. contortus (AS). The current study fulfilled that L antigen is the talented antigen for such serological diagnosis. Immunodominant band at molecular weight 57 kDa were answerable for highest specificity and accuracy of positive predictive value of this antigen. Moreover, the highest apparent prevalence value was 92 and 75% obtained by L and ESP antigens, respectively. The results of cross reactivity among AS, Monezia expansa (M. expansa) and Fasciola spp. revealed that AS antigen appeared major cross reactivity with other cestode and trematode. Best dilution of serum was (1:800) to rise above this phenomenon.

Sero-prevalence of Haemonchus contortus infection in sheep by Indirect-ELISA using somatic antigen

The present work was carried out to study the sero-prevalence of Haemonchus contortus infection in sheep by Indirect-Enzyme Linked Immuno Sorbent Assay (Indirect-ELISA) using somatic antigen. Out of 100 abomasums screened, 57 found positive for H. contortus adult worms. A total of 250 serum samples which includes, 100 serum samples from local abattoir in and around shimoga region from the animals from which the abomasums were collected and 150 serum samples from migratory sheep were used to detect the circulating antibody against H. contortus by Indirect-ELISA using somatic antigen. Of the 57 sheep harboring adult worms in their abomasums, the serum samples showed positive reaction by Indirect-ELISA with somatic antigen. However, among 43 sheep which are not showing any adult worms of H. contortus in their abomasums, but their 21 serum samples showed positive reaction by Indirect-ELISA. The sensitivity and specificity of Indirect-ELISA was found to be 100 and 67.18 %, respectively. Also, the sero-prevalence of H. contortus infection was found to be 58.66 % out of 150 migratory sheep serum samples screened for detecting circulating antibodies of H. contortus by Indirect-ELISA using somatic antigen in and around shimoga region.

Evaluation of a recombinant excretory secretory Haemonchus contortus protein for use in a diagnostic enzyme-linked immunosorbent assay

The nematode Haemonchus contortus (H. contortus) is one of the most pathogenic and economically important parasites of sheep. A 24 kDa protein is one of the important components in H. contortus excretory/secretory (ES), which was shown to have important biological function. In our research, the cDNA of its open reading frame (ES24) was obtained and analyzed. Then the ES24 was sub-cloned into pET-30a expression vector. The recombinant vector that codes hexahistidyl peptide fusion protein (His-ES24) was transformed into Escherichia coli BL21 (DE3) strain. After induction, a high expression level of His-ES24 was found at 6h taking about 26% of the total bacterial protein analyzed by gel thin-layer scanning. The expressed His-ES24 was purified and then used in an enzyme-linked immunosorbent assay (ELISA) to detect specific antibodies in serum samples. The ELISA was able to differentiate between H. contortus-infected sheep serum and Fasciola hepatica-infected sheep serum or non-infected sheep serum. No cross-reaction was observed in sheep sera that have been experimentally infected with F. hepatica. A total of 153 field sheep serum samples conserved in our laboratory were examined using the His-ES24 ELISA, and 82 (53.6%) of them were found seropositive to H. contortus. Our results demonstrate that the prokaryotic-expressed His-ES24 might be a useful diagnostic reagent for epidemiological studies of H. contortus in sheep.

Haemonchus contortus egg excretion and female length reduction in sheep previously infected with Oestrus ovis (Diptera: Oestridae) larvae

Mixed parasitic infection of animals is a common phenomenon in nature. The existence of one species often positively or negatively influences the survival of the other. Our experimental study was started with the objectives to demonstrate the interaction of Haemonchus contortus and Oestrus ovis in relation to cellular and humoral immune responses in sheep. Twenty-two sheep of Tarasconnais breed (France) were divided into four groups (O, OH, H and C) of five or six animals. Group O and OH received 5 weekly consecutive inoculations with O. ovis L1 larvae (total = 82 L1) in the first phase of the experiment between days 0 and 28. On the second phase, groups OH and H received 5000 L3 of H. contortus on day 48 while group C served as our control throughout the experimental period. Parasitological, haematological, serological and histopathological examinations were made according to standard procedures and all animals were slaughtered at day 95. There was no significant variation in the number and degree of development of O. ovis larvae between the two infected groups. Furthermore, in tissues examined in the upper respiratory tract (nasal septum, turbinate, ethmoide and sinus), group O and OH has responded similarly on the basis of cellular inflammatory responses (blood and tissue eosinophils, mast cells and globule leucocytes (GL)) and serum antibody responses against the nasal bots. This may indicate that the presence of H. contortus in the abomasa of group OH had no marked influence over the development of O. ovis larvae in the upper respiratory tract. On the other hand, we have observed a significantly lower H. contortus female worm length, fecal egg count (FEC) and in utero egg count in animals harbouring the nasal bot (OH) than in the mono-infected group (H). This was significantly associated with higher blood eosinophilia, higher packed cell volume (PCV) and increased number of tissue eosinophils and globule leucocytes. We conclude that, the establishment of O. ovis larvae in the upper respiratory tract has initiated higher inflammatory cellular activity in group OH there by influencing the development and fecundity of H. contortus in the abomasum.

Serodiagnosis of haemonchosis with a somatic antigen (Hc26) in several breeds of sheep

Sera from 53 sheep belonging to Castellano, Churro, Manchego, and Merino breeds were analyzed to test the diagnostic value of a 26-kD antigen from adult Haemonchus contortus at prepatency and early and late patency of experimental haemonchosis. Animals that received zero, 1, or 2 infections with the parasite were tested. In addition, sera from 20 experimentally infected and 10 noninfected Texel sheep were used to test the antigen. Sera from 37 infected animals at prepatency as well as at patency in primary and secondary infection were found positive with the 26-kD antigen. However, sera from 10 animals with the lowest worm burdens (second infection) did not recognize the antigen during early patency (day 28 postinfection). IgG1 was the only isotype implicated in antigen recognition because IgG2, IgA, and IgM, in the same sera, showed no reactivity with the peptide. Antigen specificity was confirmed because hyperimmune sera against infective larvae and adult stages of the most common gastrointestinal nematodes found in natural infections in sheep (Trichostrongylus colubriformis and Teladorsagia circumcincta) did not recognize this peptide. The antigen was recognized only by anti-adult H. contortus hyperimmune sera and appeared to be absent in the L3 parasite stage. In addition, the partial N-terminal amino acid sequence of the diagnostic peptide is reported.

The effect of oxfendazole terminated infections with Haemonchus contortus on the development of immunity in sheep

The relative contribution of third (L3), fourth (L4) or adult stages of Haemonchus contortus to the development of immunity was evaluated in three groups of sheep subjected to infections terminated by oxfendazole treatments at the L3, L4 or adult stage. A control group did not receive immunising infections. All the groups were challenged with 5000 L3, to evaluate the protection provided by the different protocols. All sheep were necropsied at the end of the experiment to count the abomasal worm burdens. A marked reduction in egg counts after challenge infection was only observed in sheep in which the infection was terminated in the adult stage (Group 4). A significant reduction in worm burden was also observed in Group 4. The immunising infections and/or the challenge infection resulted in moderately elevated IgG antibody levels against L3, L4 and adult somatic antigens in all the groups. In contrast, a strong IgG response against H. contortus excretory/secretory (ES) antigens was observed in the groups in which the immunising infection was terminated in the L4 and the adult stage. An elevated lymphocyte proliferation response against Haemonchus ES antigens was found only in the group that had their immunising infection terminated at the adult stage. The combined data suggest that exposure to and elicited immunological responses to ES antigens are important for the development of immunity against H. contortus.

Bovine humoral immune responses to Haemonchus placei excretory secretory antigens

The immune response of calves against excretory secretory (ES) products of adult Haemonchus placei was studied. The ES products of adult H. placei comprise at least ten polypeptides with molecular weights ranging from 10 to over 100 kDa. A primary infection of calves with H. placei did not result in a marked elevation of IgG serum antibodies reactive to ES antigens as demonstrated by ELISA. Immunoblotting experiments revealed that sera of primary infected calves recognised a 50 kDa antigen in most cases. An increase in the level of serum IgG antibodies was observed after trickle infections. The secondary immune response coincided with the recognition of a group of three ES antigens of around 50-55 kDa and one protein with a molecular weight of 24 kDa.