Comparison of Four Diagnostic Methods for Detection and Relative Quantification of Haemonchus contortus Eggs in Feces Samples

Ramming the parasites: Evaluation of quarantine procedures against Haemonchus contortus at sheep markets in Sweden

In Sweden, it is recommended to treat rams at sheep markets with ivermectin and then keep them in quarantine to minimise the risk of transmission of Haemonchus contortus between farms. The aim of this study was to evaluate the effectiveness of this practise. Accordingly the gastrointestinal parasite status of 50 rams purchased at two sheep markets in central Sweden in autumn 2019 was investigated using faecal samples collected on the day of sale (test 1), 12 ± 3 days after ivermectin injection (test 2, in quarantine) and a few months later before inclusion in the new flocks (test 3). We used both traditional diagnostic methods (i.e. identification of nematode eggs in faeces or larvae in cultures when H. contortus eggs could not be identified) and a molecular test based on the digital droplet PCR platform to further identify positive samples. In test 1, conducted in autumn, 40 % of rams were FEC-positive, but only 12 % (six rams) were infected with H. contortus according to conventional routine diagnostics. In test 2, 8 % (four rams) were FEC-positive, including one with 1050 eggs, 90 % of which were identified as H. contortus. This ram was therefore returned to the supplier. However, ivermectin was found to be effective when this animal and a group of lambs from the same farm were treated and tested again. Test 3 was performed on 44 of the same rams (in addition to the returned ram, two rams died in quarantine and the samples from three rams were never provided by the owners). The proportion of FEC-positive animals was 42 %, with an even higher proportion (27 %) of animals being H. contortus-positive than in test 1. The corresponding results for tests 1, 2 and 3 with the ddPCR assay were 18 %, 4 % and 76 %, respectively. This study demonstrates the superiority of DNA detection over microscopy, which is the mainstay in most diagnostic laboratories. Although the combined results confirm that H. contortus survived quarantine in two rams, in the other cases it is not clear whether the spring infection rates are due to re-emergence of persistent larvae from quarantine or reinfection on the new farm. These results suggest not only that we should recommend that sheep farmers use a more sensitive molecular test when purchasing and introducing new animals to their flock, but also that the reliability of injectable ivermectin as a quarantine treatment for removal of adult and larval stages needs further investigation.

Chitosan-ricobendazole complex: Synthesis, characterization and anthelmintic activity

Synthesis, characterization and assessment of therapeutic efficacy of chitosan-ricobendazole complex were carried out for the first time in this work. Study of physico-chemical properties revealed the optimal ratio of chitosan: ricobendazole (30:4). Quantum chemical modeling set the optimal parameters for the formation of the chitosan-ricobendazole molecular system (E = -3765.26 kcal/mol, η = 0.127 eV), which was confirmed by Fourier-transform infrared spectroscopy. Scanning electron microscopy showed spherical particles of chitosan-ricobendazole complex ranging in size from 100 to 200 μm. Study of therapeutic efficiency was conducted on sheep with dicroceliosis. Notably, the therapeutic efficiency of the chitosan-ricobendazole complex (4 mg/kg of ricobendazole) reached 89 %, while the therapeutic efficiency of the commercial preparation ricazole (8 mg/kg of ricobendazole) was 92 %. Biochemical blood test indicated equivalent normalization of hematological parameters in sheep after treatment with ricazole and the chitosan-ricobendazole complex. Histological examination of infected sheep liver revealed that treatment with the chitosan-ricobendazole complex leads to a decrease in the number of helminth eggs with subsequent therapeutic effect on the severity of the disease. This proves the enhanced solubility of ricobendazole at a dosage of 4 mg/kg, active interaction of the components and relatively high bioavailability without increasing the release rate of ricobendazole.

Faecal egg count reduction test in goats: Zooming in on the genus level

The faecal egg count reduction test (FECRT) is the most widely used method to assess treatment efficacy against gastrointestinal nematodes (GIN). Information on genera composition of the GIN community is not available with this test and it is commonly obtained by identifying cultured third-stage larvae (L3) or through molecular assays in the post-treatment survey, but results provided are usually only qualitative or semi-quantitative. The updated WAAVP guidelines now recommend assessing anthelmintic efficacy for each GIN genus/species separately (genus-specific FECRT), but this approach is poorly employed in Europe and in goats especially. For this reason, four FECRT trials were conducted using oxfendazole and eprinomectin in two Italian goat farms. Samples were processed individually using the McMaster technique and then pooled to create two samples from faeces of 5 animals each. Pooled samples were analysed using the McMaster and cultured for seven days at 26°C to obtain L3s. The genus-specific FECRT was based on larval identification, integrating coproculture and FEC results. Larvae were identified as Haemonchus, Trichostrongylus, Teladorsagia, Oesophagostomum / Chabertia and Bunostomum. Molecular assays (a multiplex real-time PCR and two end-point PCRs) were also implemented on pooled samples to support the morphological identification. The Spearmann Rho test confirmed a high correlation between the two approaches (Rho = 0.941 and Rho = 0.914 respectively for Haemonchus and Trichostrongylus, the two most common genera). Both oxfendazole and eprinomectin were effective in one farm, while none in the other farm (FECR = 75.9% and 73.3% respectively). In the second farm, the genus-specific FECRT highlighted a different response to treatment among genera: oxfendazole lacked efficacy against both Haemonchus and Trichostrongylus spp., eprinomectin only against Haemonchus, while all other genera were susceptible to both drugs. This study brings new attention on the importance of adopting a genus-specific approach to identify and quantify differences in susceptibility to anthelmintics among genera in goats, providing support for FECRT interpretation, anthelmintic resistance evaluation and evidence-based GIN control.

A molecular assessment of Ostertagia leptospicularis and Spiculopteragia asymmetrica among wild fallow deer in Northern Ireland and implications for false detection of livestock-associated species

BACKGROUND

Wild deer populations utilizing livestock grazing areas risk cross-species transmission of gastrointestinal nematode parasites (GINs), including GINs with anthelmintic resistance (AR) traits. Wild deer have been shown to carry problematic GIN species such as Haemonchus contortus and Trichostrongylus species in the UK, but the presence of livestock GINs in Northern Ireland deer populations is unknown. Also, is it not known whether AR traits exist among GINs of deer such as Ostertagia leptospicularis and Spiculopteragia asymmetrica in pastureland where anthelmintics are heavily used.

METHODS

Adult-stage GIN samples were retrieved from Northern Irish wild fallow deer abomasa. Individual specimens were subject to a species-specific PCR analysis for common sheep and cattle GIN species with ITS-2 sequence analysis to validate species identities. In addition, the beta-tubulin gene was subject to sequencing to identify benzimidazole (BZ) resistance markers.

RESULTS

ITS-2 sequencing revealed O. leptospicularis and S. asymmetrica, but species-specific PCR yielded false-positive hits for H. contortus, Teladorsagia circimcincta, Trichostrongylus axei, T. colubriformis, T. vitrinus and Ostertagia ostertagi. For beta-tubulin, O. leptospicularis and S. asymmetrica yielded species-specific sequences at the E198 codon, but no resistance markers were identified in either species at positions 167, 198 or 200 of the coding region.

DISCUSSION

From this report, no GIN species of significance in livestock were identified among Northern Ireland fallow deer. However, false-positive PCR hits for sheep and cattle-associated GINs is concerning as the presence of deer species in livestock areas could impact both deer and livestock diagnostics and lead to overestimation of both GIN burden in deer and the role as of deer as drivers of these pathogens. ITS-2 sequences from both O. leptospicularis and S. asymmetrica show minor sequence variations to geographically distinct isolates. AR has been noted among GINs of deer but molecular analyses are lacking for GINs of wildlife. In producing the first beta-tubulin sequences for both O. leptospicularis and S. asymmetrica, we report no BZ resistance in this cohort.

CONCLUSIONS

This work contributes to genetic resources for wildlife species and considers the implications of such species when performing livestock GIN diagnostics.

Rapid, automated quantification of Haemonchus contortus ova in sheep faecal samples

Haemonchus contortus is one of the most pathogenic nematodes affecting small ruminants globally and is responsible for large economic losses in the sheep and goat industry. Anthelmintic resistance is rampant in this parasite and thus parasite control programs must account for drug efficacy on individual farms and, sometimes, whether H. contortus is the most prevalent trichostrongylid. Historically, coproculture has been the main way to determine the prevalence of H. contortus in faecal samples due to the inability to morphologically differentiate between trichostrongylid egg types, but this process requires a skilled technician and takes multiple days to complete. Fluoresceinated peanut agglutinin (PNA) has been shown to specifically bind H. contortus and thus differentiate eggs based on whether they fluoresce, but this method has not been widely adopted. The ParasightTM System (PS) fluorescently stains helminth eggs in order to identify and quantify them, and the H. contortus PNA staining method was therefore adapted to this platform using methodology requiring only 20 min to obtain results. In this study, 74 fecal samples were collected from sheep and analyzed for PNA-stained H. contortus, using both PS and manual fluorescence microscopy. The percentage of H. contortus was determined based on standard total strongylid counts with PS or brightfield microscopy. Additionally, 15 samples were processed for coproculture with larval identification, and analyzed with both manual and automated PNA methods. All methods were compared using the coefficient of determination (R2) and the Lin's concordance correlation coefficient (ρc). ParasightTM and manual PNA percent H. contortus results were highly correlated with R2 = 0.8436 and ρc = 0.9100 for all 74 fecal samples. Coproculture versus PS percent H. contortus were also highly correlated with R2 = 0.8245 and ρc = 0.8605. Overall, this system provides a rapid and convenient method for determining the percentage of H. contortus in sheep and goat fecal samples without requiring specialized training.

Ascaridia galli - An old problem that requires new solutions

Reports of Ascaridia galli in laying hens in Europe have increased since the ban on conventional battery cages in 2012. As this parasite is transmitted directly via the faecal-oral route by parasite eggs containing a larva, it is reasonable to assume that the escalating problem is related to the increased exposure now occurring in modern welfare-friendly cage-free housing systems. On many farms, A. galli reappears in subsequent flocks, even though the birds have no access to the outdoors, biosecurity is high and empty houses are cleaned and disinfected during downtime. Since the egg production cycle lasts only ≈80 weeks and recombinant antigen production for helminth vaccines has not yet been solved, the development of a vaccine seems to be an unrealistic option. Therefore, disrupting the life cycle of the parasite by other means, including the strategic use of dewormers, appears to be the key to controlling infection. Of concern is that only one class of anthelmintics is licenced for poultry in Europe and that are usually administered indiscriminately through the birds' drinking water and often too late when the parasite is already established. If current calendar-based parasite control strategies are not changed, there is a risk that resistance to anthelmintics may develop, as has already been demonstrated with nematodes in livestock. We insist that treatments can be more effective and the risk of developing drug resistance can be mitigated if we invest in a better understanding of A. galli responses to more prudent and judicious use of anthelmintics. This review identifies knowledge gaps and highlights aspects of sustainable parasite control that require further research to support commercial egg producers.

Signs of multiple anthelmintic resistance in sheep gastrointestinal nematodes in Sweden

Gastrointestinal nematodes in small ruminants are clinically and economically important parasites that often are controlled with anthelmintics. In this study, we compiled information on the anthelmintic efficacy collected on sheep farms according to routines established by Farm & Animal Health in Sweden. The efficacies of benzimidazoles (i.e. albendazole or fenbendazole, n = 30), ivermectin (n = 47), levamisole (n = 2) or moxidectin (n = 2) were examined between 2015 and 2021 in 81 treatment groups on 49 non-randomly selected farms in south-central Sweden. Drug efficacies were estimated with the faecal egg count reduction test. In addition, efficacy data were in most cases supplemented with data on the abundance of the three most common nematode genera in sheep by performing droplet digital (dd) PCR on coprocultures. Efficacies of <95% for benzimidazoles or ivermectin were identified in 37% and 77% of the tested groups, respectively. In addition, on 27 (55%) of the 49 farms where both benzimidazoles and ivermectin were tested, multiple resistance was found on 8 (30%). In contrast, on each of the two farms tested for levamisole and moxidectin both drugs proved to be 100% effective. However, because post-sampling was performed earlier than recommended in several susceptible groups (benzimidazoles = 15, and ivermectin = 10 groups), this could have underestimated the severity of the situation. Mainly larvae from the genus Haemonchus were detected in post-treatment coprocultures, in all groups with declared resistance, suggesting that this parasite was primarily associated with anthelmintic resistance. Unexpectedly, the DNA of larvae, which survived treatment, was also detected on farms declared as susceptible. Taken together, this indicates that the situation regarding the anthelmintic efficacy has deteriorated compared with the latest nationwide study on Swedish sheep farms conducted more than a decade ago. Unlike the previous study, the farm selection here was not strictly randomized but rather opportunistic i.e., only farms with a recognized parasite problem were included. Thus, there is a need for a truly randomized study to get an update on the extent of the situation of anthelmintic resistance at a national level, as well as to identify risk factors involved in the resistance selection. Research is also required to establish the optimal intervals for sampling post-treatment.

Parasitic strongyle nemabiome communities in wild ruminants in Sweden

Background

Wildlife hosts may serve as reservoirs for strongyles, which can be transmitted to domestic livestock. Therefore, studies evaluating nemabiome compositions in wildlife ruminants are of great use in assessing the possibility of transmission of important nematode pathogens to domestic sheep in Sweden.

Methods

First, fecal samples were collected from roe deer (n = 125), fallow deer (n = 106), red deer (n = 18) and mouflon (n = 13) in south central Sweden during the hunting season in 2019. Second, after fecal examination samples were cultured and the larvae were harvested, followed by DNA extractions. Third, all samples were barcoded and processed for sequence analysis on the PacBio platform. Finally, bioinformatic sequence analysis was conducted with DADA2, while species diversity and richness, as well as interactions between the different hosts, were calculated and analyzed in R.

Results

Nematode ITS2 sequences were found in 225 of 262 (86%) samples. In total, 31 taxa were identified, among which 26 (86%) to the species level. These were found in different combinations, among which 24 (77%) occurred in roe deer, 19 (61%) in fallow deer, 20 (65%) in red deer and 10 (32%) in mouflon. Five of the species found are known to be associated with livestock (Chabertia ovina, Haemonchus contortus, Oesophagostomum venulosum, Teladorsagia circumcincta and Trichostrongylus axei). However, in the present study the relative abundance and prevalence of most of these species were low. The most striking exception was T. axei, which was relatively abundant in all wildlife hosts. Mostly a wide range of wildlife specific nematodes such as Ostertagia leptospicularis and Spiculopteragia spp. were identified including the invasive nematode Spiculopteragia houdemeri, which was found for the first time in red deer, fallow deer, and mouflon in Sweden. The difference in the number of shared species between mouflon and all cervids (n = 6) was less than among all three cervids (n = 8).

Conclusion

In this study, we investigated the community structure of parasitic intestinal nematodes in four wildlife hosts, and we found that the majority of the parasite species identified were wildlife specific. We also found a new, potentially invasive species not reported before. After comparing the nemabiome of the wildlife hosts in this study with a previous study in sheep from the same geographical region, we conclude that the horizontal transmission potential appears to be relatively low. Still, cross-infections of nematodes between game and sheep cannot be completely ignored.

Graphical Abstract

Advances in diagnosis of gastrointestinal nematodes in livestock and companion animals

Diagnosis of gastrointestinal nematodes in livestock and companion animals has been neglected for years and there has been an historical underinvestment in the development and improvement of diagnostic tools, undermining the undoubted utility of surveillance and control programmes. However, a new impetus by the scientific community and the quickening pace of technological innovations, are promoting a renaissance of interest in developing diagnostic capacity for nematode infections in veterinary parasitology. A cross-cutting priority for diagnostic tools is the development of pen-side tests and associated decision support tools that rapidly inform on the levels of infection and morbidity. This includes development of scalable, parasite detection using artificial intelligence for automated counting of parasitic elements and research towards establishing biomarkers using innovative molecular and proteomic methods. The aim of this review is to assess the state-of-the-art in the diagnosis of helminth infections in livestock and companion animals and presents the current advances of diagnostic methods for intestinal parasites harnessing (i) automated methods for copromicroscopy based on artificial intelligence, (ii) immunodiagnosis, and (iii) molecular- and proteome-based approaches. Regardless of the method used, multiple factors need to be considered before diagnostics test results can be interpreted in terms of control decisions. Guidelines on how to apply diagnostics and how to interpret test results in different animal species are increasingly requested and some were recently made available in veterinary parasitology for the different domestic species.

Estimation of the impact of three different bioinformatic pipelines on sheep nemabiome analysis

Background

Next-generation sequencing (NGS) has provided an alternative strategy to study the composition of nematode communities with increased resolution and sensitivity. However, the handling and processing of gigabytes worth of amplicon sequence data produced by an NGS platform is still a major hurdle, limiting the use and adoption of faster and more convenient analysis software.

Methods

In total 32 paired, fecal samples from Swedish sheep flocks were cultured and the larvae subsequently harvested subjected to internal transcribed spacer 2 (ITS2) amplicon sequencing using the PacBio platform. Samples were analyzed with three different bioinformatic pipelines, i.e. the DADA2, Mothur and SCATA pipelines, to determine species composition and richness.

Results

For the the major species tested in this study (Haemonchus contortus, Teladorsagia circumcinta and Trichostrongylus colubriformis) neither relative abundances nor species diversity differed significantly between the three pipelines, effectively showing that all three analysis pipelines, although different in their approaches, yield nearly identical outcomes. In addition, the samples analyzed here had especially high frequencies of H. contortus (90–95% across the three pipelines) both before and after sample treatment, followed by T. circumcinta (3.5–4%). This shows that H. contortus is the parasite of primary importance in contemporary Swedish sheep farms struggling with anthelmintic resistance. Finally, although on average a significant reduction in egg counts was achieved post-treatment, no significant shifts in major species relative frequencies occurred, indicating highly rigid community structures at sheep farms where anthelmintic resistance has been reported.

Conclusions

The findings presented here further contribute to the development and application of NGS technology to study nemabiome compositions in sheep, in addition to expanding our understanding about the most recent changes in parasite species abundances from Swedish sheep farms struggling with anthelmintic resistance.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05399-0.

A Review: Haemonchus contortus Infection in Pasture-Based Sheep Production Systems, with a Focus on the Pathogenesis of Anaemia and Changes in Haematological Parameters

Simple Summary

Infection with Haemonchus contortus parasites (haemonchosis) is an important cause of anaemia in sheep. Haemonchosis is a global problem, although sheep that are kept in warm, high rainfall environments are at the greatest risk of infection due to the favourable conditions for H. contortus survival. Following ingestion, the parasites develop in the abomasum of sheep. Various factors such as age, breed, health, nutritional status, and larval challenge influence the severity of clinical disease. Hyperacute, acute, and chronic haemonchosis are reviewed, focusing on the pathophysiology of haemonchosis, associated clinical signs, and haematological and biochemical findings.

Abstract

Haemonchosis is an important cause of anaemia in sheep worldwide, particularly those that are kept in pasture-based systems in warm, high rainfall environments. Potential outcomes vary based on the severity of infection and the sheep’s immune response, however, in some sheep infection can lead to death. The consequences of Haemonchus contortus infection mean that it has been well-studied in a range of different farming systems. However, to our knowledge, there has not been a recent review focused on the pathophysiology of anaemia caused by haemonchosis. Thus, this review provides an in-depth discussion of the literature related to the pathophysiology of haemonchosis and associated clinical signs for hyperacute, acute, and chronic haemonchosis. Additionally, haematological and biochemical findings are presented, and various diagnostic methods are assessed.

Genome-wide analysis of the response to ivermectin treatment by a Swedish field population of Haemonchus contortus

Haemonchus contortus is a pathogenic gastrointestinal nematode of small ruminants and, in part due to its capacity to develop resistance to drugs, contributes to significant losses in the animal production sector worldwide. Despite decades of research, comparatively little is known about the specific mechanism(s) driving resistance to drugs such as ivermectin in this species. Here we describe a genome-wide approach to detect evidence of selection by ivermectin treatment in a field population of H. contortus from Sweden, using parasites sampled from the same animals before and seven days after ivermectin exposure followed by whole-genome sequencing. Despite an 89% reduction in parasites recovered after treatment measured by the fecal egg count reduction test, the surviving population was highly genetically similar to the population before treatment, suggesting that resistance has likely evolved over time and that resistance alleles are present on diverse haplotypes. Pairwise gene and SNP frequency comparisons indicated the highest degree of differentiation was found at the terminal end of chromosome 4, whereas the most striking difference in nucleotide diversity was observed in a region on chromosome 5 previously reported to harbor a major quantitative trait locus involved in ivermectin resistance. These data provide novel insight into the genome-wide effect of ivermectin selection in a field population as well as confirm the importance of the previously established quantitative trait locus in the development of resistance to ivermectin.

Effects of lambing season on nematode faecal egg output in ewes

In this study, we assessed the occurrence of a periparturient rise (PPR) in winter and spring lambing ewes in Sweden and where nematode egg excretion patterns were investigated mainly for diagnostic purposes. Gastrointestinal nematodes and Haemonchus contortus presence were monitored in parallel in all animals in each experimental group on four farms in samples that were collected mainly when the animals were stabled. Faecal examinations of the same animals were conducted on four sampling occasions between January and June 2018 Each group consisted of 12 crossbreed ewes of similar genotype. One group's peak lambing was in January or February (early), and the other in March or early May (late). The first (S1) and third samples (S3) were from approximately one to two weeks before parturition in the early (winter lambing) and late (spring lambing) group respectively, whereas the second (S2) and fourth samples (S4) were collected approximately three to five weeks post-parturition in the same groups. During the course of the study, there was a significant rise in faecal egg counts (FEC) in both groups on all farms. On three farms with a substantial amount of Haemonchus, we observed a difference in the egg excretion patterns between the two groups of ewes as revealed by a significant interaction between the sampling point and lambing period. Also, when samples corresponding to each other in relation to the number of weeks that had elapsed post-parturition (three to five weeks post-parturition, S2 for early and S4 for late) were compared, FEC were significantly lower in the early group lambing in winter than the late group lambing in spring. This indicates that besides lambing, the rise in nematode egg count is also influenced by other factors unrelated to the lambing period, such as the increased daylight in spring. Due to study limitations, we cannot provide a more detailed explanation for this, but only state that the rise appeared to be more closely linked to season than physiology as measured by day relative to parturition. Still, our results suggests that when turned out, winter lambing ewes contribute to pasture contamination to a lesser extent than those lambing in spring. These results will be used in stipulating evidence-based advice to farmers in their flock management to reduce use of anthelmintics, and at the same time efficiently produce prime lambs.

Epidemiological, Morphological, and Morphometric Study on Haemonchus spp. Recovered From Goats in Egypt

Goats can be infected by multiple groups of external and internal parasites. Haemonchus spp. are among abomasal parasites that can result in higher mortality and several considerable economic losses in goats. Early detection of parasites and better understanding of the major risk factors associated with infection are among the main strategies for controlling the infection. Considering this, information on hemonchosis in goats from Egypt, and the contribution of goats in the maintenance of the epidemiological foci of the disease is limited. This study investigated the prevalence of Haemonchus species among 240 abomasum samples collected during postmortem examination of goat carcasses from Assiut Governorate, Egypt. Moreover, the association of the major risk factors to describe the epidemiological pattern of the disease was explored. This study demonstrated that 16.66% of abomasa samples harbored Haemonchus species. Additionally, age, sex, and sampling season were the most significant risk factors associated with infection. Following the variable factors under study, goats aged 1 year or older were at higher risk, with an infection rate of 22.14% (31 of 140), than those younger than 1 year (9%) [p = 0.008; odds ratio (OR) = 2.87; 95% confidence interval (CI), 1.30-6.35]. The infection rate was 25% (19 of 76) in males and 12.8% (21 of 164) in females [p = 0.024; odds ratio (OR) = 2.26; 95% confidence interval (CI), 1.13-4.53]. Moreover, the exposure to infection was higher in summer (22.22%) than in winter (8.33%) (p = 0.007; odds ratio (OR) = 0.318; 95% confidence interval (CI), 0.139-0.725). More importantly, three species of the parasite-Haemonchus contortus, Haemonchus placei, and Haemonchus longistipes-were identified for the first time, and the confirmation of the identification and morphological characterization of the worms was performed using light microscopy and SEM. Collectively, this study reveals interesting epidemiological, morphological, and morphometric findings associated with the occurrence of hemonchosis among goats in Egypt. This study suggests further research for exploring the major circulating species of the parasite in Egypt, which is mandatory for controlling the disease.

Molecular detection of Strongyloides sp. in Australian Thoroughbred foals

Background

Strongyloides westeri is found in the small intestine of young horses, mainly in foals up to about 16 weeks of age. The main source of infection for foals is through transmammary transmission, and foals can develop acute diarrhoea, weakness, dermatitis and respiratory signs. The epidemiology of S. westeri in Australia is largely unknown. Further, molecular techniques have never been employed for detection of S. westeri in horses. This pilot study aimed to assess the utility of a molecular phylogenetic method for the detection of S. westeri in the faeces of foals.

Methods

Faecal samples were collected from a foal of less than 2 months of age, and eggs of Strongyloides sp. were detected using the modified McMaster technique. DNA was extracted from purified eggs, and a partial fragment of the small subunit of the nuclear ribosomal DNA (18S) was characterised using polymerase chain reaction, DNA sequencing and phylogenetic methods.

Results

Microscopic examination of faeces revealed small ellipsoidal eggs typical of Strongyloides sp. The 18S sequence generated by PCR in this study revealed 98.4% identity with that of a reference sequence of S. westeri available from GenBank. Phylogenetic analyses revealed a polyphyletic clustering of S. westeri sequences.

Conclusion

This is the first study reporting the detection of DNA of Strongyloides sp. in faeces of a foal using a molecular phylogenetic approach targeting the variable region of 18S rDNA. It is anticipated that this study will allow future molecular epidemiological studies on S. westeri in horses.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04966-1.

Combined Molecular and Lectin Binding Assays to Identify Different Trichostrongyle Eggs in Feces of Sheep and Goats from Egypt

BACKGROUND

Trichostrongyles are common causes of parasitic gastroenteritis in sheep and goats worldwide. Accurate identification of these nematodes to the genus and/or species level is important for therapy selection and control strategies. In the present study, molecular and egg-lectin binding approaches were employed to identify the most economically important trichostrongyles circulating in sheep and goat herds from six districts in Dakahlia governorate, Egypt.

MATERIALS

Fecal samples from 653 and 205 goats reared within 17 herds were collected and tested for the trichostrongyle eggs using the modified Wisconsin sucrose flotation method. For identification of the trichostrongyle(s) present, eggs from 75 (63 sheep and 12 goats) samples which had high egg count (EPG) and pooled eggs (n = 19 pools, 15 sheep and 4 goats) from samples with moderate or low EPGs were examined. Molecular examination was conducted amplifying the ITS2 region of the rDNA for six different trichostrongyles in individual PCR reactions. For egg-lectin bindings, 4 fluorescently-labeled specific lectins were used; peanut agglutinin (PNA) for Haemonchus contortus, Aleuria aurantia agglutinin (AAL) for Trichostrongylus species, Lens culinaris agglutinin (LCA) for Teladorsagia circumcnicta and Lotus tetragonolobus lectin (LTL) for Cooperia species.

RESULTS

Fourteen (82.3%) herds were found infected, of which trichostrongyle eggs were detected in fecal samples of 26.5% (173/653) of sheep and 10.2% (21/205) of goats. Results of the PCR and lectin bindings were compatible and 4 trichostrongyles were detected: H. contortus, T. circumcincta, Trichostrongylus axei and Trichostrongylus colubriformis. Haemonchus contortus eggs were found in all the infected herds, and as the single species in 21 and 5 of sheep and goat samples, respectively. Lectin stained smears demonstrated the dominance of H. contortus eggs over eggs of the other detected trichostrongyles. Eleven herds were found infected with T. axei as the second most prevalent trichostrongyle; however, few AAL-stained eggs were noticed in the positive samples. Mixed infections were frequently detected as H. contortus-T. axei combination. Infections with T. circumcincta were noted in sheep samples from two herds, but not in any sample from the goats. No Ostertagia leptospicularis, Cooperia curticei or Nematodirus species were noted among the tested samples.

CONCLUSIONS

This is the first molecular and lectin binding survey to determine the species composition of trichostrongyles infecting sheep and goats from Egypt. Haemonchus contortus plays the principal role in small ruminant trichostrongylosis in Egypt. Egg-lectin staining shows promise for future for its application in routine diagnosis as a rapid and simple technique. Findings of the earlier reports from Egypt are tabulated and reviewed.

Triple lectin staining of trichostrongyle eggs from naturally infected small ruminants

Trichostrongyle nematodes can be a major threat to the profitability of small ruminant producers depending of the species and intensity of trichostrongyles parasitizing their herd. Haemonchus contortus, Teladorsagia circumcincta, and Trichostrongylus colubriformis are typically the most common and clinically important species. Three lectins (PNA, LCA and AAL) have been reported to bind specifically to eggs from these three genera and therefore could be used to quantify the intensity of each species in individual animals. Peanut agglutinin (PNA) has been the most commonly tested lectin because it selectively binds intensely to eggs of the most pathogenic species, H. contortus. Lens culinaris agglutinin (LCA) and Aleuria aurantia agglutinin (AAL) have shown specificity to T. circumcincta and Trichostrongylus spp. respectively, however, these lectins have only been evaluated using eggs harvested directly from adult females, and not from fecal samples. The purpose of the present study is to describe a method to sequentially stain H. contortus, T. circumcincta and Trichostrongylus spp. fecal eggs with PNA, LCA and AAL, and then evaluate the resultant staining patterns seen with eggs collected from a naturally infected goat shown with PCR to contain H. contortus, T. circumcincta, Ostertagia leptospicularis, Trichostrongylus colubriformis and Trichostrongylus axei eggs. These results were also compared with patterns observed with eggs stained with single lectins and double combinations of lectins. The various patterns were then compared to those seen with egg samples collected from an ewe shown to only contain H. contortus. PNA bound intensely and uniformly to all eggs from samples containing only H. contortus eggs; however, some eggs additionally bound LCA and AAL in localized patches of varying size, and a few eggs exhibited intense and uniform binding of all three lectins. Single PNA-staining of goat samples containing the five trichostrongyles species identified most eggs as H. contortus, and triple-staining showed patterns consistent with those seen for H. contortus. Binding of AAL to non-Haemonchus eggs was uniform but showed significant variations in intensity. Lesser staining eggs tended to also stain intensely with LCA, which is consistent with published binding pattern for T. circumcincta. Most eggs that AAL bound intensely to did not bind with LCA, which is consistent with published binding pattern for Trichostrongylus spp. Autofluorescence was observed with the DAPI filter-cube among most non-Haemonchus eggs. This study demonstrates the need for additional field studies to further validate the specificity of these three lectins for use in identifying eggs from the three species of trichostrongyles.

Using droplet digital PCR for the detection of hco-acr-8b levamisole resistance marker in H. contortus

The nematode Haemonchus contortus is one of the most prevalent and pathogenic parasites in small ruminants. Although usually controlled using anthelmintics, the development of drug resistance by the parasite has become a major issue in livestock production. While the molecular detection of benzimidazole resistance in H. contortus is well developed, the molecular tools and protocols are far less advanced for the detection of levamisole resistance. The hco-acr-8 gene encodes a critical acetylcholine susceptible subunit that confers levamisole-sensitivity to the receptor. Here, we report the development of a droplet digital PCR assay as a molecular tool to detect a 63 bp deletion in the hco-acr-8 that has been previously associated with levamisole resistance. Sanger sequencing of single adult H. contortus yielded 56 high-quality consensus sequences surrounding the region containing the deletion. Based on the sequencing data, new primers and probes were designed and validated with a novel droplet digital PCR assay for the quantification of the deletion containing “resistant” allele in genomic DNA samples. Single adult worms from six phenotypically described isolates (n = 60) and from two Swedish sheep farms (n = 30) where levamisole was effective were tested. Even though a significant difference in genotype frequencies between the resistant and susceptible reference isolates was found (p = 0.01), the homozygous “resistant” genotype was observed to be abundantly present in both the susceptible isolates as well as in some Swedish H. contortus samples. Furthermore, field larval culture samples, collected pre- (n = 7) and post- (n = 6) levamisole treatment on seven Swedish sheep farms where levamisole was fully efficacious according to Fecal Egg Count Reduction Test results, were tested to evaluate the frequency of the “resistant” allele in each. Frequencies of the deletion ranged from 35 to 80% in the pre-treatment samples, whereas no amplifiable H. contortus genomic DNA was detected in the post-treatment samples. Together, these data reveal relatively high frequencies of the 63 bp deletion in the hco-acr-8 both on individual H. contortus and field larval culture scales, and cast doubt on the utility of the deletion in the hco-acr-8 as a molecular marker for levamisole resistance detection on sheep farms.

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Acr8b – levamisole resistance marker investigated in single worms and larval cultures.

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Individuals homozygous for acr8b found more commonly, even in susceptible isolates.

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Levamisole treatment efficacy was unaffected by increased acr8b frequencies in larvae.

First case of monepantel resistant nematodes of sheep in Sweden

In this study, we describe for the first time monepantel (MOP) resistance in gastrointestinal nematodes (GIN) in a Swedish sheep flock. On the farm, which had recurrent problems with Haemonchus contortus infection, the efficacy of most available anthelmintics (AH) in Sweden (i.e. ivermectin, albendazole, levamisole and monepantel), was monitored. This was done with the faecal egg count reduction test (FECRT) on three different occasions between August 2017 and April 2020. Although, MOP was used in ewes for the first time in this herd in October 2018 and then demonstrated to be highly efficacious (100% reduction), MOP-resistant worms (52% reduction) appeared in lambs already in April 2020. Resistance was detected only after two further rounds of treatment of the lambs after weaning. It is assumed that a contributing factor to this extremely rapid development was related to the fact that ewes and lambs treated during the housing period were let out on clean pasture after treatment. The ewes were treated during the housing period 2018 and grazed a clean pasture the following spring. The same ewes were treated a second time after housing 2018. The lambs were grazed with these ewes in summer 2018 and after weaning they were treated and moved to another clean pasture during the fall 2018. Anthelmintic resistance was also confirmed on two occasions to different compounds of ivermectin and once to albendazole, but not to levamisole which was tested twice. In conclusion, this is the first description of triple resistance to AH drugs in GIN of sheep in Sweden.

The use of ITS-2 rDNA nemabiome metabarcoding to enhance anthelmintic resistance diagnosis and surveillance of ovine gastrointestinal nematodes

A lack of quantitative information on the species composition of parasite communities present in fecal samples is a major limiting factor for the sensitivity, accuracy and interpretation of the diagnostic tests commonly used to assess anthelmintic efficacy and resistance. In this paper, we investigate the ability of ITS-2 rDNA nemabiome metabarcoding to enhance fecal egg count reduction testing by providing information on the effect of drug treatments on individual parasite species. Application of ITS-2 rDNA nemabiome metabarcoding to fecal samples from ewes from over 90 flocks across western Canada revealed high gastrointestinal nematode infection intensities in many flocks with Haemonchus contortus being the most abundant species followed by Teladorsagia circumcincta and then Trichostrongylus colubriformis. Integration of ITS-2 rDNA nemabiome metabarcoding with pre- and post-treatment fecal egg counting revealed consistently poor efficacy of producer-applied ivermectin and benzimidazole treatments against H. contortus, but much better efficacy against T. circumcincta and T. colubriformis, except for in a small number of flocks. Integration of nemabiome ITS-2 rDNA metabarcoding with Fecal Egg Count Reduction Tests (FECRT), undertaken on farm visits, confirmed that ivermectin and fenbendazole resistance is widespread in H. contortus but is currently less common in T. circumcincta and T. colubriformis in western Canada. FECRT/nemabiome testing did not detect moxidectin resistance in any GIN species but suggested the early emergence of levamisole resistance specifically in T. circumcincta. It also revealed that although poor efficacy to closantel was relatively common, based on total fecal egg counts, this was due to its narrow spectrum of activity rather than the emergence of anthelmintic resistance. This study illustrates the value of ITS-2 rDNA nemabiome metabarcoding to improve fecal egg count resistance testing, perform large-scale anthelmintic resistance surveillance and direct more targeted rational anthelmintic use.

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Nemabiome metabarcoding in anthelmintic resistance diagnostics and surveillance.

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Producer-applied treatment results were consistent with controlled FECRT.

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Widespread BZ and IVM resistance in H. contortus in western Canada.

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Only sporadic BZ and IVM resistance T. circumcincta and T. colubriformis.

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Early levamisole resistance in T. circumcincta, closantel resistance not prevalent.

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.

Development and field evaluation of a species-specific mt-COI targeted SYBR-Green Real Time PCR for detection and quantification of Haemonchus contortus in cattle in Turkey

Haemonchus contortus is one of the most important gastrointestinal nematodes (GINs) infecting sheep, goats, and cattle worldwide. We developed a SYBR Green real-time PCR (qPCR) assay for detection and quantification of H. contortus by using specific primers based on a conserved region of the mitochondrial cytochrome oxidase subunit I (mt-COI) gene, and evaluated this technique in the detection of H. contortus infections in cattle in Central Anatolia Region of Turkey. The newly developed qPCR assay successfully discriminated H. contortus from other GIN species infecting cattle in the specificity evaluations, with a specific melt peak of 77.5 °C. Our results revealed the efficient amplification of the proposed target COI region within the range of plasmid copies, from 2 × 10⁶ to 2 × 10¹ per μl, with 96.9 % efficiency, R² value of 0.999, and a slope of -3.398. Among the 920 cattle fecal samples from the field, 58 samples (6.3 %) were positive with qPCR assay, whereas 45 samples (4.9 %) were positive, as determined by larval culture, suggesting the utility of SYBR Green qPCR. Phylogenetic characterization of the partial COI gene of H. contortus isolates was also evaluated for 100 eggs and third stage larvae recovered from positive cattle faecal samples, which were verified with the qPCR assay prior to analyses. COI sequences were classified into three haplotypes (THC1 to THC3) with intraspecific nucleotide differences of 0.50 to 0.76 %. Phylogenetic analyses revealed that the haplotypes grouped with H. contortus isolates from several countries in a monophyletic cluster, with evidence of at least two main haplogroups. Overall, the SYBR Green qPCR assay was highly specific and sensitive, suggesting that it can be used for screening of H. contortus infections in livestock populations in epidemiological studies and the control of this important parasite.

Molecular method for the semiquantitative identification of gastrointestinal nematodes in domestic ruminants

Standard diagnostic methods currently in use for the identification of helminth infections in ruminants are based on the morphological analysis of immature and adult stages of parasites. This paper describes a method for the semiquantitative identification of nematodes, mainly Trichostrongyloidea, at species-level resolution. The method is based on amplification and fragment analysis followed by minisequencing of the ITS-2 region (internal transcribed spacer 2) of the ribosomal DNA of parasite eggs or larvae. This method allows for the identification of seven genera (Chabertia, Cooperia, Haemonchus, Oesophagostomum, Ostertagia, Teladorsagia, and Trichostrongylus) and 12 species (Chabertia ovina, Cooperia curticei, Cooperia punctata, Cooperia oncophora/Cooperia surnabada, Haemonchus contortus, Haemonchus placei, Haemonchus longistipes, Oesophagostomum asperum, Oesophagostomum radiatum, Ostertagia ostertagi, Trichostrongylus axei, and Trichostrongylus colubriformis) of infectious nematodes of domestic ruminants. The concordance between the morphological and molecular analyses in the detection of genera ranged from 0.84 to 0.99, suggesting the proposed detection method is specific, semiquantitative, less laborious, and highly cost-efficient.

Detection of Haemonchus contortus on sheep farms increases using an enhanced sampling protocol combined with PCR based diagnostics

An enhanced sampling strategy for detection of gastrointestinal parasites of sheep based on faecal sampling covering approximately 10% of the animals in the flock was evaluated with focus on the major sheep pathogen Haemonchus contortus. We also compared traditional diagnostics based on faecal eggs counts (FEC) by microscopy with DNA detection on frozen faeces samples using a droplet digital (dd)PCR assay. The investigation was carried out in 2018 in 20 conventional and 19 organic sheep flocks in Sweden with between 70 and 250 production ewes. On 76 different sampling occasions a total of 810 individual faecal samples were collected. Samples were pooled in the laboratory into 270 triplets which were examined both by microscopy and a ddPCR assay. On most farms (95%) a minimum of three triplets were investigated, first from the ewes prior to turn-out and later from the lambs after they had been grazing for at least six weeks. Extra information about the Haemonchus status was provided on 48% of the 76 sampling occasions by including more triplets compared with the old sampling strategy applied in Sweden before 2015 based on two triplets per sampling occasion irrespective of flock size. At a farm level H. contortus was identified by microscopy in 22 (56%) of the 39 flocks and by ddPCR it was found in 28 (72%) flocks with the enhanced protocol. There was a substantial agreement between the two diagnostic tests (Cohens kappa = 0.70 ± 0.087). No significant differences in infection levels were observed between the two production systems (conventional and organic) irrespective of the diagnostic method used. However, samples from the ewes were more often Haemonchus positive than those from the lambs indicating that the level of parasite control was in general acceptable. Combined, our results show that Haemonchus infection is widespread throughout Sweden. In conclusion, we have validated a practical tool for sheep producers to assess Haemonchus infection with high precision.

Combined Use of Indirect ELISA and Western Blotting with Recombinant Hepatocellular Carcinoma-Associated Antigen 59 Is a Potential Immunodiagnostic Tool for the Detection of Prepatent Haemonchus contortus Infection in Goat

Simple Summary

The accurate and early diagnosis of Haemonchus contortus infection is crucial for effective control. Early stage detection of H. contortus infection has not been attempted in goat, even though both immature worm and fourth larval stage are blood sucking. This study was carried out to detect the H. contortus infection during early stage in goat. The results of this study assessed that rHc-HCA59 could detect the antibody in H. contortus infected goats’ sera during early period with good sensitivity and specificity using immunodiagnostic techniques. Our findings illustrated that combined use of ELISA and western blotting based on rHc-HCA59 is a powerful tool for early detection of H. contortus infection in goats.

Abstract

Haemonchus contortus is recognized as one of the important health problems in small ruminants, leading to reduced production and economic loss for farmers worldwide. Prepatent diagnosis of H. contortus infection is crucial to improve control strategies as this helminth may remove up to one-fifth of total erythrocytes and may cause anemia, edema, diarrhea, and ultimately death in young animals. In this study, one of the excretory and secretory products, rHc-HCA59, was purified and used as antigen to detect specific antibodies in H. contortus infected goats during prepatent stage of infection using indirect enzyme linked immunosorbent assay (ELISA) as screening test. All goats (n = 38) were housed indoor, experimentally infected with 8000 infective larvae (L3) of H. contortus, and serum samples were collected prior to infection and at 14th day of infection. Immunoblotting was performed to confirm the results of indirect ELISA, evaluate the cross reactivity against rHc-HCA59 in sera of most common co-infecting parasites and rectify the false negative samples. Furthermore, three different batches of rHc-HCA59 were produced to evaluate the repeatability of ELISA. No eggs were detected in feces of all goats collected at 7th and 14th day of infection but, H. contortus eggs were detected at 21 days post infection in the feces. Indirect ELISA performed in this study showed 87% sensitivity and 100% specificity. The western blot analysis confirmed immunoreactivity in serum samples which scored positive in indirect ELISA and recognized the samples as negative which had OD₄₅₀ lower than negative cut-off value in indirect ELISA. Furthermore, all false negative sera (n = 5) that had OD₄₅₀ value between positive and negative cut-off value in rHc-HCA59 based ELISA were clearly positive in western blot. Moreover, no cross-reactivity was detected in ELISA and western blotting against rHc-HCA59 in positive sera of Toxoplasma gondii, Fasciola hepatica, and Trichinella spiralis. The results of this study concluded that combined use of indirect ELISA and western blotting with rHc-HCA59 is a potential immunodiagnostic tool for the detection of H. contortus infection during prepatent period in goats.

Egg autofluorescence and options for detecting peanut agglutinin binding for the identification of Haemonchus contortus eggs in fecal samples

Quantifying eggs from Haemonchus and other trichostrongyle genera in sheep and goat fecal samples is important for evaluating control and treatment strategies for this family of nematodes with divergent pathologies, capabilities for anthelmintic resistance and environmental susceptibilities. Unfortunately, egg morphology among most of the genera do not differ enough to support the accurate identification of these genera with standard microscopic techniques. Several studies have identified specific lectins which bind selectively to sugars located on the egg surfaces for individual genera among the trichostrongyles. To detect lectins binding to these eggs, they must be directly or indirectly bound to fluorophores, and observed with an epi-fluorescence microscope. The binding of multiple lectins to isolated eggs from a fecal sample can be simultaneously detected if fluorophores are used whose excitation and emission spectra do not overlap, and this would enable the development of a fluorescence-based diagnostic test that identifies multiple trichostrongyle genera within each sample. The present study compared the usefulness of different, commercially available detection systems for use in detecting lectin binding to trichostrongyle eggs. Comparisons were made using the detection of PNA binding to H. contortus eggs with the goal of finding three systems with color spectra that do not overlap. These evaluations included both fluorophores directly conjugated to PNA in a one-step incubation protocol and a two-step incubation protocol involving biotinylated PNA and streptavidin conjugated to different fluorophores. Autofluorescence can affect the efficiency of any fluorescence-based detection system, and significant autofluorescence was observed among the unstained H. contortus eggs with the DAPI-type fluorescence filter, but it was significantly lower with the FITC-type filter and was virtually absent with the rhodamine-type filter. This study demonstrated that all the PNA detection methods tested with H. contortus eggs generated fluorescence intensities (FIs) that were significantly above the autofluorescence generated by the eggs among the three different fluorescence filters. Fluorescence intensities from PNA directly conjugated to either the FITC or rhodamine fluorophores were not different, but the lower autofluoresence in the rhodamine-type filter will enable this fluorophore to be detected more efficiently. Use of biotinylated PNA combined with streptavidin-conjugated to synthetic fluorophores (Alexa Fluor 405, 488 and 546) significantly increased FIs over that of the directly conjugated PNA, but there were no significant differences in FIs among these three biotin-avidin conjugation fluorophores. This biotin-avidin system required two incubation steps. Doubling the concentration of PNA also provided increased FI, at least for the biotin-avidin system. Adding an additional amplification step to the biotin-avidin system involving biotinylated anti-streptavidin followed by the streptavidin-Alexa Fluor complex also provided additional fluorescence.

High-throughput identification and quantification of Haemonchus contortus in fecal samples

Haemonchus contortus are gastrointestinal nematodes of the family Trichostrongylidae that naturally infect small ruminants while grazing, posing a risk to both animal health and farm profitability. Current diagnostics depend on exacting lab techniques, including manual egg counts and larval differentiation, all of which require time, effort, and specialized technicians. The goal of this study was to facilitate and accelerate the identification and quantification of H. contortus in fecal samples through the use of fluorescein-isothiocyanate peanut-agglutinin staining in order to allow automated detection using a 96-well microplate reader. Next, the model was to be validated using samples containing unknown quantities of eggs. Automated analysis of fluorescence emission of known quantities of H. contortus eggs confirmed an almost perfect linear correlation (r = 0.9984, p < 0.0001), indicating that this new approach can satisfactorily be used to quantify H. contortus eggs on a comparative fluorescence scale. As validation, clinical samples containing an unknown quantity of H. contortus eggs were then analyzed by comparing two methods: either Wisconsin Sugar Flotation (WSF) and McMaster counting followed by manual fluorescence microscopy, or WSF coupled with automated microplate reading. Pearson analysis revealed highly significant correlation between manual and automated methods (r = 0.9999, p < 0.0001), while Bland-Altman plots demonstrated excellent agreement between the two (bias = -0.817 ± 9.94 with 95% limits of agreement from -20.31 to 18.67). Overall, these results demonstrate that high-throughput screening fluorescence detection and quantification of H. contortus eggs is both accurate and rapid.

Droplet digital polymerase chain reaction (ddPCR) as a novel method for absolute quantification of major gastrointestinal nematodes in sheep

In this paper, we present for the first time a new tool, based on Droplet Digital™ Polymerase Chain Reaction (ddPCR), for absolute quantification of key genera of gastrointestinal (GI) nematode parasites of grazing livestock. Four combinations of primers/probe sets targeting the internal transcribed spacer region 2 (ITS2) of the ribosomal RNA gene array were designed using the Primer3 software, following in silico analysis of nucleotide sequences from nematodes of interest downloaded from common databases. The amplified regions include both a universal region for detection of any strongylid gastrointestinal parasite and three different genus specific regions, making it possible to differentiate between the most important GI nematodes of sheep in Sweden: Haemonchus, Teladorsagia and Trichostrongylus. Analysis of samples containing serial dilutions and different mixtures of genomic DNA extracted from different species of adult worms proved useful in assessment of different threshold settings with the QuantaSoft software. Analysis of template DNA from these worms indicated that ddPCR is a viable choice for detection and absolute quantification of the different genera and also in samples with multiple species. Interpretation of the ddPCR results was straightforward and choice of analytical approach had little influence on the final results. Thus, the results obtained in the different analytical approaches seemed to be robust and the concentrations determined were uniform. Furthermore, the linear range of the Haemonchus ddPCR assay was similar to that of real-time PCR (qPCR). Taken together, our data confirm the suitability of ddPCR for detection and absolute quantification of three major sheep pathogens when tested on larval cultures from pooled ovine faeces. The results also indicate that ddPCR can be a useful complement to applications based on conventional egg counting methods such as the faecal egg reduction test (FECRT).