Caecocaecal and caecocolic intussusceptions associated with larval cyathostomosis in four young horses

BEVA primary care clinical guidelines: Equine parasite control

BACKGROUND

There is a lack of consensus on how best to balance our need to minimise the risk of parasite-associated disease in the individual horse, with the need to limit the use of anthelmintics in the population to preserve their efficacy through delaying further development of resistance.

OBJECTIVES

To develop evidence-based guidelines utilising a modified GRADE framework.

METHODS

A panel of veterinary scientists with relevant expertise and experience was convened. Relevant research questions were identified and developed with associated search terms being defined. Evidence in the veterinary literature was evaluated using the GRADE evidence-to-decision framework. Literature searches were performed utilising CAB abstracts and PubMed. Where there was insufficient evidence to answer the research question the panel developed practical guidance based on their collective knowledge and experience.

RESULTS

Search results are presented, and recommendation or practical guidance were made in response to 37 clinically relevant questions relating to the use of anthelmintics in horses.

MAIN LIMITATIONS

There was insufficient evidence to answer many of the questions with any degree of certainty and practical guidance frequently had to be based upon extrapolation of relevant information and the panel members' collective experience and opinions.

CONCLUSIONS

Equine parasite control practices and current recommendations have a weak evidence base. These guidelines highlight changes in equine parasite control that should be considered to reduce the threat of parasite-associated disease and delay the development of further anthelmintic resistance.

Genome-wide association study in thoroughbred horses naturally infected with cyathostomins

Cyathostomins are considered one of the most important parasites of horses. A group of horses within a herd can be responsible for eliminating the majority of parasite eggs. This phenotype might be explained by genetic factors. This study aimed to identify genomic regions associated with fecal egg count (FEC) and hematological parameters by performing a genomic-wide association study (GWAS) in Thoroughbred horses naturally infected with cyathostomins. Packed cell volume (PCV), differential leukocyte, and FEC were determined from 90 horses. All animals were genotyped using the Illumina Equine 70 K BeadChip panel containing 65,157 SNP markers. The five genomic windows that have explained the highest percentage of the additive genetic variance of a specific trait (top 5) were further explored to identify candidate genes. A total of 33, 21, 30, 21, and 19 genes were identified for FEC, PCV, eosinophils, neutrophils, and lymphocyte count, respectively. The top 5 marker regions explained 2.86, 2.56, 2.73, 2.33, and 2.37% of the additive genetic variation of FEC, PCV, eosinophils, neutrophils, and lymphocytes count, respectively. This is the first study correlating phenotypic horse health traits to GWAS analysis, which may be used for animal breeding activities, reducing losses due to parasite infections.

The Use of Innovative Diagnostics to Inform Sustainable Control of Equine Helminth Infections

Helminths are commonly found in grazing equids, with cyathostomin nematodes and the cestode Anoplocephala perfoliata being the most prevalent. Most horses harbour low burdens of these parasites and do not develop signs of infection; however, in a small number of animals, high burdens can accumulate and cause disease. Cyathostomins are associated with a syndrome known as larval cyathostominosis. This occurs when large numbers of larvae emerge from the large intestinal wall. This disease has a case fatality rate of up to 50%. A. perfoliata infection has been associated with various types of colic, with burdens of >20 worms associated with pathogenicity. Anthelmintic resistance is a serious problem in cyathostomins and is emerging in A. perfoliata. Control methods that reduce reliance on anthelmintics now need to be applied, especially as no new dewormer compounds are on the horizon. Sustainable control methods must employ diagnostics to identify horses that require treatment. Coprological tests (faecal egg counts, FECs) have been used for several decades to inform treatment decisions to reduce helminth egg shedding. These tests cannot be used to assess host burdens as FECs do not correlate with cyathostomin or A. perfoliata burdens. In the last decade, new tests have become available that measure parasite-specific antibodies, the levels of which have been shown to correlate with parasite burden. These tests measure antigen-specific IgG(T) and are available in serum (cyathostomin, A. perfoliata) or saliva (A. perfoliata) formats. Tests for other helminths have been developed as research tools and need to be translated to support equine clinicians in practice. A key element of sustainable control strategies is that diagnostics must be used in combination with management approaches to reduce environmental transmission of helminths; this will help limit the proportion of horses harbouring parasite burdens that need to be targeted by treatment. This manuscript provides a review of the development, performance and general utility of various diagnostic methods for informing equine helminth management decisions.

Anthelmintic efficacy in strongyles of horses in Northern Minas Gerais, Brazil

The intensive use of anthelmintics has resulted in resistant parasite populations in horses. The objective of this trial was to evaluate the anthelmintic efficacies of the anthelmintics fenbendazole, ivermectin and abamectin in 24 horse farms in Northern Minas Gerais. Egg counts per gram of faeces (EPG) were performed individually in 619 animals. Animals presenting EPG counts greater than or equal to 150 were used in the tests on faecal egg count reduction (FECR), totalling 436 equines. These animals received the anthelmintics, fenbendazole, ivermectin, and abamectin. Faeces were collected 14 days after the administration of anthelmintics to perform the EPG. Pre- and post-treatment EPG counts were used to calculate the FECR for each anthelmintic group, and faecal culture was used to identificy of the strongyles. The resistance status was evaluated based on the FECR and LCL95%. Fenbendazole was effective in 11 (45.8%) of the horse farms. Ivermectin was effective in 17 (77.3%) and abamectin in 17 (74%) of the farms; side-resistance was detected in 3 (12.5%) of the farms. Intestinal strongyle resistance to anthelmintics was observed in 14 (58.3%) of the farms. Cyathostomin larvae were found in 100% of the farms, Strongylus vulgaris in 13 (54.2%), and S. equinus in 3 (12.5%). Only cyathostomins larvae were detected post-treatment with ivermectin and abamectin.

Prevalence of anthelmintic resistant cyathostomins in Prince Edward Island, Canada

Cyathostomins are the most common parasites of adult horses worldwide. Currently, the three classes of anthelmintics used to treat cyathostomin infections includes benzimidazoles, pyrimidines and macrocyclic lactones. However, due to widespread overuse, cyathostomins have developed varying degrees of resistance to all classes of anthelmintics. Fecal egg count reduction tests (FECRT) are currently used to determine the presence of anthelmintic resistance (AR), while egg reappearance periods (ERP) are used to investigate early macrocyclic lactone resistance. The objective of this study was to investigate the prevalence of cyathostomin pyrantel pamoate and ivermectin resistance, and to determine ERP at Prince Edward Island (PEI), Canada horse farms. In addition, fecal cultures and larval identification were performed to evaluate the prevalence of small and large strongyle egg shedding in PEI. Fecal egg counts (FEC) were performed on 270 horses on 14 horse farms across PEI. Horses with≥ 200 eggs per gram (EPG) met the inclusion criteria and were enrolled in the study (n = 101). The median (range) horses per farm was 7.5 (4-11) and 6.0 (4-8) for pyrantel pamoate and ivermectin groups, respectively. Horses were initially treated with 6.6 mg/kg of pyrantel pamoate orally (n = 101). Fecal egg counts were conducted every two weeks for 8 weeks post treatment. Once individual FEC were ≥ 200 EPG, horses were dewormed with 0.2 mg/kg of ivermectin orally (n = 80), and FEC were performed every 2-3 weeks for seven weeks. In this study the ERP was defined as the week the mean FECR were 10% below the initial mean two-week post treatment FECR. Fecal egg count reduction tests and ERP were used to evaluate the efficacy of each anthelmintic. Fecal culture was performed to confirm the shedding of cyathostomin eggs. Fecal egg count reduction tests detected pyrantel pamoate resistance on 5/14 farms. No signs of ivermectin AR were detected, while reappearance of eggs occurred at 4-6 weeks and 7-9 weeks for pyrantel pamoate and ivermectin, respectively. Fecal culture detected large strongyles on 5/14 farms, which accounted for 0.3% of strongyle type eggs cultured. The prevalence of Strongylus vulgaris among individual horses in this study was 2.8% and was detected on 2/14 farms. These findings will allow us to educate owners and veterinarians on appropriate anthelmintic protocols in PEI and can be used as a baseline for continued monitoring of ERP and anthelmintic resistance in this region.

Outbreak of acute larval cyathostominosis - A "perfect storm" of inflammation and dysbiosis

Background

Cyathostomins are prevalent and pathogenic intestinal helminths of horses, causing acute and chronic disease, including acute larval cyathostominosis, which has a mortality rate of 50%. Factors determining individual susceptibility to acute larval cyathostominosis are unknown. Investigation of these factors could lead to novel treatment and prevention strategies.

Objectives

To investigate clinicopathological and faecal microbiota changes associated with disease in individual horses in an acute larval cyathostominosis outbreak.

Study design

Case series.

Methods

The study population was a herd of 23 mixed breed horses in Ireland. The outbreak occurred in November 2018. Fourteen horses were clinically affected. Clinical status was monitored and recorded. Blood and faecal sampling allowed clinicopathological, faecal 16s rRNA gene sequencing and faecal egg count analyses.

Results

Two horses were euthanised, whilst 12 recovered. Common clinical signs included loose faecal consistency, weight loss and pyrexia. Consistent clinicopathological findings were borderline anaemia, leucocytosis, thrombocytosis, hyperfibrinogenaemia, hyperglobulinaemia and a reverse A: G ratio. Decreased alpha‐diversity of the faecal microbiota and greater relative abundance of the genus Streptococcus, class Bacilli, order Lactobacillales and family Streptococcaceae, and family Prevotelleceae was found in clinically affected horses compared to their clinically normal cohorts. An increase in obligate fibrolytic bacteria was seen in the clinically normal group compared to the clinical group. Histopathological findings of the colon and caecum revealed a severe necrotising typhlocolitis associated with cyathostomin larvae and bacterial overgrowth in the mucosa of the large intestine.

Main limitations

The study population in this outbreak is small. There are several confounding factors limiting this to a descriptive case series. Faecal microbiota has been shown to reflect the large intestinal microbiota but do not represent changes directly.

Conclusions

These findings suggest that acute larval cyathostominosis is associated with dysbiosis of the gut microbiota as well as the inflammatory stimulus of numerous emerging larvae leading to structural and functional pathology of the large intestine.

Cyathostomine egg reappearance period following ivermectin treatment in a cohort of UK Thoroughbreds

BACKGROUND

In spite of the emergence of populations of drug-resistant cyathostomines worldwide, little is known of parasite species responsible for 'early egg shedding' in cohorts of horses subjected to treatment with widely used anthelmintics, e.g. ivermectin (IVM). In this study, we determined the cyathostomine egg reappearance period (ERP) after IVM treatment in a cohort of yearlings from a large Thoroughbred (TB) stud farm in the United Kingdom, and identified species of cyathostomines with reduced ERP using a combination of fundamental parasitology techniques coupled with advanced molecular tools.

METHODS

Individual faecal samples were collected from TB yearlings with cyathostomine infection prior to IVM treatment, as well as at 14, 21, 28, 35, 42 and 49 days post-treatment. Faecal egg counts (FEC) were performed for each individual sample for determination of ERPs. In addition, individual larval cultures were performed and representative numbers of third-stage larvae (L3s) harvested from each culture were subjected to molecular species identification via PCR-Reverse Line Blot (RLB).

RESULTS

Prior to IVM treatment, 11 cyathostomine species were detected in faecal samples from TB horses enrolled in this study, i.e. Cyathostomum catinatum, Cylicostephanus longibursatus, Cylicostephanus goldi, Cylicocyclus nassatus, Cylicostephanus calicatus, Cyathostomum pateratum, Cylicocyclus radiatus, Paraposteriostomum mettami, Coronocyclus labratus, Cylicocyclus insigne and Cylicocyclus radiatus variant A. Of these, eggs of Cya. catinatum, Cys. longibursatus, Cyc. nassatus and Cyc. radiatus could be detected at 28 days post-treatment, while from day 42 onwards, cyathostomine species composition reflected data obtained pre-IVM treatment, with the exception of eggs of Cor. labratus and Cyc. insigne which could no longer be detected post-IVM administration.

CONCLUSIONS

This study provides valuable data on the occurrence of IVM-resistance in cyathostomines in the UK. Nevertheless, further investigations are needed to shed light on the prevalence and incidence of drug-resistance in this country, as well as other areas of the world where equine trade is substantial.

Searching for ivermectin resistance in a Strongylidae population of horses stabled in Poland

BACKGROUND

There are no available studies describing the possible resistance of strongyles to ivermectin in horses in Poland. One hundred seventy three horses from nine stud farms from South-Western Poland were studied. The effectiveness of ivermectin was studied on the 14th day after ivermectin administration using the fecal egg count reduction test, and a long-term observation of the egg reappearance period was carried out. The fecal study was carried out using a modified McMaster method, which typically detects 20 eggs per gram of stool. The results were subjected to statistical analysis that enabled quantification of the eggs in the stool samples.

RESULTS

The study revealed high efficacy of ivermectin on the 14th day after administration without a shortening of the egg reappearance period.

CONCLUSION

The results indicate that strongyles resistance to ivermectin in Poland is not a serious problem.

Larval cyathostominosis in a working donkey

Parasitic infections are one of the most common factors that threaten the health and working performance of donkeys. One of the life threatening parasites is the small strongyles that encyst or burrow into the large intestine and their larvae can initiate severe damage in the lining of the intestine. A 6 years old female donkey with clinical signs of diarrhea and emaciation was necropsied and gross examination of gastro-intestinal tract revealed thin-walled, hyperemic and hemorrhagic cecum. Multifocal petechial hemorrhages were particularly prominent in the submucosa of cecum. Parasitological examination revealed two cyathostomin species included Cylicocyclus elongatus and Cyathostomum pathratum. At microscopic examination, cross sections of cyathostomins larvae associated with parasitic granuloma were observed in the submucosa of cecum. The lesions were associated with non-suppurative enteritis with infiltration of eosinophils, plasma cells, lymphocytes and macrophages in the intestinal mucosa, submucosa and lamina propria.

Influência do parasitismo intestinal sobre os parâmetros hematológicos e de líquido peritoneal em equinos de tração

O objetivo do presente estudo foi avaliar a influência do parasitismo intestinal crônico sobre parâmetros hematológicos e de líquido peritoneal por meio da comparação dessas características em equinos naturalmente parasitados e após administração de anti-helmíntico. Utilizaram-se 21 cavalos de tração urbana, entre dois e 19 anos, sem raça definida e com resultado de exame parasitológico superior a 300 ovos por grama de fezes. Foi realizada avaliação física e coleta de fezes, de líquido peritoneal e de sangue em dois momentos do experimento (D0 e D15), sendo efetuado tratamento antiparasitário no D0. No fluido peritoneal foram avaliadas características físicas, bioquímicas, bem como contagem de células nucleadas (CTCN) e diferenciação celular. No sangue foram determinados valores eritrocitários, leucocitários, proteínas plasmáticas totais, glicose e fibrinogênio plasmáticos, além de fosfatase alcalina (FA) sérica. A análise dos parâmetros avaliados não demonstrou diferença significativa entre animais parasitados e após administração de anti-helmíntico, exceto para valores de CTCN, contagem de neutrófilos segmentados e grau de turbidez do líquido peritoneal. As médias se mantiveram dentro dos intervalos de referência, com exceção da CTCN do líquido peritoneal no D0. No líquido peritoneal, houve predomínio de neutrófilos segmentados, seguidos por macrófagos, linfócitos e eosinófilos em ambos os momentos de avaliação. Observaram-se tendência do quadro eritrocitário em manter-se próximo aos limites inferiores e leve leucocitose no D0. A infecção parasitária nos animais estudados foi predominantemente moderada, o que oferece poucos riscos clínicos. Nessas condições, pode-se afirmar que a CTCN, a contagem absoluta de neutrófilos segmentados e o grau de turbidez do líquido peritoneal são influenciados e podem ser considerados ferramentas diagnósticas e prognósticas úteis nas parasitoses intestinais crônicas.

The expression and activity of 5-LOX in the large intestine of horses harbouring encysted cyathostomin larvae

Leukotrienes are products of the arachidonic acid metabolism and act as potent inflammatory mediators modulating the immune response and various physiological processes. This study evaluated the expression and activity of 5-lipoxygenase (5-LOX), the enzyme that catalyzes the first two steps in the biosynthesis of leukotrienes, in horses infected by larval cyathostomins. Tissue samples from dorsal and ventral colon, and from the cecum were collected from 16 horses slaughtered for human consumption. Samples were analyzed to estimate the burdens of encysted cyathostomin larvae and adult luminal stages, and then processed for the evaluation of biochemical parameters. No significant differences were found in the protein expression and enzymatic activity of 5-LOX between animals harbouring only adult parasites and negative horses. The protein expression and enzyme activity of 5-LOX were significantly higher in horses harbouring encysted larvae in comparison with horses free of encysted larvae. Although preliminary, these results indicate that 5-LOX is an important mediator in the course of horse cyathostominosis and further studies are warranted to unveil the possible role this enzyme plays in the pathogenesis of horse cyathostominosis, and its potential as a diagnostic marker.

Determination of genomic DNA sequences for beta-tubulin isotype 1 from multiple species of cyathostomin and detection of resistance alleles in third-stage larvae from horses with naturally acquired infections

Background

Genetic resistance against benzimidazole (BZ) anthelmintics is widespread in cyathostomins, the commonest group of intestinal parasitic nematodes of horses. Studies of BZ-resistant nematodes of sheep, particularly Haemonchus contortus, have indicated that an anthelmintic resistance-conferring T/A polymorphism, encoding an F (phenylalanine) to Y (tyrosine) substitution, in beta-tubulin isotype 1 is present at two loci, codons 167 and 200 (F167Y, F200Y). Recent studies using complementary (c) DNA derived from BZ-susceptible and -resistant cyathostomins identified statistical differences in the frequency of the BZ-resistant A allele at these loci. However, the lack of high-throughput genomic DNA-based detection of polymorphisms limits the study of eggs or larvae from field isolates. In the present study, we report genomic DNA sequences for beta-tubulin isotype 1 from multiple cyathostomin species, thus facilitating the development of pyrosequencing assays to genetically characterize third-stage larvae (L3s) of cyathostomins from mixed-species field isolates.

Results

Sequence analysis of the beta-tubulin isotype 1 gene in a common species, Cylicocyclus nassatus, indicates a revised genomic structure to published data, revealing that codons 167 and 200 are located on separate exons. A consensus sequence was generated from 91 and 76 individual cyathostomins for the regions spanning codons 167 and 200, respectively. A multi-species genomic DNA-based assay was established to directly pyrosequence individual L3 from field samples of unknown species and BZ sensitivity in a 96-well plate. In this format, the assay to detect F167Y gave a 50-90% success rate. The optimisation of the assay at codon 200 is currently underway. Subsequently, the genotype at F167Y was determined for 241 L3s, collected prior to and after BZ treatment. These results demonstrated a reduction in the heterozygous genotype, TTC/TAC, and an increase in the homozygous resistant genotype TAC/TAC in post-treatment samples. However, the differences in allele frequencies determined before and after BZ treatment were not statistically significant.

Conclusion

Extensive genomic DNA sequence, spanning codons 167 and 200 of the beta-tubulin isotype 1 gene, was generated from multiple cyathostomin species. The data facilitated the development of a pyrosequencing assay, capable of detecting the genotype of individual cyathostomin L3s derived from mixed-species field samples. Differences in codon 167 allele frequencies were observed in L3s isolated pre- and post-BZ treatment.

New method for simultaneous species-specific identification of equine strongyles (nematoda, strongylida) by reverse line blot hybridization

The ability of a reverse line blot (RLB) assay to identify 13 common species of equine small strongyles (cyathostomins) and to discriminate them from three Strongylus spp. (large strongyles) was demonstrated. The assay relied on the specific hybridization of PCR-amplified intergenic spacer DNA fragments of the nuclear ribosomal DNA to membrane-bound species-specific probes. All cyathostomins examined were unequivocally identified and simultaneously discriminated from each other and from three large strongyles (Strongylus edentatus, Strongylus equinus, and Strongylus vulgaris). This assay will enable the accurate and rapid identification of equine cyathostomins irrespective of their life cycle stage, opening important avenues for a better understanding of their biology and epidemiology and of the pathogenesis of cyathostomin-associated disease. In particular, this RLB method promises to be a powerful diagnostic tool to determine the roles of individual species in the pathogenesis of mixed infections and to elucidate some aspects of cyathostominosis. Also, it could represent a basic step toward the development of a rapid and simple molecular test for the early detection of drug-resistant genotypes of horse strongyle species.

Epidemiological clues to preventing colic

Colic remains a significant problem in the horse in terms of welfare and economics; in some equine populations it is the single most common cause of death. Many causes of colic are cited in the equestrian and veterinary literature but little scientific evidence exists to substantiate these theories. Recent epidemiological investigations have confirmed that colic is complex and multi-factorial in nature. Studies have identified a number of factors that are associated with increased risk of colic including parasite burden, certain feed types, recent change in feeding practices, stabling, lack of access to pasture and water, increasing exercise and transport. These findings are reviewed together with examples of management practices that may be altered to reduce the incidence of specific types of colic. This is an opinionated, not a systematic, review focusing on those areas that are considered most relevant to the practitioner.

Molecular diagnosis and equine parasitology

The future implementation of improved and sustainable control strategies for the major equine parasites will be dependent on a greater insight into their basic biology, pathogenicity and epidemiology together with an enhanced ability for accurate diagnosis. This paper will provide a review of the current molecular methods under development for the detection of equine parasites and their application to current scientific questions. In particular, the strongyles are recognised as important pathogens of horses and recent advances made in the study of this parasitic group at the single species level will be addressed. The ribosomal (r)DNA region of the parasite genome has been employed to distinguish between closely related species. Molecular probes designed to this target region were used in combination with PCR technology to allow the identification of individual species within mixed infections. They have been applied to all parasite stages to look at the role of individual species in natural infection, disease and drug resistance. Similar techniques have been developed to detect other equine parasites and these will also be discussed. Further opportunities for employing existing techniques and the need for new diagnostic tools will be highlighted.

Isolation and characterisation of a beta tubulin isotype 2 gene from two species of cyathostomin

This study describes the isolation and characterisation of beta tubulin isotype 2 cDNA sequences from two common species of cyathostomin, Cylicocyclus nassatus and Cyathostomum catinatum. The full-length cDNAs for these species were 1709 and 1753 bp in length, respectively, including 1350 bp of sequence inferred to encode 450 amino acids of peptide sequence. They had greatest identity with previously characterised isotype 2 sequences from Trichostrongylus colubriformis, Cooperia oncophora and Haemonchus contortus (96% for C. nassatus and 95% for C. catinatum), and grouped together with these sequences in phylogenetic analysis. Both cyathostomin beta tubulin isotype 2 sequences contained the isotype-specific carboxyl terminal region described previously in other nematode species. Alignment with beta tubulin isotype 1 proteins from other trichostrongyloids, indicated 95 and 94% identity for the isotype 2 sequences of C. nassatus and C. catinatum, respectively. This comparison revealed 14 isotype-specific amino acid substitutions. Also, 2605 bp of beta tubulin isotype 2 genomic DNA sequence were isolated from C. nassatus. Comparison with the previously published isotype 1 gene of C. nassatus indicated differences in genomic organisation between the two isotypes. Reverse transcriptase (RT)-polymerase chain reaction analysis revealed constitutive temporal expression of beta tubulin isotype 1, whilst isotype 2 appeared to be developmentally expressed, with transcripts detected only in RNA derived from adult parasites.

Seasonal abundance of equine strongyles (Nematoda: Strongylidae) in the State of Rio de Janeiro, Brazil

The seasonal abundance of lumenal and larval forms of equine strongyles in the State of Rio de Janeiro, Brazil was evaluated. Thirty horses referred to the Federal Rural University of Rio de Janeiro were necropsied and their gastrointestinal tracts were separated into stomach, small intestine, cecum, ventral colon, dorsal colon and rectum. Two aliquots of 5% of the content were collected and examined for the presence of small strongyles and the rest of the content was examined for the presence of large strongyles. The mesenteric artery, liver, pancreas and peritoneum were examined for the presence of strongyle larvae. The mucosa of intestine segments was cut into parts of equal length, and each one was examined by the mural transillumination technique. Higher abundances of larvae of Strongylus equinus (P<0.10) and of adults Strongylus vulgaris (P<0.05) were observed during the dry season. Encysted cyathostome larvae had the highest abundance during the rainy season (P<0.02).

Purification and analyses of the specificity of two putative diagnostic antigens for larval cyathostomin infection in horses

Cyathostomins are important equine gastrointestinal parasites. Mass emergence of mucosal stage larvae causes a potentially fatal colitis. Mucosal stages are undetectable non-invasively. An assay that would estimate mucosal larval stage infection would greatly assist in treatment, control and prognosis. Previously, we identified two putative diagnostic antigens (20 and 25 kDa) in somatic larval preparations. Here, we describe their purification and antigen-specific IgG(T) responses to them. Western blots confirmed the purity of the antigens and showed that epitopes in the 20 kDa complex were specific to larval cyathostomins. No cross-reactive antigens appeared to be present in Parascaris equorum or Strongyloides westeri species. Low levels of cross-reactivity were observed in Strongylus edentatus and Strongylus vulgaris species. Use of purified antigens greatly reduced background binding in equine sera. These results indicate that both antigen complexes may be of use in a diagnostic assay.

A PCR–ELISA for the identification of cyathostomin fourth-stage larvae from clinical cases of larval cyathostominosis

We report the use of six oligoprobes designed from intergenic spacer region sequences to identify fourth-stage larvae (L4) of the tribe Cyathostominae. Oligoprobes were designed for identification of the following species: Cylicocyclus ashworthi, Cylicocyclus nassatus, Cylicocyclus insigne, Cyathostomum catinatum, Cylicostephanus goldi, and Cylicostephanus longibursatus. A seventh probe was designed as a positive control to identify all these members of the Cyathostominae. The intergenic spacer region was amplified by PCR using conserved primers. Initially, three oligoprobes were used in Southern blot analysis. To facilitate high-throughput identification, these and a further four oligoprobes were developed for use in a PCR-ELISA. All probes were validated for their ability to detect cyathostomin PCR products in the PCR-ELISA, using DNA from morphologically identified adult parasites. Initially, 712 L4 were isolated from the diarrhoeic faeces from horses (n=17) with clinical larval cyathostominosis. PCR products from 522 of these L4 were subjected to analysis, with 413 L4 being identified as one of the aforementioned species. With reference to individual species analysis, 28.5% of the 522 L4 were identified as C. longibursatus, 25.7% as C. nassatus, 15.9% as C. ashworthi, 7.3% as C. goldi and 1.7% as C. catinatum. No L4 were identified as being C. insigne species. When L4 within faeces from individual horses were compared, no sample was found to comprise parasites of one species. The least number of species identified in a single sample was two. This study suggests that clinical larval cyathostominosis is predominantly caused by mixed-species infections.