Larval Cyathostominosis Research Articles

Larval cyathostominosis in horses

Small strongyles are the most common parasites of horses, capable of surviving different climate conditions. Though the infection is usually asymptomatic, young horses are considered more prone to developing a parasitic syndrome called larval cyathostominosis. In most cases, gastrointestinal symptoms are most prevalent. Treatment is based on the use of fenbendazole and moxidectin. Diagnosis is difficult and serological methods are still under development. The main prevention methods include regular coprological testing, pasture rotation, co-grazing with ruminants, and regular removal of faeces from the pasture.

Case of larval cyathostominosis in a young stallion in Croatia

Case of larval cyathostominosis in a young stallion in Croatia

Demonstration of reduced efficacy against cyathostomins without change in species composition after pyrantel embonate treatment in Swedish equine establishments

Consisting of approximately 50 different species, the cyathostomin parasites are ubiquitous in grazing horses. Co-infection with several species is common, and large burdens can cause the fatal disease of larval cyathostominosis. Due to intense anthelmintic drug use, cyathostomin resistance has developed to all available anthelmintic drug groups. Resistance to the anthelmintic drug pyrantel (PYR) has been documented in over 90% of studies published over the past two decades. In Sweden, a study performed in the early 2000s only confirmed resistance in 4.5% of farms. Further, prescription-only administration of equine anthelmintic drugs was enforced in Sweden in 2007. However, it is unknown if this conservative drug use has maintained PYR efficacy in cyathostomins. The aim of the present study was to investigate the effect of PYR on cyathostomin infection in Sweden using fecal egg count reduction tests (FECRTs). Further, the effect of PYR treatment on cyathostomin species composition was studied using metabarcoding.Sixteen farms with at least six horses excreting a minimum of 100 eggs per gram feces were included. Using the current World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines, PYR resistance was demonstrated in nine of farms, with seven farms showing full susceptibility. Farms with low biosecurity measures had significantly lower efficacy of PYR treatment. The most common cyathostomin species were Cylicocyclus nassatus, Cyathostomum catinatum, Cylicostephanus longibursatus, Cys. calicatus, Cys. goldi, Cys. minutus, Coronocyclus coronatus and Cya. pateratum, accounting for 97% of all sequence reads prior to treatment. Of these, Cyc. nassatus and Cya. catinatum had the highest occurrence, accounting for 68% of all sequence reads prior to PYR treatment. Treatment did not significantly affect the species composition. The results highlight the importance of drug efficacy testing when using PYR to treat cyathostomin infection, even when selective anthelmintic treatment and thus low treatment intensity, is used on the farm.

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.

Validation of a serum ELISA test for cyathostomin infection in equines

Cyathostomins are ubiquitous equine nematodes. Infection can result in larval cyathostominosis due to mass larval emergence. Although faecal egg count (FEC) tests provide estimates of egg shedding, these correlate poorly with burden and provide no information on mucosal/luminal larvae. Previous studies describe a serum IgG(T)-based ELISA (CT3) that exhibits utility for detection of mucosal/luminal cyathostomins. Here, this ELISA is optimised/validated for commercial application using sera from horses for which burden data were available. Optimisation included addition of total IgG-based calibrators to provide standard curves for quantification of antigen-specific IgG(T) used to generate a CT3-specific ‘serum score’ for each horse. Validation dataset results were then used to assess the optimised test’s performance and select serum score cut-off values for diagnosis of burdens above 1000, 5000 and 10,000 cyathostomins. The test demonstrated excellent performance (Receiver Operating Characteristic Area Under the Curve values >0.9) in diagnosing infection, with >90% sensitivity and >70% specificity at the selected serum score cut-off values. CT3-specific serum IgG(T) profiles in equines in different settings were assessed to provide information for commercial test use. These studies demonstrated maternal transfer of CT3-specific IgG(T) in colostrum to newborns, levels of which declined before increasing as foals consumed contaminated pasture. Studies in geographically distinct populations demonstrated that the proportion of horses that reported as test positive at a 14.37 CT3 serum score (1000-cyathostomin threshold) was associated with parasite transmission risk. Based on the results, inclusion criteria for commercial use were developed. Logistic regression models were developed to predict probabilities that burdens of individuals are above defined thresholds based on the reported serum score. The models performed at a similar level to the serum score cut-off approach. In conclusion, the CT3 test provides an option for veterinarians to obtain evidence of low cyathostomin burdens that do not require anthelmintic treatment and to support diagnosis of infection.

Larval cyathostominosis: Clinicopathological data and treatment outcomes of 38 hospitalised horses (2009–2020)

SummaryBackgroundThere is limited evidence regarding the treatment and outcomes of larval cyathostominosis.ObjectivesTo describe the presentation, treatment and outcomes of horses with larval cyathostominosis in two equine hospitals.Study designRetrospective, multicentred cohort study.MethodsClinical records were reviewed (2009–2020). Inclusion criteria included a diagnosis of larval cyathostominosis (determined by faecal assessment and/or post‐mortem examination). Data were assessed for normality. Descriptive analysis was performed for frequency results and central tendencies. Statistical analysis between survivors and nonsurvivors was determined by Chi‐square/Fisher's exact test for categorical variables, and Student's t‐test/Mann–Whitney for continuous variables.ResultsOf 38 cases, 21 (55%) were nonsurvivors (3/38 dead on arrival). Nonsurvivors died by 2.9 days ± 2.4. Tachycardia (mean 61 beats/min ± 14), leucocytosis (mean 17.1 × 109/L ± 9.1), neutrophilia (mean 14.1 × 109/L ± 8.5), hypoalbuminaemia (mean 21.6 g/L ± 6.0), hyperfibrinogenaemia (mean 7.4 g/L ± 2.6) and elevated serum amyloid A (SAA) (median 315.0 mg/L, interquartile range [IQR] 117.0–1460.0) were consistent findings. Faecal shedding of Salmonella spp. occurred in four cases. The mean last recorded albumin was 18.6 g/L ± 4.5 and total protein (TP) 52.3 g/L ± 13.6. Crystalloids were administered in 25/35, synthetic colloids in 5/35 and plasma in 17/35 cases. Anthelmintic treatment was administered in 25/35 cases, of which 22 also received corticosteroids. Recumbency prior to admission (p = 0.037) and administration of isotonic fluid therapy (p = 0.027) were associated with nonsurvival. From peripheral blood analysis, lower TP (p = 0.006) and higher SAA (p = 0.050) concentrations at admission as well as lower last recorded TP (p = 0.002) and lower last recorded albumin concentrations (p = 0.028) were associated with nonsurvival.Main limitationsResults may not be applicable to other populations.ConclusionsReferred cases of larval cyathostominosis have a low survival rate. Several variables are associated with reduced survival: history of recumbency, isotonic fluid therapy, elevated SAA at admission, low TP at admission, low last recorded TP and low last recorded albumin.

Colitis associated with larval cyathostominosis: Clinical presentation and treatment outcomes of horses (2009–2020)

Colitis associated with larval cyathostominosis: Clinical presentation and treatment outcomes of horses (2009–2020)

Precision and spatial variation of cyathostomin mucosal larval counts

Cyathostomins are pervasive parasites of equids across the world. Larval stages encyst in the mucosa of the cecum, ventral and dorsal colon and can induce an inflammatory response leading to larval cyathostominosis, a life-threatening generalized typhlocolitis. Mucosal digestion is the only gold standard procedure for identifying and quantifying all larval stages. There is a lack of standardization of this technique and several aspects are ambiguous, such as precision of the method and the possibility of spatial variation of mucosal larval counts. The aim of this study was to estimate precision for enumeration of early third stage larvae (EL3) and late third stage/fourth stage (LL3/L4) larvae and investigate spatial variation of encysted counts within large intestinal organs. Six naturally infected and untreated horses aged 2–5 years were euthanized as part of an anthelmintic efficacy study, and the cecum (Cec), ventral colon (VC) and dorsal colon (DC) were collected. Each organ was rinsed, weighed, and visually separated into 3 equally sized sections. Two 5% tissue samples were collected from each section, a total of six replicates per organ. The mucosae were digested, and 2% examined under the microscope for presence of EL3 and LL3/L4 stage larvae. Overall, 59 % of the harvested larvae were EL3s, and 41 % were LL3/L4s. The ventral colons represented 45 % of the total organ weight, and contributed 37 and 41 % of the EL3s and LL3/L4s harvested, respectively. The Cec, representing only 27 % of the weight contributed 23 % of EL3s and 47 % of LL3/L4s. The DC represented 28 % of the total organ weight, and 28 % and 12 % of the total EL3s and LL3/L4s, respectively. Coefficients of variation varied from 33 to 183 % for EL3 counts and 38–245% for LL3/L4 counts. There were no statistically significant associations between EL3 counts and either organ or location. For LL3/L4 counts there were no statistically significant differences between the three locations within organs (p = 0.1166), but the DC had significantly lower counts than the other two organs (p < 0.0001). Increasing the number of mucosal replicates from each organ improved estimation, but required a considerably increased workload. In conclusion, mucosal larval cyathostomin counts are highly variable, complicating their use for treatment efficacy estimation.

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

BackgroundCyathostomins 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.ObjectivesTo investigate clinicopathological and faecal microbiota changes associated with disease in individual horses in an acute larval cyathostominosis outbreak.Study designCase series.MethodsThe 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.ResultsTwo 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 limitationsThe 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.ConclusionsThese 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.

Encysted cyathostomin larval counts: Mucosal digestion revisited

Cyathostomins are pervasive equine parasites in horses across the world, and larval stages are known to cause the deadly disease larval cyathostominosis. The mucosal digestion technique is widely used for enumeration of encysted larval stages. Previous studies have investigated the spatial variation of encysted larvae, however current protocols lack a description of a standardized area from which to take the tissue sample. This study sought to evaluate spatial variation in encysted cyathostomin larval counts among the large intestinal organs and their subsections. Following humane euthanasia, ceca, ventral, and dorsal colons were harvested from 8 foals (aged 4–8 months) raised in an anthelmintic naïve parasitology research herd. Each organ was weighed and separated into 3 equal sections by length: the orad, intermediate, and aborad portions. From each of those sections, two 5% weight tissue samples were collected and digested to quantify the early third stage larvae (EL3) and late third stage larvae/fourth stage larvae (LL3/L4). A mixed model statistical analysis was carried out to evaluate for differences of larval counts among the different organs, sections, and the interaction term between the organs and sections. There were significant differences among organs (P < 0.0001), with the ceca having higher counts than the ventral and dorsal colons. However, there were no significant differences among the three defined organ sections (P = 0.1076). Coefficients of variation (CV) were all calculated to be greater than 1, suggesting a high level of variability among the samples; the least amount of variation can be found in the cecal data with a CV of 1.4024 compared with the ventral colon’s 1.529845 and dorsal colon’s 3.339135 within the respective organ. The following sections had the highest mean counts of encysted larvae: intermediate cecum, orad ventral colon, and aborad dorsal colon. Though only a portion of the results were significant, trends were observed and these should be investigated further in future studies and potentially employed in larvicidal efficacy evaluations.

Removal of adult cyathostomins alters faecal microbiota and promotes an inflammatory phenotype in horses

The interactions between parasitic helminths and gut microbiota are considered to be an important, although as yet incompletely understood, factor in the regulation of immunity, inflammation and a range of diseases. Infection with intestinal helminths is ubiquitous in grazing horses, with cyathostomins (about 50 species of which are recorded) predominating. Consequences of infection include both chronic effects, and an acute inflammatory syndrome, acute larval cyathostominosis, which sometimes follows removal of adult helminths by administration of anthelmintic drugs. The presence of cyathostomins as a resident helminth population of the equine gut (the “helminthome”) provides an opportunity to investigate the effect helminth infection, and its perturbation, has on both the immune system and bacterial microbiome of the gut, as well as to determine the specific mechanisms of pathophysiology involved in equine acute larval cyathostominosis. We studied changes in the faecal microbiota of two groups of horses following treatment with anthelmintics (fenbendazole or moxidectin). We found decreases in both alpha diversity and beta diversity of the faecal microbiota at Day 7 post-treatment, which were reversed by Day 14. These changes were accompanied by increases in inflammatory biomarkers. The general pattern of faecal microbiota detected was similar to that seen in the relatively few equine gut microbiome studies reported to date. We conclude that interplay between resident cyathostomin populations and the bacterial microbiota of the equine large intestine is important in maintaining homeostasis and that disturbance of this ecology can lead to gut dysbiosis and play a role in the aetiology of inflammatory conditions in the horse, including acute larval cyathostominosis.

Ciatostomas: una revisión de la biología, importancia clínica y control

Members of the subfamily Cyathostominae, also known as cyathostomins or “small strongyles”. These are composed of a group of 50 species that can parasite horses, and are considered the most prevalent and resistant to anthelmintics parasites in young and adult horses. Cyathostomins may be compromised to produce a diet, forming nodules in experimental gastroenteritis. In addition, could cause larval cyathostominosis, a clinical syndrome associated with a massive emergency of encysted larvae. The control of these parasites is done through the administration of anthelmintics, but is frequent the occurrence of resistance. In order to obtain an effective anthelmintic control, it is essential the coproparasitological and veterinary monitoring, with periodic effectiveness tests, so that adequate control strategies can be established for each property.

Managing acute colitis in the adult horse

Management of adult horses with acute colitis is challenging, as intensive therapy is often required, the causative agents are frequently elusive, complications such as laminitis are common and the prognosis can be poor. The most commonly identified causes include infectious causes such as salmonellosis and clostridiosis, parasitic causes (larval cyathostominosis) and non-infectious causes such as antimicrobial administration and right dorsal colitis. Testing for infectious agents, in particular Salmonella spp., should always be performed, due to the risk of disease transmission to other animals and to people. While specific therapies exist for some conditions, supportive therapy, particularly fluid therapy and anti-inflammatory therapy, are key. The prognosis is variable, with morbidities such as laminitis often affecting the likelihood of a positive long-term outcome.

Evaluation of the mucosal inflammatory responses to equine cyathostomins in response to anthelmintic treatment

Members of Cyathostominae are pervasive parasites of equids that can cause larval cyathostominosis, a potentially life-threatening disease that occurs when a multitude of encysted larvae synchronously excyst from the wall of the large intestine. Moxidectin and fenbendazole are the two current labeled drugs that target the encysted larval stages; however, there is limited knowledge of the local inflammatory response to the larvae and to the two treatments in clinically healthy horses. This study is the first to evaluate the local inflammatory response to cyathostomin larvae and to larvicidal treatment at 2 and 5 weeks post treatment. Thirty-six ponies with naturally acquired cyathostomin infections were randomly allocated into 3 groups: Group 1, fenbendazole at 10 mg/kg for 5 days, Group 2, a single dose of moxidectin at 0.4 mg/kg, and Group 3, untreated controls. Tissue samples from the cecum and dorsal and ventral colons were used for histopathological and immunohistochemical evaluation. Tissues were stained with routine hematoxylin and eosin (H&E) for light microscopy and immunohistochemically for MAC387, CD20, and CD3 for differentiation of activated macrophages, B cells, and T cells, respectively. Semiquantitative scores were assigned for all inflammatory cell types and fibrous connective tissue. Larvae observed by light microscopy were enumerated and classified by stage. Mucosal ulcerations and submucosal granulomas were also enumerated. Mean macrophage scores were higher in the moxidectin group than the fenbendazole group (p = 0.0185) and the control group had a higher activated macrophage score than both treatment groups (p = 0.0104, p = 0.0004). T lymphocyte scores were higher in the moxidectin group when compared to the control group (p = 0.0069). Goblet cell hyperplasia scores were elevated at 5 weeks post treatment compared to 2 weeks post treatment (p = 0.0047) and were elevated in the ventral colon compared to the dorsal colon (p = 0.0301). Eosinophil scores were elevated surrounding degenerative larvae when compared to intact larvae (p = 0.0001). Mucosal ulcerations were found only in the control group at 2 weeks post treatment. This study found subtle inflammatory differences between treatment groups but provided new information about goblet cells and eosinophils in relation to encysted cyathostomin larvae.

Encysted cyathostomin larvae in foals – progression of stages and the effect of seasonality

Cyathostomins (small strongyles) are ubiquitous in grazing horses and are known pathogens as cause of larval cyathostominosis. As part of their life cycle, cyathostomin larvae invade the mucosal walls of the large intestines and undergo encystment. Newly ingested third stage larvae are known to undergo arrested development and this can lead to an accumulation of encysted burdens over the course of a grazing season. It is believed that the host immune system plays a significant role in triggering this arrestment. Little is known about the development and progression of larval stages in foals that are not expected to mount a pronounced immune response to ingested cyathostomin larvae. This study evaluated counts of encysted larvae measured in 37 foals. The foals were born in 2013, 2014, and 2015 into a parasitology research herd kept without anthelmintic intervention and were humanely euthanatized between 50 and 293days of age as part of an ongoing parasite transmission study. A mucosal digestion technique was performed to enumerate encysted early third stage (EL3) and late third stage/fourth stage (LL3/L4) larvae in the cecum, ventral colon and dorsal colon. Counts were analyzed statistically to evaluate the influence of foal age, sex, and seasonality on the counts. Total counts as well as LL3/L4 counts were significantly higher during the grazing season (March–November). Three defined age groups (>100, 100–200, >200days) did not have statistically different counts. Male foals had significantly higher total counts compared to females, and this has not been reported before. The study found that 41% of the recovered larvae were EL3s, but no indication of arrested development of these was observed. This indicates that cyathostomin infection in foals progresses in a manner substantially different from mature horses.

Local and systemic inflammatory and immunologic reactions to cyathostomin larvicidal therapy in horses

Encysted cyathostomin larvae are ubiquitous in grazing horses. Arrested development occurs in this population and can lead to an accumulation of encysted larvae. Large numbers of tissue larvae place the horse at risk for developing larval cyathostominosis. This disease complex is caused by mass emergence of these larvae and is characterized by a generalized acute typhlocolitis and manifests itself as a profuse protein-losing watery diarrhea with a reported case-fatality rate of about 50%. Two anthelmintic formulations have a label claim for larvicidal therapy of these encysted stages; moxidectin and a five-day regimen of fenbendazole. There is limited knowledge about inflammatory and immunologic reactions to larvicidal therapy. This study was designed to evaluate blood acute phase reactants as well as gene expression of pro-inflammatory cytokines, both locally in the large intestinal walls and systemically. Further, mucosal tissue samples were evaluated histopathologically as well as analyzed for gene expression of pro- and anti-inflammatory cytokines, cluster of differentiation (CD) cell surface proteins, and select transcription factors. Eighteen juvenile horses with naturally acquired cyathostomin infections were randomly assigned to three treatment groups; one group served as untreated controls (Group 1), one received a five-day regimen of fenbendazole (10mg/kg) (Group 2), and one group received moxidectin (0.4mg/kg) (Group 3). Horses were treated on day 0 and euthanatized on days 18–20. Serum and whole blood samples were collected on days 0, 5, and 18. All horses underwent necropsy with collection of tissue samples from the ventral colon and cecum. Acute phase reactants measured included serum amyloid A, iron and fibrinogen, and the cytokines evaluated included interferon γ, tumor necrosis factor α, transforming growth factor (TGF)-β, and interleukins 1β, 4, 5, 6, and 10. Transcription factors evaluated were FoxP3, GATA3 and tBet, and CD markers included CD163, CD3z, CD4, CD40, and CD8b. Histopathology revealed an inflammatory reaction with higher levels of lymphocytes, T cells, B cells, eosinophils and fibrous tissue in the moxidectin-treated group compared to controls or horses treated with fenbendazole. No apparent systemic reactions were observed. Expression of IL-5 and TGF-β in intestinal tissues was significantly lower in Group 3 compared to Group 1. This study revealed a subtle inflammatory reaction to moxidectin, which is unlikely to cause clinical issues.

A cost comparison of faecal egg count-directed anthelmintic delivery versus interval programme treatments in horses

The frequent use of anthelmintics in horses has contributed to the development of widespread anthelmintic resistance in cyathostomins (Matthews 2008, 2011), a group of parasitic nematodes comprising around 50 species....

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 6years 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.

Identification and characterisation of an immunodiagnostic marker for cyathostomin developing stage larvae

Parasitic nematodes of the group Cyathostominae are an important cause of disease in horses. This group consists of approximately 50 species, all of which have similar life cycles that involve encystment of larval stages in the large intestinal wall. Encysted larvae can persist for months to years and, occasionally, large numbers can accumulate and emerge synchronously to cause severe pathology, resulting in diarrhoea, weight loss, colic and/or oedema. This syndrome, known as larval cyathostominosis, can be fatal in up to 50% of cases, despite treatment. There is no diagnostic method that enables detection of the encysted larval burden. Previously, we identified two native antigen complexes that showed utility as diagnostic markers for the estimation of cyathostomin encysted larval burdens. This paper reports the identification of a likely protein component of one of these antigen complexes. The protein, designated cyathostomin gut-associated larval antigen-1 (Cy-GALA-1), was isolated by immunoscreening a cyathostomin mixed-species, larval complementary DNA library using sera from experimentally-infected horses. The resultant recombinant protein, rCy-GALA-1, was expressed in Escherichia coli and shown to be a target of serum IgG(T) responses in experimentally- and naturally- infected horse populations. Transcription of Cy-gala-1 was restricted to cyathostomin encysted larvae and the presence of native protein was limited to developing larval stages. Importantly, rCy-GALA-1 exhibited no reactivity to serum from horses mono-specifically infected with other helminth species, nor did antisera, raised to the recombinant protein, bind to adult stage extracts of heterologous species. Immunohistochemical experiments located Cy-GALA-1 to the nematode gut. A region of the gene encoding orthologous GALA sequences was isolated from 10 separate cyathostomin species, indicating the ubiquity of the protein in this nematode group.

A case of larval cyathostominosis

A two-year-old gelding was examined in the winter following six weeks of weight loss, despite a good appetite. Faecal consistency varied between normal and ‘cow-pat’. The gelding grazed permanent pasture shared by five other, unaffected equines of mixed ages; all the horses were managed on the same anthelmintic programme and had received oral ivermectin every two months during the preceding summer. The owner had submitted a faecal sample for a worm egg count after the first two weeks of weight loss: a negative result was obtained. The horse was moved to better pasture, however the weight loss progressed and further investigation was sought. CLINICAL EXAMINATION