Fatal Peritoneal Migration of Strongylus edentatus in a Foal.

A 7-month-old female mixed breed foal with a 2-day history of recumbency and inability to open its mouth convulsed acutely and died and was submitted for necropsy examination. The foal was thin and large patches of haemorrhage were present throughout the peritoneal wall, the diaphragmatic surfaces and the retroperitoneum. Numerous nematode larvae were visible on the serosal surfaces and penetrated and embedded into the subserosa associated with the haemorrhages. The dorsal portion of the abdominal diaphragm had a partial tear and large numbers of nematodes were within the muscle fibres. Histologically, the larvae had a smooth cuticle, polymyarian/coelomyarian musculature and multinucleated intestinal cells, and were typically surrounded by haemorrhage, neutrophils, dense fibrovascular connective tissue and rare multinucleated giant cells. Parasitological examination identified the larvae as Strongylus edentatus based on the morphology of the buccal capsule. Additionally, there was severe muscle necrosis of the tongue and liver tissue analysis detected selenium deficiency. S. edentatus infections are uncommon in California, USA, and are typically non-lethal. In this case, the selenium deficiency may have led to immunosuppression, resulting in the hyperinfection with S. edentatus, and to the muscle damage and tear of the diaphragm. Although ivermectin treatment was indicated in the history, inadequate deworming or anthelmintic resistance may have played a role in the severity of infection.

Variation in fecal egg counts in horses managed for conservation purposes: individual egg shedding consistency, age effects and seasonal variation.

Cyathostomins are the most prevalent equine intestinal parasites and resistance has been reported in these nematodes against all 3 licensed anthelmintic classes. Strategies need to be developed that are less dependent upon drugs and more reliant on management-based control. To develop these we need to understand natural transmission patterns better. Here, we analysed longitudinal fecal egg count (FEC) data from 5 pony populations used for conservation purposes. We tested how egg excretion varied amongst populations and individuals, and how this was affected by age and climate. There was evidence for consistency in FECs over time at the individual level; this was generally weak and accounted for <10% of the total variance. Animals <5 years old had higher FECs and there was profound seasonal variation in FECs, with highest levels recorded in spring/summer. Effects of monthly temperature and rainfall explained most, but not all, of the observed seasonal variation and associations between climate measures and FECs were stronger in younger versus adult animals. One population was occasionally treated with anthelmintics and analysis of this population suggested that treatment substantially altered the seasonal dynamics. This paper highlights the variability in strongyle egg excretion amongst individuals and the factors involved in this variation.

Strongylus vulgaris (Looss, 1900) in horses in Italy: is it still a problem?

A post-mortem survey was carried out on 46 Sardinian horses to evaluate the presence of Strongylus vulgaris and associated pathology. Horses were from local farms and had been treated with broad-spectrum anthelmintics at least 3 times a year. Examination of the cranial mesenteric arterial system (CMAS) showed parasite-induced lesions in all horses. S. vulgaris larvae were found in 39% of examined arteries, while their detection rate in coprocultures was 4%. Histology, carried out on 26 horses, showed mainly chronic and chronic-active lesions. Histometry showed a significant increase in thickness of the arterial wall, in particular of the intima tunic and adventitia tunic of the ileocolic artery and its colic branch. MCV, MCHC and alpha2, beta and gamma globulins were increased in horses with S. vulgaris larvae in the arteries, while the albumin/globulin ratio was decreased. Horses that were positive on faecal examination showed decreased values for RBC, PCV and the albumin/globulin ratio. Although several studies have shown a dramatic decrease of S. vulgaris infection worldwide, our data show that this parasite continues to exert its pathogenic role, even when its detection rate is quite low within the strongyle population infecting horses.

Control de parásitos gastrointestinales en caballos pura sangre de carrera (Equus Caballus) en el Hipódromo "La Rinconada" Caracas, Venezuela / Control of gastrointestinal parasites in thoroughbred horses (Eqqus Caballus) the Racetrack

Se realizo un estudio coprológico por la técnica de flotación Mc Master (Willis-Molloy), realizando contaje de Huevos por gramo de Heces (HPG), a 100 equinos Pura Sangre de Carreras, durante el periodo de cuarentena Hipodromo “La Rinconada” Caracas Venezuela. Se procedió a la desparasitacióncon una terapéutica a base de Febantel, dosis 6mg/kg, presentación en pasta, vía oral (CALOXBANTEL) Febantel 88.7 mg; Excipientes c.s.p. 1g. A los 7 días post-desparasitación se realizo un estudio coprológico por la técnica de flotación Mc Master (Willis-Molloy), realizando contaje de Huevos por gramo de Heces (HPG). El estudio coprológico evidencio un 60% de infestación (60/100) en los caballos estudiados. El 40% (40/100) fue negativo al examen coprológico. Los resultados post-tratamientos fueron 1% de infestación persistente (01/100) y un 99% (99/100) negativos al examen coprológico. En todos los casos la infestación parasitaria fue por Strongylus sp. La presencia de Strongylus sp. se mantuvo por equino infestado entre un rango de 400-1200 HPG

We study 100 Thoroughbred horses, in the Racetrack “La Rinconada” Caracas, Venezuela, by McMaster flotation technique (Willis-Molloy), making counting of eggs per gram of feces (EPG) before deworming, each of the copies, then proceeded to the parasite with a Febantel based therapy, dose 6mg/kg, pasta presentation, oral (CALOXBANTEL) Febantel 88.7 mg, Excipients 1g. At 7 days post-parasite stool study was conducted by the McMaster flotation technique (Willis- Molloy), by counting eggs per gram of faeces (EPG). The coprology study showed 60% infestation (60/100) in horses studied. The 40% (40/100) was negative. The post-treatment were 1% infestation (01/100) and 99% (99/100) was negative. In all cases, parasite infestation was by Strongylus sp. within the range of 400-1200 HPG

Strongyle egg counts in Standardbred trotters: are they associated with race performance?

REASONS FOR PERFORMING STUDY: Strongyle worm burdens are assumed to subclinically affect equine performance. This assumption appears to be particularly pronounced in the equine racing industry. HYPOTHESIS: Race results of Standardbred trotters are negatively affected by high strongyle faecal egg count levels. METHODS: Faecal samples were obtained from 213 racing Standardbred trotters, aged ≥ 2 years, and stabled at training facilities of 21 professional trainers with license at racecourses in Denmark. Strongyle egg counts were generated using a McMaster technique. Race results were recorded as the finishing position of the horse (position 1-3 vs. finishing lower) and winning purse. The effect of strongyle egg counts on performance was assessed using regression analyses. RESULTS: Strongyle egg counts ranged from 0-3500 with a mean of 319 and a median of 150 eggs/g. Finishing in positions 1-3 was significantly associated with higher egg counts. CONCLUSIONS: Race performance of the population of professionally trained Danish Standardbred trotters was not negatively affected by higher strongyle faecal egg count levels. POTENTIAL RELEVANCE: The traditional frequent anthelmintic treatments of racehorses may be inordinate.

Small strongyle infection: consequences of larvicidal treatment of horses with fenbendazole and moxidectin.

The study was undertaken to evaluate adverse effects of larvicidal treatment in horses naturally infected with cyathostomins. Out of 24 ponies kept on pasture, four animals were housed in September and anthelmintically cured to serve as worm-free controls (group C-0). The others were housed in December. Eight animals each were treated 8 weeks later with 5 x 7.5mg/kg fenbendazole (FBZ) or 1 x 0.4 mg/kg moxidectin (MOX). Four animals remained untreated (group C-i). Two, 4, 6 and 14 days after the end of treatment two animals of each of the treated groups were necropsied together with group C-0 and C-i animals. Infected animals before treatment showed weight loss, eosinophilia, increased plasma protein and globulin contents. Treatment was followed by weight gain and temporal plasma protein and globulin increase. Proportions of CD4+ and CD8+ T lymphocytes in the peripheral blood did not differ between the groups before treatment but dropped significantly temporally after FBZ treatment. Group C-0 was worm-free at necropsy. Group C-i animals contained variable numbers of luminal and tissue cyathostomins. Histological sections showed larval stages in the lamina propria und submucosa surrounded by macrophages. Either treatment was effective against luminal parasites and reduced the number of larvae in the bowel wall beginning 4-6 days after FBZ and 6-14 days after MOX treatment. Histologically, as a first reaction after FBZ application T lymphocytes accumulated around morphologically intact L4 in the submucosa. Subsequently T lymphocytes associated with eosinophils infiltrated the submucosa. Parasites became enclosed by granulomas with eosinophils adhering to and invading the larvae which started to disintegrate on day 4. Later on, particularly on day 14 inflammation extended into the mucosa and was frequently associated with ulcerations. Third stage larvae in general and L4 in the lamina propria, however, seemed not to be affected until day 14 and even then, parasites did usually not generate extensive inflammation. After MOX treatment severe morphologically detectable alterations of tissue larvae could not be observed earlier than day 14. Different from FBZ treatment, larvae disintegrated and were obviously resorbed without causing severe inflammation in the gut wall. In conclusion treatment with either drug was efficacious against tissue larvae of cyathostomins but there may be different clinical consequences: in contrast to MOX effects, killing of larvae due to FBZ was associated with severe tissue damage, which clinically may correspond to reactions caused by synchronous mass emergence of fourth stage larvae, i.e., may mimic larval cyathostominosis.

[Death by cyathostominosis]. / Sterfte door cyathostominosis.

In autumn 2002 and 2003, the Animal Health Service received several young horses for post mortem investigation that had died or had been euthanised. It was found that severe cyathostominosis was the cause of death. The aetiology, pathology and diagnosis of this infection is discussed. Advice is given for preventative measures and usage of anthelmintics.

Field evaluation of moxidectin/praziquantel oral gel in horses.

The safety and efficacy of 2% moxidectin/12.5% praziquantel oral gel administered at a rate of 0.4 mg moxidectin and 2.5 mg praziquantel/kg was studied in client-owned horses under field use conditions. Four hundred horses (300 treated with moxidectin/praziquantel oral gel and 100 treated with vehicle) were enrolled, feces were collected, and eggs were counted. Investigators as well as horse owners were masked to treatment assignment. No adverse reactions to treatment were observed in any horses. Moxidectin/praziquantel gel reduced Anoplocephala spp by more than 99% and provided a significant (P <.05) reduction (> 98%) in the strongyle egg count of treated horses.

Treatment and follow-up of clinical cyathostominosis in horses.

The results of the treatment with moxidectin or ivermectin of 20 horses with clinical cyathostominosis were studied during a 3-week observation period. Both treatments were effective in completely eliminating larvae from the faeces within 1 or 2 weeks, but no significant improvement in body weight or clinical parameters could be demonstrated over the observation period. The poor short time results of the treatment support the need for an adequate prevention of cyathostominosis in horses.

Verminous arteritis in a 3-month-old thoroughbred foal.

Strongylus vulgaris migration and cranial mesenteric arterial thrombus formation resulted in fatal colic in a 3-month-old Thoroughbred foal. Vascular damage associated with S. vulgaris occurs early in the course of infection and, despite widespread use of broad-spectrum anthelmintics, appropriate management is still essential to minimize exposure of young animals to this parasite.

Larval cyathostomiasis as a cause of death in two regularly dewormed horses.

Two horses were presented with complaints of chronic weight loss and subcutaneous oedema, one of them presenting diarrhoea. Both animals were grazed with other unaffected horses, all of them being regularly dewormed. Blood chemistry revealed hypoalbuminaemia and a low albumin-globulin ratio. Faecal egg counts were negative and no cyathostome larvae could be found in the faeces. Neither of these horses could be saved, despite intensive treatment. Postmortem examination revealed severe typhlitis and colitis due to numerous inhibited cyathostome larvae.

Two fatal cases of diarrhoea in horses associated with larvae of the small strongyles.

Detailed pathological examinations of two horses with subacute fatal diarrhoea suggested an association between the diarrhoea and damage to the colonic and caecal mucosae caused by large numbers of cyathostome larvae (larval cyathostomiasis). The affected animals deteriorated rapidly, and died after a short illness.

Necropsies of eight horses infected with Strongylus equinus and Strongylus edentatus.

Ponies (n = 8) approximately 18 months old, were infected with 20,000 to 30,000 infective larvae of Strongylus equinus with less than 10% contamination with Strongylus edentatus larvae and necropsied 7 months post-infection. Lesions were present in the omentum, liver, pancreas, ventral colon, caecum and occasionally in the lungs. There were numerous intraabdominal adhesions and severe multiple granulomatous omentitis. Pancreatic damage, which characterises S. equinus, was exceptionally mild and was manifested mainly by slight periductular infiltration of eosinophils. Granulomas associated with larvae were found in the connective tissue associated with the pancreas. Larvae were recovered from the flanks, the peritoneum, the caecum and the kidney. Larval recovery was low, with a high percentage of the total number of larvae recovered in some of the carcasses being S. edentatus.

Histology and morphometry of Strongylus vulgaris-mediated equine mesenteric arteritis.

Histological and morphometric evaluation of equine cranial mesenteric arteries was performed on 239 and 89 arteries, respectively. Histological examination revealed that thrombosis and the severity of inflammation varied on a seasonal basis and were directly associated with larval presence. Intimal and adventitial fibrosis were generally of greater severity than medial fibrosis. Fibrosis of the vasa vasorum was less frequent than fibrosis of the artery itself. Morphometry revealed a significant increase in intimal, adventitial and, to a lesser extent, medial area in affected as compared with normal arteries. This change was due to the accumulation of collagen and was considered to result in decreased arterial elasticity. The luminal area varied widely among affected arteries.

The ultrastructure of Strongylus vulgaris-mediated equine chronic mesenteric arteritis.

Cells found in the intima and media of the cranial mesenteric artery of a mature mare with chronic arteritis were identified as smooth muscle cells and occurred in association with collagen and elastin fibres. As no fibroblasts were demonstrable within these regions, the smooth muscle cells were the likely source of the extracellular matrix. In contrast, the abnormal adventitis from the same artery contained abundant fibroblasts which are considered to be the source of the adventitial collagen.

Transrectal ultrasonography of the cranial mesenteric artery of the horse.

Transrectal ultrasonography was performed on the cranial mesenteric artery and its major branches in 23 conscious adult horses. Ultrasonographically, 25 arterial segments were classified as either normal or abnormal. These ultrasonographic classifications were later compared with the gross and histologic evaluations of each artery following necropsy of each horse. In this study, transrectal ultrasonography as a diagnostic test for verminous arteritis had a 90% sensitivity for detecting normal arteries and an 86% specificity for detecting abnormal arteries, suggesting that ultrasonography may be useful in the antemortem diagnosis of verminous arteritis.

In vitro ultrasonographic appearance of the normal and verminous equine aorta, cranial mesenteric artery, and its branches.

Ninety-one equine aortic and cranial mesenteric arterial segments were evaluated ultrasonographically in a water bath. On the basis of pathologic evidence of verminous arteritis, arterial segments were classified into 4 categories, and the ultrasonographic characteristics of each group were evaluated. Normal arteries (class 1) were ultrasonographically characterized by a smooth luminal surface layer and uniform wall thickness and echogenicity. Arteries with only histopathologic evidence of verminous arteritis (class 2) were ultrasonographically characterized by a smooth luminal surface layer, uniform hyperechoic luminal layer. Arteries with both gross and histopathologic evidence of verminous arteritis (class 3) were characterized ultrasonographically by an irregular luminal surface layer, varying wall thickness, varying wall echogenicity, and the presence of a hyperechoic luminal layer. The ultrasonographic characteristics of arteries with luminal thrombosis (class 4) were an irregular luminal surface, varying wall thickness, and nonuniform echogenicity.

Plasma thromboxane B2 levels in horses experimentally infected with Strongylus vulgaris.

Plasma thromboxane B2 (TXB2) the stable inactive metabolite of thromboxane A2 (TXA2), was measured daily by specific radioimmunoassay in three groups of animals before and after experimental infection with Strongylus vulgaris. Infection of four 'parasite naive' foals produced a typical acute syndrome with intermittent but statistically insignificant rises in TXB2 levels. Interpretation of results was complicated by the presence of a non-septic peritonitis associated with implantation of the foals with electrodes for recording myoelectrical activity. In two foals of similar age, with some natural exposure to S. vulgaris, there was little or no clinical response to infection and increases in TXB2 were absent. Baseline levels were also much lower, indicating that the peritonitis may have affected the results obtained in the first group of foals. Severe mesenteric arteritis was confirmed at necropsy in all six foals. A third group of yearling horses, all with natural exposure to the parasite, were generally resistant to infection. One animal developed arteritis with clinical signs of diarrhoea and mild colic, and also showed intermittent increases in TXB2. The mean plasma TXB2 level after infection was significantly higher than in the control period, although absolute levels were lower than those recorded in the 'parasite naive' foals. Other animals in this group had low TXB2 levels and minimal arteritis was found at necropsy. These results indicate that although infection appears to have an effect on plasma TXB2, the changes are inconsistent and not reliable indicators of the presence of verminous arteritis. The results also confirm the difficulty in establishing infection and the variability of the response in animals with previous exposure.

Preliminary investigations on the effects of a Strongylus vulgaris larval extract, mononuclear factors and platelet factors on equine smooth muscle cells in vitro.

Factors involved in the proliferation of equine vascular smooth muscle cells were studied in vitro. The most prominent proliferative responses in cultured vascular smooth muscle cells were induced by Strongylus vulgaris larval antigen extract (LAE) and platelet-derived factors. Less significant proliferative responses were obtained with conditioned media from S. vulgaris LAE stimulated and from unstimulated equine mononuclear leukocytes. Additionally, vascular smooth muscle cells exposed to S. vulgaris LAE developed numerous perinuclear vacuoles and were more spindle-shaped than control or smooth muscle cells exposed to other factors. Equine mononuclear leukocytes exposed to LAE developed prominent morphological changes, including enlargement, clumping and increased numbers of mitotic figures.