Article

Strongylus vulgaris associated with usage of selective therapy on Danish horse farms-Is it reemerging?

Department of Large Animal Sciences, Faculty of Life Sciences, University of Copenhagen, Denmark. Electronic address: .
Veterinary Parasitology (Impact Factor: 2.55). 05/2012; 189(2-4):260-6. DOI: 10.1016/j.vetpar.2012.04.039
Source: PubMed

ABSTRACT Nematodes belonging to the order Strongylida are ubiquitous in grazing horses, and the large strongyle Strongylus vulgaris is considered the most pathogenic. This parasite was originally described widely prevalent in equine establishments, but decades of frequent anthelmintic treatment appears to have reduced the prevalence dramatically. Increasing levels of anthelmintic resistance in cyathostomin parasites have led to implementation of selective therapy to reduce further development of resistance. It has been hypothesized that S. vulgaris could reoccur under these less intensive treatment circumstances. The aim with the present study was to evaluate the occurrence of S. vulgaris and the possible association with usage of selective therapy. A total of 42 horse farms in Denmark were evaluated for the presence of S. vulgaris using individual larval cultures. Farms were either using a selective therapy principle based on regular fecal egg counts from all horses, or they treated strategically without using fecal egg counts. A total of 662 horses were included in the study. Covariate information at the farm and horse level was collected using a questionnaire. The overall prevalence of S. vulgaris was 12.2% at the individual level and 64.3% at the farm level. Farms using selective therapy had horse and farm prevalences of 15.4% and 83.3%, respectively, while the corresponding results for farms not using selective therapy were 7.7% and 38.9%. These findings were found statistically significant at both the horse and the farm level. Stud farms using selective therapy were especially at risk, and occurrence of S. vulgaris was significantly associated with the most recent deworming occurring more than six months prior. The results suggest that a strict interpretation of the selective therapy regimen can be associated with an increased prevalence of S. vulgaris. This suggests that modifications of the parasite control programs could be considered on the studied farms, but it remains unknown to which extent this can be associated with increased health risks for infected horses.

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    ABSTRACT: Reasons for performing studyStrongylus vulgaris is a pathogenic helminth parasite infecting horses and was once considered to be the primary cause of colic. Migrating larvae cause ischaemia and infarction of intestinal segments. This knowledge is derived from case reports and experimental inoculations of parasite-naïve foals, and it remains unknown to which extent the parasite is associated with different types of colic.Objectives To evaluate the role of S. vulgaris as a risk factor for different types of colic in horses.Study designA retrospective case-control study among horses referred with abdominal pain to the University of Copenhagen Large Animal Teaching Hospital during 2009-2011.Methods Each colic case was matched with a patient of the same type (pony, warmblooded, coldblooded), age, sex, and admitted in the same month and year, but for problems unrelated to the gastrointestinal tract. Serum samples were analysed for antibodies to migrating S. vulgaris larvae using a recently developed ELISA. Four case definitions were used; colic sensu lato i.e. all horses presenting with colic (n = 274), with further sub-groups i.e. undiagnosed colics (n = 48), strangulating obstructions (n = 76), and non-strangulating infarctions (n = 20).ResultsStrongylus vulgaris antibody levels were similar to controls in colics sensu lato and horses with undiagnosed colic. In contrast, non-strangulating intestinal infarctions associated significantly with positive S. vulgaris ELISAs (OR = 5.33, 95%CI 1.03-27.76, P = 0.05). Also, horses with non-strangulating infarctions had a significantly higher occurrence of positive ELISAs than patients with strangulating obstructions (OR = 3.79, 95%CI 1.34-10.68 P = 0.01) and the colic sensu lato group (OR = 3.09, 95%CI, 1.20-8.01, P = 0.02).Conclusions Non-strangulating intestinal infarction associated strongly with S. vulgaris-specific antibodies whereas the broader defined colic categories were not associated with positive ELISA results. Thus, the ELISA holds potential to become a helpful adjunct in diagnosis and management of horses with colic.
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