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

M. K. Nielsen, A. N. Vidyashankar, S. N. Olsen, J. Monrad, S. M. Thamsborg

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


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.

Original languageEnglish
Pages (from-to)260-266
Number of pages7
JournalVeterinary Parasitology
Issue number2-4
StatePublished - Oct 26 2012

Bibliographical note

Funding Information:
The authors are grateful to all the participating veterinary practitioners, particularly Dr. Mette Uldahl, who enthusiastically assisted in the practical planning of the data collection. Laboratory technicians Tina Roust, Maria Rhod, and Ida Trondhjem Haakanson and scientific assistant Dr. Maria Mathilde Haugaard are warmly thanked for invaluable help with sample processing in the laboratory. The study was funded by Danish Research Council's Agency for Science, Technology and Production , grant number 274-08-0081 .


  • Prescription-only
  • Reemergence
  • Selective therapy
  • Strongylus vulgaris

ASJC Scopus subject areas

  • Parasitology
  • Veterinary (all)


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