Prevalence of strongyles and efficacy of fenbendazole and ivermectin in working horses in El Sauce, Nicaragua

Niels C. Kyvsgaard, Jenny Lindbom, Line Lundberg Andreasen, Luz Adilia Luna-Olivares, Martin Krarup Nielsen, Jesper Monrad

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Horses, mules and donkeys are indispensable farming and working animals in many developing countries, and their health status is important to the farmers. Strongyle parasites are ubiquitous in grazing horses world-wide and are known to constitute a threat to equine health. This study determined the prevalence of strongyle infection, the efficacy of ivermectin and fenbendazole treatment, and strongyle re-infection rates of working horses during the dry months in Nicaragua. One hundred and five horses used by farmers for transport of people and goods were randomly allocated into three treatment groups, i.e., the IVM group treated with ivermectin, the FBZ group treated with fenbendazole and the control group treated with placebo. Determined by pre-treatment faecal egg counts (FECs), horses showed a high prevalence (94%) of strongyle parasites with high intensities of infection (mean FEC of 1117 eggs per gram (EPG) with an SD of 860 EPG, n=102). Body condition scores of all horses ranged from 1.5 to 3.5 with a mean of 2.4 (scales 1-5). Fourteen days after treatment faecal egg count reductions (FECRs) were 100% and 94% in the IVM and the FBZ groups, respectively. The egg reappearance period (ERP) defined as the time until the mean FEC reached 20% of the pre-treatment level, was estimated as 42 days for the FBZ group and 60 days for the IVM group. Individual faecal cultures were set up and the larval differentiation revealed a 36% prevalence of Strongylus vulgaris before treatment (n=45). In the FBZ group, 25% of the horses were S. vulgaris-positive 70 days post treatment compared to 11% in the IVM group. Our results indicate that strongyle infection intensities in Nicaragua are high and that S. vulgaris is endemic in the area. Furthermore, efficacies and ERPs of IVM and FBZ were within the expected range with no signs of anthelmintic resistance.

Original languageEnglish
Pages (from-to)248-254
Number of pages7
JournalVeterinary Parasitology
Issue number2-4
StatePublished - Sep 27 2011

Bibliographical note

Funding Information:
The project was supported by Danida-FFU through grant no. 104.Dan.8.L.713 . This study had never been possible without the active participation of the farmers in Valle San Antonio and San Martín.


  • Egg reappearance
  • Fenbendazole
  • Ivermectin
  • Nicaragua
  • Strongyle
  • Strongylus vulgaris

ASJC Scopus subject areas

  • Parasitology
  • Veterinary (all)


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