Peer-reviewed veterinary case report
Identification of foals infected with Parascaris equorum apparently resistant to ivermectin.
- Journal:
- Journal of the American Veterinary Medical Association
- Year:
- 2003
- Authors:
- Hearn, F Patrick D & Peregrine, Andrew S
- Affiliation:
- Hearn Veterinary Services · Canada
- Species:
- horse
Plain-English summary
In September 2002, a study looked at 16 Thoroughbred foals living on a farm near Toronto, Canada, and found that 9 of them had low to moderate levels of eggs from a type of roundworm called Parascaris equorum in their poop. The foals were treated with ivermectin, a common dewormer, but when their feces were checked again 12 days later, 7 foals had more eggs, 1 had the same amount, and 5 had fewer. The researchers also tested 21 more foals that had been treated with ivermectin and found that 12 of them still had P. equorum eggs. The results suggested that the roundworms in these foals were resistant to ivermectin, meaning the treatment didn't work as expected.
Abstract
During September 2002, routine fecal examinations performed on 16 Thoroughbred foals residing on a farm outside Toronto, Ontario, Canada, revealed low to moderate numbers of Parascaris equorum eggs in feces from 9 of the 16. All foals were then treated with ivermectin at a dose of 220 to 280 microg/kg (100 to 127 microg/lb), p.o., and fecal egg counts were repeated 12 days later. Fecal P. equorum egg counts increased between the first and second fecal examination in 7 foals, were unchanged in 1, and decreased in 5. Fecal samples were collected 13 days after treatment from 21 additional foals that had been treated with ivermectin at the same dose, and P. equorum eggs were detected in 12 of the 21. For all 37 foals, high P. equorum egg counts (> or = 100 eggs/g of feces) 12 to 13 days after ivermectin treatment were significantly more likely in foals that had been regularly treated with ivermectin since birth and permanently resided on the farm, compared with foals that had been treated with other anthelmintics or had an unknown deworming history. Collectively, these data suggested that P. equorum in these foals was resistant to ivermectin administered at the recommended dose.
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Search related cases →Original publication: https://pubmed.ncbi.nlm.nih.gov/12930086/