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  Discussion on Failure of Strongid C-another myth?
Author Message
Member:
Belhaven

Posted on Tuesday, Mar 11, 2003 - 9:06 am:

I was wondering if there has been any new information regarding resistance and Strongid C (or other daily dewormers)....I recently heard from a vet the reports have been published showing resistance of parasites.

Since this topic seems to float around every so often thought I would check here first.

thanks.
Member:
Lilo

Posted on Tuesday, Mar 11, 2003 - 1:30 pm:

I would be interested in the answer also. At a recent riding club meeting the topic came up and the feeling was that parasites would develop a resistance.
Thanks,
Lilo
Moderator:
DrO

Posted on Wednesday, Mar 12, 2003 - 6:07 am:

There have been reports as they are often mentioned in reviews on the subject but little actual published data. Perhaps most disturbing is in one published report it was the large strongyle found resistant. (Pyrantel-resistant large strongyles in racehorses.
Vet Rec. 1999 Oct 2;145(14):408.)

This emphasizes the need to check your deworming program at least once yearly to be sure it is doing the job. Here is a recently published overview of the subject:

(Vet Res 2002 Sep-Oct;33(5):491-507
Anthelmintic resistance in nematodes of horses.
Kaplan RM.

Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Athens 30602, USA. rkaplan@vet.uga.edu

Suppressive anthelmintic treatment strategies originally designed to control Strongylus vulgaris in horses were extremely successful in reducing morbidity and mortality from parasitic disease. Unfortunately, this strategy has inadvertently resulted in the selection of drug-resistant cyathostomes (Cyathostominea), which are now considered the principal parasitic pathogens of horses. Resistance in the cyathostomes to benzimidazole drugs is highly prevalent throughout the world, and resistance to pyrantel appears to be increasingly common. However, there are still no reports of ivermectin resistance in nematode parasites of horses despite 20 years of use. It is unknown why resistance to ivermectin has not yet emerged, but considering that ivermectin is the single most commonly used anthelmintic in horses most parasitologists agree that resistance is inevitable. The fecal egg count reduction test is considered the gold standard for clinical diagnosis of anthelmintic resistance in horses, but diagnosis is complicated by lack of an accepted standard for the performance of this test or for the analysis and interpretation of data. Presently there is very little data available on the molecular mechanisms of anthelmintic resistance in cyathostomes; beta-tubulin gene is the only anthelmintic-resistance associated gene that has been cloned. The increasingly high prevalence of anthelmintic-resistant cyathostomes must be taken into account when designing worm control programs for horses. Strategies to decelerate further selection for drug resistance thereby extending the lifetime of currently effective anthelmintics should be implemented whenever possible. Considering the nature of the equine industry in which horses often graze shared pastures with horses from diverse locations, transmission and widespread dispersal of resistant parasites is virtually assured. A proactive approach to this problem centered on understanding the molecular basis of anthelmintic resistance in cyathostomes is required if we are to expect chemical control of nematodes in horses to remain a viable element of parasite control in the future.)
DrO

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