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Larval Cyathastominosis
Larval Cyathostominosis, Small Strongyle Disease
Introduction
Cyathostominosis is a disease caused by the rapid emergence of many small strongyles resulting in weight loss, diarrhea, and death. Despite a feeling among horseowners that parasites are no longer much of a problem there is a growing world-wide recognition of this problem. From a 2006 article from The Canadian Veterinary Journal:
Cyathostominosis in horses in Ontario: An emerging disease?
Andrew S. Peregrine, Beverly McEwen, Dorothee Bienzle, Thomas G. Koch, and J. Scott Weese
Department of Pathobiology (Peregrine, Bienzle); Animal Health Laboratory (McEwen); Department of Clinical Studies (Koch, Weese), University of Guelph, Guelph, Ontario N1G 2W1.
Over the last few years, there has been a marked increase in the number of cases of larval cyathostominosis diagnosed at the Animal Health Laboratory. Whether this reflects a true increase in the prevalence of the disease, potentially due to drug resistance in cyathostomes, is unclear and currently under investigation. The association with drug resistance appears likely, since recent work has demonstrated resistance to fenbendazole on more than 95% of examined farms in the southern USA. In addition, resistance to pyrantel was demonstrated on 41% of the same farms. It therefore appears that drug resistance in cyathostomes is highly prevalent in this region of North America and, by comparison with earlier work, is rapidly worsening. Although resistance to ivermectin has not been demonstrated in cyathostomes, and ivermectin is commonly used for deworming horses, the spread of resistance to benzimidazoles and pyrantel is perhaps not surprising, as ivermectin does not eliminate immature cyathostomes in the wall of the intestine.
The article notes that some of the horses they saw were from horses that used regular deworming with commonly available products. This represents a problem that may be happening on a world wide scale: the growing resistance of the small strongyle to pyrantel (Strongid) and benzimadzoles along with an increasing incidence of disease from these organisms. In spite of Horseadvice.com's warnings about moving away from these products I still see many of our members post they continue to use them in a regular deworming program. This article explains what appears as a growing but preventable problem in horses and comes to conclusions that mirrors our recommendation on preventing this disease with tested anthelminthic programs for your horses. I hope this article serves as a impetus for those still not employing our recommended program to get off their duffs.
Department of Pathobiology (Peregrine, Bienzle); Animal Health Laboratory (McEwen); Department of Clinical Studies (Koch, Weese), University of Guelph, Guelph, Ontario N1G 2W1.
Over the last few years, there has been a marked increase in the number of cases of larval cyathostominosis diagnosed at the Animal Health Laboratory. Whether this reflects a true increase in the prevalence of the disease, potentially due to drug resistance in cyathostomes, is unclear and currently under investigation. The association with drug resistance appears likely, since recent work has demonstrated resistance to fenbendazole on more than 95% of examined farms in the southern USA. In addition, resistance to pyrantel was demonstrated on 41% of the same farms. It therefore appears that drug resistance in cyathostomes is highly prevalent in this region of North America and, by comparison with earlier work, is rapidly worsening. Although resistance to ivermectin has not been demonstrated in cyathostomes, and ivermectin is commonly used for deworming horses, the spread of resistance to benzimidazoles and pyrantel is perhaps not surprising, as ivermectin does not eliminate immature cyathostomes in the wall of the intestine.
Why is this a Growing Problem
Strongyles are common parasites of horses that infect the large intestine. They have a typical life cycle for parasites with the eggs passing out with the manure and hatching on the pasture. There they become infective larvae that horses ingest. These larvae then migrate through the horses tissues eventually returning to the large intestines where they attach and suck tissues from the wall of the intestine.
There are 2 primary types of strongyles: the large strongyles and the small strongyles. Small strongyles belong to the family of cyathostomes. Because of the sensitivity of their life cycle to ivermectin, large strongyles have largely disappeared from the landscape anywhere this dewormer is employed. However the small strongyle develops from the larval stage to adults much quicker with some of the larval stages being resistant to ivermectin at recommended dosages. They have also developed remarkable resistance to pyrantel (Strongid) and all the benzimidazoles. As a result the cyathostomes have become the most important parasite of horses and largely responsible for the need of regular deworming of adult horses.
The cyathostomes larvae migrate into the wall of the large bowel where they encyst as they develop. In less than 2 months they emerge and migrate back into the bowel to become attached to the bowel wall. Though small numbers of cyathostome larva do not appear to have an effect on the health of the horses the simultaneous emergence of large numbers of larvae causes a remarkable colitis and serious disease...more.
History and Clinical Signs
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