Larval cyathostomiasis.

Over the past few years, cyathostomiasis has become increasingly recognized as a clinical problem of horses in the United States. Clinical cyathostomiasis has been reported frequently in Europe for a considerable time. This clinical syndrome is usually related to the sudden release of large numbers of the larval stages of small strongyles from the mucosa of the large intestine. Typical clinical signs include diarrhea, ventral abdominal edema, pyrexia, colic, weight loss, and poor body condition. Hypoalbuminemia and the presence of large numbers of small strongyles being passed in the feces are also characteristic features of the disease. The disease may occur seasonally in late winter and early spring or after drug treatment to remove the luminal stages of small strongyles. Two commercially available drugs, moxidectin and fenbendazole, have been shown to be effective against the encysted larval stages of the parasites. Drug resistance of small strongyles to all classes of currently available antiparasitic compounds except the macrocyclic lactones (ivermectin and moxidectin) is a limiting factor in controlling these parasites and may result in an increased prevalence of clinical cyathostomiasis over time.