Equine Image Quiz: A colt with an impacted small intestine
A surgical exploration with small intestinal enterotomy was performed to relieve the ascarid impaction (see photo).
Parascaris equorum infections are found almost exclusively in juvenile horses less than 18 months of age because of a lack of acquired immunity to the parasite. Parascaris equorum resides as an adult in the small intestine where it competes with the host for digested nutrients. The female worm produces thick-walled eggs that are passed in the feces. The development of eggs to the infective stage occurs in the environment. The larvated eggs that are ingested hatch in the small intestine, and the liberated second-stage larvae (L2) enter the liver through the portal circulation. The larvae are then carried to the lungs, enter the alveoli, and are coughed up into the pharynx where they are swallowed and return to the small intestine to complete maturation.
Patent ascarid infections are easily detected by fecal examination. Adult and juvenile ascarids are susceptible to numerous anthelmintics except macrocyclic lactones (ivermectin and moxidectin) for which some resistance has been recently reported. Animals with heavy ascarid burdens can develop small intestinal impaction of dead worms after treatment with high anthelmintic doses. Initial administration of a dewormer with lesser efficacy (specifically fenbendazole 5 mg/kg) may lessen the risk of post-treatment ascarid impaction.