## Overview Ascarid impaction is a small-intestinal obstruction caused by a large mass of Parascaris equorum (or Parascaris univalens) worms. It occurs almost exclusively in foals and weanlings, typically around 5 months of age when worm burdens peak, and is often precipitated by administration of an effective anthelmintic that kills or paralyzes a heavy adult population. The resulting bolus of dead worms obstructs the jejunum or ileum, producing acute colic. ## Causes Heavy ascarid burdens develop in young horses before age-related immunity appears. Rapid kill by ivermectin, pyrantel, or other effective dewormers can create an obstructive mass. Impaction can also occur spontaneously in heavily parasitized foals. ## Diagnosis Acute colic in a recently dewormed foal or weanling is highly suggestive. Nasogastric reflux, distended small intestine on ultrasound or rectal examination (in larger foals), and sometimes worms in reflux or feces support the diagnosis. Exploratory surgery confirms the impaction. ## Treatment Medical management with fluids, analgesics, and lubricants is attempted in mild cases. Most clinically significant impactions require surgical enterotomy to remove the worm mass. Supportive care addresses dehydration and endotoxemia. ## Recovery and Prognosis Prognosis is fair with prompt surgical intervention in foals that are not yet in septic shock. Delayed treatment or intestinal rupture carries a poor prognosis. Survivors usually do well once the obstruction is relieved and parasite control is optimized. ## Prevention Strategic deworming that avoids sudden kill of massive burdens (for example, starting with fenbendazole in heavily infected foals) and environmental hygiene reduce risk. Fecal egg counts guide treatment in older foals.
acute colic in a foal or weanling; often shortly after deworming; nasogastric reflux; distended small intestine; depression
## Overview Ascarid impaction is a small-intestinal obstruction caused by a large mass of Parascaris equorum (or Parascaris univalens) worms. It occurs almost exclusively in foals and weanlings, typically around 5 months of age when worm burdens peak, and is often precipitated by administration of an effective anthelmintic that kills or paralyzes a heavy adult population. The resulting bolus of dead worms obstructs the jejunum or ileum, producing acute colic. ## Causes Heavy ascarid burdens develop in young horses before age-related immunity appears. Rapid kill by ivermectin, pyrantel, or other effective dewormers can create an obstructive mass. Impaction can also occur spontaneously in heavily parasitized foals. ## Diagnosis Acute colic in a recently dewormed foal or weanling is highly suggestive. Nasogastric reflux, distended small intestine on ultrasound or rectal examination (in larger foals), and sometimes worms in reflux or feces support the diagnosis. Exploratory surgery confirms the impaction. ## Treatment Medical management with fluids, analgesics, and lubricants is attempted in mild cases. Most clinically significant impactions require surgical enterotomy to remove the worm mass. Supportive care addresses dehydration and endotoxemia. ## Recovery and Prognosis Prognosis is fair with prompt surgical intervention in foals that are not yet in septic shock. Delayed treatment or intestinal rupture carries a poor prognosis. Survivors usually do well once the obstruction is relieved and parasite control is optimized. ## Prevention Strategic deworming that avoids sudden kill of massive burdens (for example, starting with fenbendazole in heavily infected foals) and environmental hygiene reduce risk. Fecal egg counts guide treatment in older foals.
acute colic in a foal or weanling; often shortly after deworming; nasogastric reflux; distended small intestine; depression