Scientific name: Parascaris equorum
Common name: Ascarids or Roundworms

Description: Ascarids, or roundworms, are extremely prolific parasites found in every geographic region. Adult worms produce millions of eggs that can survive for years. Ascarids are the largest internal parasites affecting horses. Adult worms can reach up to 20 inches (50 cm) in length and 1/2 inch (13 mm) in diameter. They are most commonly found in young horses (foals, weanlings and yearlings). Immunity to roundworms is normally developed during adolescence. Foals 4 to 12 weeks of age are the most susceptible to damage from roundworm infestation. Severe cases can lead to liver and lung damage, poor growth and even death. As roundworm larvae move through the blood system, foals may experience fever, pneumonia and other respiratory infections. Adult roundworms can cluster in the small intestine causing colic, impaction and in the worst case, ruptured gut.

Life cycle: When infective larvae are swallowed with contaminated feed or water, they penetrate the intestinal wall and travel through the liver and lungs. Growing worms move to the windpipe where they are coughed up and swallowed. Roundworms mature in the small intestine where adult females lay their eggs. Some eggs are passed with manure while others hatch in the small intestine, releasing infective larvae that repeat the cycle of migration. The life cycle is complete in 10 to 12 weeks.

Symptoms: Typical symptoms of roundworm infection include a dry cough, nasal discharge, loss of appetite, poor appearance, diarrhea, weight loss, pot-bellied appearance, lethargy and colic.

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