Parascaris equorum

PARASCARIS EQUORUM

General

• Ascarid, small intestine.
• Mostly in young horses, especially foals <6months old.

Morphology

• Stout worms, up to 50cm long.
• Three large lips around mouth.

Life-Cycle

• Direct.
• Infection - ingestion of embryonated egg (L2).
• Egg (100µm diameter, brown, thick pitted shell).
• Larvae → hepatotracheal migration (liver → heart → lungs → intestine, 3weeks).
• Prepatent period = 10-12weeks.

Pathogenicity

• Larvae - eosinophilic tracts and haemorrhages in liver and lungs. Clinically, latter may lead to cough and nasal discharge.
• Adult worms - may cause unthriftiness, weight loss; impaction and intestinal perforation rarely.

Epidemiology

High Fecundity of Female Parascaris:

• Infected foal may pass millions of eggs per day.

Resistance of Eggs in Environment:

• Thick, pitted shell ensures prolonged survival (>1year).
• Sticky outer shell aids passive spread.

Susceptible Animals:

• Foals (<4months) - transmission from one year's foals to the next, infection normally occurring during the first month of life.
• Adult horses - few worms only (carriers?).

Control

• Regular anthelmintic treatment.
• Remove faeces from paddocks - collect every 2weeks (takes 2weeks to reach L2 stage).