Parascaris equorum
| Predilection site | Small intestine |
| Superfamily | Ascaridoidea |
Introduction
P. equorum is a nematode that primarily affects younger horses, usually under two years of age, as their immune response is not as developed as older horses.
Identification
P. equorum is a large stout nematode, with the female capable of growing up to 40cm in length. The adults have a mouth surrounded by three large lips. The egg is spherical, brown and has a thick outer shell.
Life-Cycle
The adults live unattached in the small intestine. In heavy infections, they may form large balls, which can cause intestinal obstruction. Under optimal conditions L2 can develop in 14 days. The host ingests the embryonated egg. L2 larvae then pass through the intestinal wall, and transfrom into L3. They then migrate to the liver via the hepatic portal vein, where they stay for around a week. They then enter the vena cava and travel to the pulmonary alveoli, where they transform to L4.
They then travel up bronchi to the trachea and are coughed up and swallowed. They then return to the stomach and small intestine, where they mature into adults.
The prepatent period of P. equorum is 10-16 weeks.