Pathologic changes and pathogenesis of Parascaris equorum infection in parasite-free pony foals.

This study examines the pathogenic effects and changes caused by an oral infection of the parasite Parascaris equorum in ponies. After infecting a group of parasite-free foals, it was observed that symptoms became noticeable after seven days of infection, which included coughing, weight loss, and anemia. These symptoms were observed along with physical changes in internal organs like the lungs and liver, where necrotic foci were identified. The migratory pathway of the parasite was found to be similar to Ascaris lumbricoides, moving from the intestines through the blood and lymph system to the liver and lungs, and then back to the intestines.

Research Approach and Findings

• The research studied ten parasite-free pony foals that were orally infected with one million embryonated eggs of the parasite Parascaris equorum.
• Each foal was euthanized at different intervals after infection ranging across several days: 1, 3, 5, 7, 11, 16, 23, 27, 42, and 80.
• It was observed that pony foals infected for more than an interval of seven days showed multiple symptoms such as coughing, anorexia, rough coat, and weight loss.
• The foals also exhibited mild anemia, marked eosinophilia, and leukopenia.
• Upon postmortem examination, internal changes were revealed—hemorrhage, edema, and white-to-yellow necrotic foci in the lungs, liver, and respective lymph nodes.

Microscopic Findings

• On microscopic inspection, it was seen that the liver was hemorrhagic (bleeding extensively), had focal necrosis (localized cell death), and eosinophilic granulomas (inflammatory nodules)
• The hepatic and bronchial lymph nodes showed eosinophilic lymphadenitis (inflammation of the lymph nodes due to a high concentration of eosinophils) and edema (the accumulation of fluid in body tissues).
• Furthermore, the lungs had focal areas of necrosis with hemorrhage and interstitial pneumonia with hyalinization (the accumulation of glassy, amorphous material) of the alveolar walls.

Migration Pathway of the Parasite

• Larvae of P. equorum were first observed in the liver 24 hours after infection and in the lungs on postinfection day (PID) 11.
• The larvae were not found in the liver after PID 11 or in the lungs after PID 42, indicating their migration pattern over time.
• The average length of the larvae in the liver was 1mm and 2.5mm in the lungs.
• The migratory pathway of P. equorum was established to be similar to that of Ascaris lumbricoides—a parasite known to migrate via the lymph and blood vessels to the liver and then the lungs.
• After passing through the lungs, the larvae were coughed up and swallowed and subsequently developed in the small intestine.