Hepatotoxicity associated with pyrrolizidine alkaloid (Crotalaria spp) ingestion in a horse on Easter Island.

The study investigates a prevalent syndrome in horses on Easter Island, leading to multiple deaths since 1984. The syndrome, linked to the ingestion of pyrrolizidine alkaloid (Crotalaria spp), results in severe health issues such as anorexia, weight loss, and central nervous system abnormalities. A reported case of a horse affected by the syndrome was investigated in detail, suggesting a strong correlation between the symptoms and the ingestion of Crotalaria species plants.

Study Background and Methodology

• The research was initiated due to an ongoing issue on Easter Island involving the death of privately owned and feral horses from a specific syndrome. The symptoms of this syndrome include progressive loss of appetite, weight loss, and irregularities in the central nervous system.
• A horse showing these clinical signs was identified, examined, and underwent necropsy for detailed investigation. This allowed researchers to closely observe the symptoms and physical effects on the organs.

Clinical Signs and Observations

• Key observable symptoms in the horse included loss of appetite (inappetence), extreme weight loss (emaciation), lack of coordination (ataxia), and jaundice (icterus).
• The horse’s necropsy revealed several internal abnormalities, including an enlarged and ineffably varied liver, buildup of fluid in the abdominal cavity (ascites), and blockage in the digestive system (gastric impaction).
• The microscopic examination of the liver tissue unveiled further damage, including bleeding and cell death (necrosis), oversized cells around the portal vein area (periportal megalocytosis), scar tissue formation in the liver (portal fibrosis), excess growth of the bile duct and liver cells with multiple nuclei.

Identification of the Cause

• Two species of the Crotalaria genus, Crotalaria grahamiana and C pallida, were found in the pasture of the affected horse and were widespread across the island. These plants are known to contain pyrrolizidine alkaloids, toxic compounds that could potentially cause liver damage.
• Chemical analysis of the plants confirmed the presence of these toxic alkaloids. C grahamiana contained grahamine, monocrotalin, and a grahamine analog, while C pallida had analogs of retrorsine and senecionine.
• Thus, the distinct lesions found and the identification of highly toxic pyrrolizidine alkaloids in the plants strongly suggest that the horse’s chronic liver damage and subsequent brain disorder (hepatic encephalopathy) resulted from the ingestion of these Crotalaria species.

Implications and Conclusion

• Due to the extensive presence of C grahamiana on the island and the reported trends in disease occurrence among horses and cattle, it’s suggested that the plant could be responsible for the widespread illness and fatalities among these animals on Easter Island.
• Further research might be needed to corroborate these findings and find effective measures to prevent such incidents in the future.