Primary Photosensitization by Chamaecrista serpens in Santa Ines Sheep

Simple Summary Photosensitization is a cutaneous disorder caused by a substance that makes the skin sensitive to solar radiation. When this substance is endogenous (phylloethrin) as a result of chlorophyll not being metabolized in the liver, by hepatic failure, photosensitization is called secondary. When the substance is of exogenous origin, photosensitization is primary. Outbreaks of photosensitization caused by the ingestion of Chamaecrista serpens have been described in the semi-arid region of Bahia, Northeastern Brazil, in cattle, sheep and horses. However, there are still doubts regarding the type of photosensitization. The objective of this study was to determine if the photosensitization caused by C. serpens is primary or secondary. The disease was reproduced in three groups of two sheep each ingesting C. serpens as the only food or at daily doses of 10 and 20 g per kg bodyweight. The six sheep showed lesions of photosensitization. Two control sheep were not affected. No alterations were observed in the serum activities of aspartate-amino transferase (AST) and gamma-glutamyl transferase (GGT), suggesting that liver function was adequate. No histologic lesions were found in the livers of the sheep with photosensitization, demonstrating that the disease is a primary photosensitization caused by the consumption of C. serpens. This study aimed to clarify the type of photosensitization induced by C. serpens and to verify if the plant remains toxic after being collected and stored. Eight crossbred sheep, aged between 6 and 36 months, were divided into three groups (G1 to G3). Over 30 days, daily, G1 received an exclusive diet of C. serpens, and G2 and G3 received 10 g/kg/BW and 20 g/kg/BW, respectively. Two other sheep were used as controls (CG). Before administration, the plant had been harvested every 15 days. Liver biopsies and blood samples were taken from all sheep on day zero and weekly. All sheep that received the plant developed clinical signs of photosensitization, and no changes were observed in the serum activities of AST and GGT. On day 30, all sheep except Ov1 from G1 and Ov7 were euthanized and necropsied. All sheep that received the plant developed clinical signs. Macroscopic or histologic lesions were not observed in the liver. Ov 1 recovered 13 days after the end of ingestion. These results demonstrated that C. serpens causes primary photosensitization. It is advisable to avoid grazing on pastures invaded by the plant or to remove them from the pastures immediately after observing the first signs.