Intoxication of sheep by Astragalus arequipensis in northwestern Argentina

Abstract

Spontaneous intoxication by Astragalus arequipensis was diagnosed in a flock of 300 sheep in Jujuy province, northwestern Argentina, that grazed an area heavily invaded by this plant. The main clinical signs were intention tremors, ataxia, and progressive loss of condition. Autopsy of 2 affected animals revealed loss of body condition. The main microscopic changes were fine cytoplasmic vacuolation of cells in the cerebrum, cerebellum, thyroid and adrenal glands, kidney, liver, pancreas, urinary bladder, and lymph nodes, and swollen axons in the cerebellum. Ultrastructurally, the cytoplasmic vacuoles consisted of dilated secondary lysosomes. Composite leaf and stem samples of A. arequipensis analyzed by high-performance liquid chromatography contained 0.05% swainsonine. The diagnosis of intoxication by A. arequipensis was made based on the clinical history and signs; gross, microscopic, and ultrastructural changes; and detection of swainsonine in the plant.

Keywords: Argentina; Astragalus arequipensis; intoxication; locoism; lysosomal storage disease; sheep; swainsonine.

Figure 1.

Astragalus arequipensis. A. Specimen of A. arequipensis showing leaves, flowers, and fruits. B. Paddock with predominance of A. arequipensis.

Figure 2.

Histology of several tissues from a sheep intoxicated by Astragalus arequipensis, with fine cytoplasmic vacuolation. A. Neurons of the oculomotor nucleus in the midbrain. B. Cerebellar Purkinje cells. C. Renal convoluted tubules. D. Pancreatic acinar cells. E. Thyroid gland follicular epithelium.

Figure 3.

Transmission electron microscopy of tissues of a sheep intoxicated by Astragalus arequipensis. A. Cerebellar Purkinje cell with accumulation of secondary lysosomes (arrow). N = nucleolus. Bar = 10 µm. B. In the cytoplasm of pancreatic acinar cells, dilated secondary lysosomes contain small membrane profiles. Zymogen secretory vesicles are indicated with an arrow. N = nucleus. Bar = 1 µm. C. Accumulation of secondary dilated lysosomes in the cytoplasm of thyroid follicular epithelial cells. C = colloid; N = nucleus. Bar = 10 µm.