Natural intoxication by Solanum bonariense causing cerebellar neurodegeneration in cattle in Argentina.

Solanum bonariense is a perennial shrub widely distributed in South America and has also been introduced into other regions, including parts of Europe and North Africa. Its consumption has been associated with chronic neurodegenerative disease in grazing cattle, although well-documented natural cases remain limited, particularly those integrating clinical, epidemiological, and advanced pathological findings. This study provides a comprehensive characterization of a natural outbreak of S. bonariense intoxication in cattle under field conditions. The outbreak was observed on a beef cattle farm located on an island of the Paraná River Delta, Buenos Aires Province, Argentina, during a prolonged drought that resulted in severe forage scarcity. Neurological disease affected 20 of 76 (26%) adult Aberdeen Angus cows, with a high lethality (75%). Clinically, the affected animals exhibited recurrent, episodic neurological signs characterized by abnormal gait (ataxia, hypermetria), postural instability, muscle tremors, frequent falls, and, during recovery, occasional dog-sitting posture and stargazing, with no loss of consciousness. Postmortem examination was conducted in an affected cow; no gross lesions were observed. Histopathological examination revealed marked vacuolar degeneration, death and loss of Purkinje neurons in the cerebellum, with axonal and dendritic spheroids, and secondary demyelination. Prominent reactive cerebellar astrogliosis was demonstrated by immunofluorescence with anti-glial fibrillary acidic protein. Ultrastructural analysis demonstrated numerous membrane-bound intracytoplasmic vesicles containing electron-dense material, consistent with dilated lysosomes in Purkinje neurons. Abundant S. bonariense was botanically identified in the paddocks the affected animals grazed on for nearly 8 months. The epidemiological context, characteristic clinical presentation, and distinctive neuropathological findings support a diagnosis of chronic plant-induced cerebellar neurodegeneration. By integrating field epidemiology with detailed histopathological, ultrastructural, and immunofluorescence data, this study complements previous experimental and sporadic reports and contributes to improved recognition, differential diagnosis, and understanding of the pathogenesis of S. bonariense intoxication in diverse production systems.