Ergot poisoning. Historical photograph of a patient affected by convulsive ergot poisoning (ergotoxicosis). Ergot is a fungus (Claviceps purpurea) that infects cereal plants. Eating food made from infected cereals leads to poisoning, as the fungus contains deadly alkaloids. Convulsive ergotism causes seizures, headaches, nausea, itching skin and hallucinations. It can lead to psychosis. It can also cause constriction of the blood vessels in the extremities, which can lead to the loss of fingers and toes, and other gangrenous symptoms.