Ergot when ground produces a reddish powder which, if we are dealing with dark rye, could very easily be missed. The thing is... ergotism can produce two different results: convulsive or gangrenous.
Signs/Symptoms of convulsive ergotism: nausea, vomiting, hallucinations, mania, psychosis, itching, diarrhea, painful spasms, seizures
Signs/Symptoms of gangrenous ergotism: swelling (edema), sloughing of layers of skin (desquamation), loss of sensation in the extremities as the distal pulses halt, necrosis (tissue death)
Wasn't there evidence that Igor was vomiting blood on the slope? I believe though that's also a sign of hypothermia (hemorrhagic emesis)