Tapeworm in the brain

For four years a man in England was having problems with his head: headaches, memory problems, strange olfactory hallucinations and seizures. After many scans the doctors found an unidentified mass in the patient’s brain that appeared — after repeated scans — to be moving from one side of his head to the other. When they removed the mass, they found a 10 cm long parasitic tapeworm, known as Spirometra erinaceieuropaei. It is very rare; only 300 human patients have been identified as victims since 1953, and only two of those victims were in Europe.

They really don't know how the tapeworm entered the man's brain but think it came from contaminated food or water or burrowed in through the skin.