One of the first successful physical treatments for mental illness, the "fever cure" involved deliberately infecting someone with a febrile disease in order to treat a psychiatric disorder, particularly neurosyphilis. It was developed between 1887 and 1917 by Dr. Julius Wagner-Jauregg.
In its last stages, syphilis attacks the brain and victims suffer a variety of neurological symptoms. Before the development of effective treatments, death was a mercy that arrived after the sufferer was mad, in pain, and nearly paralyzed. The medical community, in the absence of any good reason not to, treated neurosyphilis (also known as "general paralysis of the insane" or "paresis") as just another mental illness. The discovery of the spirochete that caused syphilis didn't change this; it seemed instead a reason to hope that there were similarly simple organic explanations for other untreatable mental health problems.
People with neurosyphilis were therefore interned in asylums. By the first two decades of the 20th century they made up a substantial minority of the population of psychiatric hospitals in Europe and the United States. There they received the standard treatments: Sedatives and neglect. Other inmates sometimes recovered spontaneously; GPI patients never did.
Wagner-Jauregg was an Austrian physician interested in the possibility of physical treatments for mental illness. He had been involved in work on the connection between iodine and cretinism and knew of the slightly earlier "bromide sleep cure" of Neil McLeod (in which patients were kept under very heavy sedation for a week or two in hopes that -- as often actually happened, if they didn't choke to death on vomit -- they would wake up better). He'd noticed (or perhaps read) as a student that psychiatric symptoms sometimes abated when a patient developed a fever. He began to experiment on terminal patients with tuberculosis vaccine. Despite some promising results, Wagner-Jauregg soon gave this up. The vaccine was thought to be toxic and, anyway, he had long had a better agent in mind.
Malaria seemed ideal. The fever was severe but predictable and, by the standards of the day, very controllable and not too dangerous1. When a soldier arrived at his hospital with the tertian variety, Wagner-Jauregg seized his chance: He took some blood and injected it into a man in the last stages of neurosyphilis. Over the following weeks, the doctor watched his patient suffer nine attacks of fever.
The symptoms of syphilis gradually abated. Wagner-Jauregg treated the malaria; the improvement continued. He performed the procedure eight more times and then published the results. The fever therapy became famous. Apart from rare spontaneous remissions, people didn't recover from neurosyphilis: It was a death sentence. This new treatment significantly helped nearly half the patients who received it -- it was not a miracle cure, but it meant the salvation of thousands.
The medical community wasn't altogether sure why the treatment worked. The most popular theory held that the spirochete was destroyed by the heat of the fever; but it was soon discovered that the bacterium returned to the brain after an attack even when the remission in symptoms was permanent. Nevertheless, Wagner-Juaregg received the 1927 Nobel prize in physiology or medicine.
Within a few years, though, his therapy was completely superseded. Penicillin cured syphilis altogether, cleanly, without fuss. A few attempts were made to apply the fever cure to schizophrenia, but without much success. It was a dead end.
As far as psychiatry is concerned, the importance of the fever cure lies in the period of experimentation with physical cures that resulted. It was at the leading edge of a wave of desperate new treatments. A few of these, like insulin coma therapy, were more or less successful but dangerous and unpleasant. Some were bizarre and wildly unethical. A few were tragic and grotesque. The only survivor of the era is one of the convulsant therapies: ECT, still a standard treatment for severe depression.
In the long run, psychiatry returned to drugs. It 1951 the first effective antipsychotic appeared and most other therapies -- except for psychological therapies and ECT -- were eventually abandoned. In the years since, the treatment of mental disorders has become mostly a matter of applied pharmacology and the malaria fever cure just another historical curiosity.
1 That is, not too dangerous for someone who was about to die anyway. From Wagner-Jauregg's Nobel lecture: "The high temperatures on the one hand and the brief pauses in the quotidian type on the other, make on the usually already weakened organism of the paralytic, especially on his heart, often too great demands; and thus we and others also have seen not by any means infrequent cases of death during the fever period or immediately afterwards."
Edward Shorter, A History of Psychiatry, 1997.
The Nobel prize presentation speech: http://www.nobel.se/medicine/laureates/1927/press.html
The Nobel lecture: http://www.nobel.se/medicine/laureates/1927/wagner-jauregg-lecture.html. At the end, Wagner-Jauregg
speculates a bit about why the fever cure works; he isn't quite sure.