In 1927, the Nobel Prize in Physiology or Medicine was awarded to a man for giving people malaria, making Julius Wagner-Jauregg one of only two psychiatrists to win a Nobel Prize.
Wagner-Jauregg was a professor of psychiatry and Director of the Neuro-Psychiatric Clinic at the University of Graz, Austria in 1917, when he noticed that some of his patients with paralysis who were deemed insane showed remarkable recoveries following fevers. Naturally, he began experimenting on the rest of his patients, as was the style at the time.
He believed that by introducing a fever to these patients, he could perhaps alleviate or cure their symptoms, as he had seen naturally in other patients. The belief that fevers could cure or alleviate mental illness went back centuries and was even used as a treatment. However, what Wagner-Jauregg came up with was a reliable way to introduce a fever to patients, and scientific proof that it works. After trialing several methods of inducing a fever, including erysipelas — a relatively common bacterial infection of the skin — he settled on old, reliable malaria.
Malaria is no mild thing. Mortality rates from the resulting fever have been estimated at between 3 and 20 percent. However, the patients who he had observed making a recovery were in a late stage of syphilis known as general paralysis, where the sexually-transmitted infection had attacked the brain, making patients lethargic and eventually paralyzed, often resulting in death. For them, the risks of malaria, which would be treated with quinine, and monitored in hospital, were far less than allowing their condition to deteriorate.
The strain he chose, Plasmodium vivax, produced a long, high fever in patients and was used for decades after his discovery. Malaria was used to fight syphilis until the 1950s, when syphilis began to be treated with penicillin.