inconvenience, accounting for about 80 million cases of mostly nonfatal malaria each year. Its origins have lately been elucidated, again using molecular phylogenetics, and again one of the researchers involved is Ananias A. Escalante, formerly of the CDC, now at Arizona State University. Escalante and his partners have shown that, rather than emerging from Africa along with the earliest humans, as P. falciparum seems to have done, P. vivax may have been waiting for our ancestors when they arrived to colonize Southeast Asia. The evidence suggests that its closest relatives are plasmodia infecting Asian macaques.
I’m not going to summarize this body of work, because we’re in deep enough already; but I want to alert you to one small aspect that leads off irresistibly on a peculiar tangent. Escalante’s team reported in 2005 that P. vivax shares a recent ancestry with three kinds of macaque malaria. One of those is Plasmodium knowlesi, a parasite known from Borneo and Peninsular Malaysia, where it sometimes infects at least two native primates, the long-tailed macaque and the pig-tailed macaque. P. knowlesi occupies a strange place in medical annals, involving the treatment of neurosyphilis (syphilis of the central nervous system), which for a time in the early twentieth century was done using induced malarial fevers.
The story goes like this. Dr. Robert Knowles was a lieutenant colonel in the Indian Medical Service, assigned to Calcutta in the 1930s and doing malaria research. In July 1931 he came into possession of an unfamiliar new strain of malarial parasite, derived from an imported monkey. It was a plasmodium, he could see, but not any he recognized. Knowles and a junior colleague, an assistant surgeon named Das Gupta, decided to study it. They injected the bug into several other kinds of monkey and followed the progress of infection. This mystery strain proved devastating to rhesus macaques, causing high fevers and high loads of parasites in the blood, killing the animals quickly. In bonnet macaques, though, it had little effect. Knowles and Gupta also injected it into three human volunteers (that is to say, “volunteers,” their freedom to decline having been a dubious matter), one of whom was a local man who had come to the hospital for treatment of a rat bite on his foot. This poor guy got very sick—not from the rat bite but from the injected malaria. In those experimental subjects (monkey and human) who suffered intermittent fevers, Knowles and Gupta noticed that the period of the fever cycle was one day, as distinct from the two-day or three-day cycles known for human malarias. Knowles and Gupta published a paper on the unusual parasite but didn’t give it a name. Soon afterward another set of scientists did, labeling it Plasmodium knowlesi in honor of its senior discoverer.
Shift of scene: to Eastern Europe. Reading the literature, a well-connected malaria researcher in Romania named Mihai Ciuca got interested in the properties and potential uses of Plasmodium knowlesi and wrote to one of Knowles’s colleagues in India, asking for a sample. When the monkey blood arrived, Professor Ciuca started injecting doses of P. knowlesi into patients with neurological syphilis. This was not nearly as crazy as it sounds, though even for Romania perhaps a little edgy, since the range of effects of P. knowlesi in humans was so little known. Still, Ciuca was merely following a line of therapy that had not only proven effective but had been scientifically canonized. Back in 1917 a Viennese neurologist named Julius Wagner-Juaregg had begun inoculating advanced syphilis patients with other strains of malaria, and not only had he escaped malpractice prosecution and accusations of criminal goofiness but he had also received a Nobel Prize in medicine. Wagner-Juaregg was a man of unsavory eminence in the old style, a bilious anti-Semite who advocated “racial hygiene,” favored forced sterilization for the mentally ill, and wore a Nietzschean mustache, but his “pyrotherapy” using malaria seems to have helped many neurosyphilis patients, who otherwise would have suffered out their last days in asylums. There was cold logic—revise that, hot logic—to Wagner-Juaregg’s mode of treatment. It worked because the syphilis bug is so sensitive to temperature.
Syphilis is caused by a spiral bacterium (aka a spirochete) known as Treponema pallidum. The bacterium is usually acquired during sexual contact, whereupon it corkscrews its way across mucous membranes, multiplies in the blood and lymph nodes, and, if a patient is especially unlucky, gets into the central nervous system, including the brain, causing personality change, psychosis, depression, dementia, and death. That’s