On May 10, 1902, a 35-year-old scientist at the Department of Agriculture announced in a medical journal that he’d found a previously unknown human parasite in the southern states. He warned that the creature was causing illness and death among millions of people. This discovery forever changed public health in the U.S. and around the world.

Dr. Charles Stiles had studied with the world’s parasite experts in Germany. As part of his training, he learned about human hookworm, an intestinal parasite that had first been discovered in Europe in 1838.

Hookworms latch onto the lining of the small intestine and suck blood like tiny vampires. The steady blood loss weakens a victim, especially if hundreds of hookworms are living inside the person. Adults are transformed into dull-witted, frail individuals who have trouble working. Infected children are unable to concentrate or learn in school. A severe hookworm infection can be fatal.

America’s medical community denied that human hookworm existed in the U.S.  In fact, most physicians were unfamiliar with the symptoms of an infection. Yet Charles Stiles believed that hookworm was likely here. The South’s warm climate resembled places around the world where the parasite was common. He suspected that doctors were missing cases or misdiagnosing the sick.

By 1902, Stiles had collected proof that hookworm did infect people in the southern U.S. But he was amazed to discover that this hookworm was a completely different species from the one found elsewhere in the world. Stiles named it Necator americanus, or American Murderer.

Stiles’s work had just begun. Could he convince doctors that the threat was real? Could he find a way to cure the many infected southerners and to prevent the parasite from reinfecting them?

I tell the rest of the story in the third book of my Medical Fiascoes series, AMERICAN MURDERER: THE PARASITE THAT HAUNTED THE SOUTH, coming September 27 from Calkins Creek Books/Astra Books for Young Readers.