New evidence from the jungles of Guyana suggests Christopher Columbus and his crewmates carried syphilis-causing bacteria from America to Europe, triggering a massive epidemic that killed more than five million people there.

The findings — which scientists said are the first attempt to use molecular genetics to address the problem of the origin of the venereal disease — were published Monday in the online journal Public Library of Science/Neglected Tropical Disease.

They suggest that Columbus and his crew of explorers brought the deadly disease back from the New World during their famous voyage in 1492 while a non-sexually transmitted subspecies was already in existence in Renaissance Europe, or the Old World.

The study was based around an exceptionally large specimen provided by Canadian infectious disease specialist Dr. Michael Silverman, who leads a medical team into the rainforests of Guyana each year to treat villagers who have virtually no contact with the outside world.

There, he discovered children with ulcer-like lesions on their arms and legs, "just like you get with syphilis but in the wrong place," he told CBC.

Blood tests confirmed the children had yaws, an infectious skin disease believed to be extinct in the Western Hemisphere, though still present in parts of Africa and southeast Asia.

Yaws is considered the cousin of syphilis as they are both distinct varieties of the same bacterium.

Further testing by researchers in the United States suggested that yaws, in fact, was the elder cousin — an ancient infection that evolved from a harmless skin-to-skin condition of the limbs into a devastating sexually transmitted disease around the time of contact with Europeans.

"They couldn't really catch it because they had long sleeves, long pants," Silverman said. "So the only way they could get it, the only time they would expose their skin and might touch somebody was when they dropped their pants to have sex."

Upon the Europeans' return, many of them joined the army of Charles VIII in 1495 and invaded Italy. After their victory in Naples, the army — mostly made of mercenaries — returned home and spread syphilis across the Continent, culminating in the Great Pox.

This first outbreak of syphilis, documented just two years after Columbus and his men sailed the ocean blue in 1492, is believed to have killed more than five million Europeans.

"In this case we have an example of a disease that went the other way, from Native Americans to Europeans," said Dr. Kristin Harper, a researcher in molecular genetics at Atlanta's Emory University and the principal investigator in the study published Monday.

"So that's especially interesting, I think."

Syphilis is usually transmitted through sexual contact and initially results in a painless, open sore or ulcer in the area of exposure. The second stage consists of a rash on the palms of the hands or soles of the feet.

Left untreated, the disease eventually attacks the heart, eyes and brain and can lead to mental illness, blindness and death.