WASHINGTON Head lice taken from 1,000-year-old mummies in Peru support the idea that the little creatures accompanied humans on their first migration out of Africa, 100,000 years ago, researchers reported on Wednesday.
Genetic tests showed the lice are nearly identical to strains found around the world that have been dated to when humans first began to colonize the rest of the world.
"It tells us that this genetic type got around the globe right as humans spread and migrated around the globe," said David Reed of the University of Florida, who worked on the study.
"We know that this parasite was distributed all over the globe along with us," Reed said in a telephone interview.
Writing in Journal of Infectious Diseases, Reed and colleagues noted that there are three known strains, or clades, of head lice -- A, B and C.
Clade A is found everywhere, clade B is common in both North America and Europe, and clade C is rare. There had been a theory that clade B evolved separately in the Americas and that European explorers carried A to the Americas and brought B back to Europe with them.
Reed, who showed in 2004 that clade A dated back to early humans, said he got to test the idea by accident.
The lice were collected off the heads of two mummies found in the southern Peruvian coastal desert. "The mummies belonged to the post-Tiwanaku Chiribaya culture," the researchers wrote. They were dated to around 1000 AD.
The two heads, removed from the bodies by looters years before, had elaborately braided hair. Researchers collected more than 400 head lice from one and 500 from the other.
"They were loaded. It was amazing," Reed said. "It really was remarkable how lousy they were."
He speculated that the elaborate braids would not allow for regular combing, thus making a haven for the little parasites.
Reed was able to get intact DNA from the lice and sequencing showed they were all clade A.
That means the strain was distributed across the Americas hundreds of years before the first Europeans arrived.
Reed believes he can use gene sequencing of lice to track and date human migrations all over the world.
Type A lice include both head and body lice. The bloodsucking creatures can only live on humans -- they die very quickly away from their hosts and cannot survive on any other animals.
They can also transmit diseases such as typhus. Reed believes some mummified lice will carry the rickettsia bacteria that transmit typhus, and gene sequencing of these bacteria can also help trace routes of human migration.
It is also possible to test the theory that typhus was a New World disease carried back to Europe by explorers, Reed said.
(Editing by Stuart Grudgings)