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DNA from Peruvian Mummy Lice Reveals History

NEW YORK (GenomeWeb News) – DNA sequences from 1,000 year old lice picked from the hair of Peruvian mummies are revealing the tiny pests’ travels — and demonstrating a new trick that might also help track human migration patterns.
 
By sequencing two mitochondrial genes from ancient mummy lice found in Peru, French and American researchers determined which sub-group of modern-day lice the parasites resembled most closely, providing new insights into the parasite’s history. The findings, which will be published in the Feb. 15 issue of the Journal of Infectious Diseases, suggests a disease-carrying louse strain was in the New World earlier than suspected — before Columbus came to America.
 
While mtDNA is very precisely typed in other animals, researchers have only recently started doing the same in lice. They have discovered that there is not one, but three, distinct louse lineages — called types A, B, and C — which have different geographic distributions. For instance, most lice taking up residence on heads across the Western Hemisphere are type B lice.
 
But this may not always have been the case. The new paper used louse genetics to determine the lineage of lice discovered from the naturally preserved heads of Peruvian mummies excavated between 1999 and 2002.
 
“They looked exactly like modern [louse] samples,” David Reed, a researcher with the University of Florida’s Florida Museum of Natural History and one of the study’s lead authors, told GenomeWeb Daily News today. “It was remarkable how well preserved these lice were.”
 
The team extracted DNA from two to five lice at a time, grinding them together to maximize the amount of DNA available. Despite the age of the samples, it was relatively easy to retrieve nucleic acid from the lice using modified silica-based extraction. “It was actually very straightforward,” Reed said. “I think it was because the mummification was so rapid and complete.”
 
Using sequence-specific primers, the team sequenced two mitochondrial genes, cytochrome oxidase subunit 1 and Cytb, independently at two different labs in Florida and Marseille.
 
Both labs came up with the same sequence for the genes, which were used as markers for louse mitochondrial ancestry. Because these particular genes are well conserved over louse history, they could be easily compared with GenBank sequence data from modern lice in each of the three sub-groups.
 
Surprisingly, Reed said, the team only found one type of lice on the mummies: type A. This was particularly unexpected because these days type B, not type A, lice account for half the cases in the US, Canada, and Central America.
 
Contrary to previous ideas, this also suggests type A lice beat Columbus to America. Since these lice are the type best known for transmitting epidemic typhus, Reed said, this finding may indicate that those diseases actually originated in the Americas and spread to Europe along with type A lice later.
 
“This definitely goes against the grain of conventional thought that all diseases were transmitted from the Old World to the New World at the time of Columbus,” Reed said in a statement.
 
While this particular study reveals more about louse migration than human migration, Reed believes a similar approach comparing more variable louse genes could be used to track human movement as well. Since the parasites have co-evolved with humans, similar experiments may shed light on how and when human populations traveled between continents.
 

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