Planet Earth

Migrant Microbes


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Pottery shards, hieroglyphics, and cave art stand as testaments to the restless movements of long-vanished civilizations. So do viruses lodged in the bones of mummies. Two Japanese researchers--epidemiologist Kazuo Tajima and virologist Shunro Sonoda have spent the last decade analyzing the peopling of ancient South America by following the trail of a virus called HTLV-1. The virus, which triggers leukemia in three percent of its carriers, spreads only by direct human contact, so its movements parallel the progress of infected people.

DNA extracted from Andean mummies reveals that viruses from Asia reached the Americas long before the Hong Kong flu.

Courtesy: Kazuo Tajima

Isolated groups in Chile harbor HTLV-1, and Tajima's analysis shows that the virus apparently hitched a ride to South America in the blood of Asian immigrants who crossed the Bering Strait and wandered south 12,000 to 25,000 years ago. After examining 104 mummies in northern Chile, Tajima found the most persuasive evidence in the bone marrow of a 1,500-year-old woman in the town of San Pedro de Atacama. From those bones he managed to extract two intact stretches of DNA from HTLV-1 viruses and discovered the sequence of the stretches closely matched those of the HTLV-1 virus that infects modern Chileans and Japanese. "The Andean people carry a similar genetic background with the southern Japanese people, where HTLV-1 is very common now. This suggests that the Japanese people, in part, share the same or very similar ancestors with the people of the Andes," says Tajima.

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