Apparently Genghis, et. al., had a few stowaways:
A report in the October issue of Genome Research suggests that Genghis Khan’s invasions spanning the continent of Asia during the 13th century may have been a primary vehicle for the dissemination of one of the world’s most deadly diseases: tuberculosis….
Mokrousov’s team hypothesized that, given the strong gender bias of TB infectivity and the likely family-based mode of TB transmission during pre-industrialized times, M. tuberculosis dissemination has reflected the unidirectional inheritance of the paternally transmitted human Y chromosome. To test this hypothesis, the authors compared the genetic profiles of a common form of M. tuberculosis, called the Beijing genotype, with known patterns of prehistoric and recent human migrations, as well as with global patterns of Y-chromosome variation.
Strikingly, they observed that over the past 60,000-100,000 years, the dispersal and evolution of M. tuberculosis appears to have precisely ebbed and flowed according to human migration patterns.
The authors describe how the Beijing genotype of M. tuberculosis originated in a specific human population called the K-M9 in central Asia approximately 30,000-40,000 years ago following a second “out of Africa” migration event. The bacteria and its human host then disseminated northeast into Siberia between 20,000-30,000 years ago and throughout eastern Asia between 4,000-10,000 years ago. More recently, the Beijing genotype of M. tuberculosis was introduced into northern Eurasia, perhaps by Genghis Khan himself during the 1200′s, and into South Africa, possibly through sea trade contacts with Indonesia or China during the last 300 years.