Wednesday, 10 September 2014

TB In The Americas

For years historians have blamed Columbus for bringing tuberculosis to the Americas in 1492. However a new study has suggested that seals and sea lions brought TB to the Americas centuries before Christopher Columbus first set foot there. 
When TB was introduced to the New World it killed as many as up to 95% of the 20 million (possible) Americans who lived there before Europeans arrived, because Americans had no immunity to TB and other foreign diseases such as whooping cough, chicken pox and flu.
An international expert team analysed the DNA of bacteria from three 1,000-year-old human skeletons found in Peru, and found a type of TB closely related to strains that infect seals and sea lions today. Researchers suggest that the mammals contracted the disease from a host animal in Africa, where TB originated about 6000 years ago, and swam across the Atlantic to South America where they were eaten by coastal people who were themselves then infected and spread the bacteria to others.
Genetically, modern strains of New World TB are closely related to European ones, which led to the conclusion that Europeans introduced the disease after Columbus's first contact with Amerindians in 1492. However there is archaeological evidence in skeletons and mummies of tuberculosis in the Americas hundreds of years earlier. Some have suggested the disease must have spread from early humans in Africa, before the Bering land bridge between Siberia and Alaska was flooded at the end of the last ice age about 11,700 years ago. But this fails to explain the European genetic likeness, or the fact that TB is probably a younger disease than that. 
The latest study concluded that TB bacteria in the three ancient skeletons were different to strains found in humans in the Americas today. Having been initially brought over by sea mammals, the disease seems to have been replaced by European strains.