Seals carried tuberculosis across the Atlantic, gave it to humans

Tuberculosis, an often fatal bacterial infection of the lungs, was a scourge in the days before antibiotics. It's caused by a species of Mycobacteria, most of which live harmlessly in watery environments. Understanding how some of these have managed to make the leap to human lungs has turned out to be rather complicated. Further evidence of this comes from a study published Wednesday that suggests that infectious strains of the bacteria managed to cross the Atlantic before the first European strains did—carried in the lungs of seals.

Getting things wrong about the history of tuberculosis seems to be a regular pastime of the people who study infectious diseases. Originally, due to some genetic similarities, people had proposed that we had picked it up from farm animals. But a careful study of evolutionary trees recently showed that it's likely that cows actually picked up tuberculosis from us, rather than the other way around.

Similarly, the study of the strains found in the Americas had suggested that all of the bacteria present here had been derived from the European version. Which suggested that, along with other lovely gifts like smallpox, the disease was brought to the New World by the first European settlers.