Tuberculosis: The Cow Didn't Do It

The animals that humans share the planet with are and have been reservoirs for all sorts of nasty diseases (deer ticks and Lyme disease; mosquitoes and malaria; Ebola and lord-knows-what wildlife reservoir), but here’s one case where the beasts were accused unjustly. It had long been thought that humans contracted tuberculosis, which currently infects an estimated 2 billion of us, from cattle. But in a clever new study, scientists conclude that humans got it first, and only later did the pathogen Mycobacterium tuberculosis mutate and jump into cows.

Scientists led by Helen Donoghue of University College London and Mark Spigelman of UCL and Hebrew University in Jerusalem (a surgeon-turned-archaeologist who has done fascinating work tracing the prehistoric origins of disease, such as hepatitis B in mummies have discovered what they say are the earliest known cases of human tuberculosis in human bones. Found in the ruins of the village called Alit-Yam, a 9,000 year-old Neolithic settlement that has been submerged off the coast of Haifa for millennia, the bones appear to be of a mother and baby and have lesions characteristic of TB; the disease likely killed them.

A submerged settlement is a jackpot for archaeologists because of the excellent preservation: Atlit-Yam was in a marshland, and the graves were encased in clay. As the sea rose they were “eventually covered by thick layer of sand and later by salt water,” the scientists write, “thus providing anaerobic conditions that retard degradation” and caused “excellent preservation of the skeletal remains”--and of ancient DNA.

Analysis of those remains revealed DNA and other fragments of Mycobacterium tuberculosis, showing that the human disease is at least 9,000 years old—3,000 years older than previously thought. “This is the earliest report of [TB] in humans that has been confirmed by molecular means,” the scientists write. And here’s where the cows get acquitted: examination of the ancient DNA confirms that bovine TB evolved later than human TB.

“What is fascinating is that the infecting organism is definitely the human strain of tuberculosis, in contrast to the original theory that human TB evolved from bovine TB after animal domestication,” Donoghue said. “This gives us the best evidence yet that in a community with domesticated animals but before dairying, the infecting strain was actually the human pathogen.”