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By RANDOLPH E. SCHMID, AP Science Writer

WASHINGTON -- Tuberculosis may have been around for millions of years, much longer than had been thought. Previous studies of the TB bacteria's DNA had led to estimates that the lung disease that claims 3 million lives a year worldwide originated about 35,000 years ago.

But Veronique Vincent and colleagues at the Pasteur Institute in Paris now estimate that it could have been present in early hominids as long as 3 million years ago.

"Our results change the current paradigm of the recent origin of tuberculosis," Vincent said in a statement.

While most TB cases are caused by Mycobacterium tuberculosis, Vincent and colleagues studied cases of the disease from East Africa in which colonies of TB bacteria appear physically different from those causing TB elsewhere.

After studying genetic data from the different strains, the researchers concluded that the ancestors of these bacterial strains were also the progenitors of Mycobacterium tuberculosis.

That suggests, they reported, that both strains emerged from a more ancient species of bacteria, possibly as old as 3 million years.

"Tuberculosis could thus be much older than the plague, typhoid fever or malaria, and might have affected early hominids," the researchers say, and its expansion to the rest of the world may have coincided with the waves of human migration out of Africa.

Their findings are reported in the journal PLoS Pathogens.

PLoS, or Public Library of Science, is a nonprofit organization of scientists that publishes several research journals online, with open access so scientific information can be easily shared. PLoS Pathogens is scheduled to premiere Sept. 30, but some material is being made available early as a preview.

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On the Net:

PLoS Pathogens: http://www.plospathogens.org