The finding raises concern that although TB incidence is falling in many regions, the emergence of antibiotic resistance could see virtually untreatable strains of the disease become widespread.
A research team including Dr Mark Tanaka, Dr Fabio Luciani from UNSW’s Evolution Ecology Research Centre and Dr Scott Sisson from UNSW School of Mathematics and Statistics, found drug-resistant strains of TB were just as capable of spreading from human to human as the ordinary bacteria.
"Our results imply that drug resistant strains of TB are likely to become highly prevalent in the next few decades," Dr Luciani said.
The researchers used epidemiological and molecular data from Mycobacterium tuberculosis strains isolated from Cuba, Estonia and Venezuela to estimate the rate of evolution of drug resistance and to compare the relative "reproductive fitness" of resistant and drug-sensitive strains.
"We found that the overall fitness of drug-resistant strains is comparable to drug-sensitive strains," said Dr Tanaka. "This was especially so in Cuba and Estonia, where the there is a high prevalence of drug-resistant cases."
One in three humans already carries the TB bacterium. Although it remains latent in most cases, the World Health Organisation (WHO) has estimated there were 9.27 million new cases of TB in 2007, with 1.6 million TB-related deaths reported in 2005.