Leading public health experts at the international AIDS conference in Toronto have called for greater efforts to control tuberculosis, saying treating tuberculosis is key to managing AIDS.

Of the 40 million people living with HIV, experts say about one-third are infected with tuberculosis because of a severely weakened immune system. They say TB infection not only kills HIV-positive patients more quickly, it inhibits their treatment for AIDS.

The World Health Organization's HIV/AIDS director, Kevin De Cock, says TB "may be the Achilles heal of anti-retroviral treatment." "What it means is actually that tuberculosis is a direct threat to the success of antiretroviral scale-up. And that TB, TB management, has to become at the heart of AIDS management," he said.

The mainstay treatment for tuberculosis for more than 50 years has been a drug called isoniazid.

A team of American and Brazilian researchers conducted a two year study to see how effective the drug was in reducing the risk of TB in 11,000 HIV patients in Rio de Janeiro. The scientists found that when taken with antiviral AIDS drugs, isoniazid, taken over a six-month course, reduced the risk of contracting tuberculosis by 75 percent.

Richard Chaisson of the Johns Hopkins University School of Public Health in Baltimore led the study. "A six month course of isoniazid costs pennies. I sometimes wonder whether if we could get the price increased dramatically there would be more activism to make it available. But since it's essentially free, there's been very little activism to make it available," he said.

Chaisson and others say isoniazid therapy should be part of an overall strategy to address tuberculosis in HIV-infected individuals, one that includes automatically testing people for TB.