LONDON: Deadly strains of tuberculosis (TB) resistant to multiple drugs are spreading around the world, and authorities urgently need another $1.6 billion a year to tackle them, global health officials said on Monday.

Donors should step up with “significant funding” to help experts track down all existing cases and treat the most serious ones, said the World Health Organisation (WHO) and the Global Fund to Fight AIDS, TB and Malaria in joint statement.

“We are treading water at a time when we desperately need to scale up our response to multi drug-resistant TB,” said Margaret Chan, the WHO's director general.

TB is often seen as a disease of the past – but the emergence of strains that cannot be treated by various drugs has turned it into one of the world's most pressing health problems over the past decade.

Of all infectious diseases, only HIV (the human immunodeficiency virus that causes AIDS) kills more people.

In 2011, 8.7 million people fell ill with TB and 1.4 million died of the disease. The WHO says as many as two million people may be suffering from drug-resistant strains by 2015.

Treating even typical TB is a long process. Patients need to take a cocktail of antibiotics for six months and many fail to complete the treatment. That, alongside overuse and misuse of antibiotics, has fuelled growing drug resistance.

Multi-drug resistant TB withstands two standard drugs. And a more severe form known as extensively drug-resistant TB – which can evade even the most highly effective drugs – was reported in at least 77 countries in 2011, according to the WHO.

Doctors in India have also reported cases of totally resistant TB, for which there are no effective drugs.

The WHO and the Global Fund said they had found an anticipated gap of $1.6 billion in annual international support for the fight against TB in 118 low- and middle-income countries.

If this gap were filled, it could mean 17 million patients with TB and multi drug-resistant TB could be fully treated, saving about six million lives between 2014 and 2016, they said.

“It is critical that we raise the funding that is urgently needed to control this disease,” Mark Dybul, executive director of the Global Fund, said in the statement. “If we don't act now, our costs could skyrocket. It is invest now or pay forever.”

The agencies said most of the extra money was needed to seep up the accurate diagnosis of TB, and the process of establishing which drugs it may resist. Cash was also needed to improve access to effective medicines.

On top of the $1.6 billion funding gap, the WHO and its partner health agencies said another $1.3 billion a year was needed to boost research on TB and encourage the development of new drugs, diagnostic tests and vaccines.

The current vaccine known as Bacilli Calmette-Guerin, or BCG, is given routinely to babies in countries with high rates of TB to prevent severe disease.

But its protection wears off in a few years and it does not protect against the most common form of TB that invades the lungs of adults and adolescents.

Eagerly-awaited results last month from trials of the first new TB vaccine for 90 years were disappointing, showing it offered no added benefit over BCG.

Drug companies and research groups are working on other potential new vaccines but scientific progress is proving tricky and slow.