Image caption Some strains are becoming resistant to antibiotics

Tuberculosis which appears to be totally resistant to antibiotic treatment has been reported for the first time by Indian doctors.

Concern over drug-resistant strains of TB is growing, with similar 'incurable' TB emerging in Italy and Iran.

Doctors in Mumbai said 12 patients had a "totally drug resistant" form of the infection, and three have died.

The Indian Health Ministry is investigating the cases and has sent a team of doctors to Mumbai.

TB is one of the world's biggest killers, second only to HIV among infectious diseases.

Normally a patient with TB is given a six to nine month course of antibiotics to eradicate it.

However, new strains of the bacterium have developed which are increasingly resistant to the antibiotics most commonly used to treat it.

Partially drug-resistant TB can now found in countries across the world, and "multi-drug resistant" strains affect countries such as Russia and China.

'Serious threat'

The Indian reports will fuel concerns over the ability of doctors to contain the disease in years to come.

Anytime we see something like this, we better get on top of it before it becomes a more widespread problem Dr Kenneth Castro, Centers for Disease Control

The doctors at the Hinduja National Hospital in Mumbai who discovered it said they had treated patients for up to two years with a battery of drugs, to no avail.

The patients came from slum areas of the city, they said, where close contact between people meant further spread was likely.

The American Centers for Disease Control (CDC) confirmed that the Indian strain did appear to be completely resistant.

Dr Kenneth Castro, director of its Division of Tuberculosis Elimination, said: "Anytime we see something like this, we better get on top of it before it becomes a more widespread problem."

Patients who do not finish their lengthy course of treatment also present the bacterium with the perfect environment for developing further resistance.

However, there have been repeated calls for the pharmaceutical industry to make more efforts to develop fresh antibiotics.

TB Tuberculosis is an infectious disease that usually affects the lungs

It is transmitted via droplets from the lungs of people with the active form of the disease

Symptoms of TB include coughing, chest pains, weakness, weight loss, fever and night sweats

Tuberculosis is usually treatable with a course of antibiotics

Dr Ruth Mcnerney, a senior lecturer at the London School of Hygiene and Tropical Medicine and a trustee of charity TB Alert, said the new cases represented a "serious threat" to global efforts to control TB.

"What we're seeing is probably just the tip of the iceberg. We don't know how widespread this is because so few people are tested for drug resistance."

She said the high prevalence of TB in India, coupled with high population density within its cities, meant that the new type of TB could be a bigger problem than previous "totally resistant" strains.

"It's going to take a massive effort and change in political will to get to grips with this - not just from the Indian government but from everyone else. This is a global problem, not just an Indian one."