* WHO says many TB cases in marginalised groups are missed
* Contagious disease spreads easily but is hard to treat
* Care, treatment for drug resistant TB under-resourced
* $7 to $8 bln a year needed to get TB under control by 2015
By Kate Kelland
LONDON, Oct 23 (Reuters) - Cases of people infected with tuberculosis and the number of deaths from it fell in 2012, but progress on controlling the contagious lung disease is under threat from growing drug resistance.
In its annual report on tuberculosis, the World Health Organisation said the world was on track to meet U.N. goals for 2015 of reversing TB incidence and cutting the death rate by 50 percent compared to 1990.
Yet around 3 million people with TB are being missed by health systems, and "superbug" drug-resistant strains of the bacterial infection are putting progress at risk.
"Far too many people are still missing out on care and are suffering as a result," said Mario Raviglione, the WHO's director of the Global TB Programme.
"They are not diagnosed, or not treated, or information on the quality of care they receive is unknown."
TB is often seen as a disease of the past, but the emergence over the past decade of strains that can not be treated with existing drugs has turned it into one of the world's most pressing health problems.
Of all infectious diseases, only HIV - the human immunodeficiency virus that causes AIDS - kills more people than TB.
In 2012, an estimated 8.6 million people developed TB and 1.3 million died from the disease, including 320,000 deaths among HIV-positive people, according to Wednesday's WHO report, down from 8.7 million cases and 1.4 million deaths in 2011.
Raviglione said insufficient resources for TB were at the centre of all the hurdles to further progress. The WHO says $7 to $8 billion a year is needed for a full response to the global TB epidemic by 2015, and there is a funding shortfall of some $2 billion a year.
Many TB programmes do not have the capacity to find and care for people in hard-to-reach groups - such as the homeless, the poor, and the marginalised, who often live outside any formal or state health system.
Weak links in what health experts call the "TB chain" -connecting proper detection and diagnoses to quality treatment and care - lead to people in these groups being missed.
The WHO estimates that 75 percent of the 3 million missed TB cases are in just 12 countries, with South Africa, Bangladesh, India and Pakistan among them.
On the issue of multi-drug resistant TB (MDR-TB), the WHO report said the problem was not only that the links in the chain were weak, but that links were not even there.
The U.N. health agency estimates that 450,000 people fell ill with MDR-TB in 2012 alone, with China, India and Russia worst affected, followed by another 24 other countries.
More worrying, around 16,000 MDR-TB cases reported to WHO in 2012 were not put on treatment, with long waiting lists becoming a increasing problem.
Raviglione said it was unacceptable that increased rates of diagnosis were not matched by more access to MDR-TB care.
"We have patients diagnosed but not enough drug supplies or trained people to treat them," he said.
Grania Brigden, a TB adviser for the international medical charity Medecins Sans Frontieres, said the failure to improve rates of diagnosis and treatment for drug-resistant TB is being paid for in lives.
"The horrific scale of preventable suffering and death caused by the spiralling drug resistant TB crisis must spur governments, donors and WHO to mobilise the political will and secure the funding ... to tackle this deadly epidemic head on," she said.
The WHO's report is based on data from a total of 197 countries and territories that collectively have more than 99 percent of the world's TB cases. (Editing by Alison Williams)