Imagine if the World Health Organization announced that a new, highly infectious airborne disease would claim 1.6 million lives over the next year. With no vaccine and a lengthy treatment regimen, the development of lethal, drug-resistant strains of the bug would be a serious risk. Of course, the world’s leaders would be galvanised into action immediately.

This is not really fiction, however. It describes a disease that is as old as humankind: tuberculosis.

In the 19th century, “consumption” was the leading cause of death in the west. The combination of better housing and Alexander Fleming’s accidental discovery of antibiotics in 1928 transformed the situation. The world believed TB was beaten.

But it was never eradicated, and in the 1980s TB flared up again, on the back of the Aids epidemic. Striking opportunistically when the body’s resistance is low, it is the most common cause of death among people with Aids. TB was declared a Global Health Emergency in 1993. In the 25 years since then, nearly 50 million people have died. Today TB kills more people than Aids and malaria combined: it is the world’s deadliest infectious disease.

Why have global leaders been so slow to react? Because TB is a disease of the poor. Until recently, no new medicines for TB treatment had been approved for over 40 years. The bug is still treated with antibiotics, which are taken over a period of months, and vaccine development has been critically underfunded.

The Sustainable Development Goals agreed by the world’s leaders four years ago commit to ending the Aids, malaria and TB epidemics by 2030. Yet at the current rate of progress TB will not be beaten for over a century.

The Global Fund was set up to fight TB as well as malaria and Aids, and it provides two-thirds of all international financing for tuberculosis, yet the share of TB spend within the fund is disproportionately low. Doctors know how to treat TB: we’re just refusing to pay for it. This isn’t a medical problem – it’s a shameful political failure.

Today the United Nations will convene the first High-Level Meeting on TB, which will be attended by heads of state or government. The draft declaration calls for an “urgent global response” and reaffirms the commitment to end the epidemic by 2030. There are three reasons why it is imperative to act now. First, the humanitarian case. It is scandalous that 30 million people will die needlessly over the next 15 years when the disease has been easily and cheaply curable for over half a century. As progress has been made in fighting Aids and malaria, the failure to tackle TB has been revealed in plain sight. Our consciences should not allow that to stand.

The second reason to act is economic. Millions of sick people are an impediment to economic development in some of the world’s poorest countries. The failure to tackle TB by 2030 will cost the global economy $1 trillion. TB treatments are amongst the most cost-effective health interventions, and a relatively small boost in research and development to fight the disease could save billions of dollars in later years.

The third reason to act is to ensure global health security. Drug-resistant tuberculosis accounts for one-third of deaths due to antimicrobial resistance globally. As the UN declaration this week notes, if we fail to address this, “the grave individual and public health risks posed by multidrug-resistant tuberculosis are cause for alarm”. Only a quarter of multidrug-resistant TB cases are being diagnosed and notified. The already heavy economic toll of TB would pale by comparison with the cost of unchecked drug resistance. The UN declaration says all the right things. Resources should be increased, public health systems strengthened, and research and development boosted. Significantly, it includes a new commitment to the rapid scaling up of access to testing, so that at least 40 million people will be diagnosed and treated by 2022. Currently one in three people with the disease – and 71% of people with drug-resistant TB – are “missing”. If the new treatment target is met it will at last break the back of the epidemic.

But will it be met? Such ambitious proposals will be achieved only if every country delivers its share of the target. The key question will be how the declaration is translated into action. There is no mechanism to hold leaders to account for delivering on the promises, beyond the existing framework set by the World Health Organisation. Frankly, if that was effective we would not be so off track now.

As little as two years ago TB simply wasn’t on the political radar. It has risen rapidly up the agenda since then, with declarations at the G7 and G20, and a summit of health ministers in Moscow last year. The announcement by the Indian prime minister, Narendra Modi, earlier this year of an ambitious new plan to beat TB in his country was seen as a milestone in the fight. This week’s UN meeting has the potential to be a turning point.

Thirty heads of government will attend the meeting – but many countries will merely send a minister. Europe will be particularly poorly represented. Of course, global leaders face many other challenges, but a disease that is killing more than 4,000 people a day should no longer be ignored.

Still, every country will be signed up, so what will matter is what governments actually do when the ink on the declaration is dry. As the failure of the declaration of TB as a global health emergency a quarter of a century ago has shown us, words are not enough. We must demand that governments translate today’s promises into action.

• Nick Herbert MP is co-chairman of the Global TB Caucus