The worldwide costs of dementia will reach $604 billion in 2010, more than one percent of global GDP output, and those costs will soar as the number of sufferers triples by 2050, according to a report on Tuesday.

To show the scale of the problem, an Alzheimer's Disease International (ADI) report said that if the costs of caring for an estimated 35.6 million people with Alzheimer's disease and other dementias were seen as a country, it would be the world's 18th largest economy, ranking between Turkey and Indonesia.

World governments are woefully unprepared for the social and economic disruptions this disease will cause, said Daisy Acosta, ADI's chairman, describing dementia as the single most significant health and social crisis of the 21st century.

The report, jointly authored by Martin Prince of Britain's King's College London Institute of Psychiatry and Anders Wimo of Sweden's Karolinska Institute in Stockholm, combined the most up-to-date global data on dementia prevalence with added research from care studies in Latin America, India and China.

Alzheimer's is the most common form of dementia, a fatal brain-wasting disease that affects memory, thinking, behavior and the ability to handle daily activities.

Alzheimer's is not normal aging. It is not just a little memory loss. It is a progressive, degenerative disease... with the high risk factor being age. As that unfolds, we're going to see dramatic increases in Alzheimer's, Harry Johns, president of the Chicago-based Alzheimer's Association (AA), said in a telephone interview.

ADI predicts that as populations age, dementia cases will almost double every 20 years to around 66 million in 2030 and 115 million in 2050, with much of the rise in poorer nations.

Low-income nations currently account for under one percent of total worldwide costs, the report said, but have 14 percent of the cases of dementia, while middle-income nations account for 10 percent of the costs and 40 percent of the prevalence.

In comparison, rich nations accounted for 89 percent of the costs but 46 percent of cases. Around 70 percent of global costs now occur in two regions: Western Europe and North America.

A report by the AA in May found that from 2010 to 2050, the cost of caring for Americans over 65 with Alzheimer's will increase more than six times to $1.08 trillion per year.

The developed world is currently where the bulk of the problem is, Johns said. The developing world will be a place where the problem grows dramatically later.

Only a handful of governments have national dementia or Alzheimer's policy strategies -- France, England, Australia do, but the United States and many developing nations do not.

Governments really need to wake up to this, Prince said in a telephone interview. It's all very well for some countries at the moment to say we have families who can take care of these people... but that is a very dangerous strategy.

In the United States, the Alzheimer's Association is pushing for passage of a bill that would create a government body to focus research efforts and develop a national dementia plan.

This is a disaster that is already happening. It's not like the kind of thing that catches us off guard, Johns said.

Despite decades of research into Alzheimer's, scientists have so-far failed to develop drugs that can halt or reverse the brain-wasting disease.

About 100 compounds are being explored in clinical trials as potential future drugs, but some experts say recent failures of experimental drugs in late-stage trials may scare pharmaceutical firms away from Alzheimer's research.