New York, Oct 9 (IANS): A mysterious kidney disease that has killed over 20,000 people in Central America since 2002, and now spreading to other countries including India, may be caused by chronic, severe dehydration linked to global climate change, says a new study.

"This could be the first epidemic directly caused by global warming," said one of the researchers Richard Johnson, professor of medicine at the University of Colorado School of Medicine in the US.

So far, the manual labourers on sugar cane plantations in the hotter, lower altitudes of Central America's Pacific coast have been hit hardest by the disease. It has also been reported among farmworkers, miners, fishermen and construction and transportation workers in the region.

"Some districts of Nicaragua have been called the `land of widows' due to the high mortality rates occurring among the male workers from chronic kidney disease," Johnson pointed out.

The epidemic was first described in 2002 and has been dubbed Mesoamerican Nephropathy.

Theories abound about what may be causing it, including exposure to heavy metals, pesticides and other toxic chemicals. But Johnson believes the actual culprit is chronic recurrent dehydration.

His research team studied sugar cane workers in Nicaragua and El Salvador. They found that the labourers routinely worked in conditions exceeding the recommended heat standards of the US Occupational Safety and Health Administration (OSHA).

And even though some of them drank up to one to two litres per hour, the researchers found they still suffered serious dehydration on a daily basis.

One of the major side-effects of this dehydration was hyperuricemia or excess uric acid levels in the blood.

In one study, sugar cane workers in El Salvador had uric acid levels of 6.6 mg per decilitre in the morning which increased to 7.2 mg in the afternoon.

And 21 of 23 people with chronic kidney disease (CKD) had hyperuricemia.

Dehydration also activates a pathway in the kidney which generates fructose that, when metabolised, produces uric acid.

Johnson's team also found that these dehydrated workers had high concentrations of uric acid crystals in their urine.

The uric acid crystals are thought to trigger tubular damage and fibrosis in the kidneys.

The study suggests that this epidemic may be gaining momentum now because global warming is increasing the risk of dehydration.

Johnson said that this kind of CKD is now being observed in Sri Lanka, India, Thailand, and Egypt.

He recommends improving work conditions and hydration practices among those most at risk for developing the disease.

The study was published in the the American Journal of Kidney Diseases.