CDC will explore kidney failure epidemic among agricultural workers

The US Centers for Disease Control and Prevention (CDC) has launched three new studies to examine a lethal epidemic of kidney failure that has killed agricultural workers along Central America’s Pacific coast and in regions of Sri Lanka, India, and Egypt.

Chronic kidney disease of unknown origin, or CKDu, has crept up on health authorities in the affected countries, affecting many poor rural communities far from research centers. India’s epidemic, concentrated in the Uddanam region of Andhra Pradesh, emerged after research into typical forms of chronic kidney disease had found large numbers of young men with the disease who had neither diabetes nor hypertension—the usual precursors of kidney failure.

But the largest affected region is western Central America, where at least 20 000 men of working age are believed to have died from CKDu.1 The disease has become the leading cause of death in hospital among men of working age in El Salvador, and pockets of Nicaragua have shown even greater prevalence.

Most early documented cases involved people working with sugar cane, the region’s dominant industry. Many sugar plantations in the region now test their employees’ kidney function each year and dismiss those with failing results.

But research has shown that CKDu also strikes the area’s miners and port workers. In India and Sri Lanka, rice cultivators account for most of the cases. And preclinical markers of kidney disease have been found in the adolescent schoolchildren of Central American sugar workers.

Daniel Brooks, an epidemiologist at Boston University, Massachusetts, has extensively studied CKDu and will work on the new studies to examine heavy metal contamination, possible genetic predisposition, and kidney function in adolescents. A five year prospective study will also compare different working regimes and approaches to keeping workers hydrated.

“It’s clearly multifactorial,” said Brooks. “No single risk factor could account for the patterns we see.” A consensus has emerged among people studying Mesoamerican nephropathy that heat stress is one of the key factors; but other equally hot areas, such as the Cuban sugar fields, have had no CKDu. Heat stress and dehydration might exacerbate damage from some environmental toxin found in pesticides, soil, or drinking water, Brooks said.

The sugar industry associations in Nicaragua and El Salvador argued that they had been unfairly blamed for the disease, and they are the primary funders of the CDC’s new studies, providing $1.7m (£1.01m; €1.24m). The CDC has insisted that measures are in place to ensure the independence of the research, which will be published irrespective of findings.

In Sri Lanka, where the World Health Organization and the government have taken the lead in investigating CKDu, attention has focused more sharply on pesticides. In March Sri Lanka’s president, Mahinda Rajapaksa, ordered a ban on glyphosate, the active ingredient in the world’s best selling pesticide, Roundup. The decision was based on research from Sri Lankan scientists, which argued that glyphosate’s metal chelating properties caused it to concentrate heavy metals such as cadmium—found in soil and pesticides—and transport them to the kidneys.2

The ban has yet to be implemented, and it has faced resistance from agricultural employers and Roundup’s producer, Monsanto. El Salvador’s legislature last September banned glyphosate and 52 other agrochemicals, but that ban is also not yet confirmed.

Brooks said he feared that new regions afflicted by the disease were still to be identified. “There are plenty of anecdotal reports from other regions, but no data,” he said. The disease was only discovered in 2002,3 and its beginnings are obscured by the lack of data.

“It’s possible that something like this has always been there and has only lately been noticed,” said Brooks. “But that’s not the feeling in the affected communities themselves. The best evidence suggests that this problem dates from the early 1990s. And the evidence suggests that yes, it is probably getting worse over time.”