Nicaraguan widow Isabel Zapata Manzanares looks out over the sugarcane fields beside her home in Chichigalpa. Zapata lost her husband and four sons to kidney disease. Tim Gaynor / Al Jazeera America

CHICHIGALPA, Nicaragua — Isabel Zapata Manzanares lost her husband to kidney disease shortly after he retired from the sugarcane fields in 1993. Then, one by one, four of her sons sickened and died.

Eusebio Ernesto, a fieldworker, perished a decade ago. Victor Emmanuel died four years later, followed by Jose Graviel two years after that. Then last year Francisco took sick with disease.

"They told him it was too late for dialysis,” she recalled, sitting on a plastic chair outside her tin-roofed shack near this city in Nicaragua's coastal lowlands. “He swelled up ... he had pains in his body... and he died here at home."

The five men in Zapata's family are among tens of thousands cut down by a new form of chronic kidney disease striking like a scythe across the sweltering plains of Central America's sugar belt from Mexico to Costa Rica.

Chronic kidney disease rates began to climb in poor farming communities in the Pacific coast strip at least a decade ago, although it was not immediately clear to doctors that they were witnessing a lethal new form of the disease.

Dubbed chronic kidney disease of unknown causes, it has since killed at least 20,000 people, and probably many more, across the region just two hours' flight from the United States. The cause has baffled researchers, although there is no shortage of suspects.

The fertile strip is drenched in toxic agrochemicals. The cane cutters themselves risk heat stress toiling long hours in sauna-like conditions, while the fields they work are perfect for propagating deadly rat-borne pathogens.

As researchers puzzle over a cause, the illness is hammering communities hardest in the volcano-studded plains of Nicaragua and neighboring El Salvador, where deaths from chronic kidney disease are now four times the global rate. In El Salvador, it is currently the leading cause of hospital deaths for men, according to research published by MEDICC Review.

So many working men have died in the rural community of La Isla, or The Island, near where Zapata lives that it has become known as "The Island of Widows." And in Chichigalpa, the company town for Nicaragua's largest sugar producer, Ingenio San Antonio, almost a third of working-age men now have irreversible kidney damage.

"Most people who worked for Ingenio San Antonio have lost a family member to kidney failure, whether it be a father, a son or a cousin ... or they have someone at home who is sick," said former sugarcane worker Juan Salgado. Salgado himself is sick with the disease, as are two of his brothers. Three of his cousins are dead.