For years, Marecitta Dorsey’s four children – ages seven to 14 – suffered regular bouts of nausea, vomiting and sore stomachs. Their unexplained symptoms were bad enough to keep them out of school a few days each month.

“My eldest would tell me, ‘I feel like my tummy’s burning,’” recalled Dorsey. “Every week I was taking at least one kid to the doctor because of something with their stomach.”

She suspected their ailments had something to do with the water. Her children, she said, never had stomach problems before they moved to the Delta.

Dorsey and her family lived in Shaw, Mississippi, a town of 1,400 people about 110 miles (175km) north of Jackson. The area is plagued by sanitation problems – residents in Bolivar county filed half a dozen complaints to state officials just last year about wastewater leaks and burst pipes that have exposed them to raw sewage.

Now, researchers warn that these problems are probably contributing to widespread intestinal infections and parasites such as hookworm, roundworm and tapeworm.

“There’s this whole idea that the US eradicated these things [parasites],” said Tara Cepon-Robins, an anthropologist at the University of Colorado, Colorado Springs. “But nobody actually eradicated anything.”