What was wrong with Mama's brother?

From the text:

I heard them whispering at night that my uncle had bene bewitched, a bruja had put a curse on him. He had been sick all winter, and he had not recovered with the coming of spring. Now he was on his deathbed. My other uncles had tried everything to cure their youngest brother. But the doctor in town and even the great doctor in Las Vegas had been powerless to cure him. Even the holy priest at El Puerto had been asked to exorcise el encanto, the curse, and he had failed. It was truly the work of a bruja that was slowly killing my uncle!