What we do — and don't yet — know about the malaria cases in the U.S.

Even though the U.S. said it eliminated malaria in 1951, efforts have continued to keep the disease at bay. Above: A Stearman biplane sprays insecticide during malaria control operations in Savannah, Georgia in 1973. (Smith Collection/Gado/Getty Images)

In the 1950s, the U.S. declared that it had wiped out malaria. As NPR reported a few years ago, this public health milestone was achieved "through the use of insecticides, drainage ditches and the incredible power of window screens."

This week, headlines trumpeted the "return" of malaria: four cases in Florida and one in Texas.