Jack London 
Scarlet Plague 

"The Scarlet Plague" is a post-apocalyptic fiction novel written by Jack London and originally published in London Magazine in 1912.The story takes place in 2073, sixty years after an uncontrollable epidemic, the Red Death, [1] has depopulated the planet. James Smith is one of the survivors of the era before the scarlet plague hit and is still left alive in the San Francisco area, and he travels with his grandsons Edwin, Hoo-Hoo, and Hare-Lip. His grandsons are young and live as primeval hunter-gatherers in a heavily depopulated world. Their intellect is limited, as are their language abilities. Edwin asks Smith, whom they call "Granser", to tell them of the disease alternately referred to as scarlet plague, scarlet death, or red death. (Wikipedia)