West Nile sub-region (previously known as West Nile Province and West Nile District) is a region in north-western Uganda that consists of the districts of Adjumani, Arua, Koboko, Maracha-Terego, Moyo, Nebbi and Yumbe. The sub-region received its name from being located on the western side of the White Nile.
In 1937, during research on yellow fever, a previously unknown virus was isolated in samples taken from a feverish woman. It was subsequently designated West Nile virus.