* Outbreak blamed for 122 deaths in Guinea, 13 in Liberia
* Researchers find virus not brought in from outside region
* Raises risk of future outbreaks in West Africa (Recasts and writes through)
By Saliou Samb
CONAKRY, April 17 (Reuters) - An Ebola outbreak blamed for 135 deaths in West Africa in the past month was not imported from Central Africa but caused by a new strain of the ...