By Saliou Samb CONAKRY (Reuters) - Guinea was declared free of Ebola transmission on Tuesday after more than 2,500 people died from the virus in the West African nation, leaving Liberia as the only country still counting down the days until the end of the epidemic. The announcement comes 42 days after the last person confirmed with Ebola tested negative for a second time. The world's worst outbreak of the disease began in Gueckedou, eastern Guinea, in December 2013 before spreading to Liberia, Sierra Leone and seven other countries.