KINSHASA, Aug. 7 (Xinhua) -- Confirmed Ebola cases in the Democratic Republic of the Congo (DRC) have reached 4,053, including 1,850 deaths, as health authorities investigate whether changes in the virus may be contributing to the unprecedented outbreak and accelerate trials for potential vaccines and treatments. The outbreak, caused by the Bundibugyo ebolavirus, has become the second-largest Ebola outbreak ever