The virus causing a massive outbreak of Ebola in the Democratic Republic of the Congo could be mutating, health officials fear, as confirmed cases pass 4,000. The Ebola outbreak, caused by the Bundibugyo strain of the virus, was first reported on 15 May, although there are suspicions the disease could have been spreading since January. There have been 3,973 cases and 1,801 deaths recorded as of 4 August, according to the DRC’s national public health institute. The outbreak is now the second-largest Ebola outbreak on record. There were 20 cases recorded in neighbouring Uganda before it brought its outbreak under control.