The Ebola outbreak in the Democratic Republic of Congo is the biggest in the country's history, the World Health Organization (WHO) has said. The current outbreak is caused by the Bundibugyo strain of the virus. There is currently no approved vaccine or treatment for the Bundibugyo strain, but vaccines are being developed in the UK and Singapore. "Factors like insecurity, population displacement, and cross-border movement continue to hamper response efforts and increase the risk of further spread," it said. "The convergence of insecurity, population displacement and mobility, and cross-border movements complicate response operations and increase the risk of further geographical spread," the WHO said.