The World Health Organization (WHO) has warned that the ongoing Ebola outbreak in the Democratic Republic of the Congo may be spreading more rapidly than initially believed, as health officials struggle to contain the deadly virus.

According to WHO representative Dr Anne Ancia, investigations are revealing that the outbreak has already spread beyond its original epicentre in Ituri province and may have crossed into other provinces and neighbouring countries.

At least 131 people have died so far, while more than 513 suspected Ebola cases had been reported in DR Congo by Tuesday. Authorities in neighbouring Uganda also confirmed one Ebola-related death.

A new study by the London-based MRC Centre for Global Infectious Disease Analysis suggested the outbreak could be far larger than official figures indicate. Researchers warned there may already be more than 1,000 infections due to “substantial” under-detection of cases.

WHO Director-General Tedros Adhanom Ghebreyesus, who declared the outbreak an international public health emergency last week, expressed deep concern over the “scale and speed” of the epidemic.

Health experts fear the virus may have been circulating for several weeks before the outbreak was officially detected on 24 April.

Dr Ancia said the outbreak’s epicentre in Ituri province is a highly insecure region with significant population movement, making disease surveillance and containment extremely difficult. She added that cases have now been identified in South Kivu province and in the eastern city of Goma, home to around 850,000 people.

The humanitarian crisis and ongoing insecurity in eastern DR Congo are believed to be accelerating the spread of the virus as people frequently move between regions and across borders.

Several African countries have increased border screenings and emergency preparedness measures. Rwanda has temporarily closed its border with DR Congo, while Uganda has advised citizens to avoid physical contact such as handshakes and hugs.

Meanwhile, several foreign nationals exposed to the virus are being evacuated for treatment. An American citizen, believed to be missionary doctor Peter Stafford, is reportedly being transferred from DR Congo after developing symptoms.

There is currently no approved vaccine for the Bundibugyo strain of Ebola responsible for the latest outbreak. WHO officials are evaluating whether existing drugs and treatments may offer some level of protection.

Ebola is a severe viral disease that initially causes fever, headache and fatigue before progressing to vomiting, diarrhoea, organ failure and, in some cases, internal and external bleeding. The virus spreads through direct contact with infected bodily fluids.

The Bundibugyo strain is considered rare and has previously caused only two known outbreaks, with around one-third of infected patients dying.

The deadliest Ebola outbreak in history occurred in West Africa between 2014 and 2016, infecting more than 28,600 people and killing over 11,300 across countries including Guinea, Sierra Leone, the United States, the United Kingdom and Italy.