More than 100 people have died from Ebola less than a month after authorities declared an outbreak of the disease in eastern Congo.

Efforts to contain the outbreak, declared on 15 May, are being severely hampered by attacks on health workers, local scepticism, and armed conflict in some hotspots.

The latest report, issued on Monday, confirmed 550 cases as of Sunday, with 101 deaths and 19 recoveries.

More than 90 per cent of the cases are in Congo’s eastern Ituri province, but infections have also spread to North Kivu, South Kivu, and across the border into Uganda.

The number of cases in Congo is believed to be higher because the outbreak was confirmed weeks late.

The outbreak was declared an international health emergency by the World Health Organisation (WHO) on 17 May.

Ten other nearby countries are considered at risk by the African Union’s primary public health agency, while the US Centers for Disease Control and Prevention (CDC) warned on Friday that the outbreak could spread to be similar in scale to the worst in history.

The latest Ebola disease outbreak is caused by the rare Bundibugyo virus, which does not have an approved vaccine or treatment.

That is unlike the “Zaire virus”, another name for the Ebola virus, which was responsible for most of Congo’s past 16 outbreaks of the disease.

The rapid increase in the number of cases is in part due to the scale-up of diagnostic capacities, enabling testing of the backlog of previously collected samples, authorities said.

Frontline health workers, with little pay or rest, have been attacked multiple times by angry residents and have not been able to reach some communities due conflict involving armed rebel groups.

Eastern Congo has for years seen attacks by dozens of separate rebel and militant groups, some of them with links to foreign countries or to the extremist Islamic State group.

Read More: Ebola death toll soars to 100 just weeks after outbreak declared