A health worker is sprayed with chlorine after visiting the isolation ward at Bikoro hospital in the Democratic Republic of Congo. The hospital had just admitted a suspected Ebola case. Picture: Jean Robert N’Kengo/Reuters

Goma, Congo - Three reported Ebola cases in the Congolese city of Mbandaka have increased the number of confirmed infections to 17, reported the Health Ministry late Friday.

Four of those cases are in Mbandaka, a city of 1.2 million along a river with good road and air connections. Because of that, the World Health Organization said Friday that the risks for the disease spreading further in Congo are high, though it has not yet issued a global warning.

Ebola is a near-fatal disease that causes a haemorrhagic fever that often leads to massive internal bleeding. The last major outbreak was in 2014, in the eastern African countries of Guinea, Liberia and Sierra Leone. It claimed 11,000 lives.

Congo's Health Ministry is investigating a total of 43 possible cases of Ebola, including the 17 confirmed cases. In 21 cases, Ebola's presence is considered likely. It is only considered possible in the final five. Twenty-five people are suspected to have died from the disease, the ministry said late Thursday.

This is the ninth Ebola outbreak in 40 years in the country. But the previous ones were all in isolated areas, preventing wider outbreaks.