(Reuters) — The World Health Organization has asked six African countries to be alert for possible Ebola infections, as Guinea on Tuesday reported new cases and Democratic Republic of Congo said its new infections were a resurgence of a previous outbreak.

Guinea declared an outbreak of the virus on Sunday in the first return of the disease there since the 2013-2016 outbreak, while Congo has confirmed four new cases this month.

Health authorities have rushed to respond to the cases in Guinea, anxious to prevent a repeat of the last outbreak in West Africa, which killed more than 11,300 people, mostly in Guinea, Sierra Leone and Liberia in the worst Ebola epidemic on record.

“We have already alerted the six countries around, including of course Sierra Leone and Liberia, and they are moving very fast to prepare and be ready and to look for any potential infection,” the WHO’s Margaret Harris told a Geneva briefing on Tuesday.

Guinea’s neighbours include Senegal, Guinea-Bissau, Mali, Ivory Coast, Sierra Leone and Liberia.

Guinea has so far recorded up to 10 suspected cases of Ebola and five deaths. Since declaring the outbreak on Sunday, it has identified 115 contacts of the known cases in the southeastern city of Nzerekore and 10 in the capital Conakry, the health ministry said on Tuesday.

Gene sequencing of Ebola samples from both Congo and Guinea is being carried out to learn more about the origins of the outbreaks and identify the strains, according to the WHO.

As a result, Congo has confirmed that its latest cases are not linked to a new Ebola variant but represent a resurgence of its tenth outbreak, the second-largest on record that caused more than 2,200 deaths in 2018-2020.

“As for the infection, we’re not yet able to identify its origin,” said provincial health minister Eugene Nzanzu Salita, referring to how the first person to fall sick in this resurgence caught the virus.

Since the devastating epidemic in West Africa, the development of vaccines and treatments has greatly improved survival rates and containment efforts.

Further spread of the disease could cripple the regions’ under-funded health systems which are also battling the coronavirus pandemic. Ivory Coast, Mali and Sierra Leone have launched plans to stop any potential spread and reinforced border controls.

The Ebola virus can cause severe bleeding and organ failure and is spread through contact with body fluids. It has a much higher death rate than COVID-19, but unlike the coronavirus it is not transmitted by asymptomatic carriers.

Reporting by Emma Farge and Emma Thomasson in Geneva, Saliou Samb in Conakry and Fiston Mahamba and Hereward Holland in Goma, Democratic Republic of Congo; Writing by Alessandra Prentice Editing by Alison Williams, Bate Felix and Nick Macfie. © Copyright Thomson Reuters 2021