This brings the total of laboratory-confirmed cases to nine and probable cases to 20 since the outbreak of the deadly disease similar to Ebola was declared in February. Twenty deaths have been reported.
Of the eight new cases, two were reported from the Central African country's Kie-Ntem province, four from the Litoral province and two from Centre-Sur province, the WHO said in a statement.
The areas reporting cases are about 150km (93 miles) apart, suggesting a wider transmission of the virus, the WHO said.
"The confirmation of these new cases is a critical signal to scale up response efforts to quickly stop the chain of transmission," WHO Africa Director Matshidiso Moeti said in the statement.
Marburg virus disease is a viral haemorrhagic fever that can have a fatality rate of up to 88%, according to the WHO.
Symptoms include fever, fatigue and blood-stained vomit and diarrhoea. There are no vaccines or antiviral treatments approved to treat it.
Neighbouring Cameroon also detected two suspected cases of Marburg disease last month despite restricting movement along the border to avoid contagion.
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