Fifty new cases of Ebola and 25 deaths have been reported in Sierra Leone, Liberia and Guinea as the deadly virus continues to spread in families, the World Health Organisation (WHO) said.

In a statement, the United Nations agency said the latest figures from health ministries in the three countries showed a total of 844 cases including 518 deaths in the epidemic that began in February.

Guinea's ministry reported two deaths since July 3 but no new cases in the past week, the WHO said, calling the situation in the affected region of West Africa a "mixed picture".

Sierra Leone accounted for 34 of the new cases and 14 deaths, while Liberia reported 16 new cases and nine deaths, it said, adding: "These numbers indicate that active viral transmission continues in the community."

"This means the two main modes of transmission are home care, people who care for their relative at home, and during funerals, are still ongoing," WHO spokeswoman Fadela Chaib said.

"If we don't stop the transmission in the several hotspots in the three countries, we will not be able to say that we control the outbreak," she said.

A US citizen who was suspected of having Ebola because he fell ill after travelling to Sierra Leone and Guinea died on Monday in Ghana.

The man, who has not been named, was in quarantine at a clinic in the capital Accra.

A senior official at the Ghana Health Service said the man did not have Ebola but that further tests were being done.

If confirmed, it would be the first case of Ebola in Ghana.

West African countries and international health organisations adopted a fresh strategy last week to fight the world's deadliest Ebola epidemic to date.

Measures include better surveillance to detect the virus and enhancing cross-border cooperation.

Reuters