The Red Cross warned on Thursday of a possible rise in the rate of Ebola infections in West Africa as people travel across the region during the festive holidays.

Urging people to take extra care to limit the spread of the virus, International Federation of the Red Cross and Red Crescent Societies (IFRC) Secretary General Elhadj As Sy said increasing rates were not inevitable but a real risk.

"Now is the time to be even more vigilant," he told an audience at the Royal Institute of International Affairs in London. "We all welcome the plateauing and the signs of declines we are seeing in some places ... but that should not be a reason for complacency."

Latest World Health Organization (WHO) data show rates of infection with Ebola -- an often fatal disease which causes fever, vomiting, diarrhoea and bleeding -- appear to be slowing in Liberia and Guinea but are still raging in Sierra Leone.

The Ebola epidemic, the largest in history, has infected almost 18,000 people, killing around 6,400 of them.

The Ebola virus spreads through contact with the body fluids of an infected person, meaning suspected and confirmed cases should be quarantined or cared for in isolation to reduce spreading.

As Sy said that since many West Africans traditionally travel from urban areas to their rural homes at this time of the year, the threat of wider contagion is greater.

"If we have social gatherings and movement of people ... there may be increased risk," he said.