The risk of Ebola spreading worldwide still looms large and more health care volunteers are needed in West Africa to provide clinical care to Ebola patients, a leading US epidemiologist said on Monday.

"Although many individuals and agencies have already been working with local health institutes in terms of hunger relief, disease prevention and training, there are not enough people willing to go to take care of the patients," said Carol Rao, Chief of Epidemiology Section of the International Emerging Infections Program with the US Centers for Disease Control and Prevention.

"There is an international call for many more health care volunteers to provide clinical care," Rao said in a lecture in Beijing.

Rao had served under the US CDC program in Freetown, Sierra Leone for five weeks since late October, in charge of managing data, identifying infections and training local medical staff. She will return to her post in January for six weeks.

"As chaotic as the country was, I was impressed by the many people who are dedicated to fighting the disease in a strange country simply out of passion," she said.

As a PhD of environmental health from Harvard University, Rao has gained vast experience in outbreak investigations over the years working under the US CDC. In 2007, she went to Kenya to join the fight against the Rift Valley Fever.

Stress followed Rao the first day she arrived in Freetown. "Everything was so chaotic. And if look at the overall outbreak and what needs to be done, it is too overwhelming," she said.

Later, Rao learned to cope with the stress by focusing on her specific tasks. "If I can accomplish one task at a time, that's how I can deal with it," she said.

Rao said, in Sierra Leone, the US CDC team has built close connections with their Chinese counterparts, whose professional work has been well-received by the local community and international peers.

"We tried to be as open and transparent as possible," Rao said. "It is an international response. Everybody needs to be working together. That is one of the reasons I love to do things like this."

So far, China has provided four rounds of emergency aid worth $120 million and dispatched more than 400 medical personnel to the affected region.