UNITED NATIONS, Dec. 25 -- Despite progresses made in the fight against the ongoing Ebola outbreak that distresses large parts of West Africa as well as the rest of the world, the epidemic is yet to be put under control, a senior UN official said.

David Nabarro, who was appointed special envoy for coordinating affairs of the UN Mission for Ebola Emergency Response (UNMEER) in September, told Xinhua in a recent interview that the chains of infections are not totally known in western Sierra Leone and in some areas of Guinea's inland, while in Liberia, the situation is largely under control.

Since the start of his mandate, Nabarro has witnessed a decrease in the number of Ebola cases in the eastern part of Sierra Leone and an upsurge in the neighboring nation of Guinea.

More specifically, Nabarro said, the upsurge is in Freetown, the capital city of Sierra Leone, as well as in Porto Loko and the Bombali District of the country.

"Now in these areas we've got more cases appearing...and we don't always see them coming from known transmission chains and so what we need now is detective work," he added.

The detective work includes finding people who are infected as well as their contacts and encouraging them to stay in isolation so they can be monitored and receive treatment, Nabarro said.

According to his estimates, it will take about six to eight weeks to put the situation under control in western Sierra Leone, while it will take a little longer in Guinea due to factors including larger area and poorer infrastructure. "We don't always have easy access to all the communities there," he explained.

"(This) is why in my view we will be working in Guinea longer to get the situation under control. I can't tell you how long, but I think it will take us well into next year," the senior official said about the continuation of the outbreak.

In spite of these struggles, the senior official pointed out, the international community has been working together in integrated efforts in the face of the outbreak.

"China is one of the countries that responded very quickly to the appeal by the Secretary-General for more help," said Nabarro.

China has provided cash and at least two plane-loads of equipment to the affected countries. Besides, China has sent senior experts and has built a hospital at a local stadium to treat Ebola patients, said Nabarro.

Looking into the future, Nabarro said there will be more diseases like Ebola in the future and nations need to showcase resilience to protect themselves.

The envoy believes this Ebola outbreak will lead to stronger health systems that are very much in line with the proposed sustainable development goals.

"The sustainable development goals are about societies being resilient, being able to look after themselves, being able to avoid disturbances like disease, droughts or floods," he said.

"I believe the experience that is being gained by Sierra Leone, Guinea and Liberia will make these countries the kind of natural university where everyone will come and study how to handle diseases like Ebola," he added.