By Olivia Le Poidevin

GENEVA, Sept 8 (Reuters) - A shortage of trained staff, operational partners and funding is ‌causing a bottleneck in efforts to expand the ‌Ebola response in the Democratic Republic of Congo as the outbreak spreads ​geographically, a World Health Organization official said on Tuesday.

The outbreak has spread beyond its initial epicentre in Bunia, affecting six provinces and prompting authorities to adopt a more decentralised strategy ‌by building treatment centers ⁠closer to newly affected communities, the WHO said.

Congo's outbreak of the Bundibugyo species of Ebola ⁠has surpassed 3,175 deaths and 6,000 cases, according to the WHO, as the country's worst epidemic continues to spread across its ​northeast.

WHO technical ​officer Luca Fontana said ​nearly 1,400 treatment beds had ‌already been established across 59 treatment centres, one of the fastest scale-ups he said he had witnessed, including during the 2014-2016 West Africa Ebola epidemic.

"Yet, despite this extraordinary effort, we estimate that another 1,600 beds will be required," ‌he said.

WHO estimates around three health ​workers are needed for each Ebola ​patient bed, meaning ​around 9,000 staff would be required for the ‌planned capacity of 3,000 beds.

That ​would require the ​recruitment and training of roughly 5,000 additional health workers.

Fontana said the pool of international organisations capable of ​running Ebola treatment ‌centres was limited, partly due to the impact of ​broader global donor funding cuts.

(Reporting by Olivia Le ​Poidevin, Editing by Miranda Murray)