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* Number of cases possibly 2-4 times higher than reported
* 12,000 local staff, 750 international experts needed
* Nigeria reports spread to main African oil hub
* Air service suspension threatens aid operation - WHO (Adds details, quotes)
By Stephanie Nebehay and Tim Cocks
GENEVA/LAGOS, Aug 28 (Reuters) - The Ebola epidemic in WestAfrica could infect over 20,000 people and spread to morecountries, the U.N. health agency said on Thursday, warning thatan international effort costing almost half a billion dollars isneeded to overcome the outbreak.
The World Health Organisation (WHO) announced a $490 millionstrategic plan to contain the epidemic over the next ninemonths, saying it was based on a projection that the virus couldspread to 10 further countries beyond the four now affected -Guinea, Liberia, Sierra Leone and Nigeria.
With the IMF warning about the economic effects of theoutbreak, Nigeria reported that a doctor indirectly linked tothe Liberian-American who brought the disease to the country haddied of Ebola in Port Harcourt, Africa's largest energy hub.
In Britain, drugmaker GlaxoSmithKline said anexperimental Ebola vaccine is being fast-tracked into humanstudies and it plans to produce up to 10,000 doses for emergencydeployment if the results are good.
So far 3,069 cases have been reported in the outbreak butthe WHO said the actual number could already be two to fourtimes higher. "This is not a West African issue or an Africanissue. This is a global health security issue," WHO's AssistantDirector-General Dr Bruce Aylward told reporters in Geneva.
With a fatality rate of 52 percent, the death toll stood at1,552 as of Aug. 26. That is nearly as high as the total fromall recorded outbreaks since Ebola was discovered in what is nowDemocratic Republic of Congo in 1976.
The figures do not include deaths from a separate Ebolaoutbreak announced at the weekend in Congo, which has beenidentified as a different strain of the virus.
Aylward said tackling the epidemic would need thousands oflocal staff and 750 international experts. "It is a bigoperation. We are talking (about) well over 12,000 peopleoperating over multiple geographies and high-risk circumstances.It is an expensive operation," he said.
The operation marks a major raising of the response by theWHO, which had been accused by some aid agencies of reacting tooslowly to the outbreak.
Medical charity Medecins sans Frontieres (MSF) welcomed theWHO plan but said the important thing was now to act upon it.
"Huge questions remain about who will implement the elementsin the plan," said MSF operations director Brice de le Vingne."None of the organisations in the most-affected countries ...currently have the right set-up to respond on the scalenecessary to make a serious impact."
EXPERIMENTAL DRUGS
Early this month, the WHO classified the Ebola outbreak asan international health emergency. Concerns that the diseasecould spread beyond West Africa have led to the use of drugsstill under development for the treatment of a handful of cases.
Two American health workers, who contracted Ebola whiletreating patients in Liberia, received an experimental therapycalled ZMapp, a cocktail of antibodies made by tiny Californiabiotech Mapp Biopharmaceutical. They recovered and were releasedfrom hospital last week.
The virus has already killed an unprecedented number ofhealth workers and is still being spread in a many places, theWHO said. About 40 percent of the cases have occurred within thepast 21 days, its statistics showed.
Previous Ebola outbreaks have mainly occurred in isolatedareas of Central Africa. However the current epidemic has spreadto three West African capitals and Lagos, Africa's biggest city.The WHO said special attention would need to be given tostopping transmission in capital cities and major ports.
Authorities in Nigeria announced the doctor's death in PortHarcourt, the main oil industry terminal of Africa's largestcrude exporter. The doctor had treated a patient who evadedquarantine after coming into contact with Patrick Sawyer - aU.S. citizen who died in Lagos after flying in from Liberia lastmonth.
Health Ministry spokesman Dan Nwomeh wrote in his Twitterfeed that 70 people were now under surveillance in PortHarcourt, which is home to foreigners working for internationaloil companies.
A spokesman for leading operator Royal Dutch Shell said in London that the firm was "liaising with healthauthorities on the steps being taken to contain the disease".
Oil traders in Europe said insurance premiums for Nigeriancargoes had gone up slightly, but otherwise business wascontinuing as normal.
Analysts urged caution. "While major disruption to oilproduction appears unlikely, any further spread of Ebola ... islikely to cause serious operational challenges," said RoddyBarclay of the Control Risks consultancy.
According to new figures released on Thursday, Nigeria hasrecorded 17 cases, including six deaths, from Ebola, sinceSawyer collapsed upon arrival at Lagos airport in late July.
While Nigeria has yet to suffer any major economicdisruption, the International Monetary Fund said the smaller,poorer nations at the heart of the epidemic were being badlyhurt. "The Ebola outbreak is having an acute macroeconomic andsocial impact on three already fragile countries in WestAfrica," IMF spokesman Gerry Rice told reporters in Washington.
Rice said the IMF was assessing the impact and any extrafinancing needs with Guinea, Liberia and Sierra Leone.
AID EFFORT CHOKED OFF
The Lagos case contributed to the decision by a number ofairlines to halt services to Ebola-affected countries. AirFrance said on Wednesday it had suspended flights toSierra Leone on the advice of the Frenchgovernment.
Aylward said it was vital to restore commercial airlineroutes to the region to help transport aid workers and supplies,but in the meantime the WHO plan includes an "air bridge" to beoperated by the U.N.'s World Food Programme.
"We assume current airline limitations will stop within thenext couple of weeks. This is absolutely vital," he said. "Rightnow the aid effort risks being choked off."
West African health ministers meeting in Ghana on Thursdayechoed the WHO's concerns and called for the reopening ofborders and an end to flight bans. (Additional reporting by Kwasi Kpodo in Accra, Ben Hirschlerand Julia Payne in London, Anna Yukhananov in Washington andSharon Begley in New York; Writing by Joe Bavier; Editing byDaniel Flynn and David Stamp)
