Eight Chinese medical workers who treated Ebola patients have been quarantined in Sierra Leone, as health experts grapple with ethical questions over the use of experimental drugs to combat the killer virus.

Gripped by panic, west African nations battling the tropical disease ramped up drastic containment measures that have caused transport chaos, price hikes and food shortages.

The World Health Organization has scrambled to draft guidelines for the use of experimental medicines at a meeting in Geneva as the death toll from the worst Ebola outbreak in history neared 1,000.

It is to present its conclusions on Tuesday.

Liberia meanwhile said it had requested samples of an experimental drug and that supplies would be brought in the country "by a representative of the US government" later this week.

There is currently no available cure or vaccine for Ebola, which the WHO has declared a global public health emergency.

The disease has hit doctors hard in the ill-equipped and fragile health systems of the worst-hit west African nations of Guinea, Liberia and Sierra Leone.

China's ambassador to Sierra Leone Zhao Yanbo said that seven doctors and one nurse who treated Ebola patients had been placed under quarantine, but would not be drawn on whether they were displaying symptoms of the disease.

In addition 24 nurses in Sierra Leone, most from the military hospital in the capital, have also been quarantined, according to Yanbo and hospital director Sahr Foday.

Foday said a senior physician at Freetown's Connaught Hospital had contracted Ebola but was responding well to treatment. The nation's sole virologist, who was at the forefront of its battle against the epidemic, died from Ebola last month.

- Ethical thing to do? -

The use of an experimental drug called ZMapp on two Americans and a Spanish priest infected with the virus while working in Africa has opened up an intense ethical debate.

The drug, made by private US company Mapp Pharmaceuticals, has shown promising results but is still in an early phase of development and had only been tested previously on monkeys.

ZMapp is in very short supply, but its use on Western aid workers has sparked controversy and demands that it be made available in Africa.

"Is it ethical to use unregistered medicines to treat people, and if so, what criteria should they meet, and what conditions, and who should be treated?" said WHO assistant director-general Marie-Paule Kieny ahead of Monday's meeting.

"What is the ethical thing to do?"

Mapp Pharmaceuticals said it had sent all its available supplies to West Africa.

"In responding to the request received this weekend from a West African nation, the available supply of ZMapp is exhausted," it said in a statement.

"Any decision to use ZMapp must be made by the patients' medical team," it said, adding that the drug was "provided at no cost in all cases."

The company did not reveal which nation received the doses, or how many were sent, but Liberia said it had requested samples which would "be brought in the country by a representative of the US Government later this week".

"The White House and the United States Food and Drug Administration have approved the request for sample doses of experimental serum to treat Liberian doctors who are currently infected with the deadly Ebola virus disease," the Liberian presidency said.

- 'Everyone is afraid'-

The latest outbreak -- which the WHO says is by far the worst since Ebola was discovered four decades ago -- has left more than 960 people dead, and infected or possibly infected nearly 1,800.

In Liberia -- where Ebola has already claimed about 370 lives -- a third province, Lofa, was placed under quarantine on Monday after similar measures in Bomba and Grand Cape Mount.

"From now on, no one will be allowed to go to Lofa, no one will come out of there," President Ellen Johnson Sirfleaf said. "We want to protect areas that have not been yet affected."

Sirleaf also banned state officials from travelling abroad for a month and ordered those outside the country to return home within a week.

While impoverished Guinea, Liberia and Sierra Leone account for the bulk of the cases, the latest outbreak has spread further afield. Nigeria, Africa's most populous country, has so far counted two deaths.

Numerous countries have imposed a raft of emergency measures, including flight bans or screening of passengers.

In the latest such move, the Ivory Coast announced on Monday it was banning all flights from the three hardest-hit nations.

And it said in the past few days it had turned back around 100 Liberians trying to flee across the border into Ivory Coast, which has not reported any Ebola cases.

Niger, which also has yet to confirm any cases, has put in place an "emergency plan" to train health workers and boost checks at borders, airports and stations. Togo has also strengthened health screenings.

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