Three doctors in Liberia with Ebola who started taking an experimental drug last Thursday are showing remarkable signs of improvement, a minister says.
ZMapp was first given earlier this month to two US aid workers, who were flown home for treatment from Liberia.
Ebola has no cure but the World Health Organization (WHO) has ruled that untested drugs can be used in light of the scale of outbreak in West Africa.
Since the beginning of the year, 1,229 people have died of the virus.
It is transmitted by direct contact with the body fluids of an infected person. Initial flu-like symptoms can lead to external haemorrhaging from areas such as eyes and gums, and internal bleeding which can cause organ failure.
The outbreak began in Guinea and has since spread to Liberia, Sierra Leone and Nigeria.
Health officials in Guinea say the country has suffered a setback in its fight against the epidemic, seeing a resurgence of cases in the town of Macenta.
The BBC’s Alhassan Sillah in Guinea says the town had not had any cases for two months, and the authorities had dismantled all Ebola facilities in that area.
Analysis: Umaru Fofana, BBC News, Sierra Leone
Fighting the myths and fear surrounding Ebola is as tough as fighting the disease itself. They range from the bizarre to the ridiculous: Some see it as the culmination of some bio warfare gone awry; others say it is a cannibalistic ritual.
In the latest flashpoint – some people in Lunsar, about 120km (74 miles) east of the capital, Freetown, say the new cases are not Ebola patients at all. In fact, they insist that witches are flying around the country in aircraft and one of these crashed causing casualties.
All this, and the notion that an Ebola patient cannot recover, have led many sick people to stay at home, hoping they have something else. This is despite the fact that about 30% of patients have recovered.
The authorities have been encouraging those who become ill to report to hospitals for testing and treatment, if needed. But as the messengers are distrusted, the message is not getting through.
The health authorities believe that Guineans returning from neighbouring Liberia are carrying the virus.
In Liberia, Information Minister Lewis Brown said the government only received a small number of ZMapp doses and gave them to one Nigerian and two Liberian doctors who had caught Ebola whilst helping save the lives of other victims of the virus.
Two US missionaries who received doses of the medicine are also reportedly recovering, but a 75-year-old Spanish priest who contracted Ebola in Liberia died in Spain last week despite being given the drug.
The US pharmaceutical company that makes the drug says it has for now run out of it, so the only way to stop the current outbreak is to isolate the victims and those who have come into contact with them.
Mr Brown also said 17 suspected Ebola patients who went missing after a health centre in the capital was attacked have been found.
In Nigeria, which has had four fatal Ebola cases, health officials say five people have now recovered from the virus and have been discharged from hospital in Lagos. Another three are still being treated.
Ebola Virus Disease (EVD)
- Symptoms include high fever, bleeding and central nervous system damage
- Fatality rate can reach 90% – but current outbreak has about 55%
- Incubation period is two to 21 days
- There is no vaccine or cure
- Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery
- Fruit bats, a delicacy for some West Africans, are considered to be virus’ natural host
Since the outbreak spread to Nigeria in July, when a person infected with Ebola flew from Liberia to Lagos, several airlines have stopped flights to the worst-affected countries.
Kenya’s ban on people from Guinea, Liberia and Sierra Leone entering the East African nation comes into force on Wednesday – and Cameroon has closed its land, sea and air borders with Nigeria.