Sierra Leone on Monday confirmed its first death from Ebola and said it was restricting travel in some areas to stop the deadly haemorrhagic fever sweeping west Africa from claiming more lives.
Minister of Health and Sanitation Miatta Kargbo urged the public to remain "vigilant" and reaffirmed an earlier ban on trips to attend funerals in Guinea, the epicentre of the west African outbreak.
The eastern regions of Kailahun, where the first case was confirmed, and Kenema have been designated as "high risk" and travel there has also been restricted, she said.
"The ministry has now officially moved from a preparedness level to a response level and specifically management activities have now been put in place," Kargbo told a press conference.
"We are beginning to find out that the recent cases in the country are from individuals who went to funerals in Guinea."
Chief Medical Officer Brima Kargbo said the first Ebola victim was female traditional healer who had gone to a funeral in the neighbouring country.
The deadly haemorrhagic fever, which has no cure, erupted in Guinea in January where it claimed 81 lives—according to government figures released three weeks ago—and also spread to Liberia.
Sierra Leone health ministry official Amara Jambai said 11 people with acute diarrhoea and vomiting had been admitted to the Koindu Community Health Centre in a region bordering southern Guinea.
Four people have died, one of which was confirmed to have been caused by Ebola, and five were responding to treatment.
"The cause of death of the other three is still being investigated," he said.
Ebola is one of a handful of similar fevers that cause vomiting, diarrhoea, muscle pain, and in severe cases, organ failure and unstoppable internal bleeding.
It can be transmitted by blood and other bodily fluids, as well as the handling of contaminated corpses or infected animals, known to be vectors of the disease.
West African authorities have been scrambling to stop mourners from helping it to spread by touching bodies of the dead during traditional funeral rituals.
The World Health Organisation has described the region's first Ebola outbreak as one of the most challenging since the virus was first identified in 1976 in what is now the Democratic Republic of Congo.
The UN health agency said in a statement that it had been informed that the virus had appeared in Liberia and spoke of five possible cases.
The virus had been suspected but laboratory tests had eventually ruled out Ebola following several suspect cases earlier this year.
Gambia earlier this month lifted a ban on flights from Liberia and Sierra Leone imposed at the peak of the Ebola virus outbreak as Guinea said the spread of the deadly virus had "slowed significantly".
According to a May 23 statement by the WHO, 258 cases of viral haemorrhagic fever, of which 174 have resulted in deaths, have been reported in Guinea.
Out of the 258 cases, Conarky has confirmed 146 Ebola cases, 95 of them deadly.
In Liberia, which borders both Guinea and Sierra Leone, six cases of Ebola have been confirmed out of 12 cases of haemorrhagic fever, nine of them deadly.
No suspicious case was reported there since April 9 and the outbreak is considered under control but the border regions continue to be monitored closely.
Ebola: profile of a prolific killer
The Ebola virus now threatening Sierra Leone is one of the deadliest known to man, with more than 100 confirmed deaths from the disease in West Africa since January.
According to a May 23 statement by the World Health Organisation (WHO), 258 cases of viral haemorrhagic fever, of which 174 have resulted in deaths, have been reported in the Republic of Guinea.
Out of the 258 cases, the Guinean government has said that 146 were confirmed Ebola cases, 95 of them deadly.
Ebola has also been reported in neighbouring Liberia and Sierra Leone, with a total of 10 confirmed deaths, including one reported on Monday, out of more than a dozen cases.
The tropical virus can fell its victims within days, causing severe fever and muscle pain, weakness, vomiting and diarrhoea—in some cases shutting down organs and causing unstoppable bleeding.
No medicine or vaccine exists for the virus, which is named after a small river in the Democratic Republic of Congo.
Since the first case of Ebola was identified 38 years ago in the Democratic Republic of Congo (then Zaire), the virus has killed around 1,400 people.
Experts say that although it is extremely virulent, the virus can be contained because it kills its victims faster than it can spread to new ones.
The incubation period between exposure and the first symptoms varies from two to 21 days.
There are five species of the virus, of which three are particularly dangerous with fatality rates from 25 to 90 percent, according to the WHO.
It is transmitted through contact with the blood, body fluids, secretions or organs of an infected person.
The virus has been known to spread at burials where mourners touch the body, but doctors and nurses have also fallen ill after failing to take adequate precautions.
Even testing blood specimens for the disease presents "an extreme biohazard risk", states the WHO, and is done only in the strictest containment conditions.
People have contracted the virus after handling infected chimpanzees, gorillas, monkeys, forest antelope and porcupines, dead or alive, in the Ivory Coast, Congo and Gabon.
The only approach for the moment is to isolate patients and promptly bury the dead, said the WHO.
Hospital staff should use gloves, masks and goggles, and disinfect religiously.
"Several potential vaccines are being tested but it could be several years before any is available," says a WHO factsheet.
"A new drug therapy has shown some promise in laboratory studies and is currently being evaluated."
The virus's natural reservoir animal, possibly the bat, is believed to reside in rain forests in Africa and areas of the Western Pacific.
Explore further: Ebola toll rises to 74 in Guinea