* Death toll linked to Ebola outbreak has reached 70
* Virus reaching capital could increase population at risk
* Victims have also died in Sierra Leone and Liberia (Recasts; updates number of suspected cases in Conakry)
By Saliou Samb
CONAKRY, March 28 (Reuters) - Authorities in Guinea scrambled on Friday to halt the spread of Ebola in the capital as the Health Ministry identified another four suspected cases of a deadly virus outbreak that is estimated to have already killed 70.
Officials said the previous day that five cases of Ebola had been detected in Conakry, a city of more than 2 million people, some 300 km (185 miles) from the previous infections in the West African country's remote southeast. One elderly man died and four male relatives were quarantined.
Authorities in Guinea have launched an investigation into the movements of the infected men in Conakry and steps are being taken to deal with anyone who came into contact with them, the government said in a statement.
The arrival of the disease in the capital, where hundreds of thousands of people live tightly packed in rambling shanties, could mark a sharp increase in the population at risk compared with the sparsely populated villages of the forested interior.
In neighbouring Sierra Leone and Liberia, 11 more people have died from suspected Ebola, stirring concern that one of the most lethal infectious diseases known to man could be spreading in an impoverished region ill-equipped to cope.
In Guinea, 111 suspected cases have been detected, almost all in the remote forest region, centred on Gueckedou. The mortality rate from the infection is running at 64 percent, the World Health Organisation (WHO) said.
"Families have been decimated. When you go into rural areas, especially in Gueckedou, you see villages where there are lots of people infected," said Mariano Lugli, emergency coordinator for Doctors Without Borders (MSF).
Lugli said containing the outbreak was made difficult by the itinerant nature of the local culture, where people often travel to visit relatives and conduct commerce. "Our biggest difficulty is isolating the cases and putting them in centres for specialised care so they cannot infect other people," he said.
In Gueckedou, MSF has constructed an isolation ward with 20 beds for patients, he said. Television images from the scene showed the ward, its inside coated with plastic wrapping, and medical staff wearing protective facemasks and clothing.
There is no vaccine and no known cure for the disease, which initially induces fever, headaches, muscle pain and weakness. In its more acute phase, Ebola causes vomiting, diarrhoea and external bleeding that leaves the victim covered in the virus.
Traditional funerals, where bodies are washed by hand, have been linked to the spread of the disease, prompting authorities to ban them. The consumption of bat meat has also been forbidden: experts believe the disease - more common in Congo, Sudan and Uganda - is carried by bats, explaining how it crossed the continent.
Ebola has killed more than 1,500 people since it was first recorded in 1976 in what is now Democratic Republic of Congo, but this is the first fatal outbreak in West Africa.
A mysterious fever was first detected in Guinea in early February but it took authorities nearly six weeks to identify it as Ebola, allowing the virus to spread. Guinea is deploying a mobile laboratory to Gueckedou to speed up identification of the disease and test samples from Sierra Leone and Liberia.
West African foreign ministers this week said the outbreak was a "threat to regional security". Joining a list of countries stepping up controls, Senegal said on Friday it was imposing sanitary checks at borders and on flights arriving from Conakry.
On the streets of Conakry, people remained calm but some executives at international mining companies voiced concern. "We have asked our employees to avoid physical contact, especially in hospitals," said one executive with a mining firm that has operations in the southeast.
Many offices placed antiseptic wash outside their doors for people to wash their hands before entering. People also avoided shaking hands - an important part of West African greetings.
"All that one can ask is that we do not give in to panic, and to respect the basic rules of hygiene," said Abdourahmane Conde, a telecommunications engineer. (Additional reporting by Emma Farge and by Misha Hussain of the Thomson Reuters Foundation; Writing by Daniel Flynn; Editing by Alison Williams and Ken Wills)