A freelance cameraman working for NBC news has contracted the Ebola virus, he is the fourth American known to have contracted the disease in Liberia, report sources.
Ashoka Mukpo, 33, who was working as a freelancer for NBC news, discovered he was running a fever on Wednesday, his network said, and is in quarantine in a Medecins Sans Frontieres (MSF) treatment centre.
Hired by NBC only three days ago, he is the fourth American to contract Ebola in Liberia.
"The doctors are optimistic about his prognosis," Mukpo's father Mitchell Levy said in a message to family and friends quoted by NBC, adding that his son had worked on humanitarian projects in Liberia for several years.
By far the most deadly epidemic of Ebola on record has spread into five west African countries since the start of the year, infecting more than 7,000 people and killing about half of them.
The virus, spread through infected bodily fluids, can only be transmitted when a patient is experiencing the symptoms -- severe fever, vomiting, diarrhoea and, in some cases, massive internal haemorrhaging and external bleeding.
The alarming rate at which the contagion is spreading has triggered international action to help battle the outbreak.
On Friday, the US military announced that it now expects to ramp up the number of troops deployed to Liberia to help fight the outbreak to nearly 4,000, up from a planned 3,000-strong force.
Anthony Banbury, head of the UN Mission on Ebola Emergency Response (UNMEER), travelled to Sierra Leone on Friday for the second leg of a tour of the three hardest-hit nations.
"The only way we will end this crisis is if we end every single last case of Ebola so there is no more risk of transmission to anyone, and when that's accomplished, UNMEER will go home," he told journalists on Thursday in the Liberian capital Freetown.
The UN envoy said he was intent on contributing to "the highest priority for the international community -- for the whole world, not just the United Nations".
The World Health Organization said in its latest situation update there was still a "significant shortfall" in capacity in west Africa, with 1,500 more beds needed in Liberia and 450 in Sierra Leone.
Around 160 health professionals pledged by Cuba to Sierra Leone arrived Thursday, reported an AFP correspondent at the airport near Freetown.
Britain has pledged Ģ120 million ($190 million, 150 million euros) to help build an estimated 700 treatment beds, fund new community treatment centres, support existing public health services and support aid agencies in Sierra Leone.
- 'Unpardonable' traveler -
US health officials meanwhile sought to allay fears of an outbreak in the United States as 50 people in Texas were being monitored for contagion after potentially having contact with a Liberian diagnosed with Ebola.
Anthony Fauci, the head of the National Institute for Allergy and Infectious Diseases, said the US health care system "would make it extraordinarily unlikely that we would have an outbreak".
Thomas Eric Duncan this week became the first person to be diagnosed with Ebola on US soil.
He had flown from Liberia -- where he reportedly came into contact with a known Ebola patient -- and arrived in Texas on September 20 to visit family.
Liberian President Ellen Johnson Sirleaf said Friday Duncan had behaved irresponsibly by travelling despite knowing he was potentially infected.
"The fact that he knew and he left the country is unpardonable," Sirleaf told Canada's public broadcaster CBC.
Meanwhile, NBC News president Deborah Turness said the crew working with Mupko in Liberia were being closely monitored but were showing no symptoms.
"However, in an abundance of caution, we will fly them back on a private charter flight and then they will place themselves under quarantine in the United States for 21 days -- which is at the most conservative end of the spectrum of medical guidance," she added.
The cameraman is thought to be the first Western journalist to contract Ebola covering the west African outbreak, although several have died in Sierra Leone and Liberia.
Germany said on Friday a Ugandan doctor who had infected with Ebola in Sierra Leone while working for an Italian non-governmental organisation had been hospitalised in Frankfurt, the second Ebola patient to be treated in the country.
- 'Five infected every hour' -
Save the Children warned that five people are catching Ebola every hour in Sierra Leone and demand for treatment beds is far outstripping supply.
If the current "terrifying" rate of infection continues, 10 people will be infected every hour with the virus in Sierra Leone by the end of October, the London-based charity warned.
The extent of fear which the epidemic is engendering in the country was underlined on Friday when it emerged a middle-aged man in the quarantined city of Makeni had died after setting himself alight, fearing his family had infected him with Ebola.
Neighbours said the man became depressed after his wife and daughter were taken for Ebola tests at a holding centre.
"The man was heard saying he'd rather die than hear any news of his family being suspected of Ebola," one told AFP.
"He doused himself with petrol and then struck a match to be engulfed in fire."