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MONROVIA, Liberia -- One of Liberia's most high-profile doctors has died of Ebola, officials said Sunday, and an American physician was being treated for the deadly virus, highlighting the risks facing health workers trying to combat an outbreak that has killed more than 670 people in West Africa -- the largest ever recorded.
Dr. Samuel Brisbane was treating Ebola patients at the country's largest hospital, the John F. Kennedy Memorial Medical Center in Monrovia, when he fell ill. He died Saturday, said Tolbert Nyenswah, an assistant health minister. A Ugandan doctor died earlier this month.
The American, 33-year-old Dr. Kent Brantly, was in Liberia helping to respond to the outbreak that has killed 129 people nationwide when he fell ill, according to the North Carolina-based medical charity, Samantha's Purse.
He was receiving intensive medical care in a Monrovia hospital and was in stable condition, according to a spokeswoman for the aid group, Melissa Strickland.
"We are hopeful, but he is certainly not out of the woods yet," she said.
Early treatment improves a patient's chances of survival, and Strickland said Brantly recognized his own symptoms and began receiving care immediately.
There is no known cure for the highly contagious virus, which is one of the world's deadliest. At least 1,201 people have been infected in Liberia, Sierra Leone and Guinea, according to the World Health Organization, and 672 have died. Besides the Liberian fatalities, 319 people have died in Guinea and 224 in Sierra Leone.
Ominously, Nigerian authorities said Friday that a Liberian man died of Ebola after flying from Monrovia to Lagos via Lome, Togo. The case underscored the difficulty of preventing Ebola victims from traveling given weak screening systems and the fact that the initial symptoms of the disease -- including fever and sore throat -- resemble many other illnesses.
Health workers are among those at greatest risk of contracting the disease, which spreads through contact with bodily fluids.
Photos of Brantly working in Liberia show him swathed head-to-toe in white protective coveralls, gloves and a head-and-face mask that he wore for hours a day while treating Ebola patients.
Earlier this year, the American was quoted in a posting about the dangers facing health workers trying to contain the disease. "In past Ebola outbreaks, many of the casualties have been health care workers who contracted the disease through their work caring for infected individuals," he said.
There is no known cure for Ebola, which begins with symptoms including fever and sore throat and escalates to vomiting, diarrhea and internal and external bleeding.
The WHO says the disease is not contagious until a person begins to show symptoms. Brantly's wife and children had been living with him in Liberia but flew home to the U.S. about a week ago, before the doctor started showing any signs of illness, Strickland said.
"They have absolutely shown no symptoms," she said.
A woman who identified herself as Brantly's mother said the family was declining immediate comment when reached by phone in Indiana.
Besides Brantly and the two doctors in Liberia, Sierra Leone's top Ebola doctor and a doctor in Liberia's central Bong County have also fallen ill.
The situation "is getting more and more scary," said Nyenswah, the country's assistant health minister.
Meanwhile, the fact that a sick Liberian could board a flight to Nigeria raised new fears that other passengers could take the disease beyond Africa.
Nigeria's international airports were screening passengers arriving from foreign countries, and health officials were also working with ports and land borders to raise awareness of the disease. Togo's government also said it was on high alert.
Security analysts were skeptical about the usefulness of these measures.
"In Nigeria's case, the security set-up is currently bad, so I doubt it will help or have the minimum effectiveness they are hoping for," said Yan St. Pierre, CEO of the Berlin-based security consulting firm MOSECON.
An outbreak in Lagos, a megacity where many lived in cramped conditions, could be a major public health disaster.
The West Africa outbreak is believed to have begun as far back as January in southeast Guinea, though the first cases weren't confirmed until March.
Since then, officials have tried to contain the disease by isolating victims and educating populations on how to avoid transmission, though porous borders and widespread distrust of health workers have made the outbreak difficult to bring under control.
News of Brisbane's death first began circulating on Saturday, a national holiday marking Liberia's independence in 1847.
President Ellen Johnson Sirleaf used her Independence Day address to discuss a new taskforce to combat Ebola. Information Minister Lewis Brown said the taskforce would go "from community to community, from village to village, from town to town" to try to increase awareness.
In Sierra Leone, which has recorded the highest number of new cases in recent days, the first case originating in Freetown, the capital, came when a hairdresser, Saudata Koroma, fell ill. She was forcibly removed from a government hospital by her family, sparking a frantic search that ended Friday. Kargbo, the chief medical officer, said Sunday that Koroma died while being transported to a treatment center in the east of the country.