Health workers prepare to bury a woman who died of Ebola at the isolation unit in Lofa County, Liberia, July 2. Ahmed Jallanzo / EPA

Liberians in Monrovia read an information poster about preventing the spread of the Ebola virus, July 27. Ahmed Jallanzo / EPA

Doctors Without Borders staffers put on protective gear before entering the isolation area in Kailahun. Tommy Trenchard / Reuters

Doctors Without Borders workers take food to patients in an isolation area at the group’s Ebola treatment center in Kailahun, Sierra Leone, on July 20. Tommy Trenchard / Reuters

Dr. Kent Brantly, left, an American physician, cares for Ebola patients at a hospital in Monrovia, Liberia. Brantly, 33, has tested positive for the Ebola virus. Reuters

Members of the World Health Organization and the Red Cross hand out chlorine and medical soap to combat the spread of the Ebola virus in Bawa, Guinea, on July 10. Samuel Aranda / The New York Times / Redux

Red Cross workers carry the body of Marie Conde, 14, who died of Ebola, through the bush in Koundony, Guinea, on July 9. The virus has claimed more than 670 lives in West Africa since March. Samuel Aranda / The New York Times / Redux

One of Liberia's most high-profile doctors has died of Ebola, a government official said Sunday, and a second American aid worker has tested positive for the Ebola virus, highlighting the risks facing health workers trying to combat the dreaded disease.

Dr. Samuel Brisbane is the first Liberian doctor to die in an outbreak that the World Health Organization (WHO) said has killed 129 people in the West African nation alone. A Ugandan doctor working in the country died earlier this month.

Health workers are at serious risk of contracting the virus, which spreads through contact with bodily fluids.

The WHO says the outbreak, which began in February and represents the largest ever recorded, has also killed 319 people in Guinea and 224 in Sierra Leone. There is no known cure for Ebola, which begins with symptoms including fever and sore throat before escalating to vomiting, diarrhea and internal and external bleeding.

Brisbane's death comes amid reports of another high-profile death, in Sierra Leone. Saudatu Koroma, 32, succumbed to the virus after her family stormed a hospital in Sierra Leone's capital of Freetown Thursday and forcibly removed her from quarantine.

Koroma, a resident of the densely populated Wellington neighborhood, had been admitted to an isolation ward while blood samples were tested for the virus, according to Health ministry spokesman Sidi Yahya Tunis.

The motives for removing Koroma from the hospital were not clear, but efforts to combat the disease have met difficulties in a population skeptical of modern medicine and more trusting of traditional remedies.

After authorities launched a brief and frantic search, Koroma showed up at a hospital Saturday, but she later died. Before returning to doctors, she had gone to a traditional healer, according to Amadu Sisi, senior doctor at King Harman hospital in Freetown.

Brisbane, who once served as a medical adviser to former Liberian President Charles Taylor, was working as a consultant with the internal medicine unit at Liberia's largest hospital, the John F. Kennedy Memorial Medical Center in Monrovia, Liberia's capital.

After falling ill with Ebola, Brisbane was taken to a treatment center on the outskirts of the capital, where he died, said Tolbert Nyenswah, an assistant health minister.

Under the supervision of health workers, family members escorted the doctor's body to a burial location west of the city, Nyenswah said. He added that another doctor who had been working in Liberia's central Bong County was also being treated for Ebola at the same center where Brisbane died.

The situation "is getting more and more scary," Nyenswah said.

On Sunday, Ken Isaacs, a vice president of Samaritan's Purse, identified the second American, Nancy Writebol, as a worker with an allied aid group SIM, or Serving in Mission, which runs the hospital where Samaritan's Purse has an Ebola care center on the grounds. He said she was in stable and serious condition.

"She is showing full symptoms of the disease," Isaacs said. He added that Writebol had been working as a hygienist who decontaminated those entering and leaving the Ebola care area at the hospital.

On Saturday, Samaritan’s Purse announced that Dr. Kent Brantly, 33, of Ft. Worth, Texas, tested positive for the deadly virus and was being treated at a hospital in Monrovia. Brantly had been serving as medical director for the aid organization's case management center there. He was stable and in very serious condition on Sunday, Isaacs said.

Samaritan's Purse spokeswoman Melissa Strickland said Brantly's wife and children had been living with him in Africa but are currently in the U.S.

Authorities fear the disease could spread in West Africa's packed cities. Nigerian officials announced Friday that a Liberian official died of Ebola after flying from Monrovia to Lagos, a megacity of 21 million. The official's plane also stopped in Lome, Togo.

An outbreak in Lagos could be a major public health disaster, and the fact that the traveler from Liberia could board an international flight has also raised new fears that other passengers could take the disease beyond Africa.

Al Jazeera and wire services