(CBS News)-- BOONE, N.C. - Two U.S. citizens are now reported to be infected with the deadly and incurable Ebola virus in West Africa.
The first American reported to have contracted the disease is an American doctor working with Ebola patients in Liberia, who tested positive for the deadly virus, North Carolina-based Samaritan's Purse issued said in a news release on Saturday.
The second person who reportedly tested positive for Ebola is a woman employed by an aid organization in Liberia who is a married mother of two.
In a statement on Sunday, Samaritan's Purse said: "Nancy Writebol is employed by SIM in Liberia and was helping the joint Samaritan's Purse/SIM team that is treating Ebola patients at the Case Management Center in Monrovia."
Writebol's age and hometown have not been released at this time.
Earlier, Samaritan's Purse said Dr. Kent Brantly tested positive for the disease and was being treated at a hospital in Monrovia, Liberia. Brantly is the medical director for the aid organization's case management center in the city.
Brantly, 33, has been working with Samaritan's Purse in Liberia since October 2013 as part of the charity's post-residency program for doctors, said the group's spokeswoman Melissa Strickland. The organization's website says he had worked as a family practice physician in Fort Worth, Texas.
Photos of Brantly working in Liberia show him in white coveralls made of a synthetic material that he wore for hours a day while treating Ebola patients.
Brantly was quoted in a posting on the organization's website earlier this year about efforts to maintain an isolation ward for patients.
"The hospital is taking great effort to be prepared," Brantly said. "In past Ebola outbreaks, many of the casualties have been healthcare workers who contracted the disease through their work caring for infected individuals."
Strickland says that Brantly's wife and children had been living with him in Africa, but they are currently in the U.S.
A woman who identified herself as Brantly's mother answered a U.S. phone listing for him, but said family members are declining comment at this time.
The deadly disease has killed at least 672 in several African countries since the outbreak began earlier this year.
Meanwhile, One of Liberia's most high-profile doctors has died of Ebola, a government official said Sunday, highlighting the risks facing health workers trying to combat the deadly disease.
Dr. Samuel Brisbane is the first Liberian doctor to die in an outbreak the World Health Organization says has killed 129 people in the West African nation. A Ugandan doctor working in the country died earlier this month.
The WHO says the outbreak has also killed 319 people in Guinea and 224 in Sierra Leone.
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 the country's largest hospital, the John F. Kennedy Memorial Medical Center in Monrovia.
After falling ill with Ebola, he 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.
There is no known cure for Ebola, which begins with symptoms including fever and sore throat but then escalates to vomiting, diarrhea and internal and external bleeding.
Experts believe the ongoing West Africa outbreak could 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, satellite outbreaks and widespread distrust of health workers have made the outbreak difficult to bring under control.
Nigerian officials announced on Friday that a Liberian official died of Ebola after flying from Monrovia to Lagos. The official's plane also stopped in Lome, Togo.
An outbreak in Lagos, a megacity where many lived in cramped conditions, could be a major public health disaster.
The fact that the traveler from Liberia could board an international flight also raised new fears that other passengers could take the disease beyond Africa.