An American woman infected with the dangerous Ebola virus arrived at a US military base in Atlanta, Georgia, on Tuesday and is headed for treatment at a specially equipped hospital.
Nancy Writebol, 60, landed aboard a small medical evacuation plane, according to television images broadcast by US networks.
She is to be transported by ambulance to Emory University Hospital, where her colleague, missionary doctor Kent Brantly, is also receiving care.
Brantly, 33, was sickened with Ebola while taking care of patients in the Liberian capital. He arrived in the United States on Saturday.
The two Americans are among more than 1,600 people infected with the hemorrhagic fever in West Africa since March, marking the largest outbreak of Ebola in history.
A total of 887 people have died of the virus in Sierra Leone, Liberia, Guinea and Nigeria, a 55 percent fatality rate, according to the World Health Organization.
The World Bank has pledged up to $200 million to Guinea, Liberia and Sierra Leone to help those nations contain the outbreak.
Ebola is transmitted through close contact with bodily fluids, and people who live with or care for patients are most at risk. Experts say it is not transmissible by air.