Breaking News: Another American aid worker in Liberia has tested positive for Ebola

On Saturday, Samaritan's Purse announced that American doctor Kent Brantly had become infected. The 33-year-old former Indianapolis resident had been treating Ebola patients in Monrovia and started feeling ill, spokeswoman Melissa Strickland said. Once he started noticing the symptoms last week, Brantly isolated himself.

Brantly, the medical director for Samaritan Purse's Ebola Consolidated Case Management Center in Monrovia, has been in the country since October, Strickland said.

"When the Ebola outbreak hit, he took on responsibilities with our Ebola direct clinical treatment response, but he was serving in a missionary hospital in Liberia prior to his work with Ebola patients," she said.

Last week, a Liberian man hospitalized with Ebola in Lagos died, Nigerian Health Minister Onyebuchi Chukwu said.

Lagos, the largest city in Nigeria, has a population of more than 20 million.

The man arrived at Lagos airport on July 20 and was isolated in a local hospital after showing symptoms associated with the virus. He told officials he had no direct contact with anyone with the virus nor had he attended the burial of anyone who died of Ebola.