In this 2014 photo provided by the Samaritan's Purse aid organization, Dr. Kent Brantly, left, treats an Ebola patient at the Samaritan's Purse Ebola Case Management Center in Monrovia, Liberia. On Saturday, July 26, 2014, the North Carolina-based aid organization said Brantly tested positive for the disease and was being treated at a hospital in Monrovia. (AP Photo/Samaritan's Purse)

(AP)—A U.S. doctor working with Ebola patients in Liberia has tested positive for the deadly virus, an aid organization said Saturday.

Samaritan's Purse issued a news release saying Dr. Kent Brantly was being treated at a hospital in Monrovia, the capital. Brantly had been serving as medical director for the aid organization's case management center there.

The highly contagious virus is one of the world's most deadly. 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."

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.

The disease has already killed 672 in four West African countries since the outbreak began earlier this year.