A 33-year-old American doctor helping fight Ebola in Liberia's capital has come down with the hemorrhagic fever, Reuters reported. Dr. Kent Brantly, from Fort Worth, Texas, was working as a medical doctor at one of the country's treatment center when he noticed his own symptoms and quarantined himself. It was not immediately clear how he caught Ebola. The outbreak in Guinea, Liberia and Sierra Leone has killed 660 people, according to the World Health Organization.