ABUJA, Nigeria (AP) — Nigerian authorities on Monday confirmed a second case of Ebola in Africa's most populous country, an alarming setback as officials across the region battle to stop the spread of a disease that has killed more than 700 people.

Nigerian Health Minister Onyebuchi Chukwu also said test samples were pending for three other people who had shown symptoms of Ebola.

The confirmed second case is a doctor who had helped treat Patrick Sawyer, the Liberian-American man who died July 25 days after arriving in Nigeria amid the unprecedented outbreak in West Africa.

"Three others who participated in that treatment who are currently symptomatic have had their samples taken and hopefully by the end of today we should have the results of their own test," Chukwu said.

The emergence of a second case raises serious concerns about the infection control practices that were used while Sawyer was in Nigeria, and also raise the specter that more cases could emerge. It can take up to 21 days after exposure to the virus for symptoms to appear. They include fever, sore throat, muscle pains and headaches. Often nausea, vomiting and diarrhea follow, along with bleeding.

Sawyer, who was traveling to Nigeria on business, became ill while aboard a flight and Nigerian authorities immediately took him into isolation. They did not quarantine his fellow passengers, and have insisted that the risk of additional cases was minimal.

Nigeria is the fourth country to report Ebola cases and at least 728 other people have died in Guinea, Sierra Leone and Liberia.

Nigerian authorities said a total of 70 people are under surveillance and that they hoped to have eight people in quarantine by the end of Monday in an isolation ward in Lagos.