ABUJA, Nigeria — West Africa’s Ebola outbreak has spread to Nigeria.

A 40-year-old Liberian who arrived on a plane Tuesday died Friday. He had arrived with symptoms – which include vomiting and diarrhea – and was immediately placed in an isolation ward.

The man had recently lost his sister to Ebola in Liberia, health officials there said. It was not immediately clear how he managed to board a flight.

It is the first case of Ebola to be confirmed in Nigeria, Africa’s most populous country, since the current outbreak began in West Africa earlier this year, according to Nigerian Health Minister Onyebuchi Chukwu

“All ports of entry into Nigeria including airports, seaports and land boarders are placed on red alert,” he said. “Ministry of Health specialists have been positioned in all entry points. Active surveillance has also been stepped up.”

Authorities are currently investigating all persons who may have come into contact with the deceased, said Chukwu.

The man, a Liberian government official, arrived to attend an international conference. He died early Friday. Blood tests for Ebola returned positive from the Lagos University Teaching Hospital later in the day.

Ebola, one of the world’s most deadly and contagious diseases, has killed at least 660 and infected 1,093 in Sierra Leone, Liberia, Guinea, and now Nigeria, according to the World Health Organization.

Nigerian Health Minister Onyebuchi Chukwu said it was the first case of Ebola to be confirmed in Nigeria since the current outbreak emerged this year.

“All ports of entry into Nigeria, including airports, seaports and land borders, are placed on red alert,” he said. “Ministry of Health specialists have been positioned in all entry points. Active surveillance has also been stepped up.”

Authorities are investigating anyone who may have come into contact with the deceased, Chukwu said.

Liberia’s Chief Medical Officer Bernice Dahn identified the Ebola victim as a government official with the finance ministry.

“When his sister died, his workmates were kind of afraid for him to be around,” she said. “We received several calls from workmates on whether it was advisable for him to go to work.”

The man told health officials that he had not had any physical contact with his sister, and based on his explanation, he initially was told to report back to work but was advised not to travel. He later was asked to stay home for 21 days but apparently continued working.