ABUJA, Nigeria -- Nigerian health authorities raced to stop the spread of Ebola on Saturday after a man sick with one of the world's deadliest diseases brought it by plane to Lagos, Africa's largest city with 21 million people.
The fact that the traveler from Liberia could board an international flight also raised new fears that other passengers could take the disease beyond Africa due to weak inspection of passengers and the fact that Ebola's symptoms are similar to other diseases.
Officials in the country of Togo, where the sick man's flight had a stopover, also went on high alert after learning that Ebola could possibly have spread to a fifth country.
Screening people as they enter the country may help slow the spread of the disease, but it is no guarantee Ebola won't travel by airplane, according to Lance Plyler, who heads Ebola medical efforts in Liberia for the aid organization Samaritan's Purse.
"Unfortunately the initial signs of Ebola imitate other diseases, like malaria or typhoid," he said.
The aid organization said Saturday that a U.S. doctor working with Ebola patients in Liberia had tested positive for the deadly virus. A Samaritan's Purse news release said Kent Brantly was being treated at a hospital in Monrovia, the capital.
Ebola already had caused 672 deaths across West Africa before the Nigeria case was announced. It is the deadliest outbreak on record for Ebola.
"Lagos is completely different from other cities because we're talking about millions of people," said Plan International's disaster response and preparedness head, Unni Krishnan.
Nigerian newspapers describe the effort as a "scramble" to contain the threat after the Liberian -- identified as Patrick Sawyer, a consultant for the Liberian Ministry of Finance -- arrived in Lagos on Tuesday and then died Friday.
Airports in Nigeria are screening passengers arriving from foreign countries for symptoms of Ebola, according to Yakubu Dati, the spokesman for Federal Aviation Authority of Nigeria.
And Nigerian airports are setting up holding rooms in case another potential Ebola victim lands in Nigeria.
Airports in Guinea, Liberia and Sierra Leone, the three other West African countries affected by the current Ebola outbreak, have implemented some preventive measures, according to officials in those countries. But none of the safeguards are foolproof, say health experts.
Doctors say health screens could be effective, but Ebola has a variable incubation period of between two and 21 days and cannot be diagnosed on the spot.
Mr. Sawyer, the stricken traveler, was immediately detained by Nigerian health authorities, suspecting he might have Ebola, Dr. Plyler said.
Mr. Sawyer's plane also stopped in Lome, Togo, according to the World Health Organization.
Authorities announced Friday that blood tests from the Lagos University Teaching Hospital confirmed Mr. Sawyer died of Ebola that day.
Mr. Sawyer reportedly did not show Ebola symptoms when he boarded the plane, Dr. Plyler said, but by the time he arrived in Nigeria he was vomiting and had diarrhea. There has not been another recently recorded case of Ebola spreading through air travel, he added.
Ebola is highly contagious and kills more than 70 percent of people infected. It is passed by touching bodily fluids of patients even after they die, Dr. Krishnan said.
First Published July 26, 2014 10:54 PM