Aviation officials in Nigeria said Saturday that they are screening passengers arriving from abroad and health officials are distributing information about how to identify Ebola symptoms. 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.

Sawyer's sister also died of Ebola in Liberia, according to Liberian officials, but Patrick claimed to have had no contact with her.

Nearly 50 other passengers on the flight are being monitored for signs of Ebola but are not being kept in isolation, said an employee at Nigeria's Ministry of Health, who insisted on anonymity because he was not authorized to speak to the press.

Sawyer reportedly did not show Ebola symptoms when he boarded the plane, 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.

On his way to Lagos, Sawyer stopped for a layover in Lome, Togo, according to the WHO. Authorities said Friday that blood tests from the Lagos University Teaching Hospital confirmed Sawyer died of Ebola.

Patrick Sawyer, a consultant for the Liberian Ministry of Finance, arrived in Nigeria on Tuesday and was immediately detained by health authorities suspecting he might have Ebola, according to Dr. Lance Plyler, who heads Ebola medical efforts in Liberia for aid organization Samaritan's Purse.

Across the West African countries of Guinea , Liberia and Sierra Leone , at least 660 people have died from the illness since February, according to the World Health Organization (WHO), placing great strain on the health systems of some of Africa's poorest countries. Sierra Leone now has the highest number of cases, at 454, surpassing neighboring Guinea, where the outbreak originated.

Unni Krishnan, the head of disaster response for the international advocacy group Plan International, warned that an Ebola outbreak in Lagos could be disastrous. There is no cure or vaccine for the highly contagious virus.

Nigerian officials said Saturday that they are screening passengers arriving from foreign countries for symptoms of Ebola, following the death of an infected traveler from Liberia who died after collapsing at the airport in Lagos, Africa's largest city with a population of 21 million.

Ebola can kill up to 90 percent of those who contract it, although the fatality rate of the current outbreak is about 60 percent. Symptoms include vomiting and diarrhea as well as internal and external bleeding.

Authorities have struggled to contain the outbreak of the virus in West Africa, where poor health infrastructure, lack of medical staff and public distrust of health officials hamper efforts, the WHO has said. Many in the region put more faith in traditional medicine rather than modern remedies, according to the organization, a branch of the United Nations.

Local burial rituals, where mourners come in contact with corpses, may increase the spread of the disease.

Previous outbreaks of the dreaded virus in Africa have been smaller and more easily defeated, hitting remote areas and killing victims so fast it had little chance to spread.

In Nigeria, Yakubu Dati, spokesman for the Federal Aviation Authority, said airports are also setting up holding rooms in case another potential Ebola victim lands in the country. Doctors say health screenings could be used, but Ebola cannot be diagnosed on the spot and many symptoms are similar to more common diseases like malaria.

Skepticism of health officials’ orders has complicated attempts to contain the disease, with, for example, thousands marching on an Ebola treatment center in Sierra Leone on Friday after a former nurse alleged that the deadly virus was invented to conceal "cannibalistic rituals" at the ward, a regional police chief said.

Angry crowds gathered outside the country's main Ebola hospital in Kenema in the West African country's remote east, where dozens are receiving treatment for the virus, and threatened to burn it down and remove the patients.

Residents said that police fired tear gas to disperse the crowds and said that a 9-year-old boy was shot in the leg by a police bullet.

Assistant Inspector General Alfred Karrow-Kamara said calm had returned to Kenema on Saturday, adding that a strong, armed police presence was in place around the clinic and the local police station.

Some health workers from the clinic have been reported absent from work because of "misconceptions by some members of the community," according to a local doctor.

President Ernest Bai Koroma said Saturday that the government planned to "intensify activities and interventions in containing the disease and stopping its spread" with a view to ending the disease within 60-90 days.

The new strategy will focus on contact-tracing, surveillance, communications and social mobilization, psychosocial services, and logistics and supplies, according to the president's statement.

Amadu Sisi, senior doctor at King Harman hospital in Freetown, Sierra Leone, said Saturday that a woman infected with Ebola, who was forcibly removed from the hospital Friday, had been turned in after she sought refuge in the house of a traditional healer. The woman was the first person to be diagnosed with Ebola in the coastal town. After she was taken Friday, local authorities made radio announcements calling for her immediate return.

"Because of media and police pressure they decided to give her up," Sisi said. "Maybe they are now convinced it is Ebola.”

Al Jazeera and wire services