Ebola Virus on the Loose: World Cautioned as Infection Moves; Global Airports on High Alert; Kills Liberian Doctor, Infects American Worker

International health experts cautioned the global populace against the dreaded Ebola virus as it killed a Liberian doctor and infected a second medical worker from U.S. Authorities in Nigeria are likewise scrambling the possible spread of the flesh-eating disease following the arrival of an infected man into Lagos, Africa's largest city with 21 million people.

"Lagos is completely different from other cities because we're talking about millions of people," Dr. Unni Krishnan, Plan International's Disaster Response and Preparedness Head, said.

The second American worker, identified as Nancy Writebol, had tested positive to the deadly Ebola virus. She was working at the same medical compound in Liberia where an American doctor became infected, Ken Isaacs, vice president of program and government relations with U.S.-based Christian relief group Samaritan's Purse, said.

"It's been a shock to everyone on our team to have two of our players get pounded with the disease," the AP quoted Isaacs on Sunday.

The outbreak, which has killed more than 670 people in Liberia, Guinea and Sierra Leone since the start of 2014, is one of the most deadly diseases in the world.

Writebol, Samaritan's Purse said, is a hygienist who disinfects doctors as they leave an Ebola isolation zone.

In Nigeria, authorities are concerned the infected passenger had not only come into contact with people in the aircraft but also at the megacity's main airport. They believed he had also spent time in an airport at the uninfected African country of Togo where his flight was supposed to have a stopover.

Yakubu Dati, Federal Aviation Authority of Nigeria spokesman, said health officials have deployed representatives to work at airports, sea ports and land border crossings.

"They are giving out information ... on what to do, what to look out for," news.com.au quoted Dati.

Meantime in Liberia, border crossings have been ordered shut to eliminate further spread of the deadly Ebola virus. At the same time, it had ordered the assembly of testing centres at major entry points to the country, such as the international airport.

Still, Dr Lance Plyler, the head of efforts in Liberia to contain the Ebola outbreak, said screening may only help slow the potential spread of virus. There still remains the risk that aircraft travelers themselves will disseminate the virus.