Two new cases of Ebola have emerged in Nigeria and, in an alarming development, they are outside the group of caregivers who treated an airline passenger who arrived with Ebola and died, Health Minister Onyebuchi Chukwu said Friday.

The two new cases are spouses of medical workers who had direct contact with Liberian-American Patrick Sawyer, who flew into Nigeria last month with the virus and infected 11 others before he died in July. The male and female caregivers both subsequently died of Ebola, after infecting their spouses, Chukwu told reporters in Abuja, the capital.

Nigerian officials initially claimed the risk of exposure to others was minimal because Sawyer was whisked into isolation after arriving at the airport. But Lagos state health commissioner Jide Idris later acknowledged that Sawyer was not immediately quarantined when he arrived because doctors didn't suspect Ebola.

The two new cases were quarantined two days ago while being tested for the virus, Chukwu said. They had previously been under surveillance but were brought in when they developed Ebola symptoms.

A total of 213 people are under surveillance in Nigeria as part of efforts to monitor anyone who may have been exposed to Ebola, Chukwu said. These include six people in the southeastern state of Enugu, he said.

The latest two cases bring the total number of confirmed infections in Nigeria, including Sawyer, to 14. Five have died from the illness, five recovered and were discharged from hospital while another four are being treated in isolation in Lagos, the commercial capital where Sawyer's flight landed.

The damage has been far greater in Guinea, Sierra Leone and Liberia, which have each recorded hundreds of cases. Liberia has seen the most deaths, with 576.

The World Health Organization is concerned that the scale of the outbreak has been underestimated especially in Liberia and Sierra Leone, and that many people with Ebola symptoms have not been identified.

New treatment centers in Liberia were overwhelmed as soon as they opened over the past two weeks by patients that were not previously identified.

In a situation assessment issued Friday, the WHO said this had "never before been seen in an Ebola outbreak," adding that it suggested "an invisible caseload of patients" going undetected by the government's surveillance measures.

In Liberia, a teenage boy died after being shot by security forces in a slum community that was blockaded this week to stop the spread of Ebola, a Liberia government spokesman said Friday.

Shakie Kamara, who relatives said was either 15 or 16, was one of three people who sustained serious injuries during an altercation Wednesday that erupted after security forces blocked roads in and out of the West Point slum housing at least 50,000 people.

The death risked raising tensions in West Point, which has already been a flash point. Last weekend residents ransacked a holding center for Ebola patients after realizing that some patients had come from other parts of the city. Looters then made off with materials including blood-stained mattresses and sheets that could spread the disease.

The government began distributing rice to alleviate food shortages as a result of the cordoning off of West Point on Thursday, said Information Minister Lewis Brown.

The distributed rice included donations from the World Food Program to Liberia's national Ebola taskforce, said Fabienne Pompey, WFP's West Africa spokeswoman.

Countries in West Africa and beyond continue to impose travel restrictions even though the World Health Organization has not recommended them.

On Friday, the Central African country of Gabon announced it was barring all flights and ships from Ebola-stricken countries. Senegal announced late Thursday that it was closing air and sea borders with Guinea, Sierra Leone and Liberia. The land border with Guinea was also closed.

South Africa said Thursday it was imposing a travel ban for non-citizens traveling from those countries "unless the travel is considered absolutely essential."

Earlier this week, Cameroon said that it was barring flights from Nigeria.