ABUJA, Nigeria — Two alarming new cases of Ebola have emerged in Nigeria, widening the circle of people sickened beyond the immediate group of caregivers who treated a dying airline passenger in one of Africa’s largest cities.

The outbreak also continues to spread elsewhere in West Africa, with 142 more cases recorded, bringing the new total to 2,615 with 1,427 deaths, the World Health Organization said Friday.

Most of the new cases are in Liberia, where the government was delivering donated rice to a slum where 50,000 people have been sealed off from the rest of the capital in an attempt to contain the outbreak.

New treatment centers in Liberia are being overwhelmed by patients that were not previously identified. One center with 20 beds opened its doors to 70 possibly infected people, likely coming from “shadow-zones” where people fearing authorities won’t let doctors enter, the U.N. health agency said.

“This phenomenon strongly suggests the existence of an invisible caseload of patients who are not being detected by the surveillance system,” the agency said. This has “never before been seen in an Ebola outbreak.”

The two new cases in Nigeria were infected by their spouses, both medical workers who had direct contact with Liberian-American Patrick Sawyer, who flew into Nigeria from Liberia and Togo and infected 11 others before he died in July. The male and female caregivers also then died of Ebola, Health Minister Onyebuchi Chukwu said Friday.

Nigerian officials initially claimed the risk of exposure to others was minimal because Sawyer was whisked into isolation after arriving at the airport. Lagos state health commissioner Jide Idris later acknowledged that Sawyer was not immediately quarantined.

The two new cases were quarantined two days ago while being tested, Chukwu said. They had previously been under surveillance but their movements were not restricted.