In recent years, the WHO has declared an emergency only twice, for swine flu in 2009 and polio in May. The declaration would probably come with recommendations on travel and trade restrictions and wider Ebola screening. It also would be an acknowledgment that the situation is critical and could worsen without a fast global response.
The group did not immediately confirm the new cases reported in Nigeria. And Nigerian authorities did not release any details on the latest infections, except to say they all had come into direct contact with the sick man who arrived by plane in Lagos late last month.
In Sierra Leone, some 750 soldiers deployed to the Ebola-ravaged east as part of "Operation Octopus," aimed at enforcing quarantines of sick patients. In Spain, the Defense Ministry said a medically equipped plane was ready to fly to Liberia to bring back a Spanish missionary priest who has Ebola.
At the same time, Saudi officials reported a suspected Ebola death, underscoring the risk of the disease spreading by air travel even as many airlines curtail their flights to the most infected cities.
Ebola, which causes some victims to bleed from the eyes, mouth and ears, can only be transmitted through direct contact with the bodily fluids of someone who is sick — blood, semen, saliva, urine, feces or sweat. Millions in Lagos live in cramped conditions without access to flushable toilets. Signs posted across the city warn people not to urinate in public.
Kenneth Akihomi, a 47-year-old worker installing fiber-optic cable, said he was carefully washing his hands to avoid infection. But he said most people were relying on faith to stay healthy.
"They're not panicking. They are godly people," he said. "They believe they can pray, and maybe very soon there will be cure."
The revelation of more infections also came amid a public-sector doctors' strike in Nigeria that began in early July. So far, health workers monitoring the latest Ebola patients are still on the job.
Nigeria is the fourth West African country to be hit by the Ebola outbreak since it first emerged in March in the remote tropical forests of Guinea. The disease then spread to neighboring Sierra Leona and Liberia before reaching Nigeria, where it surfaced shortly before the government drew criticism for its response to the abduction of more than 200 schoolgirls by Islamic militants back in April. The girls are still missing.
Nigerian authorities said Tuesday that doctors did not suspect Patrick Sawyer was suffering from Ebola when the 40-year-old Liberian-American arrived by plane late last month in Lagos, where the streets are a bewildering mix of wealth and abject poverty, awash in luxury SUVs and decrepit buses.
Sawyer, who worked for the Liberian government in Monrovia and had a wife and three young daughters in Minnesota, was on a business flight to Nigeria when he fell ill. Officials say a nurse who treated him has died and five others are sick with Ebola, including a doctor involved in his care.
West African countries pledged at a meeting in July to step up their surveillance at airports and borders following the start of the outbreak. But the early symptoms of Ebola — fever, muscle aches and vomiting — are similar to much more common tropical diseases such as malaria.
The specter of the virus spreading through Nigeria is particularly alarming, said Stephen Morse, an epidemiology professor at Columbia University's Mailman School of Public Health.
"It makes you nervous when so many people are potentially at risk," he said.
Authorities in Liberia said Sawyer's sister had recently died of Ebola, though Sawyer said he had not had close contact with her while she was ill.