Nigeria has stepped up screening at its airports after the county recorded a second Ebola case.
A Nigerian doctor who treated an infected Liberian man who travelled to Lagos and later died has contracted the disease.
A third person is also being monitored.
The World Health Organisation has reported 61 new cases across West African countries in just two days.
In Sierra Leone fear of the deadly disease is crippling commerce. Only medical prevention officers are seen on the streets.
The density of Ebola cases is highest here and the government has launched a military operation involving 750 troops to implement quarantines in more remote areas.
So far the death toll in this year’s outbreak has reached nearly 900.
In response, the World Bank is giving $200 million ( 149 million euros) to the three countries worst affected – Guinea, Sierra Leone and Liberia.
In New York, a man exhibiting symptoms of the disease is being tested after having travelled to a West African nation.
Highly contagious, Ebola can kill up to 90 percent of those infected. Symptoms include fever vomiting and internal and external bleeding.
A second American aid worker who contracted the Ebola virus in Africa is being flown to Atlanta in a serious condition.
Specialists at Emory University Hospital are already treating a 33-year-old doctor who was stricken while working as part of a emergency response unit to the initial outbreak of the disease in Africa.