Experts have moved to calm fears of a US outbreak of the Ebola virus as the first victim brought from West Africa is treated at a special isolation unit.

Fears the outbreak, that has killed more than 700 people in Africa, could spread in the US has generated public anxiety. But experts say there is zero risk as Emory University Hospital in Atlanta, Georgia, treats critically ill missionary Dr Kent Brantly and a charity worker infected in Liberia.

The US Centres for Disease Control (CDC) and Prevention has received "nasty emails" and at least 100 calls from people saying "How dare you bring Ebola into the country," CDC director Dr Tom Frieden said.

Dr Brantly and Nancy Writebol, who arrived in the US on Saturday, is being treated in Emory's isolation unit for infectious diseases. Ebola is spread by close contact with bodily fluids and blood.