An American doctor who caught the Ebola virus while working in a Liberian maternity ward is showing signs of improvement, relatives say.

Rick Sacra, 51, arrived at the Nebraska Medical Center early Friday, becoming the third US healthcare worker to be evacuated from West Africa amid the largest Ebola outbreak in history.

Sacra's wife Debbie and oldest son Maxwell, 22, visited the sickened doctor on Saturday, SkyNews reports.

They spoke via videolink for about 25 minutes, as Sacra is being isolated in the hospital's biocontainment unit to avoid contamination from the highly contagious disease.

'Rick is very sick and weak, but slightly improved from when he arrived yesterday,' Debbie Sacra said. 'He asked for something to eat and had a little chicken soup.'

The Nebraska Medical Center has said that serum from a surviving patient, or drug treatments that interfere with the virus but have never been tested in people are among the options being considered for Sacra.

There are no drug treatments on the market for Ebola, and no vaccines to prevent it, though the crisis has accelerated clinical trials to test and bring remedies to the market.

The other American doctors sickened with Ebola, doctor Kent Brantly and aid worker Nancy Writebol, recovered and were discharged from Emory University Hospital in Atlanta, Georgia last month.