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

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.

More than 2,000 people have died from the contagious virus in Liberia, Guinea, Sierra Leone and Nigeria since the beginning of the year, according to the World Health Organization.

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

They spoke via video link for about 25 minutes, as Sacra is being isolated in the hospital's bio-containment 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."

She added that her husband could not remember much from his return to the United States, and was trying to rest.

Debbie Sacra said she was "relieved to see his face and hear his voice again."

She expressed hope her husband's illness would help garner more attention to the outbreak.

"We don't want this story to be about Rick," she said.

"The story is the crisis in West Africa. That is what is most important. The world is coming to this fight late."

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.

Ebola causes fever, vomiting, diarrhea and in severe cases, internal hemorrhaging. The current outbreak has been fatal to about half of those infected.

It is transmissible through close contact with the bodily fluids of an infected person, or by touching the corpse of a person who has recently died of the infection.