President Barack Obama appointed a former White House adviser as U.S. Ebola "czar" on Friday as the global death toll from the disease that has ravaged three West African countries rose to more than 4,500.

President Barack Obama appointed a former White House adviser as U.S. Ebola "czar" on Friday as the global death toll from the disease that has ravaged three West African countries rose to more than 4,500.

Obama, facing criticism from some lawmakers over his administration's handling of efforts to contain the virus, appointed Ron Klain, a lawyer who previously served as chief of staff to Vice Presidents Joe Biden and Al Gore, to oversee the U.S. response to the virus.

Klain's appointment highlighted anxiety over the threat from Ebola, even though there have been just three cases diagnosed in the country, all in Dallas. They were a Liberian, Thomas Eric Duncan, the first person diagnosed in the United States, and two nurses who were on the team of health workers caring for him up to his death last week.

The worst-hit countries have been Guinea, Liberia and Sierra Leone, where Ebola has taken 4,546 lives since the outbreak of the hemorrhagic fever began there in March, according to a report on Friday from the World Health Organization.

That marked a sharp increase from late July, when fewer than 730 people had died from the disease in West Africa. The virus is spread through direct contact with bodily fluids from an infected person.

The toll on the worst-hit countries has gone beyond the illness, because of disruptions to farming and marketing. The World Food Program said food prices in Guinea, Liberia and Sierra Leone had risen by an average of 24 percent, forcing some families to cut back to just one meal a day.