US President Barack Obama appointed an Ebola tsar for the United States yesterday, while the government said a Texas health worker who may have had contact with specimens from an Ebola patient had been isolated on a cruise ship. Obama, who has faced sharp criticism from some lawmakers over efforts to contain the deadly virus, appointed Ron Klain, a lawyer who previously served as chief of staff to Vice Presidents Joe Biden and Al Gore, the White House said. The cruise ship incident added to growing concerns about the possible spread of Ebola after two nurses who cared for Thomas Eric Duncan, the first person diagnosed with Ebola in the United States, contracted the virus, which has killed more than 4,500 people, mostly in West Africa. The worst hit countries have been Guinea, Liberia and Sierra Leone. The World Food Programme said yesterday that food prices in those countries had risen by an average of 24 per cent, forcing some families to reduce their intake to one meal a day. The Texas Health Presbyterian Hospital worker aboard the cruise ship, who did not have direct contact with the now-deceased Liberian patient but could have processed his bodily fluids, left on Sunday on a cruise from Galveston, Texas, State Department spokeswoman Jen Psaki said. The health worker had been self-monitoring since October 6 and had not developed a fever or other symptoms of Ebola, the State Department said. Carnival Cruise Lines said it had been notified by the US Centres for Disease Control and Prevention (CDC) that a passenger on the Carnival Magic was a lab supervisor at Texas Health Presbyterian Hospital. It said she was deemed to be "very low risk". The ship can carry 3,690 passengers and 1,367 crew, according to the company's website. The State Department said the worker might have processed samples from Duncan 19 days ago. The maximum incubation window for the disease is 21 days, according to the CDC. The worker and a companion voluntarily isolated themselves in their cabin. "We are working with the cruise line to safely bring them back to the United States out of an abundance of caution," Psaki said.