US President Barack Obama has urged Americans to avoid hysteria over Ebola, and played down the idea of travel bans from Ebola-ravaged countries in West Africa, explaining that restrictions could make things worse.

Lawmakers this week urged Obama to bar people from Liberia, Sierra Leone and Guinea from entering the United States. Obama has said he is not philosophically opposed to travel bans, but in his weekly address made it clear that he is not leaning toward them.

"We can't just cut ourselves off from West Africa," Obama said, explaining it would make it harder to move health workers and supplies into the region, and would motivate people trying to get out the region to evade screening, making it harder to track cases. "Trying to seal off an entire region of the world - if that were even possible - could actually make the situation worse."

Obama said it would take time to fight the disease, warning "before this is over, we may see more isolated cases here in America."

But he sought to put the disease in perspective, reminding Americans that only three cases have been diagnosed in the country, and that it is not easily contracted.

"As I've said before, fighting this disease will take time. Before this is over, we may see more isolated cases here in America. But we know how to wage this fight," Obama said. "And if we take the steps that are necessary, if we're guided by the science-the facts, not fear-then I am absolutely confident that we can prevent a serious outbreak here in the United States, and we can continue to lead the world in this urgent effort."

Yesterday, 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.