Centers for Disease Control and Prevention (CDC) Director Tom Frieden believes the spread of Ebola in the US is "inevitable."
Due to the speed and ease of international airline travel infected travelers will enter the US undetected, although any outbreak is not likely to be large scale, Frieden said.
More cases of Ebola will spread across borders by air travel amid the biggest outbreak of Ebola in history, health officials say.
One naturalized US citizen has already died from Ebola, after traveling to Lagos, Nigeria and exposing up to seven other people there to the virus.
"It is certainly possible that we could have ill people in the US who develop Ebola after having been exposed elsewhere," said Frieden, addressing a hearing of the House Subcommittee on Africa, Global Health, Global Human Rights and International Organizations.
"We are all connected and inevitably there will be travelers, American citizens and others who go from these three countries or from Lagos if they don’t get it under control," he said.
"But we are confident that there will not be a large Ebola outbreak in the US."
There is no vaccination or treatment for Ebola but can be contained if caught early and isolated.
Ebola symptoms include fever, vomiting, muscle aches and diarrhea and has caused the deaths of over 55% of cases so far during this outbreak.
