WASHINGTON — Ebola has arrived in the United States and people are frightened.

The nation’s top infectious diseases expert said it’s perfectly normal to feel anxious about a disease that kills so fast and is ravaging parts of West Africa.

“People who are scared, I say, we don’t take lightly your fear. We respect it. We understand it,” Dr. Anthony Fauci of the National Institutes of Health said Sunday.

But West Africa, because of the weaknesses in its health system, is not the United States, Fauci said, predicting “we won’t have an outbreak.” Scientists know how to stop the virus from spreading.

That’s not to say the first Ebola case diagnosed within the United States — a traveler from Liberia who began feeling the effects after arriving in Dallas — will be the only one.