Ebola has arrived in the United States and people are scared.

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.

“It’s the unknown. It’s the cataclysmic nature of it,” said Dr. Anthony Fauci of the National Institutes of Health, that “almost intuitively makes people frightened.”

Still, he said it’s “extraordinarily unlikely” that the United States will have an outbreak. Scientists know how to stop the virus from spreading, Fauci said Friday.

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.

The government took measures this past week to ensure hospitals are ready.

Despite some initial missteps in Dallas, tried-and-true methods are underway: tracking everyone who came into contact with the infected man and isolating anyone who shows symptoms.

What to know about Ebola in America:

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THERE’S GOING TO BE A LOT OF TALK

Expect to hear news reports in the coming days about people who are being cared for as potential Ebola cases. That doesn’t mean they have the disease.

Doctors and hospitals are isolating individuals they believe could be at risk. That’s based on a combination of their symptoms and recent travel from a country where Ebola is present.

The Centers for Disease Control and Prevention has consulted with hospitals about 100 or so potentially suspicious cases in recent months. More than a dozen were worrisome enough to merit Ebola blood tests. Only the Dallas patient had Ebola.

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HOW IT SPREADS

Ebola doesn’t spread easily like the flu, a cold or measles.

The virus isn’t airborne. Instead, it’s in a sick person’s bodily fluids, such as blood, vomit, urine, semen or saliva. Another person can catch the disease by getting those germs into his own body, perhaps by wiping his eyes or through a cut in the skin.

Bodily fluids aren’t contagious until the infected person begins to feel sick. The initial symptoms are easily confused with other illnesses, however: fever, headaches, flu-like body aches and abdominal pain. Vomiting, diarrhea and sometimes bleeding follow as the disease progresses, increasing the risk to others.

In West Africa, the disease has spread quickly to family members who tended the sick or handled their bodies after death, and infected doctors and nurses working under punishing conditions, without proper equipment. Bed sheets or clothing contaminated by bodily fluids also spread the disease.

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CAN YOU CATCH IT ON A BUS OR PLANE?

It’s very unlikely.

To be on the safe side, the CDC defines “contact” with the disease as spending a prolonged period of time within 3 feet of someone ill with Ebola, a distance designed to protect health workers from projectile vomiting.

But health officials haven’t seen real world cases of the virus spread by casual contact in public, such as sitting next to someone on a bus, said Tom Frieden, the CDC director.

“All of our experience with Ebola in Africa the last four decades indicates direct contact is how it spreads,” he said, “and only direct contact with someone who is ill with Ebola.”

Passengers who flew on the same plane as the Dallas patient, five days before he developed symptoms, are not considered at risk by the CDC. Nor are the schoolmates of children who came in contact with the infected Dallas man, but showed no symptoms of illness while in class.

As a precaution in case they become sick and therefore contagious, the children who were in contact with the infected man were pulled from school and are being monitored for symptoms.

Initially, about 100 people were assessed for potential exposure. Health officials said Friday that 50 were still being monitored, with 10 considered at the most risk during the disease’s 21-day incubation period. Four family members who shared their apartment with the patient are under quarantine.

Outside those circles, the odds of getting infected within the U.S. remain minuscule, health authorities say.

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WHAT HEALTH OFFICIALS ARE DOING

The CDC is overseeing multiple layers of response:

—The Ebola-hit African nations are checking people at airports for fever, and asking them about any contact with an infected person, before allowing them to board planes out of the country.

—Airlines are required by law to watch for sick travelers and alert authorities before landing.

—The CDC is warning doctors and hospitals to remember the possibility of Ebola and rapidly isolate and test sick patients with a risk of exposure to the virus, primarily those who have traveled recently from the hot spots.

“The only way to get to zero risk is to stop the outbreak in West Africa,” Frieden said.

The U.S. and other countries have stepped up aid to West African nations struggling with the disease. But the outbreak is out of control.

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CAN LOCAL HOSPITALS HANDLE THIS?

Before the Dallas case, four Americans diagnosed with Ebola in Africa returned to the U.S. enclosed in portable biohazard units, attended by health care workers protected by what looked like puffy space suits. They were treated in special isolation units; three recovered and one remains hospitalized.

The U.S. has only four of those isolation units; when people feel sick, they go to their nearest health care.

The CDC says any American hospital should be able to care for an Ebola patient.

Emergency room staff, potentially the first line, are used to safeguarding themselves from germs. They routinely treat patients with HIV, hepatitis and other infectious diseases.

The CDC says it’s fine to put a suspected Ebola case into a regular private room with its own bathroom, and doctors and nurses need only wear certain gowns, masks and eye protection to be safe, not the elaborate biohazard suits.

Yet the system isn’t perfect, as the Dallas case shows.

When the patient, Thomas Eric Duncan, first arrived at a Dallas hospital, he told a nurse that he had recently traveled from West Africa, yet the possibility of Ebola was overlooked and he was discharged into the community. He returned in worse shape, by ambulance, two days later and was diagnosed with the virus. He is in critical condition.

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THIS EBOLA OUTBREAK IS DIFFERENT, ISN’T IT?

Yes. It’s the worse Ebola outbreak in history, and still out of control in Liberia, Guinea and Sierra Leone.

Previous outbreaks in other parts of Africa have been halted more quickly.

Lack of experience with the disease in West Africa contributed to its spread this time. Other factors: a shortage of medical personnel and supplies, widespread poverty, and political instability in affected countries.

Also, the disease is crossing national borders and spreading in urban areas. Past outbreaks tended to be in relatively isolated spots.

It’s hard for Americans to grasp how much more easily diseases can spread in some of the poorest places on earth versus in the U.S., said Ebola expert Thomas Geisbert of the University of Texas Medical Branch at Galveston.

In countries where inadequate health systems have been overwhelmed by the virus, people are dying in their homes, outside clinics that are too overfilled to take them, and sometimes in the streets. Health workers have been attacked by panicked residents.

Yet the measures that have stopped past outbreaks still work, with sufficient knowledge and resources.

Senegal appears to have stopped the disease at one case this year. Nigeria had eight deaths but brought its outbreak under control by tracking 894 people who had been in contact with a man who brought the virus from Liberia, and visiting 18,500 more people to check for symptoms, the CDC said.

U.S. officials are confident they can stay on top of any more cases that arrive.

This is the first case of Ebola recorded in the United States. But some of its relatives have been here — a case of Marburg virus, considered just as deadly, and four cases of Lassa fever in the past decade.

“There is some history of people coming back with these exotic, highly lethal diseases where it’s been relatively well controlled,” Geisbert said. “Hopefully that continues.”

(AP)