DALLAS — The first case of Ebola diagnosed in the U.S. has been confirmed in a man who recently traveled from Liberia to Dallas, sending chills through the area’s West African community whose leaders urged caution to prevent spreading the virus.

The unidentified man was critically ill and has been in isolation at Texas Health Presbyterian Hospital since Sunday, federal health officials said Tuesday. They would not reveal his nationality or age.

Authorities have begun tracking down family, friends and anyone else who may have come in close contact with him and could be at risk. Officials said there are no other suspected cases in Texas.

At the Centers for Disease Control and Prevention, Director Tom Frieden said the man left Liberia on Sept. 19, arrived the next day to visit relatives and started feeling ill four or five days later. Frieden said it was not clear how the man became infected.

“I have no doubt that we’ll stop this in its tracks in the U.S. But I also have no doubt that — as long as the outbreak continues in Africa — we need to be on our guard,” Frieden said, adding that it was possible someone who has had contact with the man could develop Ebola in the coming weeks.

Stanley Gaye, president of the Liberian Community Association of Dallas-Fort Worth, said the 10,000-strong Liberian population in North Texas is skeptical of the CDC’s assurances because Ebola has ravaged their country.

“We’ve been telling people to try to stay away from social gatherings,” Gaye said at a community meeting Tuesday evening. Large get-togethers are a prominent part of Liberian culture.

“We need to know who it is so that they (family members) can all go get tested,” Gaye told The Associated Press. “If they are aware, they should let us know.”

Ebola symptoms can include fever, muscle pain, vomiting and bleeding, and can appear as long as 21 days after exposure to the virus. The disease is not contagious until symptoms begin, and it takes close contact with bodily fluids to spread.

The association’s vice president encouraged all who may have come in contact with the virus to visit a doctor and she warned against alarm in the community.

“We don’t want to get a panic going,” said vice president Roseline Sayon. “We embrace those people who are coming forward. Don’t let the stigma keep you from getting tested.”