LOS ANGELES - An American freelance cameraman working for NBC News in Liberia has tested positive for Ebola, the network said on Thursday, making him the fifth citizen of the United States and its first journalist known to have contracted the virus in West Africa.

The 33-year-old cameraman and writer, who has worked in Liberia for the past three years and has covered the recent Ebola outbreak for various US media outlets, will be flown back to the United States for treatment, NBC said in an online report.

Four other NBC News team members who have shown no signs of infection also will return to the United States to undergo a precautionary quarantine, the network said.

Word that a journalist had fallen ill with the potentially lethal virus seemed to raise the stakes for other members of the news media trying to cover the worst Ebola outbreak on record on the ground in Liberia, the nation hardest hit by the epidemic.

The outbreak has killed at least 3,300 people in West Africa.

NBC declined to give the man's name at the request of his family. He began experiencing symptoms on Wednesday that included aches and fatigue, the network said.

He was hired on Tuesday to serve as a second cameraman for NBC News chief medical editor and correspondent Dr. Nancy Snyderman, who has been with three other network employees on assignment in Liberia's capital, Monrovia.

Immediately after beginning to feel sick and discovering he was running a slight fever, the cameraman quarantined himself and sought medical advice. He then went to a Doctors Without Borders treatment center to be tested for the virus, and the positive result came back less than 12 hours later, NBC said.

"We are doing everything we can to get him the best care possible," NBC News President Deborah Turness said in a note to network staff.

Turness also said that as a precaution, Snyderman and the rest of the NBC crew would be flown back to the United States on a private charter plane and will place themselves under quarantine for 21 days, which she said is "at the most conservative end of the spectrum of medical guidance."

For now, she said, Snyderman and her crew were being closely watched and had shown no symptoms of signs of the illness.

In an interview Thursday with the host of "The Rachel Maddow Show" on NBC's sister cable network, MSNBC, Snyderman said the cameraman's exposure to the potentially lethal virus is believed to have occurred before he began working for the network.