(Reuters) - The United States has seen six cases of the Ebola virus in recent weeks affecting five Americans and a Liberian, raising concerns about wider spread of the disease, which has killed more than 3,800 people and infected more than 8,000 in the current outbreak centered in West Africa.

All of the Americans contracted the disease while in West Africa and were diagnosed there before returning home for treatment. The Liberian fell ill and tested positive during a visit to Dallas, where he died on Wednesday.

Below are details on the six U.S. cases so far:

NBC CAMERAMAN

Ashoka Mukpo, an American freelance television cameraman working for NBC News in Liberia, arrived in the United States on Monday and is being treated at Nebraska Medical Center in Omaha. He was reported in stable condition on Wednesday.

NBC, which announced the case last week, said Mukpo, 33, quarantined himself immediately after he began to feel ill and later went to a Doctors Without Borders treatment center, where he tested positive for Ebola.

The hospital has said Mukpo is being treated with experimental drug brincidofovir from Chimerix Inc.

He was expected to receive a transfusion of plasma donated by Dr. Kent Brantly, one of the first Ebola patients treated in the United States.

LIBERIAN IN DALLAS

Thomas Eric Duncan, a Liberian citizen who was the first person diagnosed with Ebola in the United States, died on Wednesday, Texas Health Presbyterian Hospital.

Duncan was visiting Dallas when he began feeling ill and sought treatment at the hospital on Sept. 25.

He was initially discharged with antibiotics, despite telling a nurse he had just come from Liberia. On Sept. 28 he returned to the same hospital by ambulance after vomiting outside the apartment complex where he was staying.

Amid questions over its handling of the case, hospital officials blamed a software error that allowed nurses to see Duncan's travel history from Liberia but not doctors, a glitch they said has now been fixed.

Story continues

EMORY PATIENT

An unnamed American who contracted Ebola in West Africa is still being treated at Emory University Hospital in Atlanta. There have been few, if any, details made public about the patient, who returned to the United States by air ambulance on Sept. 9.

According to CNN, the American is a male who contracted the virus in Sierra Leone.

About the same time, the World Health Organization said one of its doctors tested positive for Ebola at a treatment center in Sierra Leone but the two cases have not been officially linked and WHO has not identified the physician.

THREE MISSIONARIES

In the summer, three Americans contracted Ebola while working for Christian missionary organizations in Liberia and were flown to the United States for treatment and later released.

Nancy Writebol contracted the virus in July while working for a SIM USA hospital with her husband, David, who did not contract the disease. She was treated at Emory University Hospital in Atlanta and discharged Aug. 19. The couple has not ruled out returning to West Africa to continue their mission work.

Dr. Kent Brantly also was treated in isolation at Emory after contracting Ebola while working for Christian relief group Samaritan's Purse. He was released on Aug. 21.

Dr. Rick Sacra, a Boston physician who was working for SIM USA, arrived in the United States on Sept. 5 and was treated for three weeks at Nebraska Medical Center. He has said he may return to Liberia to fight the outbreak.

UNDER OBSERVATION

Hospitals across the United States have been urged to watch for possible cases and to ask patients about their recent travels to help screen for the virus, but so far there have been no other confirmed U.S. cases.

An American doctor who had been under observation at the National Institutes of Health (NIH) in Bethesda, Maryland, was discharged on Tuesday. The physician was exposed while volunteering in Sierra Leone, according to the NIH.

NIH said the patient was exposed to Ebola by being stuck by a needle. He initially had a fever but it was found not to be related to an Ebola infection.

NIH said the patient no longer had a fever and will remain in his home, where he will check his temperature twice a day, until the completion of a 21-day observation period.

Other patients have been monitored in Washington, Hawaii and Florida.

(Reporting by Susan Heavey in Washington and Colleen Jenkins in Winston-Salem; Editing by Jim Loney and Sandra Maler)