Washington, Oct 21 (IANS/EFE) Relatives and friends of Thomas Eric Duncan, who contracted Ebola in his native Liberia and died in the US, were free of symptoms Monday as they reached the end of the 21-day quarantine imposed by public health authorities.

Among the people who remained in isolation for three weeks in Dallas were Duncan's girlfriend Louise Troh and the couple's son.

Duncan became symptomatic shortly after he arrived in the US last month to marry Troh.

He died Oct 8 at the Texas Health Presbyterian Hospital in Dallas.

The Ebola virus has a 21-day incubation period, according to the World Health Organization (WHO).

Nurses Nina Pham and Amber Joy Vinson became infected with the virus while treating Duncan, while 75 additional health care workers remain under observation and are barred from travelling.

Fears of an Ebola outbreak in the US increased last week after news spread that, before being diagnosed, Vinson travelled by plane from Cleveland, Ohio, to Dallas, while she had a slight fever.

Ohio health authorities have contacted more than 150 people who may have been in contact with Vinson during the flight or her stay in Cleveland, and about 20 of them are being monitored as a precaution.

US President Barack Obama has refused so far to ban commercial flights from Guinea, Sierra Leone and Liberia, the three countries most affected by the Ebola outbreak, which has killed more than 4,500 people.

One month away from mid-term elections and with political adversaries clamouring about a lack of leadership in the face of the virus, Obama last Friday appointed Vice President Joe Biden's former chief of staff, Ron Klain, as federal coordinator of Ebola response.