FREETOWN, Sierra Leone — Authorities in Sierra Leone said Thursday they had quarantined 500 people after a man died from Ebola in an area where the deadly virus had been gone for months, in another setback for the fight against the disease.

Hassan Abdul Sesay, a member of parliament from the region, said that the victim had contracted Ebola in the capital, Freetown, and then traveled to his home village to mark the end of the Muslim holy month of Ramadan.

Northern Tonkolili District had not had a single case of Ebola in five months, and the World Health Organization said earlier this week that the lowest number of new cases in a year had been reported in West Africa.

The new case shows, however, how just one sick person can change that.

Ebola’s main symptom is fever, which is also found in more common illnesses such as malaria and typhoid.

Now the 30 nurses who treated him and his entire home village are being quarantined. Authorities are also concerned because the man’s father is a taxi driver who brought his son to at least two hospitals.

His family and friends buried him without following the special procedures required for Ebola victims to avoid spreading the disease after death.

Authorities still expressed optimism that the disease would soon be contained.