Some 160 people have been placed under medical surveillance over the deadly Ebola virus in the Nigerian city of Port Harcourt in Rivers State.

"As of today, none of them has shown symptoms of any kind. We are in touch with them constantly and they also call us to tell us their condition," Sampson Parker, the health commissioner of Rivers State, said on Friday.

The people who are being monitored had been in contact with a doctor who died from the virus.

The Nigerian government said on Thursday that the doctor, Ikyke Samuel Enuemo, was the country's sixth person to die from the disease.

On Tuesday, Nigeria announced a delay in the start of the country’s school year by one month over concerns on the spread of the virus.

“All primary and secondary schools in private and public sectors are to remain closed until Monday, October 13,” Nigerian Education Minister Ibrahim Shekarau said.

“This is to ensure that adequate preventive measures are put in place.”

Ebola is a form of hemorrhagic fever whose symptoms are diarrhea, vomiting and bleeding.

According to the latest figures by the World Health Organization (WHO), some 3,070 infections and over 1,550 deaths of the disease have been reported in West Africa.

Ebola has mainly affected Guinea, Liberia, Nigeria and Sierra Leone, with Liberia reporting most deaths among the other countries.

The virus spreads through direct contact with infected blood, feces or sweat. It can also be spread through sexual contact or the unprotected handling of contaminated corpses.

It remains one of the world’s most virulent diseases, which kills between 25 to 90 percent of those who fall sick.