A viral haemorrhagic fever that killed four people in Johannesburg has been identified as a new strain of the deadly arenavirus, health officials said Thursday.

According to the department of health, the disease was first identified in a woman airlifted from Zambia to a Johannesburg hospital in September.

The woman later died. A member of the medical staff who accompanied her, a nurse and a hospital cleaner who came into contact with them, also died.

"A last person who is currently under observation at a hospital is responding well to (anti-viral) treatment," said Janusz Paweska, head of a special pathogens unit at NICD.