A new virus that causes fatal hemorrhagic fevers has been discovered in southern Africa. It killed four people in South Africa and sickened a fifth, but health authorities believe the outbreak has been contained.

The virus is a member of the arenavirus family, which also includes the causes of Lassa fever in West Africa and several South American fevers. While new viruses are often found in animals — a new blue-tongue virus was found in Swiss goats last month, for example — it is relatively rare to discover one fatal to humans, like the SARS coronavirus in 2002 or the sin nombre hantavirus in 1993.

How the first victim was infected is unknown, but arenaviruses are common in rodents; their dried urine, inhaled while sweeping, can transmit infection.

Confirmation that it is a new virus was made by the National Institute for Communicable Diseases in South Africa and by the Centers for Disease Control and Prevention in Atlanta.

The first victim was Cecilia Van Deventer, a safari tour booker in Lusaka, Zambia, who fell ill on Sept. 2 and was airlifted to Johannesburg. She apparently infected Hannes Els, the paramedic who accompanied her, and Gladys Mthembu, a nurse tending her at the Morningside Medi-Clinic in a Johannesburg suburb.

The fourth to die was Maria Mokubung, who cleaned the room where Ms. Van Deventer died on Sept. 14. According to South African news reports, the last death was originally misdiagnosed because the victim had tuberculosis and meningitis and was hemorrhaging and confused when her family sought medical care.

A fifth victim, a nurse who cared for Mr. Els, was in critical condition but responded to early treatment with the antiviral drug Ribavirin.

The disease progresses from flu symptoms to diarrhea and a measles-like rash and then to respiratory and circulatory collapse.

The authorities said they knew of no new cases but would wait until 21 days from the last infection to declare the outbreak over.

Disease detective work was difficult, South African news media said. Because Ms. Van Deventer feared needles, little blood was drawn from her in Zambia; also, her body was cremated before the alarm was raised. Tissue samples from later victims had to be taken carefully in a high-security laboratory that was under renovation and had to be reopened.

Arenaviruses are named for their round sandy granules; "arena" is Latin for sand. A name for the new virus is being debated; Zambian authorities do not want one that will hurt tourism.

According to a government news service, Zambia's first response to the outbreak was to close its border with Congo, the former Zaire, where Ebola fever, which is not related, originated.