The World Health Organization is currently investigating a mysterious disease that has killed three people so far in the South African city of Johannesburg.  Apparently the disease is a form of hemorrhagic fever.

The first death occurred Sept. 13 and was a female tour guide who had fallen ill in Zambia before being evacuated to South Africa. The following two deaths, one on Sept. 30 and the other on Oct. 4, involved a paramedic and a nurse who treated the women.

Moreover, 121 people were in contact with the victims and they are currently being monitored.

“One hundred twenty-one known contacts of the fatal cases are being traced in South Africa and 23 in Zambia,” the World Health Organization said in a statement.

According to agency epidemiologists, the disease could be a viral hemorrhagic fever, a disease caused by five distinct families of RNA viruses (that have ribonucleic acid as their genetic material).

The three victims experienced fever, headache, diarrhea and myalgia developing into rash and hepatic dysfunction, followed by rapid deterioration and death, the WHO said.

Tests done on the victims have proved negative for Ebola, Lassa fever, Rift Valley fever, Marburg fever and other main types of hemorrhagic fever. However the tests are continuing in South Africa and further testing will be performed in the United States.

Those being under observations will have their temperatures taken four times daily for the next three weeks. Intensive care specialist professor Guy Richards was quoted by a local newspaper saying “the public at large are not at risk.”