JOHANNESBURG – A mystery disease that has killed three people in South Africa and put medical authorities on high alert may be Crimean-Congo hemorrhagic fever, a health official said on Tuesday.

'We suspect that it may be Congo hemorrhagic fever but we have not made a diagnosis yet,' Frew Benson, the South African Health Department's deputy director of communicable diseases, told Reuters. South African health officials said they were closely monitoring the illness, which causes external and internal bleeding, but called on the public not to panic. There were no signs it was airborne.

Officials said on Tuesday they were observing a total of 111 people who had come into contact with the deceased patients.

'These are mostly people who may have had specific high risk contact with the patients. They are not admitted to hospital but are having their temperatures checked every six hours,' Dr Nivesh Sewlall, who treated the first patient who died from the disease, told reporters at a press conference.

South African authorities were due to send blood samples to the U.S. Centers for Disease Control and Prevention in Atlanta on Tuesday, Benson said. The tests would take a number of days.

The first fatality from the mystery disease was a patient from Zambia flown to South Africa for treatment. A paramedic who accompanied her later died from the same symptoms, health authorities said. A third person also died from the illness.

A cleaner at Johannesburg's Morningside Clinic who was suspected of contracting the disease died of an unrelated condition, said the hospital's spokeswoman, Melinda Pelser.

CCHF, which causes death in around 30 percent of hospitalised patients, is carried by domestic animals and can be transmitted by ticks. It is found in Africa, Eastern Europe and Asia.

The first patient was originally treated for tick bite fever and had evidence of a tick bite on her, Sewlall said.

TREATMENT POSSIBLE

CCHF first appeared in Crimea in 1944 and was later identified in 1956 as the cause of an illness in what is now Democratic Republic of Congo.

Cases have been recorded in Kosovo, Albania, Iran, Pakistan and South Africa. Symptoms include headaches, back pains, vomiting, severe bruising and nose bleeds.

According to the World Health Organisation, CCHF can be treated but recovery is slow. If treatment is not provided in time, death can occur in the second week of illness.

There are several other strains of hemorrhagic fever, including Ebola and Marburg, which have killed hundreds of people in outbreaks in Africa. These diseases cause bleeding from multiple sites and can have very high death rates.

Ebola is rare, but there is no known cure and the virus usually kills between 50 and 90 percent of its victims.

It is spread through contact with bodily fluids of a patient. As with other hemorrhagic fevers, patients die from dehydration, bleeding, and shock.

The latest outbreak, which ended in February in Uganda, was unusually mild, killing 37 people out of 149 infected.

(Additional reporting by Muchena Zigomo; Editing by Dominic Evans)