The death of his six-year-old sister when he was a boy may have been one of the saddest moments of his life, but it charted a course for Robert Gallo to become a virus hunter.
The US scientist made the joint discovery in 1984 that the HI-virus causes Aids, and developed the blood test to detect it.
Gallo received an honorary doctorate at the University of KwaZulu-Natal last week.
"I was in the centre of the worst epidemic in the world," said the 79-year-old, who is renowned for his achievements, including discoveries that have led to both diagnostic and therapeutic advances in cancer, Aids and other viral disorders.
He said he had no plans to retire yet.
Gallo is the director of the Institute of Human Virology at the University of Maryland School of Medicine.
He cites the death of his sister of leukaemia as the inspiration for his interest in science and medicine.
In his address to graduates, Gallo said: "Believe in medical research. Without interest in it we become doomed to the acceptance of things as they are."
