It is believed by Australian historians that the mortal illness which, in April 1789, afflicted the indigenous population in the vicinity of Sydney Cove was smallpox. The problem has always been the impossibility of finding a plausible means by which the disease entered the colony. The fundamental question is really the reliability of the diagnosis and that has rarely been critically addressed. The identification of the disease depends solely on the journal opinions of non-medical observers. But the naval surgeons would have been no more reliable because they would have been unaware of the distinction between smallpox and chickenpox - the latter having traditionally been considered a milder form of smallpox. That distinction was defined by William Heberden only in 1767. I contend that the disease of 1789 was chickenpox which, though mild in European children, can be very severe in adults and populations not previously exposed to it. In such immunologically ‘naïve’ communities the death rate can be 20%. Indeed, all of the evidence rejects the identification of the disease as smallpox but argues, rather, that it was chickenpox.

John Carmody, Professor Emeritus, Centre for Medical Humanities and Discipline of Physiology, University of Sydney.