The “Contagious Distemper” of Hirta – 1727
As we saw last time, a “contagious distemper”, thought to have been smallpox, wiped out all but four adults of the population on the island of Hirta on the St Kilda archipelago and left three men and eight boys marooned on Stac an Armin for nine months. But was it smallpox?
In 1727 smallpox was not well understood. It was not until 1767 that the Cambridge physician, William Heberden, successfully differentiated chickenpox from smallpox. “These pocks”, he wrote, “break out on many without any illness or previous sign: in others they are preceded by a little degree of chillness, lassitude, cough, broken sleep, wandering pains, loss of appetite and feverishness for three days. Most of them are of the common size of the smallpox. I never saw them confluent nor very numerous. The principal marks, by which the chicken pox may be distinguished from the smallpox are,
1. The appearance on the second or third day from the eruption of that vesicle full of serum from the top of the pock.
2. The crust, which covers the pocks on the fifth day; at which time those of the smallpox are not at the height of their suppuration”.
While there are no precise contemporaneous clinical records of the precise symptoms of the 1727 outbreak on Hirta, chickenpox has a high mortality rate in adults who have no immunity to the disease, some twenty-five times higher than in children, a ratio remarkably similar to that experienced in Hirta. Smallpox generally has a much lower death rate amongst adults.
The epidemic spread widely and rapidly around Hirta, a characteristic more attributable to chickenpox than smallpox. Smallpox sufferers usually only infect up to five others, usually members of their family or close circle and hardly ever other members of a community or even every member of their own family. On the other hand, chickenpox infects 90% of household contacts and spreads far more rapidly and in an unhealthy population can lead to other fatal complications such as pneumonia and hepatitis.
Chickenpox is transmitted rapidly whereas smallpox has a much slower rate of transmission and needs especially helpful conditions to flourish. The fate of those marooned on Stac an Armin is testament to the speed with which the virus was transmitted throughout Hirta. They left a healthy community in mid-August and yet between ten and fourteen days later there were not four adult males healthy enough out of a population of around 30 to 50 to row the four miles to pick them up, a transmission rate more in line with that of chickenpox than smallpox. No infection was recorded amongst those marooned.
Smallpox outbreaks were not uncommon in the Scottish islands, the Shetlands recording ten between 1700 and 1830. During the 1740 outbreak Thomas Gifford in Busta recorded what happened to his daughters in his diary, two of whom became unwell and were bed-bound. Five days later they had developed a rash, dying a further eight and nine days later respectively. Eleven of Gifford’s other children developed rashes but all survived. Unwittingly, Gifford had produced one of the first detailed written accounts of smallpox.
What is interesting is that the rate of transmission, the victims and the mortality rate and the mortality rate are radically different from the virus that ravaged Hirta in 1727. Although we cannot be certain, it looks very much like chickenpox rather than smallpox.
Those that survived and those rescued from Stac an Armin slowly reconstituted the island’s population.
