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Scottish Plagues and the Basic Reproductive Number

The National Library of Scotland will feature a new exhibition about famous epidemics in Scotland’s history that decimated their population. Plagues! will feature many documents from the library’s archives including letters, diaries, writer’s accounts, case studies, and media from those time periods. The exhibit will explore public beliefs and reactions when the country experienced outbreaks of typhus, cholera, smallpox, and of course the bubonic plague. Scotland actually experienced two outbreaks of the bubonic plague, the second being as recent as 1900. That latter outbreak resulted in 16 deaths but did not cause a national panic as the crisis was purposefully not publicized. Methods to prevent further spread of the disease included fumigating the houses of victims, disinfecting their bed sheets and clothes, and inoculating all doctors and nurses that would be treating them. The former outbreak was of course the Black Death that affected all of Europe, causing the death of approximately half of its population.  Also known as “the foul death of England’ in Scotland, it was probably introduced by the fleas on rats carried into the country by foreign ships. At the time, very little was known about the cause of the disease or how it spread so quickly. The most prevalent beliefs were that the disease was spread by miasma or was a punishment from God. Plague doctors believed in that miasma theory and to prevent their own infection they wore masks filled with pungent herbs that would hopefully minimize inhalation of harmful air. Other strategies to prevent spread of the disease included quarantining ships and hospitals, as well as burning the clothes and corpses of victims.

An important property of an epidemic is its basic reproductive number. This number is defined as the product of p, the independent probability that the disease will be passed from an infected individual to a new individual, and k, the number of individuals at a time exposed to the disease by contact with infected individuals. If the basic reproductive number is greater than 1, the disease will persist in a population, but if it is less than 1, the disease will disappear from the population eventually. The goal for populations dealing with epidemics is then to make the basic reproductive number of the disease dip below 1 by reducing both p and k. This is essentially what Scotland officials and doctors were trying to do during both bubonic plague epidemics. During the Black Death epidemic, doctors trying to guard themselves against the disease reduced k, as they were constantly in contact with victims. Quarantining ships and hospitals also reduced k, while burning infected clothes and corpses created more sanitary conditions and reduced p. During the 1900 epidemic, was again reduced by protecting doctors, though inoculation was much more effective than herbs. Disinfection of clothes and bed sheets, as well as house fumigation, reduced p. In both cases, these methods were effective enough to reduce the basic reproductive number below 1 and eventually bring an end to both epidemics.


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November 2015