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The great leveller: humanity's struggle against infectious disease

Blane on yellow fever

Title page with inscription from the authorTitle page with inscription from the authorSir Gilbert Blane (1749-1834), head of the Navy’s Medical Board and personal physician to a number of aristocrats and eventually to the king, was one of an influential minority of senior medical officers whose insistence that yellow fever was contagious helped to ensure the continued use of quarantine.

In an essay in this collection he propagates the commonly held belief that importation implies contagion. Thus, Blane stressed the role of ship carriers in spreading the disease, highlighting a case in which yellow fever had been passed from one ship to another as providing further evidence of contagion. That yellow fever could newly appear in cities where there was no prior history of the disease, yet fail to emerge in other cities on the same latitude, provided clear evidence for Blane that it was not a product of environmental conditions.

As was common amongst contagionists, he argued that yellow fever was often confused with other less serious types of fever, which really were related to climate and non-contagious. He writes:

It has accordingly been from want of precision, in naming and classifying these fevers, that contests highly unbecoming a liberal profession, and what is more unfortunate, errors of the most fatal practical tendency have been engendered by this confusion.

As Blane’s language might be seen to suggest, the debate between contagionists and anti-contagionists was a heated one; both sides sure of the superior empirical weight in support of their viewpoint. It was not until well into the 20th century that the role of the vector in spreading yellow fever was identified - revealing that, though these competing lines of reasoning both got some things right, they were each missing a key piece of the puzzle.

Ships certainly were responsible for carrying the disease to new shores, but person-to-person transmission of yellow fever is not possible; and though a tropical environment is required in order for the disease to be maintained, this is not because of any direct effect which such an environment might have on humans. The missing link in both cases, of course, was the aedes aegypti mosquito.

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