King's College London
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The great leveller: humanity's struggle against infectious disease

Yellow fever in Cadiz

The portraits reproduced in the gallery below trace the development of the disease in a young man, young adults being the group most at risk from yellow fever. They are taken from an 1820 work by the French physicians Étienne Pariset (1770-1847) and André Mazet (1793-1821), who were sent by the French government to investigate the 1819 yellow fever epidemic in Cadiz, Spain.

It may seem surprising that a tropical disease such as this ever reached Europe, but the outbreak in Cadiz in 1819 was by no means unique or unprecedented. Whilst it is true that the European ports where outbreaks occurred all had trade links with America and relatively warm climates – as required for the survival of aedes aegypti mosquitoes - it is also true that no mosquito could survive the 50-90 day trip from America to Spain, and that their human victims’ blood was only infectious for 3-6 days.

The answer appears to lie in the conditions on board. Aedes aegypti mosquitoes breed mainly in clean water, which meant that the numerous barrels of fresh water on board ships allowed successive generations of mosquitoes to feed on the plentiful supply of human blood on hand, spreading the disease as they did so. That mothers are able to pass the virus to their offspring made this task all the easier.

Pariset and Mazet identify a sugar-cane carrier from Brazil as responsible for bringing the disease to Cadiz in 1819. The sugar trade played a key role in the spread of the disease, with many of the worst outbreaks of the 18th and 19th centuries occurring in the sugar plantations of the West Indies. Sugar grows in the same humid climates that the aedes aegypti mosquitoes require to thrive. Indeed, the mosquitoes are able to live off sugar alone, though the blood of plantation workers was crucial in order for females of the species to sustain ovulation.

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