Agricultural revolution, demographic change, or medical modernization? The disappearance of malaria from Denmark

Malaria is regarded as an old and very common disease in in northern Europe that began to decline in the 19th century and disappeared only in the mid-20th century. The disappearance of malaria is still a conundrum, where multiple theories have been put forth, without having been properly discussed in relation to each other. We examine the disappearance of malaria from 19th century Denmark using qualitative descriptions from the early 19th century and statistical modelling of the late 19th century period. Descriptions of malaria were absent from Danish medical records between 1815 and 1825, suggesting that an epidemiological change had taken place by then. Throughout the century, malaria flared up in epidemics, and by the 1890’s, it disappeared once and for all. Drainage was the most important factor in explaining the disappearance of malaria from Denmark. Major drainages took place across the malarious eastern Denmark from the late 18th century. This coincides with the qualitative observations of malaria having declined by the early 19th century. We conclude that drainage played the most important role for the disappearance of malaria. Improvements in housing conditions and clothes were however additional important factors. The distancing between humans and mosquitoes because of the drainage meant that mosquitoes became increasingly zoophilic, which meant that humans were less bitten by Anopheles mosquitoes and experienced less malaria infections. The study provides evidence for the efficiency of drainage as an anti-malarial strategy in modern settings.