The Epidemiology and Medical History of Malaria in nineteenth-century Denmark

In this thesis, I investigate malaria in nineteenth century Denmark. Despite being one of the most common diseases in tropical parts of the world today, the geographical range of malaria was even larger in the past. It expanded across most of Europe, including Scandinavia. Fundamental questions about the history of malaria remain unanswered. It has often been mistaken with other diseases, and the state of endemicity in past northern Europe remains unclear. Finally, it is still not clear, why malaria disappeared from this part of the world. This PhD thesis engages with these questions in the Danish context.

I argue that because diagnosis was based on clinical observations of the patient in the nineteenth century, and because physicians operated with a wide array of disease categories, intermittent fever – the widely accepted historical synonym for malaria – and its Danish equivalent “koldfeber” were merely umbrella-diagnoses for a wide variety of infections. During a mortality crisis in the period 1826-1832, induced by a concurring subsistence crisis, “koldfeber” was used, despite the symptoms not being similar to malaria. As medical thinking developed in the nineteenth century, the nosography of these diagnoses changed and began to resemble that of modern malaria.

My work demonstrates that malaria was an epidemic disease in Denmark with the highest disease burden in the south-eastern part of the country. In western Lolland - the part of the country with the highest malaria burden – a combination of clay soil and wetlands created an environment, where mosquitoes had plenty of sites for breeding and for egg-laying, which consequently led to a high density of mosquitoes. A high agricultural production in eastern Denmark also contributed to a high malaria burden. Overall, the malaria burden was largest in the Danish province towns, probably due to a combination of high population density, urban farming, and proximity to breeding sites in pastures and stables. However, since physicians often lived in the province towns, residents here had a better access to medical treatment than their rural counterparts, which probably led to considerable rural underreporting.

Malaria began to decline in the early nineteenth century and the disease eventually disappeared from Denmark in the 1890’s. My work suggests that the most important factors driving the disappearance of malaria were farmland drainage, improvements in housing conditions, and changing sleeping habits. The drainage of Denmark altered the mosquitoes’ feeding preferences and biting rates, and the mosquitoes eventually became zoophilic. Moreover, better housing conditions in farmhouses meant that indoor environments became less hospitable for the mosquitoes. In conclusion, I argue that the disappearance of malaria was the consequence of the agricultural and social modernization that Danish rural society underwent in the nineteenth century.