The disappearance of malaria from Denmark, 1862–1900

The reason for malaria’s disappearance from northwestern Europe in the early twentieth century has long been discussed but remains an unresolved conundrum. This is partially due to a previous focus on the early modern era, and partially because various theories have never been tested against each other. In this study, we test some of the proposed hypotheses using nineteenth-century Denmark as a case. We found that the accelerating agricultural improvements with drainage and increasing livestock per km² explained much of the declining incidence rates, whilst other factors such as household size, temperatures, and precipitation did not seem to matter. Increased drainage meant dryer surface environment, and this led to a reduced size of the mosquito populations and therefore fewer malaria infections, and increased access to livestock led to changes in the mosquitoes’ feeding preferences. Whilst drainage may have played a key role, it is possible that improvements in housing and clothing materials as well as use of quinine could also have affected malaria trends, although this could not be tested. We conclude that the disappearance of malaria was likely an unanticipated benefit of the agricultural developments related to the modernization of rural Denmark during the nineteenth century.