Temperate climate malaria in nineteenth century Denmark.

Area of Science:

• Historical epidemiology
• Environmental science
• Public health

Background:

• Plasmodium vivax was historically endemic in Northern Europe.
• Understanding past malaria dynamics is crucial given climate change and emerging vector-borne diseases.
• This study examines malaria epidemiology in late 19th-century Denmark.

Purpose of the Study:

• To describe the seasonality and spatial patterns of malaria in Denmark (1862-1914).
• To investigate the relationship between malaria and environmental factors (soil type, clay content, elevation).
• To analyze demographic patterns, mortality, and climate correlations.

Main Methods:

• Descriptive epidemiological analysis of malaria incidence and mortality.
• Spatial analysis correlating malaria patterns with soil types, agricultural production, and elevation.
• Spearman correlation to assess the relationship between malaria seasonality, temperature, and precipitation.

Main Results:

• Highest malaria incidence was observed in eastern Denmark, particularly Lolland-Falster, linked to high soil clay content, agricultural production, and low elevation.
• Malaria incidence peaked in May, correlating with high temperatures in the previous July and August, but not precipitation.
• Case fatality rate was 0.17%; malaria affected all ages except infants. A 1873 epidemic followed storm surge flooding.

Conclusions:

• Malaria incidence declined in Denmark, disappearing by 1900.
• High adult and low child morbidity suggest malaria was not highly endemic during 1862-1880.
• Environmental factors like soil, agriculture, and elevation are critical for sustaining endemic malaria, offering insights for potential reintroduction scenarios in temperate climates.