Abstract
Modern plague outbreaks exhibit a distinct seasonal pattern. By contrast, the seasonality of historical outbreaks and its drivers has not been studied systematically. Here, we investigate the seasonal pattern, the epidemic peak timing and growth rates, and the association with latitude, temperature, and precipitation using a large, novel dataset of plague- and all-cause mortality during the Second Pandemic in Europe and the Mediterranean. We show that epidemic peak timing followed a latitudinal gradient, with mean annual temperature negatively associated with peak timing. Based on modern temperature data, the predicted epidemic growth of all outbreaks was positive between 11.7°C and 21.5°C with a maximum around 17.3°C. Hence, our study provides evidence that the growth of plague epidemics across the whole study region depended on similar absolute temperature thresholds. Here, we present a systematic analysis of the seasonality of historical plague in the Northern Hemisphere, and we show consistent evidence for a temperature-related process influencing the epidemic peak timing and growth rates of plague epidemics.
Highlights
Seasonality is a salient feature of many infectious diseases [1]
We further show that places with repeated outbreaks had a consistent plague season and that epidemic peak timing followed a latitudinal gradient
We show that the predicted epidemic growth of all outbreaks was positive between 11.7°C and 21.5°C with a maximum at 17.3°C
Summary
Seasonality is a salient feature of many infectious diseases [1]. For example, in the Northern Hemisphere, influenza is known to occur almost exclusively in winter, chickenpox peaks mainly in spring, West Nile Virus circulates mostly in summer [2]. Influenza and respiratory syncytial virus both show a clear latitudinal gradient with peak activity being shifted towards the end of the year for increasing latitudes and decreasing average temperatures [4]. Modern plague is another example of a highly seasonal disease. Humans develop bubonic plague when bitten by infectious rodent fleas, which is usually fatal in about 66% of the cases if untreated [5] They may develop secondary pneumonic plague if the disease spreads to the lungs. Quantifying the seasonality of an infectious disease and its drivers may provide insight into the mechanisms of historical plague in Europe. We conclude our analysis with a discussion about potential mechanisms and limitations of our work
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