The spatiotemporal distribution of historical malaria cases in Sweden: a climatic perspective

Abstract

Background Understanding of the impacts of climatic variability on human health remains poor despite a possibly increasing burden of vector-borne diseases under global warming. Numerous socioeconomic variables make such studies challenging during the modern period while studies of climate–disease relationships in historical times are constrained by a lack of long datasets. Previous studies have identified the occurrence of malaria vectors, and their dependence on climate variables, during historical times in northern Europe. Yet, malaria in Sweden in relation to climate variables is understudied and relationships have never been rigorously statistically established. This study seeks to examine the relationship between malaria and climate fluctuations, and to characterise the spatio-temporal variations at parish level during severe malaria years in Sweden 1749–1859. Methods Symptom-based annual malaria case/death data were obtained from nationwide parish records and military hospital records in Stockholm. Pearson (rp) and Spearman’s rank (rs) correlation analyses were conducted to evaluate inter-annual relationship between malaria data and long meteorological series. The climate response to larger malaria events was further explored by Superposed Epoch Analysis, and through Geographic Information Systems analysis to map spatial variations of malaria deaths. Results The number of malaria deaths showed the most significant positive relationship with warm-season temperature of the preceding year. The strongest correlation was found between malaria deaths and the mean temperature of the preceding June–August (rs = 0.57, p < 0.01) during the 1756–1820 period. Only non-linear patterns can be found in response to precipitation variations. Most malaria hot-spots, during severe malaria years, concentrated in areas around big inland lakes and southern-most Sweden. Conclusions Unusually warm and/or dry summers appear to have contributed to malaria epidemics due to both indoor winter transmission and the evidenced long incubation and relapse time of P. vivax, but the results also highlight the difficulties in modelling climate–malaria associations. The inter-annual spatial variation of malaria hot-spots further shows that malaria outbreaks were more pronounced in the southern-most region of Sweden in the first half of the nineteenth century compared to the second half of the eighteenth century.

Anopheles mosquitoes in Morocco: implication for public health and underlined challenges for malaria re‐establishment prevention under current and future climate conditions

“…58 Unusually warm and/or dry summers appear to have contributed to malaria epidemics due to both indoor winter transmission and the evidenced long incubation and relapse time of P. vivax in Sweden between 1749 and 1859. 59 A short-term increase in temperature and precipitation related to the extreme El Niño of 2015-2016 has been found exceptionally favourable for the spread of ZIKV in South America. 60 Previous studies have suggested that the occurrence of CHIKV epidemics in India and Indonesia has been strongly linked to El Nino conditions which favoured the accelerated development of mosquito vectors.…”

“…For example, a time series analysis of monthly malaria cases in the highlands of Colombia and Ethiopia provided evidence of a shift in the altitudinal distribution of malaria to higher elevations in warmer years, suggesting that malaria will increase at higher altitudes as the climate warms 58 . Unusually warm and/or dry summers appear to have contributed to malaria epidemics due to both indoor winter transmission and the evidenced long incubation and relapse time of P. vivax in Sweden between 1749 and 1859 59 . A short‐term increase in temperature and precipitation related to the extreme El Niño of 2015–2016 has been found exceptionally favourable for the spread of ZIKV in South America 60 .…”

Interdisciplinary insights into navigating the maze of landscape multifunctionality

“…However, this does not mean that increasing biodiversity per se is always and everywhere a suitable goal. The introduction of a new malaria‐carrying mosquito species into to a European city is an increase in the biodiversity of the area (Chen et al., 2021), but certainly not a desirable outcome. The spread of boreal species into the arctic with climate change is also an increase in biodiversity (at least temporarily) but neither is that a cause for celebration.…”

Panorama geral dos efeitos da temperatura na saúde humana – Revisão sistemática

“…A temperatura determina o desenvolvimento de parasitas e vetores e tem um impacto significativo na reprodução, sobrevivência e número de picadas de mosquitos transmissores de malária (WHO, 2012;CRAIG, 2004). A transmissão da malária é claramente sazonal, com transmissão limitada à estação quente (CHEN, 2021;ADEOLA, 2017;XIAO, 2010;JURI, 2009;CRAIG, 2004). Estudos têm demonstrado que certas temperaturas são necessárias para manter os parasitas no ambiente e transmiti-los por vetores (JURI, 2009).…”