Potential malaria outbreak in Germany due to climate warming: risk modelling based on temperature measurements and regional climate models

PURPOSE

Climate warming can change the geographic distribution and intensity of the transmission of vector-borne diseases such as malaria. The transmitted parasites usually benefit from increased temperatures as both their reproduction and development are accelerated. Lower Saxony (northwestern Germany) has been a malaria region until the 1950s, and the vector species are still present throughout Germany. This gave reason to investigate whether a new autochthonous transmission could take place if the malaria pathogen was introduced again in Germany.

MATERIALS AND METHODS

The spatial distribution of potential temperature-driven malaria transmissions was investigated using the basic reproduction rate (R (0)) to model and geostatistically map areas at risk of an outbreak of tertian malaria based on measured (1961-1990, 1991-2007) and predicted (1991-2020, 2021-2050, 2051-2080) monthly mean air temperature data.

RESULTS

From the computations, maps were derived showing that during the period 1961-1990, the seasonal transmission gate ranges from 0 to 4 months and then expands up to 5 months in the period 1991-2007. For the projection of future trends, the regional climate models REMO and WettReg were used each with two different scenarios (A1B and B1). Both modelling approaches resulted in prolonged seasonal transmission gates in the future, enabling malaria transmissions up to 6 months in the climate reference period 2051-2080 (REMO, scenario A1B).

DISCUSSION

The presented risk prognosis is based on the R (0) formula for the estimation of the reproduction of the malaria pathogen Plasmodium vivax. The presented model focuses on mean air temperatures; thus, other driving factors like the distribution of water bodies (breeding habitats) or population density are not integrated. Nevertheless, the modelling presented in this study can help identify areas at risk and initiate prevention. The described findings may also help in the investigation and assessment of related diseases caused by temperature-dependent vectors and pathogens, including those being dangerous for livestock as well, e.g. insect-borne bluetongue disease transmitted by culicoids.

Pilot-study on GIS-based risk modelling of a climate warming induced tertian malaria outbreak in Lower Saxony (Germany)

The area under investigation, Lower Saxony (Northwest Germany), is a former malaria region with highest incidences along the coastal zones. Malaria had finally become extinct in the early 1950s. Subsequently, further scientific investigations in that field declined. Nevertheless, the vector in shape of Anopheles mosquitoes has still been present in Lower Saxony. Thus, the question arises, whether a new autochthon transmission could take place if the pathogen is introduced again and could develop in Anopheles mosquitoes. Answering this question was the first aim of the investigation at hand. The second one was to examine the spatial and temporal structure of potential transmissions in respect to the predicted increase of air temperatures according to the IPCC scenarios. To answer these questions, current information about Anophelinae and their distribution and habitat preferences within Germany were collected by literature research as well as temperature measurements and Anopheles findings were compiled from the German Weather Survey and the Niedersächsisches Landesamt für Okologie (NLO), respectively. The results reveal a climate warming between the 30-years period from 1961 to 1990 and the years between 1985 and 2004. Induced by higher monthly mean temperatures, the risk of a malaria tertiana transmission is consequently increasing for Lower Saxony as temperature is the determining variable of the mathematical model. The study could demonstrate that most parts of the country are located within a 2 months lasting transmission zone. Although Germany is not an endemic malaria zone, the pathogen can enter the country most likely by infected people or imported mosquitoes that transport it in their guts.