Mapping the potential temperature-dependent tertian malaria transmission within the ecoregions of Lower Saxony (Germany)

Abstract

One of the effects of climate change can be the change in geographic distribution and intensity of the transmission of vector-borne diseases such as malaria. Given the most conservative estimate of change, these diseases are expected to occur, compared with the past and presence, at higher latitudes and altitudes. A slight rise in ambient temperature and rainfall can extend the duration of the season in which mosquito vectors are transmitting the causative agents of malaria. The parasites that they transmit usually benefit from increased temperatures, as both their reproduction and development are then accelerated, too. Thus, it seemed prudent to examine potential effects on the seasonal transmission gate due to the predicted climate changes. Lower Saxony (north-western Germany) is a former malaria region with highest incidences of Anopheles atroparvus and tertian malaria along the coastal zones before malaria had finally become extinct in the early 1950s. Nevertheless, the Anopheles mosquitoes which transmit the malaria pathogens have still been present in Lower Saxony up to now. This together with the climate change-related implications gave reason to investigate whether a new autochthonous transmission could take place if the malaria pathogen is introduced again in Lower Saxony. Thus, the spatial and temporal structure of temperature-driven malaria transmissions was investigated using the basic reproduction rate ( R 0) to model and geostatistically map areas at risk for an outbreak of tertian malaria due to measured (1947–1960, 1961–1990, 1985–2004) and predicted (2020, 2060, 2100, each best case and worst case scenario) air temperatures. The respective risk maps show that the gate of potential tertian malaria transmissions in terms of R 0 could be expected to increase from 2 months in the past to 6 months in the future in Lower Saxony. Past and recent findings of A. atroparvus coincide with those regions where the potential malaria transmission gate accounts for 4 months in 2060 (best case scenario) and for 6 months in 2100 (worst case scenario) and, in addition, where tertian malaria occurred up to the 1950s. The geostatistically estimated malaria risk maps were intersected by a map on ecological land units. This approach made an ecoregionalisation of the risk estimation possible.