The Role of Environmental Factors in Lyme Disease Transmission in the European Union: A Systematic Review

Abstract

Background: Lyme disease (LD) is an emergent vector-borne disease caused by Borrelia spp. and transmitted through infected ticks, mainly Ixodes spp. Our objective was to determine meteorological and environmental factors associated with LD transmission in Europe and the effect of climate change on LD.

Materials and methods: A systematic review following the PRISMA guidelines was performed. We selected studies on LD transmission in the European Union (EU) and the European Economic Area (EEA) published between 2000 and 2022. The protocol was registered in the PROSPERO database.

Results: We included 81 studies. The impact of environmental, meteorological or climate change factors on tick vectors was studied in 65 papers (80%), and the impact on human LD cases was studied in 16 papers (19%), whereas animal hosts were only addressed in one study (1%). A significant positive relationship was observed between temperature and precipitation and the epidemiology of LD, although contrasting results were found among studies. Other positive factors were humidity and the expansion of anthropized habitats.

Conclusions: The epidemiology of LD seems to be related to climatic factors that are changing globally due to ongoing climate change. Unfortunately, the complete zoonotic cycle was not systematically analyzed. It is important to adopt a One Health approach to understand LD epidemiology.

Keywords: Europe; Ixodes; Lyme disease; climate; emerging infectious diseases; mediterranean.

Figure 1

Study selection process.

Figure 2

Articles by analyzed countries (n = 81). Countries where no studies were performed are displayed in gray.

Figure 3

Significant effects of analyzed environmental variables on LD vector abundance and density (n = 65). Countries with significant negative relationships between environmental factors and LD vector abundance and density are shown in orange (left), and countries with significant positive relationships between environmental factors and LD vector abundance and density are shown in yellow (right). The factors significantly related to vector abundance and density in each country are shown inside the country’s shape. The distribution of environmental variables inside each country’s shape is arbitrary. Countries with no data are shown in gray.

Figure 4

Significant effects of analyzed environmental variables on human LD incidence (n = 16). Countries with significant negative relationships between environmental factors and human LD incidence are shown in orange (left) and countries with significant positive relationships between environmental factors and human LD incidence are shown in yellow (right). The factors significantly related to vector density in each country are shown inside the country’s shape. The distribution of environmental variables inside each country’s shape is arbitrary. Countries with no data are shown in gray.