The role of host diversity in Borrelia burgdorferi s.l. dynamics

There has been substantial debate about the influence of vertebrate host diversity on Lyme borreliosis risk. In North America, studies investigating Borrelia burgdorferi s.l. and the Black-legged tick (Ixodes scapularis) have shown that on a large spatial scale there seems to be a negative correlation between host species diversity and Lyme borreliosis risk. However, studies on this relationship in Europe are lacking. I discuss the work done in North America and translate the findings and assumptions of these studies to the European situation, where the sheep tick (Ixodes ricinus) is the most important vector of B. burgdorferi s.l. The European situation is fundamentally different compared to the North American situation due to the high diversity of B. burgdorferi s.l. genospecies, which are transmitted by different groups of vertebrate species. Disease risk in Europe is hypothesised to increase with vertebrate diversity due to an increase in B. burgdorferi s.l. genospecies diversity. However, it seems that the majority of genospecies in Europe is transmitted by two functional groups of host species, rodents and thrushes, which are present in most vertebrate assemblages. Therefore, it seems plausible that a dilution effect can also occur in Europe. This might result in high risk in urban areas where a few dominant species are very abundant, among which the most important reservoir hosts for B. burgdorferi s.l. in Europe