Figure 2.

Hypothetical epidemiological cycles of A. phagocytophilum in ruminants (A) and in humans, dogs, and horses (B) in Europe. I. ricinus is the main European vector of A. phagocytophilum. Several studies suggest that red deer could be reservoir hosts for domestic ruminant variants. Roe deer are unlikely to be reservoir hosts for human, horse or pet variants, nor for domestic ruminant variants. Roe deer may be involved in another epidemiological cycle, and could maintain their “own” specific variant(s). Hedgehogs have been suspected as reservoir hosts for human variants, but this remains unproven. Similar to roe deer, hedgehogs could also be involved in an alternative epidemiological cycle, in which I. hexagonus could be the vector. Different rodent species could be involved in an independent epidemiological cycle involving I. trianguliceps as vector. In purple, vectors; in red, reservoir hosts; in green, dead-end hosts (or clinical hosts); Large solid arrow, known transmission; Solid arrow, unknown, but possible transmission; Dotted arrow, unknown, but unexpected transmission.