Anaplasma phagocytophilum ecotype distribution and zoonotic potential in questing and feeding Ixodes ricinus from Germany.

Anaplasma phagocytophilum is a genetically diverse tick-borne pathogen, subdivided into different phylogenetic clusters, so-called ecotypes, with distinct transmission cycles. European variants pathogenic for humans, dogs, cats and horses are transmitted by Ixodes ricinus and belong to a distinct subgroup within Ecotype I. Ecotype II is also transmitted by I. ricinus, but considered primarily adapted to roe deer. The present study investigated the A. phagocytophilum ecotype distribution in questing and feeding I. ricinus from Germany, based on sequence analysis of the partial groEL gene. Of 94 positive questing ticks (34 nymphs, 60 adults) from the city of Hanover, 90.4% harboured Ecotype I and 9.6% Ecotype II, with 78.7% of sequences clustering within the zoonotic subgroup. The proportion of Ecotype I was significantly lower in feeding ticks collected countrywide. Among 27 ticks (10 nymphs, 17 adults) from humans, the Ecotype I/Ecotype II ratio was 55.6%/44.4%, with potentially zoonotic isolates in 40.7% of ticks. From dogs and cats, 57 and 28 positive female ticks yielded groEL sequences, respectively, with an Ecotype I/Ecotype II ratio of 68.4%/31.6% in ticks from dogs, and 60.7%/39.3% in ticks from cats. Potentially zoonotic isolates were detected in 54.4% of positive ticks from dogs, and 14.3% from cats. The differences in ecotype distribution may be due to geographical differences, variation between urban and rural habitats, and differences in host behaviour. The high proportion of isolates potentially pathogenic to humans and pets highlights the importance of preventive measures to avoid tick infestation.