Detection of Anaplasma phagocytophilum in Dermacentor reticulatus ticks.

IN Europe, cases of Lyme borreliosis, tickborne encephalitis and granulocytic anaplasmosis have increased in human beings, domestic animals and wildlife, expanding their geographical ranges to much of Scandinavia and eastern Europe. Proposed explanations include improved surveillance and diagnosis, changes in human behaviour, climate change, and increasing numbers of reservoir hosts and vectors (Heyman and others 2010). With respect to reservoirs of Anaplasma phagocytophilum, the causative agent of granulocytic anaplasmosis, the red deer (Cervus elaphus) is included in the list of European reservoirs, with roe deer (Capreolus capreolus), bank voles (Myodes species) and wood mice (Apodemus species). This letter describes a new possible vector species. The disease monitoring activities of our WILDSCREEN network (Linden and others 2011) include collection of ticks from wild species and testing them for infectious agents. In the autumn of 2010, as well as the usual Ixodes ricinus ticks, we unexpectedly found 35 ticks morphologically compatible with Dermacentor reticulatus on an adult male red deer. The species was confirmed by sequencing the amplicon retrieved from a PCR targeting the Dermacentor-specific ITS2 genomic segment (Dobec and others 2009), thus confirming recent findings showing that D reticulatus occurs at far more sites than were previously known in northern Europe (Dautel and others 2006). Moreover, a PCR targeting the A phagocytophilumspecific major surface protein-2 (MSP2)encoding gene (Massung and Slater 2003) yielded five positive D reticulatus ticks; the DNA sequence of the PCR showed 96.8 per cent homology with the reference sequence. Vectors of A phagocytophilum have always been considered to be ticks in the I ricinus subgroup of hard ticks, including the sheep tick (I ricinus) in Europe, the taiga tick (Ixodes persulcatus) in Asia, the deer tick (Ixodes scapularis) in eastern North America and the western black-legged tick (Ixodes pacificus) in western North America (Brown and others 2005). According to our results, D reticulatus ticks in general, or at least some D reticulatus isolates, should now be included in the list of putative vectors. It remains to be seen whether the presence of A phagocytophilum DNA results in effective transmission capacity by D reticulatus, and whether A phagocytophilum variants isolated from D reticulatus display a pathotype similar to that of variants transmitted by I ricinus ticks.