The tick-borne pathogen Anaplasma phagocytophilum causes great concern for livestock farmers. Tick-borne fever is a widespread disease in Norway, and antibodies have been produced amongst sheep, roe deer, red deer, and moose. The main vector Ixodes ricinus is found along the Norwegian coastline as far north as the Arctic Circle. A total number of 1804 I. ricinus ticks were collected and the prevalence of the pathogen was determined by species-specific qPCR. The overall infection rate varied from 2.83% to 3.32%, but there were no significant differences ( ) in the overall infection rate in 2010, 2011, or 2012. A multilocus sequencing analysis was performed to further characterise the isolates. The genotyping of 27 strains resulted in classification into 19 different sequences types (ST), none of which was found in the MLST database. The nucleotide diversity was for every locus <0.01, and the number of SNPs was between 1 and 2.8 per 100？bp. The majority of SNPs were synonymous. A goeBURST analysis demonstrated that the strains from northwest Norway cluster together with other Norwegian strains in the MLST database and the strains that are included in this study constitute clonal complexes (CC) 9, 10, and 11 in addition to the singleton. 1. Introduction Anaplasma phagocytophilum, formerly Ehrlichia phagocytophila, is a vector-borne pathogen known to cause tick-borne fever (TBF) in ruminants and human granulocytic anaplasmosis (HGA) [1]. A. phagocytophilum of the order Rickettsiales is a Gram-negative bacterium that invades neutrophils [1, 2]. Ixodes ticks act as natural reservoirs for the bacterium. Uninfected ticks can acquire the pathogen while feeding on an infected mammal and can transmit the pathogen to mammals during a blood meal [3]. In Norway, Ixodes ricinus ticks are the main vector for A. phagocytophilum, and although HGA is not a common disease in Norway [4–6], A. phagocytophilum antibodies have been detected in sheep, roe deer, red deer, and moose [7]. The clinical symptoms include fever, leucopenia, and thrombocytopenia [8]. During an A. phagocytophilum infection, the 44？kDa major surface protein (msp2) plays an important role in adhesion to the surface receptors of neutrophils [9]. A. phagocytophilum colonises within the invaded cells and interferes with the normal cellular function, thus affecting the normal regulation of the immune response [10]. A deprived immune response enables secondary infections to thrive and cause severe illness and even death [3]. The complete A. phagocytophilum genome sequence has been assembled, and like that of
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