Prevalence of Rickettsiales (Anaplasma phagocytophilum and Rickettsia spp.) in hard ticks (Ixodes ricinus) in the city of Hamburg, Germany

To narrow the gap of missing knowledge on Rickettsia spp. and Anaplasma phagocytophilum infections in ticks in northwestern Germany and, at the same time, to provide first prevalence data on these pathogens in the city of Hamburg, a total of 1,400 questing Ixodes ricinus ticks were collected at ten different public green areas from April until October 2011. Ticks were examined using probe-based quantitative real-time PCR. A percentage of 3.6 % (51/1,400) ticks were tested positive for A. phagocytophilum infections divided into 2.1 % (3/141) adults [1.7 % (1/60) females and 2.5 % (2/81) males] and 3.8 % (48/1,259) nymphs. The percentage of infected ticks per sampling site varied statistically significantly from 0.7 % (1/140) to 12.1 % (17/140), whereas between sampling months, no statistically significant differences were observed (2.0-6.5 %, 4-13/140). The overall Rickettsia spp. infection rate was 52.5 % (735/1,400). In adult ticks, Rickettsia spp. infection rate was 56 % (79/141) divided into 61.7 % (37/60) infected females and 51.9 % (42/81) infected males. Nymphs showed an infection rate of 52.1 % (656/1,259). In contrast to A. phagocytophilum infections, no statistically significant differences in Rickettsia spp. infection rates among sampling sites (44.3-63.6 %, 62-89/140) were observed, whereas seasonal variations were obvious: the percentage of Rickettsia-positive ticks was significantly lower in April (36.5 %, 73/200) and May (29.5 %, 59/200) compared to the summer and fall months (55.0-64.5 %, 110-129/200). Rickettsia species differentiation via real-time pyrosequencing revealed Rickettsia helvetica as the only occurring species. Co-infections with both Rickettsia spp. and A. phagocytophilum were detected in 2.0 % (28/1,400) of the ticks. The present study revealed that in the city of Hamburg, the tick infection rate with A. phagocytophilum is comparable with other German data, whereas the Rickettsia spp. infection rate of 52.5 % is by far the highest prevalence detected in Germany so far. As the city of Hamburg has 1.8 million inhabitants and attracts millions of tourists every year, the potential health risk should not be underestimated.