Variability of tick infection with R. Helvetica. R. helvetica-positive ticks from DK were divided per life stage and were expressed as a percentage per year (A) or per month (B). Monthly averages and standard deviations were calculated. In figure 2A, the percentage of infected adult ticks in 2006 is not representative, because only three adult ticks were caught. In other years between 12 and 26 adults were caught and tested.