In-vitro experiments suggest Ixodes ricinus nymphs prefer blood with Borrelia infection and low glucocorticoid levels.

Ticks play a significant role in the transmission of various pathogens, impacting both human and animal health. Understanding the factors influencing tick feeding preferences is crucial for mitigating the risk of tick-borne diseases. This study investigates the blood preference of Ixodes ricinus nymphs, focusing on host species, stress hormone levels (glucocorticoids), and the presence of Borrelia burgdorferi s.l. bacteria. We conducted three series of in vitro experiments using a setup where individual blood drops (15 μl) were placed on filter paper over a 37 °C plate. Ticks were placed in the center, and their movements were tracked for 2 min to record preferences. The first experiment tested preferences for blood from different hosts (mouse, bird, sheep). The second examined the role of stress hormones by offering blood with varying levels of added cortisol and corticosterone (0, 10, 100, 1000 ng/ml). The third experiment investigated the potential influence of Borrelia infection, combined with elevated stress hormone levels, on blood preference. Our results show that I. ricinus nymphs preferred blood without added glucocorticoids and, in mice, blood with Borrelia infection. No clear preference for a specific host species was observed. These findings offer insights into how host physiological state may affect tick host selection, even though I. ricinus may not always have the opportunity to choose between hosts. Future studies should explore these interactions in more biologically relevant models to better understand the dynamics of tick attachment and feeding. Unraveling these mechanisms could aid in developing new strategies to control tick-borne diseases.