The woodmouse (Apodemus sylvaticus) as a reservoir of tick-transmitted spirochetes (Borrelia burgdorferi) in The Netherlands.

In three widely separated locations in the Netherlands, woodmice (Apodemus sylvaticus) were trapped, examined for ticks and subjected to xenodiagnosis for the detection of tick-transmitted spirochetes (Borrelia burgdorferi). During the spring and summer, an average of 2.4 Ixodes larvae/mouse (n = 170) was observed, but the true numbers were probably greater. The numbers of nymphs could be determined more accurately and amounted to 0.46 nymphs/mouse. The percentage of mice that were infected with tick-transmitted spirochetes was 47% (n = 45), 29% (n = 58) and 0% (n = 64) for the three locations respectively. The absence of spirochete-infected mice in location 3 is puzzling because spirochete-infected I. ricinus nymphs were collected (infection rate up to 11%) in the same location during the subsequent spring. Sexually active mice were more frequently infected with spirochetes than juveniles and non-sexually active ones. On location 1, the island of Texel, a sample of mice was also caught during the subsequent winter and subjected to xenodiagnosis. The results indicate that B. burgdorferi survives the winter in the vector tick rather than in the reservoir rodents.