Transmission of Borrelia garinii OspA serotype 4 to BALB/c mice by Ixodes ricinus ticks collected in the field

In Europe, Borrelia garinii OspA serotype 4 has been isolated from the cere brospinal fluid of patients but, up to now, has never been identified among culture isolates from Ixodes ricinus ticks. This information raises the qu estion of whether OspA serotype 4 is transmitted by I. ricinus in nature. I n the present study, L ricinus nymphs collected in an area of endemicity in southern Germany were allowed to feed on mice. Cultivation of ear biopsy s pecimens showed that six of seven B. garinii-infected mice were infected by OspA serotype 4. In contrast, very few B. garinii OspA serotype 4 organism s were isolated directly from the ticks which infected the mice; most isola tes were B. afzelii. The infected mice transmitted mainly OspA serotype 4 t o xenodiagnostic ticks, preferentially in combination with B. afzelii.