EXPRESSION OF OUTER SURFACE-PROTEIN-A AND SURFACE-PROTEIN-C OF BORRELIA-BURGDORFERI IN IXODES-RICINUS TICKS REMOVED FROM HUMANS

A total of 131 Ixodes ricinus (51 females, 1 male and 79 nymphs) remov ed from persons living in Southern Germany were investigated by immuno fluorescence assay for the presence of Borrelia burgdorferi with a pol yvalent rabbit immune serum and monoclonal antibodies specific for out er surface proteins (Osp) A or C. Borreliae were detectable in 48 (36. 6%) of the ticks. Infection rates of these adults and nymphs were sign ificantly higher than infection rates of unfed ticks from Southern Ger many. Borreliae in 31.3% (n = 15) of the infected ticks expressed sole ly OspA, solely OspC in 12.5% (n = 6), and both OspA and OspC in 39.6% (n = 19) of ticks, while in 16.7% (n = 8) of ticks neither were expre ssed. Presentation of OspC by B. burgdorferi in I. ricinus was correla ted with tick weight: in females, OspC was detectable only in ticks wi th a minimum weight of about 3.5 mg, and in nymphs weighing at least 1 mg. These results indicate that in I. ricinus removed from humans Osp C is up-regulated during the blood meal of the tick, but in most ticks OspA is still detectable and might even be present in the absence of OspC expression in the midgut and salivary glands of nearly fully engo rged nymphal ticks. Furthermore, we found strong evidence that borreli ae expressing solely OspA while in the salivary glands can cause Lyme borreliosis. Our findings indicate that during tick feeding, humans ar e exposed to borreliae that may express either OspA or OspC or both, o r lack both OspA and C. These findings suggests that, at the minimum, both OspA and C should be considered as vaccine candidates for prophyl axis of Lyme borreliosis in Europe.