We report that outbred Hartley guinea pigs are susceptible to Borrelia burgdorferi. We recovered spirochetes from 57 of 60 (95%) guinea pigs inoculated when < or = 3 months of age. In contrast, animals inoculated when > or = 6 months of age were resistant to infection as defined by recovery of organisms at > or = 4 weeks postinoculation. Infection was widely disseminated: B. burgdorferi was recovered from 83% of bladders, 64% of knee joints, 57% of hearts, 48% of spleens, and 38% of spinal cords examined within 4 weeks of inoculation. Histopathologic changes were common in the heart (88%) (preferential involvement of perineural tissues near the annulus fibrosus) and bladder (76%) and were also noted in a minority of spinal cords (13%) and knee joints (9%). Western immunoblots demonstrated an immunoglobulin G response to B. burgdorferi, particularly to the 24-, 31- (OspA), 39-, and 41-kDa (flagellin) antigens. Infection was cleared from most tissues with the passage of time; spirochetes were recovered from 63% of tissues removed from guinea pigs at < or = 4 weeks after inoculation but from only 32% at > or = 8 weeks postinoculation (P < 0.001). An exception was the failure to clear spirochetes from infected knees, 90% of which were culture positive even when evaluated at > or = 8 weeks postinoculation. The guinea pig provides a new model useful for studying host-spirochete interactions in Lyme disease.
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