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In order to determine if Peromyscus spp. could become infected with the
Lyme disease spirochete (Borrelia burgdorferi) by direct inoculation and to determine the duration of spirochetemia, 4 P. leucopus and 5 P. maniculatus were inoculated by the intramuscular, intraperitoneal, and subcutaneous routes with an isolate of B. burgdorferi obtained from the blood of a trapped wild P. leucopus from Camp McCoy, Wisconsin. All of the mice developed antibodies to B. burgdorferi which reached a peak indirect immunofluorescent (IFA) geometric mean antibody titer of 10 log2 21 days post-inoculation. B burgdorferi was recovered from the blood of 1 P. maniculatus 21 days post-inoculation. One uninfected Peromyscus of each species was housed in the same cage with the infected Peromyscus as a contact control. Both of the contact controls developed IFA B. burgdorferi antibodies by day 14, indicating contact infection. To determine if B. burgdorferi was being transmitted by direct contact, 5 uninfected P. leucopus and 5 uninfected P. maniculatus were caged with 3 B. burgdorferi infected P. leucopus and 3 infected P. maniculatus, respectively. Each of these contact-exposed P. leucopus and P. maniculatus developed antibodies to B. burgdorferi, and B. burgdorferi was isolated from the blood of 1 contact-exposed P. maniculatus 42 days post-initial contact. These findings show that B. burgdorferi can be transmitted by direct contact without an arthropod vector.