Experimental inoculation of Peromyscus spp. with Borrelia burgdorferi: evidence of contact transmission.

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.