INTRAUTERINE TRANSMISSION OF BORRELIA-BURGDORFERI IN DOGS

To determine whether intrauterine transmission of Borrelia burgdorferi could exist in dogs, 10 female Beagles were inoculated intradermally with approximately 1,000 B burgdorferi on day 1 of proestrus; inoculat ion was repeated every 2 weeks during the gestation period. Ten female control Beagles were similarly inoculated with phosphate-buffered sal ine solution. Prior to the start of the study, all females and 3 males used for breeding were seronegative for B burgdorferi on the basis of results of the indirect fluorescent antibody test and immunoblot (wes tern blot) analysis. Similarly, results of culture of blood for B burg dorferi were negative. All 20 of the females were bred naturally. Bloo d samples were collected weekly for serologic testing and culture. Blo od samples were obtained from live pups on day 1 of life, then weekly until pups were 6 weeks old when they were euthanatized. Tissues were obtained for culture and testing by use of polymerase chain reaction ( PCR). Of 10 spirochete-inoculated (si) females, 8 became infected with B burgdorferi as evidenced by spirochete culture results and/or PCR-d etected B burgdorferi DNA in the tissues of females or their pups. Of the 10 si females, 8 delivered litters (3 to 7 pups) that had at least 1 neonatal or 6-week-old pup with B burgdorferi DNA-positive tissues (by PCR), and spirochetes were cultured from tissues from pups of 2 li tters. Four pups of 3 separate litters (a stillborn, a neonate that su rvived to 30 minutes of age, a 20-hour-old, and a 48-hour-old) had B b urgdorferi-positive tissues (by PCR), and the 20-hour-old pup was also culture-positive, indicating intrauterine infection. Further evidence of intrauterine exposure was the presence of IgM antibodies to B burg dorferi detectable by western blot in 3 of 7 one-day-old pups that did not receive colostrum, indicating a primary immune response. Eight of 10 si females and 10 of 10 control females carried litters to term. D ifferences between SI and control Beagles were seen in the duration of gestation, number of resorptions, and number of dystocias. All contro l females and pups remained seronegative, culture-negative, and B burg dorferi-negative throughout the study. Intrauterine infection by B bur gdorferi does occur in dogs and is a potential means by which the spir ochete can be transmitted in a breeding population in the absence of a tick vector.