Characterization of the Horizontal and Vertical Sexual Transmission of Chlamydia Genital Infections in a New Mouse Model.

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen worldwide, and there is a need to control this epidemic. So far there is no established animal model in which both the horizontal and the vertical transmission of Chlamydia can be studied. To implement a horizontal sexual transmission model, male mice were inoculated in the meatus urethra with Chlamydia muridarum and they were caged with naive female mice. Urine and vaginal swab specimens were collected for culture. To study vertical transmission, newborns were euthanized and specimens were cultured. As controls, females were mated with sham-infected male mice. All C. muridarum-inoculated male mice had positive urine cultures. As determined by serology, all females caged with C. muridarum-inoculated males became infected, and 93% of them had positive vaginal swab specimen cultures. More females mated with C. muridarum-infected male mice (35%) than females mated with sham-infected male mice (0%) were infertile (P < 0.05). Also, C. muridarum-infected females delivered significantly fewer pups (3.8 ± 3.2/mouse) than control females (6.3 ± 1.6/mouse) (P < 0.05). Of the newborn mice, 32% were C. muridarum positive either in the lungs or in the intestines. Female mice housed with sham-infected males had no positive vaginal swab specimen cultures or C. muridarum-positive pups. This new mouse model of horizontal and vertical sexual transmission of Chlamydia closely parallels C. trachomatis sexual transmission in humans and may be a good model system to better understand the pathogenesis of these infections.