The effects of a single cervical inoculation of Chlamydia trachomatis on the female reproductive tract of the baboon (Papio anubis)

Abstract

Background: The baboon (Papio hamadryas anubis) can be transcervically instrumented, facilitating studies of intrauterine contraception and reproductive tract infection. We sought to determine if the baboon could become infected with a single cervical inoculation of Chlamydia trachomatis.

Methods: Ten female baboons were randomized and inoculated cervically with C. trachomatis serovar E (or buffer alone). Animals underwent weekly clinical and laparoscopic evaluations for four weeks and at post-inoculation week 8, to monitor upper tract infection. Cervical culture and nucleic acid amplification testing (NAAT) were completed weekly throughout the study. Animals were euthanized at week 16 and the reproductive tracts were examined histologically.

Results: All inoculated animals developed cervical infection. The average duration of positive NAAT results was 6.8 weeks (range 2-16). Two of eight (25%) animals tested positive from fallopian tube samples. Infected animals showed histological findings consistent with chlamydial infection, such as germinal centers. Five of ten animals seroconverted to C. trachomatis.

Conclusions: Baboons cervically inoculated once with C. trachomatis develop infection similar to humans, with a low incidence of upper tract infection. This novel model of Chlamydia infection closely resembles human disease and opens new avenues for studying the pathogenesis of sexually transmitted infections and contraceptive safety.

Figure 1.

Representative fallopian tube C. trachomatis-associated histological findings at low (A, C, E) and high (B, D, E) magnification. In animal S5 (A and B), which met disease criteria for PID, the tubal propria (interstitium) was significantly and extensively thickened (long arrows) by numerous mononuclear cells, predominantly lymphocytes (short arrows). In animal S2 (C and D), which had 2 minor criteria consistent with infection but was not classified as PID, there was mild, localized expansion of the propria (long arrows) and scant lymphocytic inflammation in the propria and tubal wall (short arrow). In control animal S9 (E and F), the tubal propria was thin (long arrow) and lacked significant infiltrating inflammatory cells. Hematoxylin and eosin. Original magnifications panels A, C, E: 200×. Panels B, D, F: 600×.

Figure 2.

Representative cervical and vaginal histological findings in C. trachomatis colonized (animal S7; A) and uninfected control (animal S10; B). Animal S7 (A), which had positive NAAT findings for 16 weeks, had robust lymphocytic and plasmacytic submucosal inflammation at the cervical squamocolumnar junction (long arrows). Inset shows plasma cells (short arrows) from area with asterisk. There was also extensive lymphocytic and plasmacytic submucosal inflammation in a control animal (S10; B) in the proximal vagina adjacent to the cervix (arrow). Inset shows plasma cell (short arrow) in area with asterisk. Hematoxylin and eosin. Original magnifications 100×.