**8. Animal models**

Extending the *in vitro* observations of Chlamydial persistence to an animal infection model has remained challenging. The first and only animal model to study *Chlamydia* persistence was reported a decade ago [112]. The study showed that amoxicillin could induce persistence in BALB/c mice infected intravaginally with the murine pathogen *C. muridarum,* a close relative of *C. trachomatis*. Another relevant observation is that amoxicillin-induced persistence resulted in increased failure of subsequent treatment with the first-choice antiChlamydial antibiotic azithromycin [112]. Interestingly, a murine model of naturally chronic nonhuman Chlamydial infection has been recently developed [113].

Other animal models to study *Chlamydia* genital tract pathogenesis, including guinea pig, nonhuman primate, pig, rat, and the rabbit, have been developed (Reviewed in Ref. [114]). However, none of the animal models perfectly mimics the anatomy, histology, and endocrinology of the human reproductive system or the pathogenesis and immune responses occurring during a chronic human genital *C. trachomatis* infection [114]. In addition, the use of animal models possesses important ethical issues [114].
