Models for sexually transmitted infections

Extensive research on sexually transmitted infections (STI) in the last century has led to a better understanding of disease prevention and treatment options. Nowadays, bacterial infections with chlamydia, gonorrhea or syphilis are curable with antibiotics. Also, infection with HIV has lost its terror as there exists a treatment allowing patients a normal life. Pre- and post-exposure prophylaxis of HIV with anti-retroviral drugs prevents infection of sexual partners. However, health organizations report that STI are on the rise again, being problematic as many infections remain undetected, thereby causing cancers, infertility or congenital infection. To circumvent this, development of vaccines against different STI are urgently needed. As it is difficult to study interaction between host and pathogen in humans, model systems including animal models and in vitro approaches are necessary. Within this review, we give an overview on animal models of STI with a focus on chlamydia infection, discussing advantages and disadvantages of modeling infection with species-specific or human pathogens. Moreover, we present available in vitro models of STI, pointing out current advances in the development of three-dimensional (3D) culture systems closely resembling human tissue architecture. This allows to explore infection under physiological conditions in human cells without ethical concerns. A toolbox full of tightly coordinated in vivo and in vitro infection models will be required to advance STI research and vaccine design in the future.