Johanna Norenhag: Vaginal microbiota composition and function: Its relation to HPV, cervical dysplasia, and reproductive and general health

Abstract

The overall aim of this thesis was to study the vaginal microbiota and its role in both health and pathogenic processes, with a particular focus on HPV infection and the dysplastic progression to cervical cancer. 

In paper I, a systematic review and meta-analysis were conducted to assess current findings on the association between the vaginal microbiota and HPV-related disease. It was found that a vaginal microbiota dominated by non-Lactobacilli species or L. iners was associated with HPV infection and dysplasia/cervical cancer, while L. crispatus was associated with healthy women.

Paper II investigated the association between different compositions of the vaginal microbiota and HPV infection in a population of young Swedish women. A strong association was identified between non-lactobacilli dominated vaginal microbiota and HPV infection. This association was observed for both low-risk and high-risk HPV, as well as for infections involving single and multiple HPV types. Bacteria more prevalent among women with HPV infection included BVAB 1, BVAB 2, Sneathia, Prevotella and Megasphaera. 

In paper III, the association between different compositions of the vaginal microbiota and cervical dysplasia was explored. The study demonstrated that women with cervical dysplasia had higher microbiota diversity and were more likely to have a non-lactobacilli dominated microbiota. Women with dysplasia exhibited a higher abundance of Gardnerella vaginalis, Aerococcus christensenii, Peptoniphilus lacrimalis and Fannyhessae vaginae, while healthy controls had higher abundance of L. crispatus. Furthermore, differences in functional pathways were found, suggesting a more active role of the vaginal microbiota in the development of cervical dysplasia. 

In paper IV, the vaginal microbiota among healthy women was characterised, and health and lifestyle factors that contribute to microbial variations were identified. The study revealed that the most prevalent species in the vaginal microbiota were L. crispatus, followed by L. iners and G. vaginalis. Furthermore, it showed that the main factors influencing microbial composition were age, BMI and having biological children. 

In conclusion, the vaginal microbiota of most women consists mainly of lactobacilli species. Both intrinsic factors (e.g. age and BMI) as well as external factors (e.g. infections) contribute to compositional and functional variations of the vaginal microbiota. Further studies are needed to better understand the potential role of the microbiota in both gynaecological health and disease. In addition, more research on the vaginal microbiota and its association with HPV-related disease could prove beneficial for prevention, early detection and treatment.