The vaginal eukaryotic DNA virome and preterm birth

Despite decades of attempts to link infectious agents to preterm birth, an exact causative microbe or community of microbes remains elusive. Culture-independent sequencing of vaginal bacterial communities demonstrates community characteristics are associated with preterm birth, although none are specific enough to apply clinically. Viruses are important components of the vaginal microbiome and have dynamic relationships with vaginal bacterial communities. We hypothesized that vaginal eukaryotic DNA viral communities (the "vaginal virome") either alone or in the context of bacterial communities are associated with preterm birth.

The objective of this study was to use high-throughput sequencing to examine the vaginal eukaryotic DNA virome in a cohort of pregnant women and examine associations between vaginal community characteristics and preterm birth.

This is a nested case-control study within a prospective cohort study of women with singleton pregnancies, not on supplemental progesterone, and without cervical cerclage in situ. Serial midvaginal swabs were obtained at routine prenatal visits. DNA was extracted, bacterial communities were characterized by 16S ribosomal RNA gene sequencing, and eukaryotic viral communities were characterized by enrichment of viral nucleic acid with the ViroCap targeted sequence capture panel followed by nucleic acid sequencing. Viral communities were analyzed according to presence/absence of viruses, diversity, dynamics over time, and association with bacterial community data obtained from the same specimens.

Sixty subjects contributed 128 vaginal swabs longitudinally across pregnancy. In all, 24 patients delivered preterm. Participants were predominantly African American (65%). Six families of eukaryotic DNA viruses were detected in the vaginal samples. At least 1 virus was detected in 80% of women. No specific virus or group of viruses was associated with preterm delivery. Higher viral richness was significantly associated with preterm delivery in the full group and in the African American subgroup (P = .0005 and P = .0003, respectively). Having both high bacterial diversity and high viral diversity in the first trimester was associated with the highest risk for preterm birth.

Higher vaginal viral diversity is associated with preterm birth. Changes in vaginal virome diversity appear similar to changes in the vaginal bacterial microbiome over pregnancy, suggesting that underlying physiology of pregnancy may regulate both bacterial and viral communities.