Development and characterization of a mouse model of HSV-2 infection during pregnancy

Abstract

Problem: Primary HSV-2 infection during pregnancy is associated with adverse pregnancy outcomes. However the mechanisms underlying these outcomes remain largely unknown. In this study we developed and characterized a mouse model of primary HSV-2 infection during early pregnancy and examined its effects on pregnancy and fetal outcomes. Methods of Study: C57BL/6 female mice positive for vaginal plugs were infected intravaginally (IVAG) with 10^3/10^4/10^5 PFU/mouse of HSV-2 (333) or saline (control) on gestational day (GD) 5. For comparison, female mice in diestrus stage were infected with HSV-2 at the same doses. Survival, pathology scores and vaginal viral shedding were measured post-infection. Systemic viral dissemination was examined by real-time PCR. Vaginal tissue, implantation sites, placenta and fetuses were examined by histology. Maternal serum (GD 13) and amniotic fluid (GD 8) was collected for multiplex cytokine analysis. Results: The minimum viral inoculation dose for infection in pregnant mice was 10^3 PFU of HSV-2, compared to 100-fold higher dose required to infect diestrus mice (10^5 PFU). There was a dose-dependent increase in implantation failure and number of resorptions with increasing dose of viral inoculum in pregnant mice at GD 8. In the 10^3 PFU group, although vaginal viral shedding was observed in all mice, 75% survived the infection, while all the mice in 10^4 and 10^5 PFU groups succumbed to infection by GD 13-15. There was evidence of abnormal placental morphology and necrotic fetal tissues in HSV-2 infected, pregnant mice compared to controls. Presence of HSV-2 DNA was measured in the vaginal tract, uterus (mated non-pregnant mice), and implantations of infected mated mice. HSV-2 DNA was also present in the spleen of the GD 13 time point group. Conclusions: These results indicate a 100-fold increase in susceptibility to HSV-2 infection during early pregnancy. At higher inoculation doses, IVAG HSV-2 infection spread systemically resulting in poor pregnancy outcomes and maternal mortality, especially in later gestation. At lower inoculation dose, the infection was localized in the reproductive tract and implantation sites, resulting in increased inflammation and adverse outcomes. This model will help to understand pathological mechanisms underlying adverse outcomes following primary HSV-2 infection in pregnancy.