101: Maternal microbiome diminishes fetal infection and demise in a murine model of congenital zika syndrome

Abstract

Maternal ZIKV infection periconception results in CZS in a significant minority of cases. Our recent data demonstrated that ZIKA infection also results in early pregnancy loss in several non-human primate models (PMID 29967348, 29717225). However, estimates of rates of ZIKV vertical transmission and associated pregnancy loss vary in human populations, and are likely dependent on host, viral and other factors. Commensal bacterial microbes, for example, may be important mediators of immunity and viral infection. Here we hypothesized that host bacteria would mediate ZIKV vertical transmission and associated pregnancy loss. Timed-pregnant Swiss-Webster mice, that were either conventional or bred and housed in the absence of bacteria (gnotobiotic germ-free; Fig. A), were inoculated with 1x104PFU of a contemporaneous first passage ZIKV or a mock injection (M) on embryonic days 4 through 7. A group was also treated with anti-IFNI1 antibody + ZIKV as a positive control. Caesarean deliveries of pups and placentae were performed at day 18.5. Animals were assessed for viral levels, as well as fetal demise and growth restriction. Mothers were asymptomatic for ZIKV infection based on daily monitoring. Overall, germ-free (GF) mice had higher rates of vertical transmission as measured by fetal growth restriction (1.0 g vs 1.2 g, GF vs conventional p<0.01), and a significantly higher rate intrauterine demise on day 18.5 (OR 8.7 c2p=0.01) (Fig. B). Among ZIKA infected gestations, placentae were positive in 82% of demised fetus’ compared to 52% of live pups (p=0.04) (Fig. C). 11 days after infection, viral RNA was recovered from maternal spleen and uterus, and was highest by an order of magnitude in fetal placental tissue overall (7.9x103, 1.9x103vs 6.1x104, respectively, p<0.001). Of particular interest, ZIKV levels among GF mice when compared with conventional were higher in spleen (2.1 x 104vs 8.7 x103 RNA copies/g; p=0.04) and uterus (1.0 x104 vs 6.1 x 102 RNA copies/g, p=0.04) (Fig D). Overall, 25% of conventional dams were infected compared to 78% of GF (c2, p=0.03). We tested the novel hypothesis that maternal antiviral immunity may be stimulated or augmented by the presence of commensal bacteria in pregnancy. We have shown for the first time that germ-free dams and their pups are more susceptible to ZIKV infection and CZS, suggesting the mitigating potential of commensal bacteria in congenital viral infections.