270: Commensal microbes confer protection against Zika virus infection in a murine gnotobiotic model of congenital Zika syndrome

Abstract

Recent findings reveal that commensal microbiota may play a role in protection against viral infections. For example, bacteria isolated from the human stomach confer resistance against rotavirus infection in mice. Vertical transmission of ZIKV has been shown cause IUGR in mice. Here we sought to determine the contribution of commensal bacteria in protecting against ZIKV infection, vertical transmission, and IUGR. Current pandemic ZIKV was isolated from a traveler returning from Central America and propagated in Vero cells (ZIKV HN16). Pregnant germ-free (GF) and conventional (CONV) Swiss-Webster mice were intravenously inoculated with 104 PFU of second passage ZIKV (n=11) or a mock (n=10) injection on embryonic day 6 (e6), then daily until day e9 (Figure 1). Mice (n=2) were given anti-IFNI1 ab prior to and after infection as positive infection controls. On e18, Cesareans were performed and mice assessed for intrauterine reabsorption and demise as well as embryonic pup weight. Tissues were assessed for ZIKV infection by TaqMan viral qPCR assay. Inoculated mice were asymptomatic based on daily assessment of mobility and paralysis. Overall, GF-ZIKV pups had a greater rate of in utero demise with ZIKV infection (p< 0.01), while there was no difference for conventional controls (Fig 2A). In GF-ZIKV dams, ZIKV was detected in 3 of 4 spleens assessed, but only detected in 1 of 4 spleens from GF-ZIKV mice, and with 100-fold less viral load (B). The uterus was positive for ZIKV in 75% (3/4) GF-ZIKV dams in comparison to 50% (2/4) CONV-ZIKV dams, also with 100-fold less viral load (B). Of the mice positive for ZIKV in the uterus, 3 of 4 had associated in utero demise, while all pregnancies with undetectable levels of ZIKV in the uterus had no incidences of in utero demise (Fig A/B?). Pups of Zika infected conventional mothers showed no difference in fetal weight compared to mock, while germ free mothers were 25% smaller by weight (Fig C) (p<0.0001), indicating protection of the native flora. The findings demonstrate that commensal bacteria confer protection against fetal/placental ZIKV infection and transmission either through direct host defense or mediated through adaptive immunity.View Large Image Figure ViewerDownload Hi-res image Download (PPT)