Experimental Infection of Mid-Gestation Pregnant Female and Intact Male Sheep with Zika Virus

Abstract

Zika virus (ZIKV) is an arbovirus that causes birth defects, persistent male infection, and sexual transmission in humans. The purpose of this study was to continue the development of an ovine ZIKV infection model; thus, two experiments were undertaken. In the first experiment, we built on previous pregnant sheep experiments by developing a mid-gestation model of ZIKV infection. Four pregnant sheep were challenged with ZIKV at 57-64 days gestation; two animals served as controls. After 13-15 days (corresponding with 70-79 days of gestation), one control and two infected animals were euthanized; the remaining animals were euthanized at 20-22 days post-infection (corresponding with 77-86 days of gestation). In the second experiment, six sexually mature, intact, male sheep were challenged with ZIKV and two animals served as controls. Infected animals were serially euthanized on days 2-6 and day 9 post-infection with the goal of isolating ZIKV from the male reproductive tract. In the mid-gestation study, virus was detected in maternal placenta and spleen, and in fetal organs, including the brains, spleens/liver, and umbilicus of infected fetuses. Fetuses from infected animals had visibly misshapen heads and morphometrics revealed significantly smaller head sizes in infected fetuses when compared to controls. Placental pathology was evident in infected dams. In the male experiment, ZIKV was detected in the spleen, liver, testes/epididymides, and accessory sex glands of infected animals. Results from both experiments indicate that mid-gestation ewes can be infected with ZIKV with subsequent disruption of fetal development and that intact male sheep are susceptible to ZIKV infection and viral dissemination and replication occurs in highly vascular tissues (including those of the male reproductive tract).Viruses 2020, 12, 291 2 of 23 and negative gestational outcomes when infection occurs during pregnancy. In humans, ZIKV is believed to result in trimester-specific effects to the fetus [2][3][4][5][6][7]. Established animal models of ZIKV infection during pregnancy that result in vertical transmission include non-human primates (NHP) and type-1 interferon/interferon receptor deficient mice. In NHP models, first trimester infection most frequently results in fetal demise and reduced fetal development even in asymptomatic mothers, while second trimester infections tend to produce fetuses with higher viral loads but greater fetal viability [8][9][10]. In all NHP models, fetal pathology ranges from mild to severe manifestations, consistent with Congenital Zika Syndrome (CZS) seen in humans [11][12][13][14][15][16]. While NHP models of ZIKV infection during pregnancy recapitulate human infection, other outbred host models can serve as surrogates when ethical and economic constraints create obstacles to the use of NHP.Sheep offer a unique animal model for translational biomedical research, and have long been used as a model for human pregnancy and fetal development due to longer gestation and comparably staged rates of fetal d...

Post-Vaccination Yellow Fever Antiserum Reduces Zika Virus in Embryoid Bodies When Placental Cells are Present

“…In this study, the EBs from co-cultures had lower viral loads as compared to the placental cell lines. This supports reports of ZIKV titers in fetal and placental tissues in vivo [ 28 , 65 , 66 ]. Since macrophages or other monocytes were not used in this study, the enhancement we observed was likely due to antibody-mediated enhancement (AME).…”

“…The data in this study show that within 72 h p.i., ZIKV effectively crosses two monolayers, a basement membrane, and infects an EB. The detection of ZIKV in cells located on each side of the membrane as a model for the maternal–fetal axis supports reports of the isolation of ZIKV from placentas and fetuses [ 28 , 50 , 65 , 66 ]. However, the permissiveness of the cells observed in this study may not reflect the cellular tropism of ZIKV in actual placentas [ 67 , 68 , 69 , 70 ].…”

Post-Vaccination Yellow Fever Antibodies Enhance Zika Virus Infection in Embryoid Bodies

“…In this study, EBs had enhanced ZIKV infection along with lower viral loads as compared to the placental cell lines. This supports reports of ZIKV titers in fetal and placental tissues in vivo [28,68,69]. Since macrophages or other monocytes were not used in this study, the enhancement we observed was likely due to antibody mediated enhancement (AME).…”

Animal models of congenital zika syndrome provide mechanistic insight into viral pathogenesis during pregnancy

“…ZIKV infection during the first trimester also causes placental pathology, fetal growth restriction, and fetal loss [ 42 ]. Infection of pregnant sheep (gestational day 57 to 64) with a high dose of ZIKV (strain R103451, 10 8 PFU) via the intravenous and subcutaneous route results in detectable infectious virus in the maternal spleen, placenta, and fetal organs including brain, spleen, and liver, with fetuses exhibiting significantly smaller head sizes as well as gross pathology following euthanasia by 15 dpi [ 43 ]. Taken together, these findings suggest that pregnant sheep are a useful large animal model to study ZIKV pathogenesis in the context of CZS.…”