Infection of the maternal-fetal interface and vertical transmission following low-dose inoculation of pregnant rhesus macaques (Macaca mulatta) with an African-lineage Zika virus

Abstract

Background Congenital Zika virus (ZIKV) infection can result in birth defects, including malformations in the fetal brain and visual system. There are two distinct genetic lineages of ZIKV: African and Asian. Asian-lineage ZIKVs have been associated with adverse pregnancy outcomes in humans; however, recent evidence from experimental models suggests that African-lineage viruses can also be vertically transmitted and cause fetal harm. Methodology/Principal findings To evaluate the pathway of vertical transmission of African-lineage ZIKV, we inoculated nine pregnant rhesus macaques (Macaca mulatta) subcutaneously with 44 plaque-forming units of a ZIKV strain from Senegal, (ZIKV-DAK). Dams were inoculated either at gestational day 30 or 45. Following maternal inoculation, pregnancies were surgically terminated seven or 14 days later and fetal and maternal-fetal interface tissues were collected and evaluated. Infection in the dams was evaluated via plasma viremia and neutralizing antibody titers pre- and post- ZIKV inoculation. All dams became productively infected and developed strong neutralizing antibody responses. ZIKV RNA was detected in maternal-fetal interface tissues (placenta, decidua, and fetal membranes) by RT-qPCR and in situ hybridization. In situ hybridization detected ZIKV predominantly in the decidua and revealed that the fetal membranes may play a role in ZIKV vertical transmission. Infectious ZIKV was detected in the amniotic fluid of three pregnancies and one fetus had ZIKV RNA detected in multiple tissues. No significant pathology was observed in any fetus; and ZIKV did not have a substantial effect on the placenta. Conclusions/Significance This study demonstrates that a very low dose of African-lineage ZIKV can be vertically transmitted to the macaque fetus during pregnancy. The low inoculating dose used in this study suggests a low minimal infectious dose for rhesus macaques. Vertical transmission with a low dose in macaques further supports the high epidemic potential of African ZIKV strains.

Control of maternal Zika virus infection during pregnancy is associated with lower antibody titers in a macaque model

“…We hypothesize that in the viral non-controllers ZIKV reaches this site by 7 DPI, when infectious virus is still detectable in the maternal blood, and that establishment of this viral reservoir leads to the prolonged plasma vRNA burden and increased vRNA burden in the MFI that is observed. This is consistent with a recent report that ZIKV is able to reach the MFI tissues as early as 7 DPI ( 60 ). Maternal plasma vRNA burden was cleared prior to delivery in all dams regardless of the level of vRNA burden in the MFI tissues at delivery.…”

Vertical transmission of African-lineage Zika virus through the fetal membranes in a rhesus macaque (Macaca mulatta) model

“…Evidence for the transplacental route of ZIKV vertical transmission is currently sparse in human cases of congenital ZIKV infection and non-human primate (NHP) in vivo studies. To our knowledge, there are no published results that show STB infection in cases of human congenital ZIKV infection, and ZIKV has rarely been found in STBs in NHP studies [11][12][13][14][15]. Reports of the vulnerability of STBs and CTBs to infection have primarily been obtained from ex vivo or in vitro studies using both Asian and African-lineage ZIKV.…”

“…Once the chorionic membrane is infected, the fetus is no longer protected by trophoblasts and ZIKV can, theoretically, easily spread to fetal vessels in the chorionic plate and into the amniotic fluid. Substantial evidence supports that the fetal membranes are susceptible to ZIKV infection [10,11,14,15,17,[22][23][24][25][26][27]. The fetal membranes have been found to be infected in a human case of congenital ZIKV infection that resulted in a miscarriage [22].…”

“…The fetal membranes have been found to be infected in a human case of congenital ZIKV infection that resulted in a miscarriage [22]. The vulnerability of the fetal membranes has been demonstrated in a wide range of studies, including NHP studies and various ex vivo and in vitro studies [10,11,14,15,17,[23][24][25][26][27]. Additionally, studies show that the fetal membranes are susceptible to both African and Asian-lineage ZIKV and remain susceptible throughout gestation [10,17,27].…”

Implication of viruses in the etiology of preeclampsia

“…However, another in vivo study investigating the effect of low-dose Zika virus in rhesus macaques showed that this virus does not have a substantial effect on the placenta. 177 Moreover, no clinical studies have reported an association between this virus and hypertensive disorder during pregnancy. Therefore, future studies are required to establish the link between preeclampsia and Zika virus infection.…”