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

BackgroundCongenital 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 FindingsTo evaluate the potential for 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; however, we did find an increase in the occurrence of decidual vasculitis and necrosis in ZIKV-exposed pregnancies compared to gestational-age-matched controls.Conclusions/SignificanceThis study demonstrates that African-lineage ZIKV, like Asian-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.Author SummaryZika virus infection during pregnancy can result in adverse pregnancy outcomes including birth defects and miscarriage. There are two distinct genetic backgrounds of Zika virus: Asian-lineage and African-lineage. Currently, only Asian-lineage Zika virus is causally associated with adverse pregnancy outcomes in people. However, experimental studies have shown that African-lineage Zika virus can infect the fetus during pregnancy and cause adverse outcomes. Adverse pregnancy outcomes may not be associated with infection in people until there is an outbreak in a naive population. Thus, as African-lineage Zika virus continues to spread globally, the risk that it may pose to pregnant people remains a public health concern. In this study, we demonstrate that African-lineage Zika virus can be transmitted from the mother to the fetus during pregnancy. This study is significant because we used rhesus macaques, an animal that shares many key elements of Zika virus infection in pregnant people. This study is also significant because we inoculated pregnant macaques with a very small amount of virus, suggesting that fetal infection reported in previously published macaque studies is not limited to high-dose inoculation.

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

“…Physical examination of infected dams found none of the ZIKV-associated symptoms reported in human infections, such as rash or conjunctivitis following inoculation. This finding is consistent with previously reported studies of ZIKV-DAK infection in rhesus macaques [14,15,23].…”

“…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, no published results 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 Africanlineage 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].…”

“…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 [10,11,14,15,17,23–27]. Additionally, studies show that the fetal membranes are susceptible to both African and Asian-lineage ZIKV and remain susceptible throughout gestation [10,17,27].…”