Early Embryonic Loss Following Intravaginal Zika Virus Challenge in Rhesus Macaques

Abstract

Zika virus (ZIKV) is an arthropod-borne virus (arbovirus) and is primarily transmitted by Aedes species mosquitoes; however, ZIKV can also be sexually transmitted. During the initial epidemic and in places where ZIKV is now considered endemic, it is difficult to disentangle the risks and contributions of sexual versus vector-borne transmission to adverse pregnancy outcomes. To examine the potential impact of sexual transmission of ZIKV on pregnancy outcome, we challenged three rhesus macaques (Macaca mulatta) three times intravaginally with 1 x 107 PFU of a low passage, African lineage ZIKV isolate (ZIKV-DAK) in the first trimester (~30 days gestational age). Samples were collected from all animals initially on days 3 through 10 post challenge, followed by twice, and then once weekly sample collection; ultrasound examinations were performed every 3-4 days then weekly as pregnancies progressed. All three dams had ZIKV RNA detectable in plasma on day 3 post-ZIKV challenge. At approximately 45 days gestation (17-18 days post-challenge), two of the three dams were found with nonviable embryos by ultrasound. Viral RNA was detected in recovered tissues and at the maternal-fetal interface (MFI) in both cases. The remaining viable pregnancy proceeded to near term (~155 days gestational age) and ZIKV RNA was detected at the MFI but not in fetal tissues. These results suggest that sexual transmission of ZIKV may represent an underappreciated risk of pregnancy loss during early gestation.

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

“…ZIKV RNA was also found in the fetus in two of those three pregnancies. Although the current study used a very small inoculation dose, our results are consistent with what has been found in two other non-human primate studies that show maternal infection with African-lineage ZIKV results in MFI infection and vertical transmission to the fetus [19][20].…”

“…As far as we are aware, this is the first observation of ZIKV infection of endovascular trophoblasts in situ in decidual spiral arteries. Newman et al reported persistent muscularization in spiral arteries in the decidua of a near-term rhesus macaque pregnancy vaginally challenged with ZIKV-DAK [20]. The importance of the remodeling of these vessels for the establishment of a successful pregnancy [40] [41] provides potential insight into the risk of adverse pregnancy outcomes with early pregnancy maternal ZIKV infection [7] [9].…”

“…Recently, African-lineage has been found in Brazil, highlighting the risk of this virus to emerge outside the African continent [14]; [15]; [16]. African-lineage ZIKV has been shown to cause fetal demise in in vivo studies done in mice and macaques [18] [20], further supporting the potential of African-lineage ZIKV to cause adverse pregnancy outcomes in humans. The current study further supports those findings.…”

“…Congenital birth defects or adverse pregnancy outcomes have not been formally associated with African-lineage ZIKV infection during pregnancy in people. However, in vivo studies done in mice and macaques suggest that African-lineage ZIKV could pose a substantial risk when infection occurs during pregnancy [17] [18] [19] [20]. African- lineage infection in pregnant immune-deficient mice revealed the potential for vertical transmission during pregnancy [17][18].…”

“…Crooks et al found that a subcutaneous maternal inoculation of 1X10 4 plaque forming units (PFU) at gestation day (gd) 45 resulted in a higher viral burden in the placenta than the same dose of an Asian-lineage virus [19], but did not find any evidence of vertical transmission. Newman et al showed that maternal vaginal inoculation with 3X10 8 PFU at gd 30 resulted in vertical transmission and fetal loss in two of three pregnancies [20]. Raasch et al demonstrated that a maternal subcutaneous dose of 1X10 8 gd 45 resulted in vertical transmission and fetal demise in three out of eight pregnancies [22].…”