Zika virus infection at mid-gestation results in fetal cerebral cortical injury and fetal death in the olive baboon
Authors: Gurung Sunam , Reuter Nicole , Preno Alisha , Dubaut Jamie , Nadeau Hugh , Hyatt Kimberly , Singleton Krista , Martin Ashley , Parks W. Tony , Papin James F. , Myers Dean A. 
Published: May 2018

Zika virus (ZIKV) infection during pregnancy in humans is associated with an increased incidence of congenital anomalies including microcephaly as well as fetal death and miscarriage and collectively has been referred to a Congenital Zika Syndrome (CZS). Animal models for ZIKV infection in pregnancy have been developed including mice and macaques. While microcephaly has been achieved in mice via direct injection of ZIKV into the fetal brain or via interference with interferon signaling, in macaques the primary fetal CZS outcome are ocular defects. In the present study we develope the olive baboon (Papio anubis), as a model for the vertical transfer of ZIKV during pregnancy. We infected four mid-gestation, timed-pregnant baboons with the French Polynesian ZIKV isolate (104ffu) and examined the acute phase of vertical transfer by stopping the study of one dam at 7 days post infection (dpi), two at 14 dpi and one at 21 dpi. All dams exhibited mild to moderate rash and conjunctivitis; three of four dams exhibited viremia at 7 dpi. Of the three dams studied to 14 to 21 days, only one still exhibited viremia on day 14. Vertical transfer of ZIKV to the fetus was found in two pregnancies; in one, vertical transfer was associated with fetal death at ∼14 dpi. In the other, vertical transfer was observed at 21 dpi. Both fetuses had ZIKV RNA in the fetal cerebral cortex as well as other tissues. The 21 dpi fetal cerebral cortex exhibited notable defects in radial glia, radial glial fibers, loss and or damage of immature oligodendrocytes and a loss in neuroprogenitor cells (NPCs). In addition, indices of pronounced neuroinflammation were observed including astrogliosis, increased microglia and IL-6 expression. The dams studied to 14 dpi (n=2) and 21 dpi (n=1) exhibited a anti-ZIKV IgM response and IgG response (21 dpi) that included transfer of the IgG to the fetal compartment (cord blood). The severity of systemic inflammatory response (cytokines and chemokines) reflected the vertical transfer of ZIKV in the two pregnancies. As such, these events likely represent the early mechanisms that lead to microcephaly and/or other CNS pathologies in a primate infected with ZIKV and are the first to be described in a non-human primate during the acute phase of ZIKV infection with a contemporaneous ZIKV strain. The baboon thus represents a major NHP for advancing as a model for ZIKV induced brain pathologies to contrast and compare to humans as well as other NHPs such as macaques.

AUTHOR SUMMARY

Zika virus is endemic in the Americas, primarily spread through mosquitos and sexual contact. Zika virus infection during pregnancy in women is associated with a variety of fetal pathologies now referred to as Congenital Zika Syndrome (CZS), with the most severe pathology being fetal microcephaly. Developing model organisms that faithfully recreate Zika infection in humans is critical for future development of treatments and preventions. In our present study, we infected Olive baboons at mid-gestation with Zika virus and studied the acute period of viremia and transfer of Zika virus to the fetus during the first three weeks after infection to better understand the timing and mechanisms leading to CZS. We observed Zika virus transfer to fetuses resulting in fetal death in one pregnancy and in a second pregnancy, significant damage to the frontal cortex of the fetal brain consistent with development of microcephaly, closely resembling infection in pregnant women. Our baboon model differs from macaque non-human primate models where the primary fetal outcome during pregnancy following infection with contemporary strains of Zika virus is ocular pathology. Thus, the baboon provides a promising new non-human primate model to further compare and contrast the consequences of Zika virus infection in pregnancy to humans and macaques to better understand the disease.