The African strain of Zika virus causes more severe in utero infection than Asian strain in a porcine fetal transmission model

Abstract

Studies in mice showed that African Zika virus (ZIKV) strains cause more damage in embryos. These studies, however, were limited to the mouse-adapted African MR766 strain or infection at early gestation. Here, we compared infection of Asian and African strains in the fetal pig model at midgestation. Both strains caused fetal infection. ZIKV was detected in placenta, amniotic membrane, amniotic fluid, fetal blood, and brain. The African strain produced more vigorous in utero infection as represented by more efficient virus transmission between siblings, and higher viral loads in fetal organs and membranes. Infection with both strains was associated with reduced fetal brain weight and increased number of placental CD163-positive cells, as well as elevated in utero interferon alpha and cortisol levels. This is the first large animal model study which demonstrated that African strain of ZIKV, with no passage history in experimental animals, can cause persistent infection in fetuses and fetal membranes at midgestation. Our studies also suggest that similar to Asian strains, ZIKV of African lineage might cause silent pathology which is difficult to identify in deceptively healthy fetuses. The findings emphasize the need for further studies to highlight the impact of ZIKV heterogeneity on infection outcomes during pregnancy.

CpG-Recoding in Zika Virus Genome Causes Host-Age-Dependent Attenuation of Infection With Protection Against Lethal Heterologous Challenge in Mice

“…Infected plates were incubated (5% CO 2 , +37 • C) until the sampling time point when supernatants were collected, clarified (2,000 g, 5 min) and frozen (−80 • C) for subsequent infectious virus quantification (34)(35)(36)(37). After the supernatant collection, the plate with infected cells was dried and frozen (−20 • C).…”

“…After the supernatant collection, the plate with infected cells was dried and frozen (−20 • C). Plates were stained with virus-specific 4G2 Abs (36), and infected cells were counted in the well with bright-field microscopy at 200x magnification and expressed per cm 2 . Cell culture supernatants and fixed plates were collected daily at 0-5 days post inoculation (or at other time points indicated in figure legends), with three technical replicates and three biological replicates per time point for each ZIKV variant.…”

“…For quantification of infectious ZIKV loads in cell culture media the endpoint dilution assay was used as described before (34)(35)(36)(37)42). Cell culture media were serially diluted 5-fold in four replicates starting from 1:5, and 50 µl of each dilution was added to confluent VERO cells cultured in 96-well plates.…”

“…After washing and drying, the plates were kept at −20 • C at least for 2 h or until use. Cell fixation and staining were done, as previously described (34)(35)(36)(37)42); anti-pan flavivirus E protein monoclonal Abs 4G2 (ATCC HB-112) were used to detect ZIKV-infected cells. Fifty percent endpoint titers were calculated by the Spearman-Kärber formula and expressed in a decimal logarithm of TCID 50 .…”

A single nonsynonymous mutation on gene encoding E protein of Zika virus leads to increased neurovirulencein vivo

“…A Serine to Asparagine (S139N) mutation on the prM protein of Zika virus strains isolated between 2013-2014 has been associated with neurovirulence (15). By comparing functional differences between African and Asian Zika virus strains, however, it was found that the Asian strains responsible for the recent outbreaks and linked to microcephaly do not have more infectivity to neuronal cells in cell culture in vitro (16), or more neurovirulence in vivo than the older African strains (17, 18). Other studies have placed more emphasis on the global interations between virus and host.…”