**1. Introduction**

Zika virus (ZIKV), which is a flavivirus belonging to the Flaviviridae family, like Dengue virus (DENV), yellow fever virus (YFV) or West Nile virus (WNV), has become a major medical problem worldwide. The human disease known as Zika fever is characterized by mild flu-like symptoms including fever, maculopapular rash, headache and sometimes conjunctivitis, arthralgia and myalgia. Symptoms usually subside within a week [1]. However, during the latest outbreaks, serious pathological features of the disease have been reported. Complications such as microcephaly in newborns or Guillain–Barré syndrome (GBS) in adults were documented during the French Polynesia outbreak in 2013 and in Brazil in 2015 [2,3]. ZIKV is an arbovirus, mainly transmitted to humans through the bite of a mosquito vector from *Aedes* species [4]. Due to an increasingly global distribution of *Aedes*, ZIKV emergence is a threat in many areas that are no longer necessarily located in intertropical areas [5]. The ZIKV particle is composed of a single strand RNA molecule of about 11 kb, inside a nucleocapsid, surrounded by a host-derived membrane that contains two virus encoded proteins (E and M). Phylogenetic analysis of viral sequences has identified two main virus lineages, African and Asian [6], the latter being the main cause of large current epidemics with millions of cases of infection, in particular those that recently affected Brazil and the Americas [7]. Once ZIKV has entered the human body, it targets many types of cells such as epithelial cells, in order to replicate and produce a viral progeny. The life cycle of ZIKV, like other flaviviruses, leads to the release of its single-strand positive sense genomic RNA in the cell cytoplasm where it is translated into a single polyprotein, which is then cleaved by host and viral proteases into three structural proteins (C, prM/M and E), and seven nonstructural proteins (NS; NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5) [8]. The viral

cycle continues with the replication process and the production and maturation of envelope proteins, encapsidation, budding and release of virions by exocytosis.

As with many other viruses, interactions between ZIKV and its host trigger a variety of host responses in the body's attempt to resolve the infection [9]. Among these responses, apoptosis plays an important role as a host defense mechanism [10]. Apoptosis can quickly remove intracellular niches of viral replication and thus bypass the virus as it multiplies and spreads. As a result, many viruses have developed strategies to evade, delay or divert the cell death responses, often to their advantage [11]. One example is the case of chikungunya virus (CHIKV), an arbovirus of the alphavirus family, which takes advantage of massive apoptosis to hide in disseminating blebs and thus optimizes its spread [12]. Typically, alphaviruses such as CHIKV (but also Sindbis virus, Ross River virus and Semliki Virus) replicate extremely quickly and the infected cells are characterized by rapid and concomitant apoptosis [13]. Unlike alphaviruses, flaviviruses replication is relatively slow. For several of them such as DENV, Japanese encephalitis virus (JEV) and WNV, apoptosis has been shown to be inhibited during the early stages of the viral cycle [14]. The role of viral proteins in the control of apoptosis has been extensively studied, with many observations in support of both pro-apoptotic activity and antiapoptotic e ffects. For WNV, a nuclear localization of the capsid was shown to induce a caspase-9-dependent apoptosis [15]. Whereas the WNV capsid protein was shown to suppress the activation of caspases 3 and 8 via Akt through a phosphatidylinositol 3-kinase-dependent mechanism (PI3K) [16]. Concerning ZIKV, in cellulo models have shown that infection can lead to cytopathic effects that are typical of apoptosis, and in previous work we observed late-onset apoptosis 48 h after infection of A549 cells with ZIKV isolate PF13 [17]. In some other cell types (human fetal astrocytes), moderate apoptosis can occur even later and possibly contribute to persistent infection [18]. In the particular case of Zika pathology, homeostasis disorder; involving a lack of apoptosis control, a persistent inflammatory response and even viral persistence in the brain has been reported to explain the microcephaly observed in infected newborns [19].

In this study we examined the time course of cellular death associated with ZIKV infection. We confirm that, in A549 cells infected with the epidemic strain from Asian lineage (BeH819015, BR15MC), apoptosis is quantitatively moderate and occurs late, after the maximum production of viral progeny. We investigated whether this delay was due to a protective e ffect of the virus itself. When intrinsic or extrinsic apoptosis was induced within 2 h after infection, we could observe a significant decrease in cell death. As this protection was also obtained in cells expressing ZIKV "replicons", we deduced that viral replication was e fficient at inhibiting apoptosis. ABT-737, an inhibitor of the anti-apoptotic Bcl-2 family proteins, abrogates the protective e ffects provided by ZIKV. This implies that, with a subversion mechanism that remains to be elucidated, ZIKV is able to maintain an anti-apoptotic status in infected cells while it completes its viral cycle.
