Zika Fetal Neuropathogenesis: Etiology of a Viral Syndrome

The ongoing Zika Virus epidemic in the Americas, and the observed association with both fetal abnormalities (primary microcephaly) and adult autoimmune pathology (Guillain-Barre syndrome) has brought attention to this neglected pathogen. While initial case studies generated significant interest in the Zika virus outbreak, larger prospective epidemiology and basic virology studies examining the mechanisms of Zika viral infection and associated pathophysiology are only now starting to be published. In this review, we analyze Zika fetal neuropathogenesis from a comparative pathology perspective, using the historic metaphor of \"TORCH\" viral pathogenesis to provide context. By drawing parallels to other viral infections of the fetus, we identify common themes and mechanisms that may illuminate the observed pathology. The existing data on the susceptibility of various cells to both Zika and other flavivirus infections are summarized. Finally, we highlight relevant aspects of the known molecular mechanisms of flavivirus replication.\n\nKey Learning PointsO_LIViral TORCH pathogens reveal common patterns of fetal pathophysiology and vertical transmission which are relevant to Zika Virus fetal neuropathogenesis.\nC_LIO_LIThe teratogenic effects of Zika Virus infection during the first trimester may involve infection of the trophoblast, viral translocation across the placenta, migration of infected cells resulting in embryonic infection, or indirect effects associated with high levels of inflammatory cytokines produced by infected placenta.\nC_LIO_LIPre-existing maternal non-neutralizing antibody to Zika virus may enhance the probability of infection or more severe disease in the fetus.\nC_LIO_LIAXL has been identified as a major receptor for Zika Virus.\nC_LIO_LIZika virus activation of Toll Like Receptor 3 (TLR-3) pathways in central nervous system cells may trigger apoptosis and attenuate neurogenesis, directly contributing to fetal neuropathology.\nC_LIO_LIFlaviviruses subvert host autophagy and noncoding RNA regulatory pathways.\nC_LIO_LIRecognition of viral sequences by regulatory RNA binding proteins such as Musashi may have a role in Zika pathogenesis and host tissue tropism.\nC_LIO_LIEvidence from other TORCH viral pathogen studies indicate multiple plausible hypotheses for transplacental infection by Zika virus during the second or third trimester, including transcytosis of non-neutralizing antibody-coated Zika virus complexes.\nC_LI\n\nKey ReferencesAdibi JJ, Marques ET Jr, Cartus A, Beigi RH. Teratogenic effects of the Zika virus and the role of the placenta. Lancet 2016; 387: 1587-90 (Hypothesis)\nAdams Waldorf KM, McAdams RM. Influence of infection during pregnancy on fetal development. Reproduction. 2013 Oct 1;146(5) (Review)\nHamel R, Dejarnac O, Wichit S, Ekchariyawat P, Neyret A, Luplertlop N, et al. Biology of Zika Virus Infection in Human Skin Cells. J Virol. 2015;89(17):8880-96.\nMlakar J, Korva M, Tul N, Popovi[c] M, Polj[s]ak-Prijatelj M, Mraz J, et al. Zika Virus Associated with Microcephaly. N Engl J Med. 2016 Feb 10.\nPaul LM, Carlin ER, Jenkins MM, Tan AL, Barcellona CM, Nicholson CO, Trautmann L, Michael SF, Isern S. Dengue Virus Antibodies Enhance Zika Virus Infection. bioRxiv doi: http://dx.doi.org/10.1101/050112\nCrow YJ, Manel N. Aicardi-Goutieres syndrome and the type I interferonopathies. Nat Rev Immunol. 2015;15(7):429-40.\nTonduti D, Orcesi S, Jenkinson EM, Dorboz I, Renaldo F, Panteghini C, et al. Clinical, radiological and possible pathological overlap of cystic leukoencephalopathy without megalencephaly and Aicardi-Goutieres syndrome. Eur J Paediatr Neurol. 2016.\nCipolat Mis MS, Brajkovic S, Frattini E, Di Fonzo A, Corti S. Autophagy in motor neuron disease: Key pathogenetic mechanisms and therapeutic targets. Molecular and Cellular Neurosciences. 2016;72:84-90.\nDang J, Tiwari SK, Lichinchi G, Qin Y, Patil VS, Eroshkin AM, Rana TM. Zika Virus Depletes Neural Progenitors in Human Cerebral Organoids through Activation of the Innate Immune Receptor TLR3. Cell Stem Cell. 2016: 19: 1-8.\nVianna FS, Schuler-Faccini L, Leite JC, de Sousa SH, da Costa LM, Dias MF, et al. Recognition of the phenotype of thalidomide embryopathy in countries endemic for leprosy: new cases and review of the main dysmorphological findings. Clin Dysmorphol. 2013;22(2):59-63.