Lecture Overview • Structure Filoviridae & the Ebola Virus • Virus Replication Cycle – Protein Synthesis • Pathogenesis Presented by David Gerber Filoviridae Family Structure • Filo: from latin meaning threadlike1 • Pleimorphic, • Structurally & Genetically similar to Filamentous Rhabdoviridae and Paramyxoviridae • Striated • 80nm diameter • Two Genera: • 130-140,000nm long – Marburg-like virus • Enveloped – Ebola-like virus Genome Ebola Virus Proteins • GP- Transmembrane glycoprotein • NP- Nucleoprotein necessary for capsid assembly • VP24- Anti-viral inhibitor? • VP35- Inhibits IFN production • Negative Sense ssRNA • VP30- Transcription anti-terminator • Unsegmented • VP40- necessary for capsid assembly and budding • 7 proteins •L-Viral Polymerase • Gene overlap 1 Replication Cycle Replication cont. 2 1 Host Entry 2 Adsorption- Glycoprotein (GP1) binds 3 - Contact with infected bodily fluids cellular receptor - Mediated by cellular cofactors. i.e. folate receptor α - Enters through mucous membrane or - Mononuclear phagocytic cells & monocytes are directly into blood (needle stick) primary targets4 - No confirmed spreading of virus by 3 Endocytosis aerosol in nature -pH lowering in endosome -GP2 mediates membrane fusion; release of viral particle into cytoplasm Replication Cont. Ebola Glycoprotein 4 Protein Synthesis - requires viral polymerase (L) • GP1/GP2- transmembrane protein - VP30 anti-terminator allows transcription of genes downstream – Binding/Fusion from first gene (Ebola Only) - VP35 prevents anti-viral response to dsRNA 5 • sGP- truncated soluble protein (Ebola Only) – Secreted -GP synthesis1 -Complex post-translational processing – Decoy for immune system? - O-linked/N-linked glycosylation - proteolitic cleaving by proteases • Give rise to neutralizing & protective antibody - acylation Glycoprotein Synthesis Replication cont. 5 Virus Assembly & release - Exact mechanism not known - NP essential for RNA packaging -VP40 essential for Budding at membrane -VP40 and GP give filamentous morphology Complete Virion contains: ssRNA, NP, VP35, VP24, L, VP30 (Ebola Only) 2 Ebola Virus: Interactions With Immune Interaction with Immune System Cont. System • Innate Immune System • Over expression of proinflammatory signals • Monocytes Primary targets – Cytokines – Does not clear infection – Carry virus throughout body • VP35 inhibition of IRF3 – Lysis releases cytokines – No transcription of IFN genes • Early infection of Dendritic Cells6 – No antiviral response to dsRNA – Delays specific immune response • Inhibition/Destruction of immune cells – Neutrophils & macrophages Pathogenesis Pathogenesis • Glycoprotein responsible for CPE of virus • Massive Immune Response – Breakdown of extracellular matrix • Activation of macrophages and monocytes • Rounding and detachment of endothelial cells – Clumping may cause coagulation observed in • sGP inhibits Neutrophils some clinical cases – Evidence suggests virus does NOT directly – Proinflammotory signals released cause most of the disease pathology • Cytokines, TNF, IFN • Breaks downs endothelial barrier • Blood leaks into tissue- blood pressure drops-Shock most frequent cause of death. Ebola Hemorrhagic Fever Ebola Hemorrhagic Fever • 2-21 day incubation period • Not known why some are able to survive • Abrupt onset: flu-like symptoms • Larger Early Immune response in those that – Fever, headache, muscle aches, stomach pains do • Rash, red eyes, internal/external bleeding • Virus May remain up to 3 months • Death (50-90% according to WHO) – Convalescents potential human reservoir – Virus present in seminal fluid 3 Treatment/Vaccine Ebola as a Biological Weapon • No effective treatment • As late as 1992 Russia was producing large – Research on treating inflammatory immune quantities of Ebola virus for use as a weapon. response – No vaccine • Anti-INF, Anti-cytokine antibodies – No treatment • Steroids – High infectivity (as few as 17 particles necessary to cause disease) • No approved vaccine – Can potentially be spread by aerosols – GP protective antibodies • Japanese Terrorist Cult, Aum Shinrikyo, • Also immunosuppressive unsuccessfully attempted to obtain Ebola virus References 1 Filoviruses. University of Leicester Department of Microbiology. www.micro.msb.le.ac.uk/3035/Filoviruses.html 2 Center for Disease Control Ebola Hemorrhagic Fever. www.cdc.gov/ncidod/dvrd/spb/mnpages/ebola.htm 3 H.D. Klenk, H. Feldmann eds. Ebola and Marburg Viruses: Molecular and Cellular Biology. Horizon Bioscience, Norfolk, U.K: 2004 4 U. Stroher, E. West, H Bugany, H.D. Klenk, H.J Schnittler, H. Feldmann. Infection and Activation of Monocytes by Marburg and Ebola Viruses. J Virol. 75(22) Nov 2001: 11025-11033 5 C.F. Basler, A. Mikulasova, L. Martinex-Sorbido, J. Paragas, E. Muhlberger, M. Bray, H.D. Klenk, P. Palese, A. Garcia-Sastre. The Ebola virus VP35 protein inhibits activation of interferon regulatory factor 3. J Virol. 77(14) Jul 2003: 7945-56. 6 CM Bosio, MJ Aman, C Grogan, R Hogan, G Ruthel, D Negley, M Mohamadzadeh, S Bavari, A Schmaljohn. Ebola and Marburg viruses replicate in monocyte derived dendritic cells without inducing the production of cytokines and full maturation. 7 Borio et al. Hemorrhagic fever as biological weapons. JAMA 287(18) May 8, 2002, 2391-2405. 4.