Transcript Document
Bunyaviridae Clayton M. Johnston Bunyaviridae • Largest family of mammal affecting viruses (250 viruses) • Arthropod- or rodent-borne vectors • Most are amplified in vertebrate hosts Bunyaviridae Genus Disease(s) Bunyavirus LaCrosse encephalitis Phlebovirus Rift Valley Fever Nairovirus Tospovirus Crimean-Congo Hemorrhagic Fever Plant Virus Hantavirus Hemorrhagic Fever with Renal Syndrome Hantavirus Pulmonary Syndrome Structure • Virion Structure • Genomic Structure • Structural Proteins Virion Structure • • • • • Spherical 80-120 nm diameter Enveloped Helical nucleocapsid NO matrix protein Genomic Structure • (-) sense • Linear ssRNA • Three segments: – Large (L) codes for viral polymerase – Medium (M) codes for G1 and G2 glycoproteins – Small (S) codes for nucleocapsid Structural Proteins • Membrane Glycoproteins • Nucleocapsid Protein • Viral Polymerase Structural Proteins Membrane glycoproteins (G1 and G2) Nucleocapsid proteins (N) Polymerase (L) Membrane Glycoproteins • G1 and G2 • Integral membrane proteins • Important in cell entry and pathogenesis Nucleocapsid Protein • Complexes with genomic vRNA in virus, as well as with cRNA after infection, but not with mRNA • Necessary for virus replication and packaging Viral Polymerase • • • • RNA-dependent RNA polymerase Complexed with ribonucleocapsid in virion Endonuclease activity to cleave host mRNA Transcriptase activity for making cRNA and mRNA from vRNA • Helicase activity to unwind vRNA during transcription Viral Replication • Receptor mediated endocytosis • Occurs in cytoplasm • Budding at Golgi apparatus or cell membrane Hantavirus Replication Cycle • • • • • • • • Attachment Entry and Uncoating Primary Transcription Translation Genome Replication Secondary Transcription Virion Assembly Virion Release Attachment • Viral G1 and G2 glycoproteins interact with cell surface receptors • Pathogenic hantavirus bind β3 integrins • Non-pathogenic hantaviruses bind β1 receptors Entry and Uncoating • Virus particles bound to integrin receptors are taken in by receptor mediated endocytosis • Newly formed vesicles are acidified • Acidic environment changes confirmation of G1 and G2 glycoproteins • Viral and cell membranes fuse • Genomic material and polymerase are released into cytoplasm Attachment and Entry Primary Transcription • Transcription of negative sense vRNA to mRNA • Viral polymerase transcribes nucleoproteincoated vRNA • Capped oligonucleotides from cell’s own mRNA are used to prime transcription (similar to Influenza virus) Translation • L and S segments of mRNA are translated on free ribosomes in cytoplasm • M segment mRNA is translated on ERbound ribosomes Translation Genome Replication • vRNA is used as a template by viral polymerase to make cRNA • cRNA is used as a template to make more negative sense strands of vRNA Secondary Transcription • Extra vRNA synthesized during replication is used as template to make mRNA • Since more template is present after vRNA is replicated, more mRNA can be transcribed, and more viral proteins can be made • Persistent infection Virion Assembly • Membrane-bound G1 and G2 peptides are transported to Golgi apparatus and carbohydrates are attached by N-linked glycosylation • vRNA complexes with N nucleocapsid protein, forms looped panhandle structure, and complexes with polymerase Virion Assembly Virion Release Two Mechanisms • Nucleocapsid complexes bud into the Golgi membrane with G1 and G2 embedded • Virion particle is formed inside Golgi apparatus • Virions are transported to cell membrane by vesicles and released by exocytosis • G1 and G2 embed into cell membrane through Golgi vesicles • Virions bud from cell membrane, not through Golgi apparatus Attachment Entry Uncoating Release Transcription Replication Assembly Translation LaCrosse Encephalatis Bunyavirus • Mostly infects children younger than 16 • Ades mosquitoes are the common vector • Squirrels and chipmunks are the amplifying host • Most common bunyavirus infection in the United States LaCrosse Encephalatis Bunyavirus • Targets the brain • Symptoms may include: – – – – Fever Convulsions Drowsiness Focal neurological signs Rift Valley Fever Phlebovirus • Most spread by sandfly or Ades species of mosquitoes • Causes abortion in livestock • Highly infectious by aerosolized blood • Distribution follows that of the host vectors • Immunization of livestock is the most effective way to control and prevent the disease Rift Valley Fever Phlebovirus • Febrile disease in humans • Targets the liver • Symptoms often include: – Fever – Encephalitis – Retinal vasculitis (which may lead to blindness) Rift Valley Fever Distribution Map Crimean-Congo Hemorrhagic Fever Nairovirus • • • • Transmitted by ticks Appears in the Middle East and Africa Targets the liver and vascular endothelium Symptoms include: – Headache – Pain in limbs – Often bleeding from many orifices Crimean-Congo Hemorrhagic Fever Nairovirus Hantavirus • Enveloped • ssRNA • Virions 98 nm in diameter • Genome consists of three RNA segments Transmission Vectors • Transmitted via aerosolized rodent urine, feces, and saliva – – – – – – Deer mouse (Peromyscus maniculatus) Cotton rat (Sigmodon hispidus) White-footed mouse (Peromyscus leucopus) Striped field mours (Apodemus agrarius) Bank vole (Clethrionomys glareolus) Rat (Rattus) Hemorrhagic Fever with Renal Syndrome Hantavirus • Liver and vascular enothelium are targeted • Symptoms include: – Hemorrhage – Acute renal failure – Fever • Over 15% mortality rate Hantavirus Pulmonary Syndrome Hantavirus • Lungs are targeted • Symptoms include – Fever – Acute respiratory distress • Over 50% mortality rate • Shock and cardiac complications often contribute to death Prevention and Control • Vaccines • Hygiene • Vector Control Vaccines • E. coli expressed truncated nucleocapsid as an immunogen • Naked DNA • Recombinant non-pathogenic virus • Rodent brain-derived • Cell culture derived • Inactivated virus – being tried out in China Hygiene • Prevent aerosolization of virus from roden excrement • Dampen surfaces with bleach before cleaning • Control rodents and human contact with rodents Host Defenses and Immune Response • Interferon is produced • Humor antibody has been shown to be related to the disappearance of virus from blood • Cytotoxic T-cells attack infected host cells • Inflammatory response Treatment • • • • Early aggressive intensive care Early use of inotropic agents (Dobutamine) Early ventilation Careful monitoring: – Oxygenation – Fluid balance – Blood pressure Treatment • General care, alleviation of symptoms • Ribavirin (Hemorrhagic Fever with Renal Syndrome) • ECMO (Hantavirus Pulmonary Syndrome) Ribavirin • Administered intravenously • Shown to be effective against Hemorrhagic Fever with Renal Syndrome • Not shown to be effective against Hantavirus Pulmonary Syndrome causing strains Extra Corporeal Membrane Oxygenation (ECMO) • Removes blood from the body and artificially removes CO2 and adds O2 • Costly • Difficult ECMO Laboratory Diagnosis • Serology (ELISE for IgM) • Immunohistochemistry • Reverse transcription and polymerase chain reaction (RT-PCR) • Virus isolation • Direct detection of antigen in blood and urine • Immunofluorescent test for antibodies Problems Diagnosing Hantavirus • Symptoms often confused with influenza • Common signs of upper respiratory disease such as sore throat, sinusitis, and ear pain not usually present • Abdominal pain often misinterpreted as appendicitis • Many doctors outside endemic regions fail to recognize or have sufficient testing Friday, March 26, 2004 PARKS AND PEOPLE Glacier National Park Death of Jerry O'Neal The employees of Glacier National Park are deeply saddened to learn of the untimely passing of Deputy Superintendent Jerry O'Neal. O’Neal died early yesterday morning at a Kalispell, Mont., hospital following a brief illness. O'Neal, 61, came down with an unknown illness last week and had undergone blood work and other diagnostic tests over the past few days. He was admitted to the Kalispell Regional Medical Center on Wednesday and died at 5:30 a.m. Thursday. Friday, April 2, 2004 OPERATIONS NOTE Public Health Hantavirus Update In view of the untimely death of Glacier National Park Deputy Superintendent Jerry O'Neal on March 25th from hantavirus pulmonary syndrome, we are issuing the following precautions and annual reminders. Hantavirus pulmonary syndrome (HPS) is a viral disease transmitted to humans primarily through the inhalation of airborne dusts laden with the virus from infected rodent droppings (urine and saliva may also be sources of infection). Although hantaviruses have been a threat to human health worldwide for at least 50 years, HPS was first recognized in the United States in 1993 around the Four Corners area of the Southwest. Since then it has since been identified throughout the United States. Although rare, HPS is potentially deadly – mortality rates between 40 and 50% are common.