Bunyaviridae

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Bunyaviridae

• Clayton M. Johnston

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Bunyaviridae

• Largest family of mammal affecting viruses (250
  viruses)
• Arthropod- or rodent-borne vectors
• Most are amplified in vertebrate hosts

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Bunyaviridae
Genus Disease(s)
Bunyavirus LaCrosse encephalitis
Phlebovirus Rift Valley Fever
Nairovirus Crimean-Congo Hemorrhagic Fever
Tospovirus Plant Virus
Hantavirus Hemorrhagic Fever with Renal Syndrome Hantavirus Pulmonary Syndrome
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Structure

• Virion Structure
• Genomic Structure
• Structural Proteins

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Virion Structure

• Spherical
• 80-120 nm diameter
• Enveloped
• Helical nucleocapsid
• NO matrix protein

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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

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Structural Proteins

• Membrane Glycoproteins
• Nucleocapsid Protein
• Viral Polymerase

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Structural Proteins
Membrane glycoproteins (G1 and G2)
Polymerase (L)
Nucleocapsid proteins (N)
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Membrane Glycoproteins

• G1 and G2
• Integral membrane proteins
• Important in cell entry and pathogenesis

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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

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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

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Viral Replication

• Receptor mediated endocytosis
• Occurs in cytoplasm
• Budding at Golgi apparatus or cell membrane

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Hantavirus Replication Cycle

• Attachment
• Entry and Uncoating
• Primary Transcription
• Translation
• Genome Replication
• Secondary Transcription
• Virion Assembly
• Virion Release

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Attachment

• Viral G1 and G2 glycoproteins interact with cell
  surface receptors
• Pathogenic hantavirus bind ß3 integrins
• Non-pathogenic hantaviruses bind ß1 receptors

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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

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Attachment and Entry
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Primary Transcription

• Transcription of negative sense vRNA to mRNA
• Viral polymerase transcribes nucleoprotein-coated
  vRNA
• Capped oligonucleotides from cells own mRNA are
  used to prime transcription (similar to Influenza
  virus)

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Translation

• L and S segments of mRNA are translated on free
  ribosomes in cytoplasm
• M segment mRNA is translated on ER-bound ribosomes

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Translation
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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

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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

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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

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Virion Assembly
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Virion ReleaseTwo 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

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Attachment
Entry
Uncoating
Release
Transcription
Replication
Assembly
Translation
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LaCrosse EncephalatisBunyavirus

• 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

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LaCrosse EncephalatisBunyavirus

• Targets the brain
• Symptoms may include
• Fever
• Convulsions
• Drowsiness
• Focal neurological signs

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Rift Valley FeverPhlebovirus

• 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

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Rift Valley FeverPhlebovirus

• Febrile disease in humans
• Targets the liver
• Symptoms often include
• Fever
• Encephalitis
• Retinal vasculitis (which may lead to blindness)

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Rift Valley FeverDistribution Map
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Crimean-Congo Hemorrhagic FeverNairovirus

• 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

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Crimean-Congo Hemorrhagic FeverNairovirus
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Hantavirus

• Enveloped
• ssRNA
• Virions 98 nm in diameter
• Genome consists of three RNA segments

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TransmissionVectors

• 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)

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Hemorrhagic Fever with Renal SyndromeHantavirus

• Liver and vascular enothelium are targeted
• Symptoms include
• Hemorrhage
• Acute renal failure
• Fever
• Over 15 mortality rate

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Hantavirus Pulmonary SyndromeHantavirus

• Lungs are targeted
• Symptoms include
• Fever
• Acute respiratory distress
• Over 50 mortality rate
• Shock and cardiac complications often contribute
  to death

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Prevention and Control

• Vaccines
• Hygiene
• Vector Control

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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

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Hygiene

• Prevent aerosolization of virus from roden
  excrement
• Dampen surfaces with bleach before cleaning
• Control rodents and human contact with rodents

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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

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Treatment

• Early aggressive intensive care
• Early use of inotropic agents (Dobutamine)
• Early ventilation
• Careful monitoring
• Oxygenation
• Fluid balance
• Blood pressure

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Treatment

• General care, alleviation of symptoms
• Ribavirin (Hemorrhagic Fever with Renal Syndrome)
• ECMO (Hantavirus Pulmonary Syndrome)

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Ribavirin

• Administered intravenously
• Shown to be effective against Hemorrhagic Fever
  with Renal Syndrome
• Not shown to be effective against Hantavirus
  Pulmonary Syndrome causing strains

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Extra Corporeal Membrane Oxygenation(ECMO)

• Removes blood from the body and artificially
  removes CO2 and adds O2
• Costly
• Difficult

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ECMO
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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

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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

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• 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. ONeal 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 530 a.m. Thursday.

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• 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.