Viruses

1
Viruses

• Prof. Khaled H. Abu-Elteen
• Hashemite University

2
Viruses

• smallest infections agents
• intracellular parasites-can reproduce only in
  host cells.
• can not carry on independent metabolism
• first virus discovered was tobacco mosaic virus
  TMV in 1892.
• in 1931 virus cultured in the lab using tissue
  culture.
• viruses are not cellular
• consist only of a nucleic acid either DNA or RNA,
  surrounded by a protein coat.

3
Virus facts

• generally more resistant to some disinfectants
  than most bacteria.
• most are susceptible to heat, except hepatitis
  virus
• not affected by antibiotics

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VIRUS STRUCTURE

• Basic rules of virus architecture, structure, and
  assembly are the same for all families, some
  structures are much more complex than others.
• The capsid (coat) protein is the basic unit of
  structure functions that may be fulfilled by the
  capsid protein are to
• Protect viral nucleic acid
• Interact specifically with the viral nucleic acid
  for packaging
• Interact with vector for specific transmission
• Interact with host receptors for entry to cell
• Allow for release of nucleic acid upon entry into
  new cell
• Assist in processes of viral and/or host gene
  regulation

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Nucleoprotein has two basic structure types

• HELICAL Rod shaped, varying widths and specific
  architectures no theoretical limit to the amount
  of nucleic acid that can be packaged
• CUBIC (Icosahedral) Spherical, amount of nucleic
  acid that can be packaged is limited by the of
  the particle
• Virus structure is studied by
• Transmission electron microscopy (EM)
• Cryo EM one of the most powerful methods
  currently available
• X-Ray diffraction

6
Principles of basic virus structure

• Nucleoprotein must be stable but dissociatable
• Capsid is held together by non-covalent,
  reversible bonds hydrophobic, salt, hydrogen
  bonds
• Capsid is a polymer of identical subunits
• Terms
• Capsid protein coat
• Structural unit protein subunit
• Nucleocapsid nucleic acid protein
• Virion virus particle
• Capsid proteins are compactly folded proteins
  which
• Fold only one way, and robustly
• Vary in size, generally 50-350 aa residues
• Have identifiable domains
• Can be described topologically similar
  topological features do not imply evolutionary
  relationships

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Basic virus structure
Capsid protein
Naked capsid virus
Nucleocapsid


Lipid membrane, glycoproteins
Enveloped virus
Nucleocapsid

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Capsid symmetry
Icosahedral
Helical
Naked capsid
Enveloped
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Icosahedral naked capsid viruses
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Helical naked capsid viruses
RNA
Protein
Tobacco mosaic virus Electron micrograph
Tobacco mosaic virus Model
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Icosahedral enveloped viruses
Herpes simplex virus Electron micrograph
Herpes simplex virus Nucleocapsid cryoEM model
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Helical enveloped viruses
Influneza A virus Electron micrograph
Paramyxovirus Electron micrograph
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Properties of enveloped viruses

• Envelope is sensitive to
• Drying
• Heat
• Detergents
• Acid
• Consequences
• Must stay wet during transmission
• Transmission in large droplets and secretions
• Cannot survive in the gastrointestinal tract
• Do not need to kill cells in order to spread
• May require both a humoral and a cellular immune
  response

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Properties of naked capsid viruses

• Capsid is resistant to
• Drying
• Heat
• Detergents
• Acids
• Proteases
• Consequences
• Can survive in the gastrointestinal tract
• Retain infectivity on drying
• Survive well on environmental surfaces
• Spread easily via fomites
• Must kill host cells for release of mature virus
  particles
• Humoral antibody response may be sufficient to
  neutralize infection

15
Atomic Resolution Microscope at UC Berkeley The
Atomic Resolution Microscope is specifically
designed for performance in the high resolution
imaging mode with a point-to-point resolution of
1.5Å.
Typical modern transmission EM This JEOL
Transmission Electron Microscope, similar to the
one we use at Rutgers, is housed at Colorado
State University
16
Classification of viruses

• on the basis of
• nucleic acid they contain ( DNA or RNA )
• the size, shape and structure of the virus
• the tissue the infect

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DNA viruses

• i) Poxivirus group (DNA) virus pathogenic to
  skin small pox, cow pox
• ii) Herpes virus group (DNA)
• Latent infection may occur and lasts the life
  span of the host.
• Cold sores
• Shingles
• Chicken pox
• iii) Adenovirus group (DNA)
• Catarrhs
• Conjunctivitis
• iv) Papovirus group (DNA)
• Wart virus

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Adeno viruses
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Adenovirus-Associated Human Disease
     Pharyngitis    Acute Respiratory Disease
   Pneumonia    Pharyngoconjunctival Fever
   Epidemic Keratoconjuntivitis   
Genitourinary Infections (cervicitis, urethritis
)    Gasteroenteritis    Some asymptomatic
and persistent infection    Adenovirus
oncogenically tranforms rodent cells but not
human cells.
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AIDS Virus
21
HIV
22
HIV
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Herpes Simplex Virus I
24
Human T- cell Lymphotropic Virus (HTLV)
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Human T- cell Lymphotropic Virus

• HTLV-1 stands for Human T-cell Lymphotropic
  Virus.
• It is a retrovirus, in the same class of virus as
  the AIDS virus, HIV-1.
• HTLV-I is associated with a rare form of blood
  dsycrasia known as Adult T-cell Leukemia/lymphoma
  (ATLL) and a myelopathy, tropical spastic
  paresis.
• However, even with infection, fewer than 4 of
  seropositive persons will experience overt
  associated disease.

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Herpes Simplex Type II Virus
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Herpes Simplex Type II Virus
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Herpes Simplex Type II Virus
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Herpes Simplex Type I Virus
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Hepatitis

• Hepatitis
• a. chemically induced
• b. viral infection A, B, C, D, E, F
• Viral hepatitis is the most common liver disease
  found worldwide.
• Epstein Barr virus
• Herpes virus
• Cytomegalovirus

31
Hepatitis B (HBV)

• DNA virus
• has an outer surface structure known as hepatitis
  B surface antigen (HBs Ag) an inner core
  component known as hepatitis B core Antigen (HBc
  Ag)
• Long incubation periodup to 6 months.
• Transmitted through blood contact.
• Some modes of transmission as those for HIV.
• HBV is very serious illness.
• Series of 3 immunizations are given on day 0, 30,
  180.

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Hepatitis C

• Blood borne pathogen.
• Also found in water like HV-A
• Many become carriers

33
Hepatitis D

• Super-infects some patients who are already
  infected with HBV.
• HBV is required as a helper to initiate
  infection.
• blood borne.

34
Hepatitis A Virus
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Hepatitis B Causes
36
Hepatitis B
37
Hepatitis C Getting Tattoos
38
Infectious mononucleosis
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Picorna Virus
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Picorna Virus
Primary site of infection is lymphoid tissue
associated with the oropharynx and gut (GALT).
41
Polio Virus
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Poliomyelitis
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Human Papilloma Virus
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Genital Warts - HPV

• Causes genital warts

45
Measles
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Mumps
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German Measles (Rubella)
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Chicken pox
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Chicken Pox

• Active lesions

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Small pox
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AIDS
Candida albicans
Kaposis Sarcoma
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HIV

• Incubation period (the period between becoming
  infected and the actual development of the
  symptoms)
• 6 months-5 or more years, up to 10 years.
• Sometimes a mild illness--flu like symptoms
  appears 7-14 days after infection
• Sometimes no symptoms appear for years.
• It is accepted that once infected with HIV, AIDS
  will develop at some time in the future in all
  cases.
• At present there is no cure.
• Opportunistic infections associated with AIDS can
  be treated.

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HIV

• HIV is carried in blood, semen, body fluids.
• usually fatal
• known to be dormant for years
• certain drug combinations slow the rate of
  invasion of the White Blood cells by the virus.
• cure is not yet on the horizon
• leading cause of death in young adults, aged 25-44

54
AIDS

• Retrovirus- an RNA virus that carries an enzyme
  capable of forming DNA from RNA.
• Aids virus infects T. Lymphocytes (Helper T-
  cells)
• patient may be asymptomatic before diagnosis
• affects the immune system
• patients are prone to develop opportunistic
  infections, malignancies, and neurological
• disorders
• fatal disease
• no treatment

55
AIDS

• More common in I.V. drug users homosexuals.
• Pneumocytic carinii infection and blood vessel
  malignancy-Kaposis Sarcoma

56
Atomic Resolution Microscope at UC Berkeley The
Atomic Resolution Microscope is specifically
designed for performance in the high resolution
imaging mode with a point-to-point resolution of
1.5Å.
Typical modern transmission EM This JEOL
Transmission Electron Microscope, similar to the
one we use at Rutgers, is housed at Colorado
State University