Viruses
Prof. Khaled H. Abu-Elteen
Hashemite University
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.
Virus facts
• generally more resistant to some
disinfectants than most bacteria.
• most are susceptible to heat, except hepatitis
virus
• not affected by antibiotics
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:
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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
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
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:
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Capsid = protein coat
Structural unit = protein subunit
Nucleocapsid = nucleic acid + protein
Virion = virus particle
• Capsid proteins are compactly folded proteins which:
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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
Basic virus structure
DNA
or
+
Capsid
protein
Nucleocapsid
=
Naked
capsid virus
RNA
Nucleocapsid
+
Lipid membrane,
glycoproteins
Enveloped virus
Capsid symmetry
Icosahedral
Helical
Naked capsid
Enveloped
Matrix
Lipid
Glycoprotein
Icosahedral naked capsid viruses
Adenovirus
Electron micrograph
Foot and mouth disease virus
Crystallographic model
Helical naked capsid viruses
RNA
Tobacco mosaic virus
Electron micrograph
Protein
Tobacco mosaic virus
Model
Icosahedral enveloped viruses
Herpes simplex virus
Electron micrograph
Herpes simplex virus
Nucleocapsid cryoEM model
Helical enveloped viruses
Influneza A virus
Electron micrograph
Paramyxovirus
Electron micrograph
Properties of enveloped viruses
• Envelope is sensitive to
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Drying
Heat
Detergents
Acid
• Consequences
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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
Properties of naked capsid viruses
• Capsid is resistant to
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Drying
Heat
Detergents
Acids
Proteases
• Consequences
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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
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
Classification of viruses
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•
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on the basis of:
nucleic acid they contain ( DNA or RNA )
the size, shape and structure of the virus
the tissue the infect
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
Adeno viruses
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.
AIDS Virus
HIV
HIV
Herpes Simplex Virus I
Human T- cell Lymphotropic Virus
(HTLV)
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.
Herpes Simplex Type II Virus
Herpes Simplex Type II Virus
Herpes Simplex Type II Virus
Herpes Simplex Type I Virus
Hepatitis
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•
•
•
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
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 period—up 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.
Hepatitis C
• Blood borne pathogen.
• Also found in water like HV-A
• Many become carriers
Hepatitis D
• Super-infects some patients who are
already infected with HBV.
• HBV is required as a helper to initiate
infection.
• blood borne.
Hepatitis A Virus
Hepatitis B: Causes
Hepatitis B
Hepatitis C: Getting Tattoos
Infectious mononucleosis
Picorna Virus
Picorna Virus
Primary site of infection is lymphoid tissue
associated with the oropharynx and gut
(GALT).
Polio Virus
Poliomyelitis
Human Papilloma Virus
Genital Warts - HPV
• Causes genital warts
Measles
Mumps
German Measles (Rubella)
Chicken pox
Chicken Pox
Active lesions
Small pox
AIDS
Candida albicans
Kaposi’s Sarcoma
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.
HIV
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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
AIDS
• Retrovirus- an RNA virus that carries an enzyme
capable of forming DNA from RNA.
• Aids virus infects T. Lymphocytes (Helper Tcells)
• 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
AIDS
• More common in I.V. drug users & homosexuals.
• Pneumocytic carinii infection and blood vessel
malignancy-Kaposi’s Sarcoma
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