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:
– 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:
– 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

Basic virus structure
Capsid
protein
Nucleocapsid
Naked
capsid virus
DNA
RNA
or =
+
Nucleocapsid
Lipid membrane,
glycoproteins
Enveloped virus
+

Capsid symmetry
Icosahedral Helical
Naked capsid
Enveloped
Lipid
Glycoprotein
Matrix

Icosahedral naked capsid viruses
Adenovirus
Electron micrograph
Foot and mouth disease virus
Crystallographic model

Helical naked capsid viruses
Tobacco mosaic virus
Electron micrograph
Tobacco mosaic virus
Model
RNA Protein

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
– 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

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

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
• 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
• 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
• 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 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

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