1. health and fitness
2. disease
3. aids and hiv

General Virology
Shape of Viruses
 Spherical
 Rod-shaped
 Brick-shaped
 Tadpole-shaped
 Bullet-shaped
 Filament
Shapes of Viruses:Spherical
Shapes of Viruses :Rod-shaped
Shapes of Viruses :Brick-shaped
.
Tadpole-shaped
Shapes of Viruses
:Bullet-shaped
Shapes of Viruses
:Filament
Definition of Virus
Viruses may be defined as acellular organisms whose
genomes consist of nucleic acid, and which obligately
replicate inside host cells using the host cell
metabolic machinery and ribosomes to form a pool of
components which assemble into particles called
VIRIONS, which serve to protect the genome and to
transfer it to other cells
Viral Properties
 Viruses are obligate intracellular parasites
 Viruses cannot make energy or proteins
independent of a host cell
 Viral genome are RNA or DNA but not both.
 Viruses have a naked capsid or envelope with
attached proteins
 Viruses do not have the genetic capability to
multiply by division.
Consequences of Viral Properties
 Viruses are not living
 Viruses must be able to use host cell processes
to produce their components (viral messenger
RNA, protein, and identical copies of the
genome)
 Viruses must encode any required processes
not provided by the cell
 Viral components must self-assemble
Structure of Viruses
Virion
 the complete infectious unit of virus
particle
 Structurally mature, extracellular virus
particles.
Virion
envelope
Capsid
Viral core
Genome
 The genome of a virus can be either DNA or RNA
 DNA-double stranded (ds): linear or circular
Single stranded (ss) : linear or circular
 RNA- ss: segmented or non-segmented
ss: polarity+(sense) or polarity –(non-sense)
ds: linear (only reovirus family)
Viral Capsid
 The protein shell, or coat, that encloses the nucleic acid
genome.
 Capsomer: subunit of capsid (one or several proteins)
 Functions
-Protect the viral nucleic acid
-Participate in the viral infection (i.e. mediate attachment
to specific receptors on host cell)
-Share the antigenicity
Nucleocapsid
 The core of a virus particle
consisting of the genome plus a
complex of proteins.
 complex of proteins = Structural
proteins
+Non- Structural proteins (Enzymes and
nucleic acid binding proteins)
Symmetry of Nucleocapsid
 Helical
 Cubic /Icosahedral/Spherical
 Complex
Helical symmetry
Capsomers are arranged
in a hollow coil
Viruses with helical
symmetry possess
envelope
Influenza Virus (Flu Virus)
Measles Virus
Mumps Virus
Parainfluenza Virus
Rabies Virus
Respiratory Syncytial Virus(RSV)
Cubic or icosahedral symmetry
20 triangles
Icosahedral
 Adeno-associated Virus (AAV)  Herpes Simplex Virus 1 (HHV1)
Adenovirus
B19
Coxsackievirus - A
Coxsackievirus - B
Cytomegalovirus (CMV)
Eastern Equine Encephalitis
Virus (EEEV)
Echovirus
Epstein-Barr Virus (EBV)
Hepatitis A Virus (HAV)
Hepatitis B Virus (HBV)
Hepatitis C Virus (HCV)
Hepatitis Delta Virus (HDV)
Hepatitis E Virus (HEV)
Herpes Simplex Virus 2 (HHV2)
Human Immunodeficiency Virus (HIV)
Human T-lymphotrophic Virus (HTLV)
Norwalk Virus
Papilloma Virus (HPV)
Polio virus
Rhinovirus
Rubella Virus
Saint Louis Encephalitis Virus
Varicella-Zoster Virus (HHV3)
Western Equine Encephalitis Virus
(WEEV)
Yellow Fever Virus
Complex Virus Structures
 A well known example is the
tailed bacteriophages such as
T4.
 The head of these viruses is
cubic with a triangulation
number of 7. This is attached
by a collar to a contractile tail
with helical symmetry.
Viral proteins
 Surface proteins mediate attachment to host
cell receptors
 Targets of antibody (good antigens, induce
protective immune response)
 Some internal proteins are DNA or RNA
polymerases
 Matrix proteins mediate the interaction
between nucleocapsid proteins and the
envelope proteins
Envelope
A lipid-containing membrane that surrounds some viral particles.
It is acquired during viral maturation by a budding process through a
cellular membrane
Properties of enveloped viruses
 Labile in dry , arid environment
 Damaged by drying, acid, detergent, and
heat
 Pick up new cell membrane during
multiplication
 Insert new virus-specific proteins after
assembly
 Virus is released by budding
Consequences of Properties for enveloped
viruses
 Must stay moist
 Must not infect the GI tract for survival
 Must be transmitted in the protective droplets,
secretions, blood and body fluids
 Must reinfect another host cell to sustain
 Humoral and cell-mediated immunity are needed to
control the infection
Enveloped









California Encephalitis Virus
Coronavirus
Cytomegalovirus (CMV)
Eastern Equine Encephalitis Virus
(EEEV)
Epstein-Barr Virus (EBV)
Hantavirus
Hepatitis B Virus (HBV)
Hepatitis C Virus (HCV)
Hepatitis Delta Virus (HDV)
Herpes Simplex Virus 1 (HHV1)
Rotavirus
Rubella Virus
Saint Louis Encephalitis Virus
Smallpox Virus (Variola)
Vaccinia Virus
 Herpes Simplex Virus 2
(HHV2)
Human Immunodeficiency
Virus (HIV)
Human T-lymphotrophic Virus
(HTLV)
Influenza Virus (Flu Virus)
Molluscum contagiosum
Papilloma Virus (HPV)
Polio virus
Rhinovirus
Varicella-Zoster Virus (HHV3)
Venezuelan Equine Encephal.
Vir. (VEEV)
Western Equine Encephalitis
Virus (WEEV)
Yellow Fever Virus
Properties of naked viruses





Stable in hostile environment
Not damaged by drying, acid, detergent, and heat
Released by lysis of host cells
Can sustain in dry environment
Can infect the GI tract and survive the acid and
bile
 Can spread easily via hands, dust, fomites, etc
 Can stay dry and still retain infectivity
 Neutralizing mucosal and systemic antibodies are
needed to control the establishment of infection
Naked viruses (non enveloped )
Adenovirus
B19
Coxsackievirus - A
Coxsackievirus - B
Echovirus
Hepatitis A Virus (HAV)
Hepatitis E Virus (HEV)
Norwalk Virus
CLASSIFICATION OF VIRUSES
 Virion morphology
 Physicochemical properties of the virion
 Virus genome properties
 Virus protein proteries
 Genome organization and replication
 Antigenic properties
 Biologic properties
RNA-containing Viruses
 Picornaviruses
 Retroviruses
 Astroviruses
 Bunyaviruses
 Caliciviruses
 Othomyxoviruses
 Reoviruses
 Paramyxoviruses:
 Arboviruses
 Rhabdoviruses:rabies virus
 Togaviruses
 Filoviruses
 Flaviviruses
 Other viruses
 Arenaviruses
 Viroids
 Coronaviruses: SARS
Viral Pathogenesis
 Viral pathogenesis is the process by which a
viral infection leads to disease.
 The majority of viral infections are subclinical.
It is not in the interest of the virus to severely
harm or kill the host.
 The consequences of viral infections depend
on the interplay between a number of viral and
host factors.
Viral Entry
 Skin - Most viruses which infect via the skin require a breach in the
physical integrity of this effective barrier, e.g. cuts or abrasions.
Many viruses employ vectors, e.g. ticks, mosquitos or vampire bats
to breach the barrier.
 Conjunctiva and other mucous membranes - rather exposed site
and relatively unprotected
 Respiratory tract - In contrast to skin, the respiratory tract and all
other mucosal surfaces possess sophisticated immune defense
mechanisms, as well as non-specific inhibitory mechanisms
(ciliated epithelium, mucus secretion, lower temperature) which
viruses must overcome.
 Gastrointestinal tract - a hostile environment; gastric acid, bile
salts, etc. Viruses that spread by the GI tract must be adapted to this
hostile environment.
 Genitourinary tract - less frequently
Outcome of Viral Infection
 Acute Infection

Recovery with no residue effects

Recovery with residue effects e.g. acute viral encephalitis leading to
neurological sequelae.
Death
Proceed to chronic infection


 Chronic Infection





Silent subclinical infection for life e.g. CMV, EBV
A long silent period before disease e.g. HIV, SSPE, PML
Reactivation to cause acute disease e.g. herpes and shingles.
Chronic disease with relapses and excerbations e.g. HBV, HCV.
Cancers e.g. EBV, HTLV-1, HPV, HBV, HCV, HHV-8
Virus shedding
 Frequently at the portal of entry
 Skin, mucous membranes: HSV, HPV
 Resp. tract: aerosol (influenzav.)
 Intestinal tract: faeces (Rotav.)
 Genital secretions: HIV, HBV, CMV
 Milk: HTLV-I, (HIV), encephalitis viruses
 Blood: HIV, HBV, HCV, CMV, HTLV-I
Viral Clearance or Persistence
 The majority of viral infections are cleared but certain
viruses may cause persistent infections. There are 2
types of chronic persistent infections.
 True Latency - the virus remains completely latent
following primary infection e.g. HSV, VZV. Its
genome may be integrated into the cellular genome or
exists as episomes.
 Persistence - the virus replicates continuously in the
body at a very low level e.g. HIV, HBV, CMV, EBV.
Mechanisms of persistence
 Limited cytopathic effect
 Persistence in non-dividing cells (HSV)
 Constant replication of the viral genome (HPV)
 Integration of the viral genome into host genome (HIV)
 Evading the immune response
 EBV latency in B lymphocytes (EBNA-1)
 Persistence in special sites (CMV, HPV)
 Immunosuppression (HIV)

MHC-I és MHC-II inhibition (adenov. , HIV)
Prions
 Protein only
 No DNA or RNA
 Encoded by cellular gene
 Alpha helix changes to beta-bleated sheet
 No antibody response
 They are inactivated by hypochlorite, NaOH
and autoclaving