Transcript Introduction to virology cont.. What is virus

INTRODUCTION TO VIROLOGY
What is Virology:
Virology is the study of viruses and virus-like
agents: their structure, classification and
evolution, their ways of infection and exploitation
of cells for reproduction, the diseases they cause,
the techniques to isolate and culture them, and
their use in research and therapy
Introduction to virology cont..
• What is virus:
• Is an invasive biological agent
that reproduces inside the cells of living hosts
• In a host cell viruses produce many thousands
of identical copies of the original viruses, at an
extraordinary rate.
• Unlike most living things, viruses do not have
cells that divide
Introduction to virology cont..
• Viruses are not cells that are capable of
independent replication
• They neither synthesize their own energy nor
protein
• They are too small to be seen in the microscope
• New viruses assemble in the infected host cell
General Characteristics of Viruses:
• Viruses non-cellular, non-cytoplasmic infectious
agents.
• They are smaller than bacteria, and they can pass
through bacteriological filter.
• Viruses are transmissible from diseased to
healthy organisms.
• All viruses are obligate parasites and can multiply
only within the living host cells.
Characteristics….
• They are particles composed of internal core
containing nucleic acid (DNA or RNA) but not
both
• They are host specific that they infect only a
single species and definite cells of the host
organisms.
• They are effective in very small doses.
• They are highly resistant to germicides and
extremes of physical conditions
Taxonomy of Viruses
• Family names end in -viridae.
• Genus names end in -virus.
• Viral species: A group of viruses sharing
the same genetic information and
ecological niche (host). Common names
are used for species.
• Subspecies are designated by a number.
6
Taxonomy of Viruses cont…
• Herpesviridae
• Herpesvirus
• Human herpes
virus HHV-1, HHV2, HHV-3
• Retroviridae
• Lentivirus
• Human
immunodeficienc
y virus HIV-1,
HIV-2
7
Viral structure
Shape and size
• The shapes vary.
• They may be spherical or
• Golf ball-like
• Rod-shaped
• Tadpole-like
• Helical or Polyhedral.
Viral structure cont…
• Chemical structure and function:
• Viruses have a very simple structure.
• The core of the viruses is made upon of
nucleic acid, which is surrounded by a protein
coat called capsid.
• The nucleic acid always contains only a single
kind of nucleic acid i.e. either DNA or RNA.
• The infectious property of a virus is due to its
nucleic acid.
Viral Structure cont……
• Capsid or the protein coats:
• It is made up of many identical protein sub-units
called capsomeres.
• The capsomeres are composed of either one or
several type of proteins.
• Capsomeres give a specific shape to a particular
virus.
• The host specificity of virus is due to proteins of
the capsid.
Morphology of a Polyhedral Virus
12
Figure 13.2
Morphology of an Enveloped Virus
13
Figure 13.3
Enveloped Viruses
14
Figure 13.16b
Morphology of a Helical Virus
15
Figure 13.4
Morphology of a Complex Virus
16
Figure 13.5
17
Biological properties of viruses
• Viruses lack a cytoplasmic membrane and
they do not have the basic component of a
cell.
• They can only replicate inside the host cell.
• Outside the host cell, they are non-living. thus
show characters of both living and non-living
Non Living characteristics
• Can be crystallized.
• Behave like inert chemicals.
• Do not show growth, development, nutrition,
reproduction, etc.
• Can be precipitated.
Characteristics cont…
•
•
•
•
•
•
Living characters of viruses:
Multiply within host cells.
Possess genetic material, either DNA or RNA.
They have definitive races or strains.
They exhibit mutations
Due to the above reasons, viruses form unique
bridge between living and non-living things
Classification of viruses
• Classification of viruses is done on basis of :
The host cell they infect eg: animal viruses,
plant viruses, fungal viruses, and bacteriophages
Geometrical shape of their capsid (often a helix
or an icosahedron
The type of nucleic acid they use as genetic
material (RNA or DNA)
Common differences btn Non enveloped
and Enveloped
Property
Nonenveloped
Viruses
Enveloped Viruses
Components
Proteins
Phospholipids,protein,
glycoproteins
Sensitivity to heat , acid,
detergent,drying
Resistant(stable)
Sensitive(Labile)
Release from host cell
By cell lysis(host cell
killed)
By budding(host cell
survives) and cell lysis
Transmission(Mode of
spread)
Fomites,dust,
fecal -oral
Large
droplets,secretions,organ or
transplant
Effect of drying
Survival within GIT
Retain infectivity
Yes
Lose infectivity
No
Host immune
response(Protective)
Antibody response
Antibody and CM response
Ways of Virus attacking the human/Virus
Life cycle
• Attachment is the binding of the virus to specific
molecules on the surface of the cell and this is
specific
• Penetration follows attachment; viruses
penetrate the host cell by endocytosis or by
fusion with the cell.
• Uncoating happens inside the cell when the viral
capsid is removed and destroyed by viral enzymes
or host enzymes
Ways……
• Replication: is the stage where a cell uses viral
messenger RNA in its protein synthesis systems to
produce viral proteins
• Assembly: When the newly created viral proteins
and nucleic acid combine to form hundreds of
new virus particles
• Release: New viruses escape or are released from
the cell , then cells burst, a process called lysis.
Other viruses such as HIV are released more
gently by a process called budding
Effect of Virus to the host cell
• Due to bursting there will be death of host cell
(lyisis)
• Also death cell can be caused by cessation of
normal activity of the cell due to protein
produced by virus.
• Alterations to the cell's surface membrane
and apoptosis (cell "suicide)
• Some viruses cause no apparent changes to the
infected cell. Cells in which the virus is latent and
inactive show few signs of infection and often
function normally.
Effect of Virus to the host cell cont..
• This causes persistent infections and the virus is
often dormant for many months or years.
• This is appreciated with herpes viruses infection
• Some viruses, such as Epstein-Barr virus, often
cause cells to proliferate without causing
malignancy.
• But some other viruses, such as papillomavirus,
are an established cause of cancer
Effect cont……..
• When a cell's DNA is damaged by a virus, and if
the cell cannot repair itself, this often triggers
apoptosis. One of the results of apoptosis is
destruction of the damaged DNA by the cell
itself. Some viruses have mechanisms to limit
apoptosis so that the host cell does not die
before progeny viruses have been
produced; HIV, for example, does this.
Viruses cause diseases:
• Ways of transmission:
• From bite of the vector usually blood-sucking
insects.
• Direct transmission is more common. Some
virus infections, (norovirus and rotavirus),
• Contaminated food and water, hands and
communal objects and
• Intimate contact with another infected
person,
Ways of Transmission
• Airborne (influenza virus).
• Unprotected sex- Viruses such as HIV, hepatitis B
and hepatitis C
• Contaminated hypodermic needles.
 It is important to know how each virus spreads
to prevent infections and epidemics
Classification of viruses
DNA Viruses
Single
strand
Double
strand
Enveloped.
Eg:
hepadnaviruses,
Herpseviruses
&Poxvirus
Undeveloped.
Eg:
Undeveloped.
Adenoviruses,
Papovaviruses
Eg: Parvoviruses
Classification of viruses cont
• .
RNA Viruses
(_)RNA
(+)RNA
(+/_)RNA
(+)RNA via
DNA
Enveloped
Enveloped
Eg:
Unenveloped
Eg: Calciviruses,
Picornaviruses
Corona
virus,
Flavivirus,
Togavirus.
Eg: Arenavirus,
Bunyaviruses,
Filoviruses,
Orthoxoviruses
,
Paramyxovirus
&
Rhabdoviruses
Double
capsid.
Eg:
Reovirus
es
Enveloped
Eg:
Retroviruses
Isolation, Cultivation,
and
Identification
32
Growing Viruses
• Viruses must be
grown in living
cells
– Bacteriophages
form plaques on a
lawn of bacteria
33
Viruses Growing
• Animal viruses
may be grown
in living
animals or in
embryonated
eggs
34
Figure 13.7
Virus Identification
• Cytopathic effects(Structural changes in host cell
that are caused by viral invasion)
• Serological tests
– Detection of antibodies against viruses in a
patient
– Use antibodies to identify viruses in
neutralization tests, viral hemagglutination, and
Western blot
– Nucleic acids
Restriction Fragment Length Polymorphisms
(RFLPs)
35
Virus Identification
USE OF EM
36
Figure 13.9
• Parvovirus
Parvovirus
Family Parvoviridae
It includes human Parvovirus B19 (single serotype)
and adeno-associated virus.
Parvovirus
• Structure
• Are non-enveloped, icosahedral particles 18 to
26 nm in diameter.
• Plus and minus DNA strands are packaged into
separate virions in approximately equal
proportion.
• They have two capsid proteins
Parvovirus
• Multiplication
• Replication takes place in the nucleus of
dividing cells.
• The single-stranded DNA genome forms an
intermediate double-stranded form, which
replicates to form progeny-positive and negative single-stranded DNA.
• Positive and negative strands are packaged
separately in viral capsids in equal numbers.
• Pathogenesis
• The disease is transmitted by the respiratory
route.
• The virus replicates in committed erythroid
precursor cells in the bone marrow, leading to
erythroid aplasia.
• Aplastic anemia develops in patients with
underlying hemolytic anemia, and rash and
arthralgia develop at the time specific antibody
appears.
• Host defenses:
• Specific IgM and IgG antibodies develop in
response to infection.
• Disease:
• B19 parvovirus causes a mild disease, erythema
infections in children with a slapped cheek” rash.
• . Clinical symptoms develop in a biphasic fashion
• 7 to 8 days after infection, a prodromal influenza-like
illness develops, characterized by headache, malaise,
chills, and pyrexia.
• Aplastic crisis may occur following B19 virus infection
in individuals with underlying hemolytic anemias
Disease
• B19 virus infection cause intense viremia develops.
• In a pregnant woman the virus may cross the
placenta and establish infection in the fetus.
• The fetus is unable to control and eradicate B19 virus,
and viral replication continues for several weeks.
• In the first and second trimesters of pregnancy, B19
virus infection is associated with an increased risk of
fetal abortion and nonimmune hydrops fetalis.
Parvovirus
• Disease:
• Severe fetal anemia (the aplastic anemia seen in
patients with hemolytic anemia) and edema
occur up to 12 weeks after maternal infection
and may cause the fetal hydrops.
• Infection in the third trimester of pregnancy
has been less intensively studied, but a
macerated stillbirth fetus has been reported at
39 weeks of gestation.
Transmission
• Via respiratory droplets
• Pathogenesis: Virus spreads from respiratory
tract and can infect hemopoietic cells in bone
marrow
Laboratory diagnosis
• Detection of parvovirus – specific IgM
antibody or viral DNA-PCR
Treatment and Prevention
• There is no specific antiviral treatment and no
vaccine.
• Supportive measure includes: fetal exchange
transfusion, in hydrops fetal and using human
intravenous immunoglobulin which contains
b19 IgG to damp down viral replication in
infected immunosuppressed patient with
recurrent episodes of anemia
Adenoviruses
Adenoviruses
•Adenoviruses are medium-sized (90-100 nm),
nonenveloped icosohedral viruses containing
double-stranded DNA.
•cause human infections.
•unusually stable to chemical or physical agents
and adverse pH conditions, allowing for prolonged
survival outside of the body.
Adenoviruses Cont….
• Pathogenesis :
• Adenoviruses infect epithelium of respiratory
tract, and probably intestine. Spread to lymphoid
tissue to tonsil and viral interfere the immune
system by blocking action of interferon and Tc
cells.
Adenoviruses Cont….
• Transmission :
• Via respiratory droplets, feces,and sometimes
from eye to eye via contaminated hands, towels,
or eye drops.
Adenoviruses Cont….
• Diseases caused:
• Pharyngoconjuctival fever, epidemics of acute
respiratory diseases including pneumonia,
intestine illnes, keratoconjuctivitis, hepatitis
and disseminate diseases to
immunosuppressed individuals.
• Common cold ( Read on it symptoms,
treatment, prevention)
Adenoviruses Cont….
Common cold symptoms:
Symptoms of the common cold are generally mild
and include runny nose, sneezing, and nasal
congestion.
Symptoms can vary depending on the specific type
of virus causing the common cold. Some people can
also experience fever, cough, body aches, headache,
fatigue, post- nasal drip, and sore throat
Adenoviruses Cont….
• Treatment:
Fluids
Cold-and-flu medications
Aspirin - but not for babies, children or teenagers
because of the risk of Reye's syndrome.
Acetaminophen
Adenoviruses Cont….
• Laboratory identification:
• Viral isolation in cell culture in samples includes
throat swab, feces, and urine to detect antigen in
nasopharyngeal aspirate by immunofluorescence
• DNA detection in various sample by PCR
• Serology by detecting a rise in complement fixing
antibody.
.
Wishing U a Happy and Prosperous
New Year(2017)