Transcript PowerPoint Presentation - Introduction to viruses

Viruses
Sarita
Department of Botany
DAVCG, Yamunanagar
Definition of a Virus
Sub microscopic entity consisting
of a single nucleic acid surrounded
by a protein coat and capable of
replication only within the living
cells of bacteria, animals or
plants.
Definition of a Virus
Obligate
Intracellular
Parasite
Virion Structure
Lipid Envelope
Nucleic Acid
Protein
Capsid
Virion
Associated
Polymerase
Spike
Projections
Virion Morphology
• Simple Structure
• Repetitive Structure
• High Level of
Redundancy
Virus Morphology
Helical
Icosahedral
Virus Replication
1 Virus attachment
2
3
1
5
4
5
6
4
2
3
7
8
7
6
8
and entry
Uncoating of virion
Migration of
genome nucleic
acid to nucleus
Transcription
Genome replication
Translation of virus
mRNAs
Virion assembly
Release of new
virus particles
Cytopathic Effect (cpe)
Adenovirus
Herpes virus
Transmission of Viruses
•
•
•
•
•
Respiratory transmission
 Influenza A virus
Faecal-oral transmission
 Enterovirus
Blood-borne transmission
 Hepatitis B virus
Sexual Transmission
 HIV
Animal or insect vectors
 Rabies virus
Virus Tissue Tropism
•
Targeting of the virus to specific tissue
and cell types
•
Receptor Recognition
 CD4+ cells infected by HIV
 CD155 acts as the receptor for
poliovirus
In vivo Disease Processes
•
Cell destruction
•
Virus-induced changes to gene
expression
•
Immunopathogenic disease
Acute Virus Infection
Amount of virus
Symptoms
Virus
Time
Acute Virus Infections
• Localised to specific site of
body
• Development of viraemia
with widespread infection of
tissues
Poliovirus
Poliovirus
Properties of the virus
•
•
•
•
Enterovirus.
Possesses a RNA
genome.
Transmitted by the
faecal oral route.
Cause of
gastrointestinal illness
and poliomyelitis.
Poliovirus Infection
Virus
Infection
Gut
Non-neuronal
tissues
Viraemia
Neuronal
tissues
Virus excretion
in the faeces
Paralysis
Incidence of Poliomyelitis
A
B
Number of cases (in thousands)
40
Poliovirus vaccines
A: Salk – killed inactivated
vaccine.
B: Sabin – live attenuated
vaccine
30
20
10
0
1950
1960
1970
1980
Influenza A virus
Properties of the virus
•
•
•
•
•
Myxovirus
Enveloped virus with a
segmented RNA
genome
Infects a wide range of
animals other than
humans
Undergoes extensive
antigenic variation
Major cause of
respiratory infections
Influenza A virus Infection
• Spread by respiratory route
• Virus infects cells of the respiratory
•
tract
Destruction of respiratory epithelium
 Secondary bacterial infections
• Altered cytokine expression leading to
fever
 e.g interleukin-1 and interferon
Spread of influenza virus
Respiratory Tract
Weekly consultation rates for influenza and influenza-like illness: Weekly
Returns Service of the Royal College of General Practitioners, 1988 to
1999
Rate per 100 000 population
600
500
Epidemic activity
400
300
200
Higher than expected
seasonal activity
Baseline activity
Normal seasonal activity
100
0
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Year
CDR Weekly Report: 5th November 1999
Generation of Novel Influenza A Viruses
Human H2N2
ANTIGENIC SHIFT
Genetic Reassortment
Avian H3N8
Point mutation of HA and NA
genes
ANTIGENIC DRIFT
Human H3N2
Viruses and Human Tumours
• Epstein Barr Virus
 Burkitt’s Lymphoma
• Human papillomavirus
 Benign warts
 Cervical Carcinoma
• Human T-cell Leukaemia Virus (HTLV-1)
 Leukaemia
• Hepatitis C virus
 Liver carcinoma
Virus-induced tumours
Virus
Infection
[ ]
Uninfected
Cell
?
Uncontrolled cell
growth and tumour
formation
Virus-induced transformation
Normal cells
Transformed cells
Virus-Induced Tumours
• Virus infects cell.
• Virus nucleic acid, as DNA,
•
•
integrates into cellular genome.
Virus causes changes in cellular gene
expression.
Uncontrolled cell multiplication and
tumour formation.
Treatment and Prevention
of Virus Infections
• Antivirals
• Vaccines and immunisation
Antiviral Targets
• Attachment/Entry
• Nucleic acid replication
• Virus protein processing
• Virus maturation
Problems with Antivirals
•
Identification of virus-specific
target.
•
Generation of resistant variants.
Thank You…..