Download VIROLOGY -Multiplication Cycle

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Virology
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DEFINITION – the study of viruses and
virus-like agents.
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Structure
Classification and evolution
Methods of multiplication
Diseases
Techniques to isolate/culture
Use in research and therapy
Virology
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VIRUS (from the latin virus meaning toxin or
poison) is a microscopic infectious agent that is an
obligatory intracellular parasite.
VIRUSES infect all types of organisms from
animals and plants to bacteria
Viruses lack organelles
Virology
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AVIAN INFLUENZA
Each virus contains a nucleic acid, capsid
protein, enzymes, and sometimes a surrounding
envelope.
Each virus particle is the same size and does not
grow or differentiate.
Virus particles are seen under the electron
microscope.
VIROLOGY - Classification of
Viruses
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Host range
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Very specific
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Enveloped or non-enveloped
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Type of nucleic acid in the virion (DNA or RNA)
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Shape ( symmetry of the viral capsid)
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Dimensions of the virion and capsid
VIROLOGY - Viral Size
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20 nm - 1000 nm
VIROLOGY - Viral Structure
VIROLOGY – NUCLEIC ACIDS
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RNA or DNA
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Double or singlestranded
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Segmented or
nonsegmented
ds DNA
ss RNA
non-segmented
ss DNA
ds RNA
segmented
VIROLOGY - Capsids
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Composed of protein
subunits called
capsomeres.
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Functions
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Protective nucleic acid
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Recognition/attachment to
host cells
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Introduction of nucleic acid
into host cell
VIROLOGY - Envelopes
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Composition: lipids, proteins and glycoproteins
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Lipids from host cell membrane
 more pleomorphic and fragile than the capsid
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Easily lysed by detergents, disinfectants or damaged
by the outside environment.
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Function
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Camouflage?
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Recognition/attachment to host cell
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Helps introduce nucleic acid into host cell
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Protects nucleic acid
Viral Shape
Helical (ex: rabies, ebola)
PolyhedraI/icosohedral (ex:
adenovirus, poliovirus)
Viral Shape
Complex
(ex: bacteriophage)
Animal RNA Viruses
Retro: FeLV, FIV (lenti –
slow)
Paramyxo: Canine
distemper, measles
rinderpest
Corona: FIP
Rhabdo: Rabies
Animal DNA viruses
VIROLOGY – Multiplication
of Animal Viruses
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Transmission:
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Attachment/Penetration:
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aerosols, break in skin, fluids (blood, saliva, sexual
contact)
bind to specific surface receptors
Entry: fuse with or engulfed by the plasma membrane
Release:
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lyse cells or bud through (plasma) membrane
Several hundred in one cell during one replication cycle of several
hours.
Viral Life Cycle – 5 steps
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Entry into host cell
Uncoating
Replication of nucleic acids & production
of proteins
Maturation/assembly
Release of virus
Multiplication Cycle: Entry I
1. Entry – Engulfment (Endocytosis)
Multiplication Cycle: Entry II
1. Entry
(Fusion of cell membrane with viral envelope via
spikes)
Multiplication Cycle
2. Uncoating
Nucleic acid is released
from nucleocapsid
VIROLOGY -Multiplication
Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Viral proteins
3. Replication of Nucleic
Acids & Proteins
A. DNA enters nucleus.
B. DNA is transcribed.
C. RNA is exported to cytoplasm
& translated.
D. DNA is replicated in nucleus.
E. Viral DNA inserted into host
genome.
Cytoplasm
Viral DNA
A
C
Nuclear pore
B
Viral mRNA
D
Nucleus
Replicated
viral DNA
E
Mature
virus
Host DNA
VIROLOGY -Multiplication
Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Viral proteins
Cytoplasm
Viral DNA
Nuclear pore
4. Maturation/Assembly
 New nucleocapsids selfassemble
Viral mRNA
Nucleus
5
Replicated
viral DNA
Mature
virus
Host DNA
Multiplication Cycle
5. Release of virus
ATTACHMENT
Click after each step to view process
PENETRATION
HOST
FUNCTIONS
UNCOATING
Transcription
Translation
REPLICATION
VIRAL
LIFE
CYCLE
ASSEMBLY
(MATURATION)
RELEASE
23
MULTIPLICATION
Transmission of Viruses Between Hosts
ANIMAL
VIRUSES
AEROSOLS
(airborne) OR
INGESTION
(water- or
foodborne)
FLUIDS
(direct
contact)
PARENT TO
OFFSPRING
VECTORS
MOST
Picorna (FMD)
Orthomyxo
(Influenza)
Corona (FIP)
Reo
FEW
Hepadna
Retro (FeLV,
FIV)
Herpes
Papilloma
FEW
Retro
Herpes
Arena
MANY
Toga
Flavi
Bunya
Rhabdo
VIROLOGY - Outcomes of
Animal Virus Infections
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Acute Infection
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Latent Infections
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Virus has a short duration and often not fatal, and disappears when the
disease process ends.
 ( ex: parvovirus, measles in people)
Virus can remain in equilibrium with the host and not actually produce
disease for a long period, often many years.
 ( ex: human herpes simplex, Feline Herpes)
Persistent/Chronic Infections
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Virus is often fatal and occurs gradually over a long period.
 ( ex: HIV/AIDS, FeLV, FIV (Feline immuodeficiency virus)
Methods of diagnosis for viral
diseases
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I. Serology
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ELISA
Antibody titers
Virus isolation
II. Cytology or Histology
Serology
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Look for viral antigens or anti-viral antibodies
A four fold or greater rise in antibody titer
between two serum specimens provides a positive
diagnosis.
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Paired sera, the first taken as early as possible in the
illness and the second 10 to 14 days after the onset of
symptoms.
Serology Methods
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ELISA (enzyme-linked immunosorbent
assay)
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Most common test
FeLV/FIV/Heartworm
Histology and cytology
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Inclusion bodies - nuclear or cytoplasmic aggregates,
usually proteins
 They usually represent sites of viral multiplication
 Negri bodies - a particular type of cytoplasmic
inclusion
VIROLOGY – INCLUSION
BODIES
A.Lung lesion in an
African
wild dog
B. Inclusion bodies
Negri bodies
can be seen with a light microscope. A section through a Purkinje cell
with Negri body in the cytoplasm
Negri body
PREVENTION
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Isolation of animals to keep them free from
infection. Vaccination against likely
infections.
Notification of reportable diseases
References
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http://www.pitt.edu/~super1/lecture/lec3331
/004.htm
http://www.idexx.com/view/xhtml/en_us/s
mallanimal/in-house-diagnostics.jsf