PERSEVERENCE

“He who has a why to live can bear almost any how.”

-Friedrich Nietzsche

Virology

DEFINITION – the study of viruses and virus-like agents. Structure Classification and evolution Methods of multiplication Diseases Techniques to isolate/culture Use in research and therapy

Virology

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

VIROLOGY - Classification of Viruses

Host range Very specific (small pox in humans)

Enveloped or non-enveloped (presence or absence)

Type of nucleic acid in the virion (DNA or RNA)

Shape ( symmetry of the viral capsid)

Dimensions of the virion and capsid

VIROLOGY - Viral Size

20 nm - 1000 nm

VIROLOGY - Viral Structure

VIROLOGY – NUCLEIC ACIDS

RNA or DNA

Double or single-stranded

Segmented or nonsegmented

ds DNA ss DNA

ss RNA non-segmented

ds RNA segmented

VIROLOGY - Capsids

Composed of protein subunits called capsomeres.

Functions Protective

Recognition/attachment to host cells

Introduction of nucleic acid into host cell

VIROLOGY - Envelopes

Composition Lipids from host cell membrane Proteins Glycoproteins

Function Camouflage? Recognition/attachment to host

cell Helps introduce nucleic acid into

host cell Protects nucleic acid

Viral Shape

Helical (ex: rabies, ebola)

PolyhedraI/icosohedral (ex: adenovirus, poliovirus)

Viral Shape

Complex

(ex: bacteriophage)

Animal RNA Viruses

Animal DNA viruses

VIROLOGY – Multiplication of Animal Viruses

Transmission:animal viruses: aerosols, break in skin, fluids [blood, saliva, sexualcontact]

Attachment/Penetration:animal viruses bind to specific surface receptors;Entry: fuse with or engulfed by the plasma membrane

Release:animal viruses lyse cells or bud through (plasma) membrane

Viral Life Cycle

Entry into host cell Uncoating Replication of nucleic acids & production

of proteins Maturation/assembly Release of virus

Multiplication Cycle: Entry I

2. Entry – Engulfment (Endocytosis)

Multiplication Cycle: Entry II

2. Entry

(Fusion of cell membrane with viral envelope via spikes)

Multiplication Cycle

3. Uncoating

Nucleic acid is released from nucleocapsid

VIROLOGY -Multiplication Cycle

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Nuclear pore

Viral DNACytoplasm

Replicatedviral DNA Mature

virus

Viral mRNA

Nucleus

Host DNA

D

A

B

C

E

Viral proteins

4. 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.

VIROLOGY -Multiplication Cycle

5. Maturation/Assembly New nucleocapsids self-

assemble

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Nuclear pore

Viral DNACytoplasm

Replicatedviral DNA Mature

virus

Viral mRNA

Nucleus

Host DNA

5

Viral proteins

Multiplication Cycle

6. Release of virus

22

VIRAL LIFE

CYCLE

VIRAL LIFE

CYCLE

ATTACHMENT

PENETRATIONPENETRATION HOSTFUNCTIONS

ASSEMBLY(MATURATION)

Transcription

REPLICATION

RELEASE

UNCOATINGUNCOATING

Translation

MULTIPLICATION

Click after each step to view process

Transmission of Viruses Between Hosts

AEROSOLS(airborne) ORINGESTION(water- orfoodborne)

FLUIDS(directcontact)

PARENT TOOFFSPRING

VECTORS

ANIMALVIRUSES

MOSTPicornaOrthomyxoCoronaReo

FEWHepadnaRetroHerpesPapilloma

FEWRetroHerpesArena

MANYTogaFlaviBunyaRhabdo

VIROLOGY - Outcomes of Animal Virus Infections

Acute Infection Virus has a short duration and often not fatal, and disappears when the

disease process ends. ( ex: parvovirus, measles in people)

Latent Infections 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 Virus is often fatal and occurs gradually over a long period.

( ex: HIV/AIDS, FeLV, FIV (Feline immuodeficiency virus)

Methods of diagnosis for viraldiseases

I. Serology II. Cytology or Histology

Serology

Look for viral antigens or anti-viral antibodies A four fold or greater rise in titer between two

serum specimens provides a positive diagnosis. 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

ELISA (enzyme-linked immunosorbent assay)

-Most common test

-(ex: in animals Parvovirus)

Histology and cytology

Inclusion bodies - nuclear or cytoplasmic aggregates of stainable substances, usually proteins

They usually represent sites of viral multiplication, ex: distemper

Negri bodies - a particular type of cytoplasmic inclusion body, ex: rabies

VIROLOGY – INCLUSION BODIES

A.Lung lesion in an African

wild dogB. 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