1. “He who has a why to live can bear almost any how.”
PERSEVERENCE
“He who has a why to live can bear almost any how.”
-Friedrich Nietzsche

2. 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

3. 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

4. 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

5. VIROLOGY - Viral Size
20 nm nm

6. VIROLOGY - Viral Structure

7. VIROLOGY – NUCLEIC ACIDS
RNA or DNA
Double or single-stranded
Segmented or nonsegmented
ds DNA
ss DNA
ds RNA segmented
ss RNA
non-segmented

8. VIROLOGY - Capsids Composed of protein subunits called capsomeres.
Functions
Protective
Recognition/attachment to host cells
Introduction of nucleic acid into host cell

9. 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

10. PolyhedraI/icosohedral (ex: adenovirus, poliovirus)
Viral Shape
Helical (ex: rabies, ebola)
PolyhedraI/icosohedral (ex: adenovirus, poliovirus)

11. Viral Shape
Complex
(ex: bacteriophage)

12. Animal RNA Viruses

13. Animal DNA viruses

14. VIROLOGY – Multiplication of Animal Viruses
Transmission:
animal viruses: aerosols, break in skin, fluids [blood, saliva, sexual
contact]
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

15. Viral Life Cycle Entry into host cell Uncoating
Replication of nucleic acids & production of proteins
Maturation/assembly
Release of virus

16. Multiplication Cycle: Entry I
2. Entry – Engulfment (Endocytosis)

17. Multiplication Cycle: Entry II
(Fusion of cell membrane with viral envelope via spikes)

18. Multiplication Cycle 3. Uncoating
Nucleic acid is released from nucleocapsid

19. VIROLOGY -Multiplication Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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.
Viral proteins
Cytoplasm
Viral DNA A C
Nuclear pore B D
Viral mRNA
Nucleus
Replicated
viral DNA
Mature
virus E
Host DNA

20. VIROLOGY -Multiplication Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Viral proteins
Cytoplasm
Viral DNA
Nuclear pore
5. Maturation/Assembly
New nucleocapsids self-assemble
Viral mRNA
Nucleus 5
Replicated
viral DNA
Mature
virus
Host DNA

21. Multiplication Cycle
6. Release of virus

22. VIRAL LIFE CYCLE Click after each step to view process ATTACHMENT
PENETRATION
HOST
FUNCTIONS
UNCOATING
Transcription
Translation
REPLICATION
VIRAL LIFE CYCLE
ASSEMBLY
(MATURATION)
RELEASE 22
MULTIPLICATION

23. Transmission of Viruses Between Hosts
AEROSOLS
(airborne) OR
INGESTION
(water- or
foodborne)
FLUIDS
(direct
contact)
PARENT TO
OFFSPRING
VECTORS
ANIMAL
VIRUSES
MOST
Picorna
Orthomyxo
Corona
Reo
FEW
Hepadna
Retro
Herpes
Papilloma
Arena
MANY
Toga
Flavi
Bunya
Rhabdo

24. 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)

25. Methods of diagnosis for viral diseases
I. Serology
II. Cytology or Histology

26. 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.

27. Serology Methods ELISA (enzyme-linked immunosorbent assay)
-Most common test
-(ex: in animals Parvovirus)

28. 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

29. VIROLOGY – INCLUSION BODIES
Lung lesion in an African
wild dog
B. Inclusion bodies

30. Negri bodies can be seen with a light microscope
Negri bodies can be seen with a light microscope. A section through a Purkinje cell with Negri body in the cytoplasm
Negri body