“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

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 ds RNA segmented ss RNA non-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

PolyhedraI/icosohedral (ex: adenovirus, poliovirus) 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, 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

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 (Fusion of cell membrane with viral envelope via spikes)

Multiplication Cycle 3. Uncoating Nucleic acid is released from nucleocapsid

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

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

Multiplication Cycle 6. Release of virus

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

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

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 viral diseases 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 Lung lesion in an African wild dog B. Inclusion bodies

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