• Acellular
• Viruses cannot metabolize on their own
• Don't divide or grow
• Contain DNA or RNA
• Proteinaceous capsid around genome
• 10 nm to 300 nm

• Extracellular State: Virion -- infective
• Intracellular State: Virus
• Consists of protein coat (capsid) that is made of protein subunits (capsomeres)
• The nucleic acid and capsid together are called nucleocapsid

• Oral-Fecal (rotavirus, hepatitis A)
• Airborne (influenza, orthomyxovirus)
• Sexual (HIV, HPV, HSV)
• Direct Inoculation (hepatitis B, west nile virus)
• Congenital (CMV)

Cold

Hep A

Rubella

Encephalitis

Yellow Fever

Hepatitis

Cold

SARS

Cold

Measles

Mumps

Small pox

Warts

Cervical Cancer

Upper Respiratory Infections

Conjunctivitis

Mononucleosis

Chicken pox

Fever blisters

Cytomegalovirus

Genital herpes

1. Attachment of the virion to the host cell
2. Entry of the virion or its genome into the host cell
3. Synthesis of new nucleic acids and viral proteins by the host's enzymes, ribosomes
4. Assembly of new viruses within the host cell
5. Release of new virions from the host cell

• No resistance development
• Less C. difficile
• Selective for bacteria
• No deleterious effects

1.  Attachment: animal viruses lack tails and tail fibers -- has glycoprotein spikes or other attachment molecules
2.  Entry

• Direct Penetration
• Membrane fusion
• Phagocytosis

3.  Release

• Enveloped viruses often released via budding which allows infected cells to remain intact
• Naked viruses extruded by exocytosis or causes lysis and cell death

• Most nucleated cells make IFN-β and IFN-α
• They bind to specific receptors on adjacent cells to protect them from viral infection
• They enhance expression of MHC Class I (Cytotoxic T-Cells) and Class II (T-Helper Cells) molecules, which then increases viral antigen presentation to specific T-cells
• Cells develop an antiviral state -- replication of virus is inhibited
• Restrict growth at: penetration, uncoating, synthesis of mRNA, protein synthesis and assembly