microbiology

• obligate itracellular parasites
• require a host to replicate
• lack cellular structure

complete virus particle in the extracellular state (outside host)

• nucleocapsid - genome - dna or rna
• capsid - protein coat or shell 
• capsomere - subunit to build capsid
• envelope - lipid bilayer, host derived when the virus exits
• spikes (peplomers) - viral proteins, used for attachment to host
• enzymes - aid infection process

• 1. neuraminidase - breaks down glycoproteins and glycolipids; penetrate mucous, spread
• 2. hemagluttinin - attach to host cell receptors, includes RBC's
• 3. reverse transcriptase - vRNA which makes a molecule of vDNA

• icosahedral - 20 icosahedral triangles
• helical capsid - cylindrical, DNA coiled inside
• complex - includes bacteriophages

• 1. attachment - host specific
• 2. penetration - injects nucleic acid
• 3. biosynthesis - make capsid protein & copies of the genome
• 4. maturation - assembly, self directed
• 5. release - lysis of host cell to release new virions

• 1. attachment (adsorption) - host specific; tropism = affinity for (neurotropic virus means affinity for nervous tissue)
• 2. penetration - 2choices  a) host - phagocytize the virus; receptor mediated endocytosis.  b) fusion of viral envelope with host cell membrane
• 3. biosynthesis - early proteins, proteins involved with replication; late proteins - capsid protein
• 4. maturation
• 5. release - 2 ways, depends on naked vs. enveloped.  naked viruses - released by host cell lysis.  enveloped virus - bud off of the host cell.

virus released

viral DNA lays dormant in a host cell.  Latent or dormant in CNS.  ex: VZV - varicella zoster virus.

• by family (ex: veridae)
• by genus (ex: herpes)
• by species (ex: 1 or 2)
• ex: HSV1

• living animals - infect mice, rabbits, guinea pigs, etc
• embryonic eggs - grow virus in fertilized chicken eggs; may infect chick or membrane
• tissue cultures - homogenize and separate cells in a tissue

viral infection can cause changes in host cell.  CPE's - cytopathic effects.  ex: rabies virus - leaves negri bodies in cytoplasm

• titer - determine amount of virus in sample
• elisa test kit - color change when substrate is added to a positive test.  ELISA = Enzume linked immunosorbent assay
• lates bead agglutination - anti vrus clumpls together

plague - zone of host cell lysis; holes formed by virus

• phagocytes - engulf and destroy viruses
• T lymphocytes - CD8+ cells, killer T cells, recognize and destroy viral infected host cells
• Interferon - chemical released by viral infected cells, signals neighboring cells to produce anti viral protein; recruits natural killer cells

• base analogs - mimic nucleotides, so when a virus inserts a base analog replication stops
• reverse transcriptase inhibitors - treating retroviral infections
• protease inhibitors - viral mRNA- protease, cut the polypeptide
• neuraminidase inhibitors - disrupt the release of virus (progeny)

• inactivated (killed) - treat the virus with formaldehide to inactivate
• attenuated - weakened strain, infected without symptoms
• viral subunits - proteins from surface
• DNA vaccines - shoot the beads into muscle, muscle cells express the viral DNA

• formaldehyde - denatures protein
• lipid solvents - detergents - effective against enveloped viruses

• heat - denatures protein
• UV radiation - disrupt nucleic acid
• X rays - disrupt nucleic acids

• smaller than viruses but cause infection; no capsid or genome
• viroid - plant pathogens, consist of small RNA genome, insects transmit between plants
• prion - proteinaceous infectious particle. 

• spongiform encephalopathy
• degeneration of brain tissue
• PrPc - normal protein in brain tissue
• PrPsc - improper folding, builds up in tissues, affects structure of brain tissue
• Kuru - cannibalistic tribe
• BSE - bovine spongiform encephalopathy- mad cow disease
• scrapie - sheep

• healthy cells become cancerous
• proto-oncogenes; genes that regulate cell growth and differentiation; vDNA take over control of gene.  ex: HPV triggers cervical cancer