Lytic Viruses

Question 1

Lytic viruses

Answer 1

Viruses that induce destruction of a cell

Question 2

Picornavirus Physical Properties

Size:

Morphology:

Nucleic Acid:

Lipid Envelope:

Tegument:

pH stability:

Answer 2

Size: 22-30nm

Morphology: Icosahedral

Nucleic Acid: ssRNA (+ polarity)

Lipid Envelope: NO

Tegument: NO

pH stability: Enteroviruses stable at pH 3-9; Rhinoviruses unstable below pH 6

Question 3

Diseases associated with these simple viruses

Enteroviruses:

Rhinoviruses:

Hepatoviruses:

Parechovirus:

Kobuvirus:

Answer 3

Enteroviruses: paralysis, common cold, meningitis, diarrhea, hand-foot-and-mouth disease

Rhinoviruses: common cold

Hepatoviruses: hepatitis

Parechovirus: gastroenteritis, myocarditis, encephalitis

Kobuvirus: gastroenteritis

Question 4

Enterovirus pathway

Answer 4

Fecal/oral pathway

Question 5

Polio - Infection vs. Disease

Answer 5

• Inapparent infections (90-95%)
  
  • Virus recoverd from throat and/or stool
  • asymptomatic
• Mild illness (4-8%)
  
  • Minor undifferentiated ferbile illness
  • Influenza like
• Asceptic meningitis (1-2%) - non paralytic
  
  • Minor illness progresses to CNS infasion
  • Disease lasts 2-10 days; rapid and complete recovery
    *

Question 6

Paralytic poliomyelitis (0.1-2%)

Answer 6

• Initial nonspecific febrile illness
• Spectrum of paralytic disease is variable
• Asymmetric flaccid paralysis
• Lower extremeties involved more than upper
• Large muscle groups involved more often
• Bulbar paralysis: involvement of cranial nerves, medulla, respiratory compromise, death 5%
• Slow recovery
• Complications - resiudal paralysis

Question 7

How does infection happen

Answer 7

Virus passes into Gastro-associated lymph tissues, then to local lymph nodes and then to the blood stream via lymphatic system

Question 8

Picornavirus - Diagnosis

Answer 8

• Virus isolation
  
  • Stool specimens and throat washings
  • Cerebrospinal fluid
  • Specific cell culture
• Serology
  
  • 4 fold greater rise in titer
  • neutralization
• PCR (multiplex)

Question 9

Polio epidemiology

Answer 9

• An ancient disease
• Exclusively a human disease
• fecal - oral transmission
• Transmission enhanced by persons with sub-clinical infections
• Summer epidemics in temperate climates

Question 10

Three major epidemiological phases: Endemic

Answer 10

• Children encounter virus at an early age
• Maternal antibody offers protection
• High rate of subclinical infections
• Very low incidence of paralytic disease

Question 11

Three major epidemiological phases: Epidemic

Answer 11

• Late 1800s and Early 1900s in US
• Coincides with advent of indoor plumbing
• Patients are older when they first encounter virus
• Higher incidence of paralytic disease in older children and adults (no longer have maternal antibody)

Question 12

Three major epidemiological phases: Post-vaccine

Answer 12

• Small number of cases
• Most all cases are vaccine related

Question 13

How many proteins are made by the polio virus? Why is this important?

Answer 13

1 protein - which uses protesases to cut itself into many smaller proteins - these proteases are a good target for treatment

Question 14

Poliovirus entry and genome release

Answer 14

Requires receptor interaction and injection of RNA genome into cytoplasm

Question 15

Viral Effect on host cell; Inhibition of ________ plays a role in cell death

Answer 15

Translation

Question 16

Picornavirus prevention and control

Answer 16

• Virus attachment
  
  • block receptors (antibody or chemicals)
• Virus entry and genome release
• Protease processing
• RNA-dependent RNA polymerase inhibitors

Question 17

Polio - Public Health success

Answer 17

1955 - Inactivated virus vaccine (Salk)

1962 - Live attenuated virus vaccine (Sabin)

Question 18

Other RNA viruses - Different challenges

Answer 18

Negative strand RNA - can’t immediatedly translate genome (Don’t come with their own ribosomes)

• Have to bring along their own protein to get to positive strand RNA

Double stranded RNA - segmented genomes with each segment transcribed separeately to produce monocistronic mRNAs

Question 19

Adenovirus

Answer 19

• Original isolate form normal adenoid tissues
• 51 serotypes
• Cross reactivity - family common antigen - reduces infection with other types and re-infection is rare
• Double-stranded DNA genome not enveloped
• Spread via fecal/oral route or respiratory
• Frequently causes unapparent respiratory infections
• Icosahedral capsid

Question 20

The adenovirus particle is much more ______ than the picornavirus particle

Answer 20

complicated

Question 21

Adenovirus disease

Answer 21

• Gastrointestinal in children
• More severe in immunosuppressed
• Enteric adenovirus infections
  
  • Incubation 3-10 days
  • Diarrhea lasts 6-9 days
  • May have vomiting and fever preceding diarrhea
  • More common in children than adults

Question 22

Adenovirus infectious progression

Answer 22

Eye, Upper respiratory, Gastrointestinal

Question 23

Adenovirus attachment and entry

Answer 23

1. Viral surfing
2. Clathrin mediated endocytosis
3. Viral fusion pore control

Question 24

Production and Release of Adenovirus from epithelial cells

Answer 24

Virus attaches to apical surface

Virus shed into intestinal lumin

Virus released from basal surface

Excess virus penton spike fiber released from cells - disrupts adhesion junctions

Question 25

Where in the cell does adenovirus undergo intracellular production

Answer 25

Nucleus

Question 26

How is adenovirus gene expression complex

Answer 26

* Not simple partitioning into early and late segments * Clusters of genes are expressed from a limited number of shared promoters

Question 27

Adenovirus vaccine

Answer 27

* A live adenovirus vaccine became available and is routinely administered upon entry into the armed forces * Prevoius vaccine was discontinued in 1999