Virology: quick characteristics

Question 1

ssRNA enveloped

Answer 1

• Orthomyxovirus
  
  • Influenza A/B/C
• Coronavirus
  
  • Respiratory viruses
• Togavirus
  
  • Rubella
• Flavivirus
  
  • Hepatitis C, West Nile virus
• Paramyxovirus
  
  • Mumps, measles, parainfluenza
• Rhabdovirus
  
  • rabies
• Retrovirus
  
  • HIV, Adult T-cell leukemia
• Hepatitis D

Question 2

ssRNA naked

Answer 2

• Picornavirus
  
  • enteroviruses, polio, coxsackie, rhinovirus, hepatitis A
• Calicivirus
  
  • Norwalk virus
• Hepatitis E

Question 3

dsRNA naked

Answer 3

• Reovirus
  
  • rotavirus

Question 4

dsDNA enveloped

Answer 4

• Herpesvirus
  
  • Herpes simplex virus 1/2, Varicella zoster virus, cytomegalovirus, Epstein-Barr virus, Human herpes virus 6/7/8
• Hepadnavirus
  
  • Hepatitis B
• Poxvirus
  
  • Smallpox, Molluscum contagiosum

Question 5

dsDNA naked

Answer 5

• Adenovirus
  
  • Respiratory diseases & gastroenteritis
• Papillomavirus

Question 6

ssDNA naked

Answer 6

Parvovirus

Question 7

DNA Viruses - enveloped

Answer 7

Herpesvirus
• Herpes simplex virus 1 & 2
• Varicella-zoster virus
• Cytomegalovirus
• Epstein-Barr virus
• Human herpesvirus 6, 7, 8

• Hepadnavirus
• Hepatitis B
• Poxvirus
• Smallpox
• Molluscum contagiosum

DNA Viruses – Nonenveloped

• Adenovirus
• Respiratory diseases and gastroenteritis
• Papillomavirus
• Parvovirus – SINGLE STRANDED

Question 8

DNA Viruses “naked” - nonenveloped

Answer 8

• Adenovirus
• Respiratory diseases and gastroenteritis
• Papillomavirus
• Parvovirus – SINGLE STRANDED

Question 9

Prions

Answer 9

• Exception to the basic viral
structure
• Composed entirely of protein

• Normal, misconfigured human
proteins

• Disrupts neuron function

• Causes transmissible spongiform
encephalopathies
• Mad cow disease

• Creutzfeldt-Jakob disease
• Kuru

Question 10

Viral Transmission & Replication – Early steps

Answer 10

Attachment to host cell
• Penetration/Entry
• Virion surface proteins attach to
• Naked viruses engulfed by vesicle
receptor proteins on the cell
• Enveloped viruses undergo fusion
surface

Uncoating to release the
genome
• Low vesicle pH uncoats virion • Rupture or fusion

Question 11

Viral Transmission & Replication – Middle step

Answer 11

Gene expression
• Virus specific mRNA synthesis • Synthesis of viral proteins
• Genome replication
• DNA viruses replicate in the nucleus using host cell DNA-dependent RNA
polymerase
• Exception = poxviruses – cytoplasm
• RNA viruses replicate in the cytoplasm
• Exception = retroviruses and influenza viruses – nucleus

Question 12

Viral Transmission & Replication – Late steps

Answer 12

• Assembly
• Viral nucleic acid packaged within
capsid proteins • Release from cell
• Rupture of cell membrane
releasing assembled virions
(usually naked viruses) OR • Budding process (enveloped
viruses)

Question 13

Infected cells

Answer 13

• Death
  
  • Host cell protein synthesis inhibited
• Fusion of cells to form multinucleated cells
  
  • Due to cell membrane changes
• Malignant transformation
  
  • Unrestrained growth
  • Prolonged survival
  • Morphologic changes
• No effect - rare

Question 14

Infection stages

Answer 14

• Incubation
  
  • Asymptomatic
• Prodromal
  
  • Non-specific symptoms
• Specific-illness
  
  • Characteristic symptoms and signs
• Recovery
  
  • Illness wanes

Question 15

Cell culture

Answer 15

• Monitor for characteristic cytopathic
effect – provides presumptive diagnosis
• Can arrive at definitive identification
by using known antibody with a variety of tests
• Complement fixation,
• Hemagluttination inhibition
• CPE neutralization
• Fluorescent antibody
• Radioimmunoassay
• ELISA
• Immunoelectron microscopy

Question 16

Microscopic identification

Answer 16

Identified by microscopic exam of
clinical specimen
• Light microscopy – characteristic
inclusion bodies or multinucleated giant cells
• Tzanck smear – shows herpesvirus-
induced multinucleated giant cells • UV microscopy – fluorescent antibody
staining of virus • Electron microscopy – detects virus
particles characterized by size and
shape

Question 17

Serology

Answer 17

Antibody to the virus is measured
• Acute and convalescent phase
samples

Question 18

Viral antigen detection

Answer 18

• Enzyme-linked immunosorbent
assay (ELISA)

Question 19

Viral nucleic acid detection

Answer 19

Test for viral genome or viral
mRNA by using complementary DNA or RNA
• Can use polymerase chain reaction
(PCR) to amplify small amounts of viral nucleic acids

Question 20

Disease prevention

Answer 20

Active immunity
• Attenuated live virus – greater, longer lasting protection
• Killed virus
• Subunit vaccines – contain purified viral proteins • Passive immunity
• Preformed antibody administered in immune globulins • Herd immunity – “community immunity”

Question 21

Disease control

Answer 21

Challenges: • Difficult to obtain selective toxicity
against the virus since replication
so closely involved with normal
synthetic processes of the cell
• Extensive viral replication occurs
during the incubation period
• Drug-resistant viral mutants

Question 22

Virion

Answer 22

• Contains: Genome PLUS protein coat
• +/-enzymesneededfortranscription - RNA-dependent RNA polymerase
• No energy source
• No metabolic processes

Question 23

Internal core

Answer 23

Contains the genetic sequence

Question 24

Coat

Answer 24

• protein capsid or envelope
  
  • Protection
  • Attachment
  • Recognition

Question 25

Enveloped virus

Answer 25

* Outer lipid bilayer * More sensitive to heat, drying, detergents, and lipid solvents (alcohol, ether) * Usually transmitted by direct contact (blood, sexual) or respiratory aerosol droplets * Other terminology * Nucleocapsidvs.nakednucleocapsid

Question 26

Glycoprotein spikes

Answer 26

* Facilitate attachment to host * After infection act as an antigen * Surface antigens * Responsibleforserotypes

Question 27

Important points

Answer 27

* All viral genomes must make mRNA * mRNA is then translated to start making proteins * RNA Viruses * Most replicate in cytoplasm * Different strategies for synthesizing mRNA * DNA Viruses * Most replicate in the nucleus * Use host-cell DNA dependent RNA polymerase

Question 28

Positive stranded RNA viruses

Answer 28

* Equivalent of preformed mRNA * Ready for translation once they enter the cell * Use host ribosomal proteins

Question 29

Negative stranded RNA viruses

Answer 29

* A copy of mRNA * Can not be directly translated * Carry viral RNA-dependent RNA polymerase * Used to transcribe a positive strand * Canthenbetranslated

Question 30

RNA Retroviruses

Answer 30

* Single stranded (+) RNA virus with DNA intermediate * Reverse transcriptase – allows for incorporation of viral genome into host genome

Question 31

Reverse transcriptase

Answer 31

* RNA of retrovirus is converted to double stranded(ds) DNA * Original genome RNA degraded * dsDNA is integrated into host cell DNA * Integrated DNA transcribed by host cell RNA polymerase to produce more viral mRNA

Question 32

List the RNA Viruses – Enveloped

Answer 32

* Orthomyxovirus * Influenza A, B, C * 8 piece segmented RNA * Coronavirus * Respiratory viruses * Togavirus * Rubella * Flavivirus * Hepatitis C * West Nile virus * Paramyxovirus * Mumps * Measles * Parainfluenza * Rhabdovirus * Rabies * Retrovirus * HIV * Adult T cell leukemia * Hepatitis D

Question 33

List the RNA Viruses – Nonenveloped

Answer 33

* Picornavirus * Enteroviruses * Polio * Coxsackie * Rhinovirus * Hepatitis A * Reovirus – DOUBLE STRANDED * Rotavirus * Calicivirus * Norwalk virus * Hepatitis E

Question 34

DNA Viruses

Answer 34

* DNA must first be transcribed into RNA, then translated into proteins • Synthesize their mRNA using host RNA polymerase * Most DNA viruses are double stranded, having both a positive and negative strand * Positive strand is read and transcribed into mRNA • Negative strand is ignored * Exception: Parvoviruses – single stranded DNA MOST ARE DOUBLE STRANDED

Question 35

Viral exanthems

Answer 35

Chickenpox, shingles, measles, roseola, rubella, and fifth disease

Question 36

Viral respiratory illnesses:

Answer 36

common cold, viral pharyngitis, influenza, covid-19

Question 37

Viral gastrointestinal illness

Answer 37

Rotavirus, Norwalk virus, and Hepatitis A-E

Question 38

Viral CNS diseases

Answer 38

Enterovirus, meningitis, encephalitis, arthropod-borne viral meningitis and encephalitis, and rabies encephalitis