Microbiology - Virology (1)

Question 1

Viral structure

• Naked virus with icosahedral capsid
• Enveloped virus with icosahedral capsid
• Enveloped virus with helical capsid

Answer 1

• Naked virus with icosahedral capsid
  
  • Capsid
  • Nucleic acid
• Enveloped virus with icosahedral capsid
  
  • Surface protein
  • Lipid bilayer
  • Capsid
  • Nucleic acid
• Enveloped virus with helical capsid
  
  • Surface protein
  • Lipid bilayer
  • Helical capsid with nucleic acid inside

Question 2

Viral genetics

• Recombination
• Reassortment
• Complementation
• Phenotypic mixing

Answer 2

• Recombination
  
  • Exchange of genes between 2 chromosomes by crossing over within regions of significant base sequence homology.
• Reassortment
  
  • When viruses with segmented genomes (e.g., influenza virus) exchange segments.
  • High-frequency recombination.
  • Cause of worldwide influenza pandemics.
• Complementation
  
  • When 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein.
  • The nonmutated virus “complements” the mutated one by making a functional protein that serves both viruses.
• Phenotypic mixing
  
  • Occurs with simultaneous infection of a cell with 2 viruses.
  • Genome of virus A can be partially or completely coated (forming pseudovirion) with the surface proteins of virus B.
  • Type B protein coat determines the tropism (infectivity) of the hybrid virus.
  • However, the progeny from this infection have a type A coat that is encoded by its type A genetic material.

Question 3

Viral vaccines

• Live attenuated vaccines
• Killed
• Recombinant

Answer 3

• Live attenuated vaccines
  
  • Induce humoral and cell-mediated immunity but have reverted to virulence on rare occasions.
  • Live attenuated—smallpox, yellow fever, chickenpox (VZV), Sabin polio virus, MMR, Influenza (intranasal).
    
    • MMR = measles, mumps, rubella
      
      • Live attenuated vaccine that can be given to HIV-positive patients who do not show signs of immunodeficiency
    • “Live! One night only! See small yellow chickens get vaccinated with Sabin and MMR! It’s incredible!”
  • No booster needed for live attenuated vaccines.
  • Dangerous to give live vaccines to immunocompromised patients or their close contacts.
• Killed
  
  • Induce only humoral immunity but are stable.
  • Rabies, Influenza (injected), Salk Polio, and HAV vaccines.
    
    • SalK** = Killed.**
    • RIP Always.
• Recombinant
  
  • HBV (antigen = recombinant HBsAg)
  • HPV (types 6, 11, 16, and 18).

Question 4

DNA viral genomes

• Single vs. double stranded
• Circular vs. linear

Answer 4

• All DNA viruses except the Parvoviridae are dsDNA.
  
  • All are dsDNA (like our cells), except “part-of-a-virus” (parvovirus) is ssDNA.
• All are linear except papilloma-, polyoma-, and hepadnaviruses (circular).
• Parvus = small.

Question 5

RNA viral genomes

• Single vs. double stranded
• Positive-stranded RNA viruses

Answer 5

• All RNA viruses except Reoviridae are ssRNA.
  
  • All are ssRNA (like our mRNA), except “repeato-virus” (reovirus) is dsRNA.
• Positive-stranded RNA viruses
  
  • Retrovirus, togavirus, flavivirus, coronavirus, hepevirus, calicivirus, picornavirus.
  • I went to a retro toga party, where I drank flavored Corona and ate hippy California pickles.

Question 6

Naked viral genome infectivity

Answer 6

• Purified nucleic acids of most dsDNA (except poxviruses and HBV) and (+) strand ssRNA (≈ mRNA) viruses are infectious.
• Naked nucleic acids of (-) strand ssRNA and dsRNA viruses are not infectious.
  
  • They require polymerases contained in the complete virion.

Question 7

Viral replication location

• DNA viruses
• RNA viruses

Answer 7

• DNA viruses
  
  • All replicate in the nucleus (except poxvirus).
• RNA viruses
  
  • All replicate in the cytoplasm (except influenza virus and retroviruses).

Question 8

Viral envelopes

• Naked (nonenveloped) viruses
  
  • DNA
  • RNA
• Enveloped viruses & exceptions

Answer 8

• Naked (nonenveloped) viruses
  
  • DNA
    
    • Papillomavirus, Adenovirus, Parvovirus, Polyomavirus (PAPP).
  • RNA
    
    • Calicivirus, Picornavirus, Reovirus, and Hepevirus (CPR and Hep).
  • Give PAPP smears and CPR to a naked Heppy (hippy).
• Generally, enveloped viruses acquire their envelopes from plasma membrane when they exit from cell.
  
  • Exceptions include herpesviruses, which acquire envelopes from nuclear membrane.

Question 9

DNA virus characteristics

• Viruses
• Single vs. double stranded
• Circular vs. linear
• Capsid shape
• Replication location

Answer 9

• All are HHAPPPPy viruses
  
  • Hepadna, Herpes, Adeno, Pox, Parvo, Papilloma, Polyoma.
• All are double stranded
  
  • Except parvo (single stranded).
• All are linear
  
  • Except papilloma and polyoma (circular, supercoiled) and hepadna (circular, incomplete).
• All are icosahedral
  
  • Except pox (complex).
• Replicate in the nucleus
  
  • Except pox (carries own DNA-dependent RNA polymerase).

Question 10

Herpesviruses

• Enveloped?
• DNA structure
• Medical importance

Answer 10

• Enveloped?
  
  • Yes
• DNA structure
  
  • DS and linear
• Medical importance
  
  • HSV-1—oral (and some genital) lesions, spontaneous temporal lobe encephalitis, keratoconjunctivitis
  • HSV-2—genital (and some oral) lesions
  • VZV (HHV-3)—chickenpox, zoster (shingles); vaccine available
  • EBV (HHV-4)—mononucleosis, Burkitt lymphoma, Hodgkin lymphoma
  • CMV (HHV-5)—infection in immunosuppressed patients (AIDS retinitis), especially transplant recipients; congenital defects (“sightomegalovirus”)
  • HHV-6—roseola (exanthem subitum)
  • HHV-7—less common cause of roseola
  • HHV-8—causes Kaposi sarcoma

Question 11

Hepadnavirus

• Enveloped?
• DNA structure
• Medical importance

Answer 11

• Enveloped?
  
  • Yes
• DNA structure
  
  • Partially DS and circular
• Medical importance
  
  • HBV:
    
    • Acute or chronic hepatitis
    • Vaccine available—contains HBV surface antigen
    • ƒƒNot a retrovirus but has reverse transcriptase

Question 12

Adenovirus

• Enveloped?
• DNA structure
• Medical importance

Answer 12

• Enveloped?
  
  • No
• DNA structure
  
  • DS and linear
• Medical importance
  
  • Febrile pharyngitis—sore throat
  • Acute hemorrhagic cystitis
  • Pneumonia
  • Conjunctivitis—“pink eye”

Question 13

Parvovirus

• Enveloped?
• DNA structure
• Medical importance

Answer 13

• Enveloped?
  
  • No
• DNA structure
  
  • SS and linear (-) (smallest DNA virus)
• Medical importance
  
  • B19 virus—aplastic crises in sickle cell disease, “slapped cheeks” rash in children
  • Erythema infectiosum (fifth disease)
  • RBC destruction in fetus leads to hydrops fetalis and death
  • Pure RBC aplasia and rheumatoid arthritis–like symptoms in adults

Question 14

Papillomavirus

• Enveloped?
• DNA structure
• Medical importance

Answer 14

• Enveloped?
  
  • No
• DNA structure
  
  • DS and circular
• Medical importance
  
  • HPV—warts (1, 2, 6, 11), CIN, cervical cancer (16, 18) vaccine available

Question 15

Polyomavirus

• Enveloped?
• DNA structure
• Medical importance

Answer 15

• Enveloped?
  
  • No
• DNA structure
  
  • DS and circular
• Medical importance
  
  • JC virus—progressive multifocal leukoencephalopathy (PML) in HIV
    
    • JC: Junky Cerebrum
  • BK virus—transplant patients, commonly targets kidney
    
    • BK: Bad Kidney

Question 16

Poxvirus

• Enveloped?
• DNA structure
• Medical importance

Answer 16

• Enveloped?
  
  • Yes
• DNA structure
  
  • DS and linear (largest DNA virus)
• Medical importance
  
  • Smallpox, although eradicated, could be used in germ warfare
  • Cowpox (“milkmaid blisters”)
  • Molluscum contagiosum—flesh-colored dome lesions with central umbilicated dimple

Question 17

Herpesviruses

• HSV-1
• HSV-2
• VZV
• EBV
• CMV
• HHV-6
• HHV-8

Answer 17

• HSV-1
  
  • Gingivostomatitis, keratoconjunctivitis [A], temporal lobe encephalitis (most common cause of sporadic encephalitis in the United States), herpes labialis [B].
  • Latent in trigeminal ganglia.
  • Transmitted by respiratory secretions, saliva.
• HSV-2
  
  • Herpes genitalis [C], neonatal herpes.
  • Latent in sacral ganglia.
  • Transmitted by sexual contact, perinatally.
• VZV
  
  • Varicella-zoster (chickenpox, shingles) [D], encephalitis, pneumonia.
  • Latent in dorsal root or trigeminal ganglia.
  • Most common complication of shingles is post-herpetic neuralgia.
  • Transmitted by respiratory secretions.
• EBV
  
  • Mononucleosis.
    
    • Characterized by fever, hepatosplenomegaly, pharyngitis, and lymphadenopathy (especially posterior cervical nodes).
  • Transmitted by respiratory secretions and saliva
    
    • Also called “kissing disease” since commonly seen in teens, young adults.
  • Infects B cells.
    
    • Atypical lymphocytes seen on peripheral blood smear [E] are not infected B cells but rather reactive cytotoxic T cells.
  • Detect by (+) Monospot test—heterophile antibodies detected by agglutination of sheep or horse RBCs.
  • Associated with Hodgkin lymphoma, endemic Burkitt lymphoma, nasopharyngeal carcinoma.
• CMV
  
  • Congenital infection, mononucleosis ((-) Monospot), pneumonia, retinitis.
  • Infected cells have characteristic “owl eye” inclusions [F].
  • Latent in mononuclear cells.
  • Transmitted congenitally and by transfusion, sexual contact, saliva, urine, transplant.
• HHV-6
  
  • Roseola: high fevers for several days that can cause seizures, followed by a diffuse macular rash [G].
  • Transmitted by saliva.
• HHV-8
  
  • Kaposi sarcoma, a neoplasm of endothelial cells.
    
    • Seen in HIV/AIDS and transplant patients.
  • Dark/violaceous flat and nodular skin lesions [H] representing endothelial growths.
    
    • Can also affect GI tract and lungs.
  • Transmitted by sexual contact.

Question 18

HSV identification

Answer 18

• Viral culture for skin/genitalia.
• CSF PCR for herpes encephalitis.
• Tzanck test (genital herpes)—a smear of an opened skin vesicle to detect multinucleated giant cells [A].
  
  • Tzanck heavens I do not have herpes.
• Infected cells also have intranuclear Cowdry A inclusions.

Question 19

RNA viruses

Answer 19

• “Grab our hoppy bunny fellow ROP to get a corona flavored drink…picalreo!”
• Rhabdo
• Arena
• Hepe
• Bunya
• Filo
• Retro
• Orthomyxo
• Paramyxo
• Toga
• Corona
• Flavi
• Delta
• Picorna
• Calci
• Reo

Question 20

Reoviruses

• Enveloped?
• RNA structure
• Capsid symmetry
• Medical importance

Answer 20

• Enveloped?
  
  • No
• RNA structure
  
  • DS linear
  • 10–12 segments
• Capsid symmetry
  
  • Icosahedral (double)
• Medical importance
  
  • Coltivirusa—Colorado tick fever
    
    • Arbovirus, transmitted by arthropods (mosquitoes, ticks)
  • Rotavirus—#1 cause of fatal diarrhea in children

Question 21

Picornaviruses

• Enveloped?
• RNA structure
• Capsid symmetry
• Medical importance

Answer 21

• Enveloped?
  
  • No
• RNA structure
  
  • SS (+) linear
• Capsid symmetry
  
  • Icosahedral
• Medical importance (PERCH)
  
  • Poliovirus—polio-Salk/Sabin vaccines—IPV/OPV
  • Echovirus—aseptic meningitis
  • Rhinovirus—“common cold”
  • Coxsackievirus—aseptic meningitis; herpangina (mouth blisters, fever); hand, foot, and mouth disease; myocarditis; pericarditis
  • HAV—acute viral hepatitis

Question 22

Hepevirus

• Enveloped?
• RNA structure
• Capsid symmetry
• Medical importance

Answer 22

• Enveloped?
  
  • No
• RNA structure
  
  • SS (+) linear
• Capsid symmetry
  
  • Icosahedral
• Medical importance
  
  • HEV

Question 23

Caliciviruses

• Enveloped?
• RNA structure
• Capsid symmetry
• Medical importance

Answer 23

• Enveloped?
  
  • No
• RNA structure
  
  • SS (+) linear
• Capsid symmetry
  
  • Icosahedral
• Medical importance
  
  • Norovirus—viral gastroenteritis

Question 24

Flaviviruses

• Enveloped?
• RNA structure
• Capsid symmetry
• Medical importance

Answer 24

• Enveloped?
  
  • Yes
• RNA structure
  
  • SS (+) linear
• Capsid symmetry
  
  • Icosahedral
• Medical importance
  
  • HCV
  • Arbovirus, transmitted by arthropods (mosquitoes, ticks).
    
    • Yellow fever
    • Dengue
    • St. Louis encephalitis
    • West Nile virus

Question 25

Togaviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 25

* Enveloped? * Yes * RNA structure * SS (+) linear * Capsid symmetry * Icosahedral * Medical importance * Rubella * Arbovirus, transmitted by arthropods (mosquitoes, ticks). * Eastern equine encephalitis * Western equine encephalitis

Question 26

Retroviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 26

* Enveloped? * Yes * RNA structure * SS (+) linear * Capsid symmetry * Icosahedral (HTLV), complex and conical (HIV) * Medical importance * Have reverse transcriptase * HTLV—T-cell leukemia * HIV—AIDS

Question 27

Coronaviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 27

* Enveloped? * Yes * RNA structure * SS (+) linear * Capsid symmetry * Helical * Medical importance * Coronavirus—“common cold” and SARS

Question 28

Orthomyxoviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 28

* Enveloped? * Yes * RNA structure * SS (-) linear * 8 segments * Capsid symmetry * Helical * Medical importance * Influenza virus

Question 29

Paramyxoviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 29

* Enveloped? * Yes * RNA structure * SS (-) linear * Nonsegmented * Capsid symmetry * Helical * Medical importance * ****_P_**a_R_a**_M_**yxovirus**: * **_P_**arainfluenza—croup * **_R_**SV—bronchiolitis in babies; **_R_**x—**_r_**ibavirin * **_M_**easles, **_M_**umps

Question 30

Rhabdoviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 30

* Enveloped? * Yes * RNA structure * SS (-) linear * Capsid symmetry * Helical * Medical importance * Rabies

Question 31

Filoviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 31

* Enveloped? * Yes * RNA structure * SS (-) linear * Capsid symmetry * Helical * Medical importance * Ebola/Marburg hemorrhagic fever—often fatal

Question 32

Arenaviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 32

* Enveloped? * Yes * RNA structure * SS (-) circular * 2 segments * Capsid symmetry * Helical * Medical importance * LCMV—lymphocytic choriomeningitis virus * Lassa fever encephalitis—spread by mice

Question 33

Bunyaviruses * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 33

* Enveloped? * Yes * RNA structure * SS (-) circular * 3 segments * Capsid symmetry * Helical * Medical importance * California encephalitisa * Sandfly/Rift Valley feversa * Crimean-Congo hemorrhagic fevera * Hantavirus—hemorrhagic fever, pneumonia

Question 34

Delta virus * Enveloped? * RNA structure * Capsid symmetry * Medical importance

Answer 34

* Enveloped? * Yes * RNA structure * SS (-) circular * Capsid symmetry * Uncertain * Medical importance * HDV is a “defective” virus that requires HBV co-infection

Question 35

Negative-stranded viruses

Answer 35

* Must transcribe (-) strand to (+). * Virion brings its own RNA-dependent RNA polymerase. * They include **_A_**renaviruses, **_B_**unyaviruses, **_P_**aramyxoviruses, **_O_**rthomyxoviruses, **_F_**iloviruses, and **_R_**habdoviruses. * ****_A_**lways **_B_**ring **_P_**olymerase **_O_**r **_F_**ail **_R_**eplication.**

Question 36

Segmented viruses

Answer 36

* All are RNA viruses. * They include **_B_**unyaviruses, **_O_**rthomyxoviruses (influenza viruses), **_A_**renaviruses, and **_R_**eoviruses. * **_BOAR_.**

Question 37

Picornavirus

Answer 37

* Includes **_P_**oliovirus, **_E_**chovirus, **_R_**hinovirus, **_C_**oxsackievirus, **_H_**AV. * **_PERCH_ on a “_peak_” (**_pic_**o).** * RNA is translated into 1 large polypeptide that is cleaved by proteases into functional viral proteins. * **Pico**_RNA_**virus = small _RNA_ virus.** * Can cause aseptic (viral) meningitis (except rhinovirus and HAV). * All are enteroviruses (fecal-oral spread) except rhinovirus.

Question 38

Rhinovirus

Answer 38

* A picornavirus. * Nonenveloped RNA virus. * Cause of common cold; \> 100 serologic types. * **_Rhino_ has a runny _nose_.** * Acid labile * Destroyed by stomach acid * Does not infect the GI tract (unlike the other picornaviruses).

Question 39

Yellow fever virus

Answer 39

* A flavivirus (also an arbovirus) transmitted by Aedes mosquitoes. * Virus has a monkey or human reservoir. * Symptoms: high fever, black vomitus, and jaundice. * **Flavi = yellow, jaundice.**

Question 40

Rotavirus

Answer 40

* Rotavirus [A], the most important global cause of infantile gastroenteritis, is a segmented dsRNA virus (a reovirus). * ****_ROTA_**virus = **_R_**ight **_O_**ut **_T_**he **_A_**nus.** * Major cause of acute diarrhea in the United States during winter, especially in day-care centers, kindergartens. * CDC recommends routine vaccination of all infants. * Villous destruction with atrophy leads to decreased absorption of Na+ and loss of K+.