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Flashcards in Microbiology - Virology (1) Deck (40):
1

Viral structure

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

  • 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

2

Viral genetics

  • Recombination 
  • Reassortment
  • Complementation
  • Phenotypic mixing

  • 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.

3

Viral vaccines

  • Live attenuated vaccines
  • Killed
  • Recombinant

  • 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, MMRInfluenza (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).

4

DNA viral genomes

  • Single vs. double stranded
  • Circular vs. linear

  • 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.

5

RNA viral genomes

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

  • 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.

6

Naked viral genome infectivity

  • 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.

7

Viral replication location

  • DNA viruses
  • RNA viruses

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

8

Viral envelopes

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

  • 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.

9

DNA virus characteristics

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

  • 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).

10

Herpesviruses

  • Enveloped?
  • DNA structure
  • Medical importance

  • 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

11

Hepadnavirus

  • Enveloped?
  • DNA structure
  • Medical importance

  • 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

12

Adenovirus

  • Enveloped?
  • DNA structure
  • Medical importance

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

13

Parvovirus

  • Enveloped?
  • DNA structure
  • Medical importance

  • 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

14

Papillomavirus

  • Enveloped?
  • DNA structure
  • Medical importance

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

15

Polyomavirus

  • Enveloped?
  • DNA structure
  • Medical importance

  • 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

16

Poxvirus

  • Enveloped?
  • DNA structure
  • Medical importance

  • 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

17

Herpesviruses

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

  • 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.

18

HSV identification

  • 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.

19

RNA viruses

  • "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

20

Reoviruses

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

  • 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

21

Picornaviruses

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

  • 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

22

Hepevirus

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

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

23

Caliciviruses

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

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

24

Flaviviruses

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

  • 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

25

Togaviruses

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

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

26

Retroviruses

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

  • 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

27

Coronaviruses

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

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

28

Orthomyxoviruses

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

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

29

Paramyxoviruses

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

  • Enveloped?
    • Yes
  • RNA structure
    • SS (-) linear
    • Nonsegmented
  • Capsid symmetry
    • Helical
  • Medical importance
    • PaRaMyxovirus:
      • Parainfluenza—croup
      • RSV—bronchiolitis in babies; Rx—ribavirin
      • Measles, Mumps

30

Rhabdoviruses

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

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

31

Filoviruses

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

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

32

Arenaviruses

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

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

33

Bunyaviruses

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

  • 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

34

Delta virus

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

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

35

Negative-stranded viruses

  • Must transcribe (-) strand to (+).
  • Virion brings its own RNA-dependent RNA polymerase.
  • They include Arenaviruses, Bunyaviruses, Paramyxoviruses, Orthomyxoviruses, Filoviruses, and Rhabdoviruses.
    • Always Bring Polymerase Or Fail Replication.

36

Segmented viruses

  • All are RNA viruses.
  • They include Bunyaviruses, Orthomyxoviruses (influenza viruses), Arenaviruses, and Reoviruses.
    • BOAR.

37

Picornavirus

  • Includes Poliovirus, Echovirus, Rhinovirus, Coxsackievirus, HAV.
    • PERCH on a “peak” (pico).
  • RNA is translated into 1 large polypeptide that is cleaved by proteases into functional viral proteins.
    • PicoRNAvirus = small RNA virus.
  • Can cause aseptic (viral) meningitis (except rhinovirus and HAV).
  • All are enteroviruses (fecal-oral spread) except rhinovirus.

38

Rhinovirus

  • 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).

39

Yellow fever virus

  • 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.

40

Rotavirus

  • Rotavirus [A], the most important global cause of infantile gastroenteritis, is a segmented dsRNA virus (a reovirus).
    • ROTAvirus = Right Out The Anus.
  • 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+.

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