Microbiology - Virology (1) Flashcards
1
Q
Viral structure
- Naked virus with icosahedral capsid
- Enveloped virus with icosahedral capsid
- Enveloped virus with helical capsid
A
- 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
Q
Viral genetics
- Recombination
- Reassortment
- Complementation
- Phenotypic mixing
A
- 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
Q
Viral vaccines
- Live attenuated vaccines
- Killed
- Recombinant
A
- 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!”
- MMR = measles, mumps, rubella
- 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
Q
DNA viral genomes
- Single vs. double stranded
- Circular vs. linear
A
- 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
Q
RNA viral genomes
- Single vs. double stranded
- Positive-stranded RNA viruses
A
- 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
Q
Naked viral genome infectivity
A
- 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
Q
Viral replication location
- DNA viruses
- RNA viruses
A
- DNA viruses
- All replicate in the nucleus (except poxvirus).
- RNA viruses
- All replicate in the cytoplasm (except influenza virus and retroviruses).
8
Q
Viral envelopes
- Naked (nonenveloped) viruses
- DNA
- RNA
- Enveloped viruses & exceptions
A
- 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).
- DNA
- Generally, enveloped viruses acquire their envelopes from plasma membrane when they exit from cell.
- Exceptions include herpesviruses, which acquire envelopes from nuclear membrane.
9
Q
DNA virus characteristics
- Viruses
- Single vs. double stranded
- Circular vs. linear
- Capsid shape
- Replication location
A
- 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
Q
Herpesviruses
- Enveloped?
- DNA structure
- Medical importance
A
- 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
Q
Hepadnavirus
- Enveloped?
- DNA structure
- Medical importance
A
- Enveloped?
- Yes
- DNA structure
- Partially DS and circular
- Medical importance
- HBV:
- Acute or chronic hepatitis
- Vaccine available—contains HBV surface antigen
- Not a retrovirus but has reverse transcriptase
- HBV:
12
Q
Adenovirus
- Enveloped?
- DNA structure
- Medical importance
A
- Enveloped?
- No
- DNA structure
- DS and linear
- Medical importance
- Febrile pharyngitis—sore throat
- Acute hemorrhagic cystitis
- Pneumonia
- Conjunctivitis—“pink eye”
13
Q
Parvovirus
- Enveloped?
- DNA structure
- Medical importance
A
- 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
Q
Papillomavirus
- Enveloped?
- DNA structure
- Medical importance
A
- Enveloped?
- No
- DNA structure
- DS and circular
- Medical importance
- HPV—warts (1, 2, 6, 11), CIN, cervical cancer (16, 18) vaccine available
15
Q
Polyomavirus
- Enveloped?
- DNA structure
- Medical importance
A
- 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
- JC virus—progressive multifocal leukoencephalopathy (PML) in HIV
16
Q
Poxvirus
- Enveloped?
- DNA structure
- Medical importance
A
- 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
Q
Herpesviruses
- HSV-1
- HSV-2
- VZV
- EBV
- CMV
- HHV-6
- HHV-8
A
- 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.
- Mononucleosis.
- 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.
- Kaposi sarcoma, a neoplasm of endothelial cells.
18
Q
HSV identification
A
- 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.
40
Q
Rotavirus
A
- 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+.
