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DNA Viruses

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Topic updated on 01/05/17 4:16pm

Snapshot
  • A 17-year-old patient presents to your clinic with a new rash. He is a wrestler on his high school varsity team. The rash is mildly itchy, but the patient denies any oozing or bleeding. On exam, you note umbilicated, waxy spots along his neck, arms, and waist in a nonspecific pattern. What are the characteristics of the most likely virus affecting this patient? 
Microbiology Overview
 
DNA Virus Table 
 
DNA Enveloped
Herpesvirus
  Disease Treatment
HSV type I Gingivosomastitis/herpes labialis (lip lesions)
Keratoconjunctivitis
Temporal lobe encephalitis
Acyclovir
HSV type II Genital vesicles
Neonatal herpes
Acyclovir
Varicella zoster Chickenpox
Shingles
Acyclovir
Epstein-Barr Infectious mononucleosis
Burkitt's lymphoma
Nasopharyngeal carcinoma
Treat symptoms
Cytomegalovirus Mononucleosis
Cytomegalic inclusion disease
Pneumonia
Ganciclovir
HHV Type 6 Roseola (fevers, seizures, rash) Treat symptoms
HHV Type 8 Kaposi's sarcoma None
Hepadnavirus
Hepatitis B Hepatitis IFN
Lamivudine
Poxvirus
Variola Smallpox No known treatment (30% die)
Molluscum contagiosum Molluscum contagiosum (wart-like benign tumors) Self-limiting
Ritonavir
DNA Non-Enveloped
Adenovirus
Adenovirus Acute respiratory disease
Pharyngoconjunctivitis
Epidemic keratoconjunctivitis
Gastroenteritis (pediatric)
Self-limiting
Papillomavirus
Human papilloma virus Warts
Cervical intraepithelial neoplasia
Treat with cryotherapy
Polyomavirus
JC virus Progressive multifocal leukoencephalopathy (PML) Supportive
Parvovirus
B19 Erythema infectiosum
Aplastic crisis (in sickle cell)
Hydrops fetalis
Self-limiting or immunoglobulin for aplastic crisis
 
Introduction to Viruses
  • Viruses are obligate intracellular infectious agents with the following basic components
    • DNA or RNA
      • never both
    • capsid
      • a protein coat that surrounds the genetic material
      • icosahedral or helical symmetry
      • made of capsomers
        • polypeptide chains organized into a globular subunit
        • in helical symmetry, capsomers are bound to RNA and coiled
          • forms a helical nucleoprotein capsid
    • sometimes an envelope
  • Viruses are classified by
    • nucleic acid
      • DNA or RNA
      • double stranded or single stranded
      • (+) positive or (-) negative stranded RNA
      • single or segmented pieces of nucleic acid
      • complexity of genome
    • capsid
      • icosahedral or helical
    • envelope
      • naked
        • DNA or RNA + capsomers and other structural proteins = nucleocapsid (no host membrane)
      • enveloped
        • nucleocapsid + host membrane with viral-specified glycoproteins = enveloped virus
    • size
      • diameter or number of capsomers
    • ploidy
      • all viruses are haploid (1 copy of DNA or RNA)
      • except retroviruses
        • retroviruses have 2 identical copies of their ssRNA, approximating diploidy
    • infectivity of purified nucleic acid
      • purified nucleic acid that is intrinsically infectious
        • dsDNA from most viruses
          • except poxviridae
          • except HBV
        • (+) ssRNA from most viruses
          • (+) linear, nonsegmented ssRNA can be translated immediately into a large protein by host machinery
          • virus must carry protease to cleave the 1 large protein product that will be generated by the host machinery
      • purified nucleic acid that is NOT intrinsically infectious
        • (-) ssRNA
          • viruses must carry an RNA-dependent RNA polymerase to generate mRNA the host machinery can read
        • dsRNA
        • they require enzymes contained in the complete virion for infectivity
DNA Viruses
  • Most DNA viruses
    • are double-stranded (dsDNA, like human DNA)
    • have icosahedral symmetry
    • replicate in the nucleus
    • are linear
  • Exceptions
    • parvoviridae
      • only 1 strand of DNA (ssDNA)
    • poxviridae
      • no icosahedral symmetry
        • surrounded by complex structural proteins
      • replicates in cytoplasm
    • papilloma, polyoma, and hepadna
      • are non-linear (circular)
  •  Enveloped vs naked
    • 3 DNA viruses are enveloped
      • herpes
      • hepadna
      • pox
    • the rest are naked
  • The DNA viruses are "HHAPPPPy" 
    • herpes
    • hepadna
    • adeno
    • pox
    • polyoma
    • papilloma
    • parvo


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