DNA Viruses

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?

DNA Virus Table

Enveloped DNA Viruses
Herpesvirus
Virus	Disease	Treatment
HSV type I	Gingivosomastitis/herpes labialis (lip lesions)KeratoconjunctivitisTemporal lobe encephalitis	Acyclovir
HSV type II	Genital vesiclesNeonatal herpes	Acyclovir
Varicella zoster	ChickenpoxShingles	Acyclovir
Epstein-Barr	Infectious mononucleosisBurkitt lymphomaNasopharyngeal carcinoma	Treat symptoms
Cytomegalovirus	MononucleosisCytomegalic inclusion diseasePneumonia	Ganciclovir
HHV Type 6	Roseola (fevers, seizures, rash)	Treat symptoms
HHV Type 8	Kaposi’s sarcoma	None
Hepadnavirus
Hepatitis B	Hepatitis	IFNLamivudine
Poxvirus
Variola	Smallpox	No known treatment (30% mortality)
Molluscum contagiosum	Molluscum contagiosum (wart-like benign tumors)	Self-limitingRitonavir
Non-Enveloped DNA Viruses
Adenovirus
Adenovirus	Acute respiratory diseasePharyngoconjunctivitisEpidemic keratoconjunctivitisGastroenteritis (pediatric)	Self-limiting
Papillomavirus
Human papilloma virus	WartsCervical intraepithelial neoplasia	Treat with cryotherapy
Polyomavirus
JC virus	Progressive multifocal leukoencephalopathy (PML)	Supportive
Parvovirus
Parvovirus B19	Erythema infectiosumAplastic 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

Useful Links

Information

Socials