MB449 Module 9 - DNA Viruses

• DNA viruses

  Viruses that have DNA as their genetic material
• General properties of DNA viruses

  • DNA (single or double-stranded, circular or linear)
  • Replication of nucleic acid (early transcription, early translation, late transcription, late translation)
  • Viruses cannot contain both DNA and RNA
  • Many viruses do not follow the central dogma
  • Hijack host cell for replication
  • Transcription and translation first before replication
• Parvoviruses


  • Icosahedral
  • Very small (18-26 nm diameter)
  • Single-stranded DNA
  • Non-enveloped
  • 2-5 proteins
  • Resistant to inactivation
  • Hard to treat
• Subfamilies of Parvoviridae


  • Densovirinae (infect invertebrates, require helper viruses)
  • Parvovirinae (infect vertebrates)
• Genera of Parvovirinae


  • Erythroparvovirus (includes parvovirus B19)
  • Bocaparvovirus
  • Protoparvovirus
  • Dependoparvovirus
• Dependoparvovirus


  Requires and depends on helper cells for successful infection
• Parvoviruses always need helper viruses or viral replication will not proceed
• Human parvovirus B19

  • First discovered in 1975
  • Predominant parvovirus pathogen in humans
  • Three genotypes (III common in Africa, I and II common in West Hemisphere)
• Parvovirus B19 only affects humans
• Clinical manifestations of parvovirus B19

  • Erythema infectiosum (Fifth's disease, most common manifestation)
  • Transient aplastic crisis
  • Pure red blood cell aplasia
  • Pregnancy complications (hydrops fetalis, miscarriage)
• Erythema infectiosum (Fifth's disease)


  Mild, self-limiting rash in children, does not require hospitalization or special medication
• Transient aplastic crisis


  Abrupt cessation of red blood cell synthesis, lowers hemoglobin, usually occurs in people with chronic hemolytic anemia
• Pure red blood cell aplasia

  Occurs in immunocompromised individuals, very few immature red blood cells, usually chronic
• Pregnancy complications


  Hydrops fetalis (fluid accumulation), higher miscarriage rate if infected in first half of pregnancy
• Transmission of parvovirus B19

  • Respiratory aerosol
  • Mother-to-child
  • Blood products
• Parvovirus B19 has a very high viral load in acute infection before immune response is detectable
• Parvovirus B19 ligand


  Non-structural protein 1 (NS1)
• Vaccine can prevent deaths in pets, without vaccination the mortality rate is 90%
• Adenoviruses

  • Icosahedral
  • 70-90 nm
  • Double-stranded DNA
  • Non-enveloped
  • Infect epithelial cells
• Genera of Adenoviridae


  • Atadenovirus
  • Aviadenovirus
  • Siadenovirus
  • Ichtadenovirus
  • Testadenovirus
  • Mastadenovirus (human adenovirus A-G)
• Currently there are 88 adenoviruses that infect humans
• Clinical manifestations of adenovirus infections

  • Upper respiratory tract (rhinitis, pharyngitis, tonsillitis)
  • Lower respiratory tract (pneumonia, chest pains)
  • Eye infections (conjunctivitis, epidemic keratoconjunctivitis)
  • Gastrointestinal tract (gastroenteritis)
  • Urinary tract (hemorrhagic cystitis)
• Adenovirus infections start mild but can develop into more severe disease if left untreated
• There is a vaccine for adenovirus but it is only given to severe cases or immunocompromised individuals as the virus is usually mild
• Transmission of adenoviruses


  • Respiratory droplets
  • Fecal-oral route (fluids, fields, flies, fingers)
  • Mother to newborn
  • Organ transplant
• Adenovirus infections are common in settings like daycares, military barracks, and classrooms
• Herpesviruses


  • Icosahedral
  • 150-200 nm
  • Double-stranded DNA
  • Enveloped
• Subfamilies of Herpesviridae


  • Alphaherpesvirinae (Simplexvirus, Varicellovirus)
  • Betaherpesvirinae (Cytomegalovirus, Roseolovirus)
  • Gammaherpesvirinae (Lymphocryptovirus, Rhadinovirus)
• Herpes simplex virus (HSV-1 and HSV-2)

  • Oral herpes (HSV-1) transmitted through contact with oral secretions
  • Genital herpes (HSV-2) transmitted through contact with genital secretions
• Primary HSV infection


  • Virus must encounter mucosal surfaces or broken skin to initiate infection
  • HSV-1 and HSV-2 also infect nearby sensory neurons and travel to the neuron's cell body to start latent cycle
• Majority of HSV cases are mild and asymptomatic
• HSV latent infection

  • Virus resides in latently infected ganglia in a nonreplicating state
  • Only very few viral genes are expressed
  • Viral persistence in latently infected ganglia lasts for the lifetime of the host
• HSV recurrence


  • Provocative stimuli can reactivate virus from the latent state
  • Virus travels back to the peripheral site and replication proceeds to the skin or mucous membrane
  • Recurrence is usually milder than primary infection
• Clinical manifestations of HSV

  • Oral herpes (herpetic gingivostomatitis)
  • Genital herpes
  • HSV keratoconjunctivitis
  • Skin infections (herpetic whitlow, herpes gladitorum)
  • Neonatal HSV
• Oral herpes


  Primarily asymptomatic, symptoms usually appear in children, incubation period of 2-12 days, illness lasts 2-3 weeks
• Genital herpes


  Usually caused by HSV-2, primary infection can be severe, generally lasts 3 weeks, characterized by painful lesions on the genitals
• HSV keratoconjunctivitis


  Recurrent lesions of the eye appear as dendritic keratitis or corneal ulcers, can lead to permanent opacification and blindness
• Skin infections


  Rare for healthy people, usually seen in fingers (herpetic whitlow) or body (herpes gladitorum), can be serious for people with certain skin conditions
• Neonatal HSV


  Transmission happens at birth, can appear as disseminated multiorgan disease, localized CNS disease, or localized skin/eye/mouth infection
• Treatments for HSV


  • Acyclovir
  • Famciclovir
  • Valacyclovir