DNA Viruses: Poxviruses and Adenoviruses

Poxviruses - Big Bricks of DNA

• Largest & most complex DNA viruses; brick-shaped morphology.
• Unique: Replicate entirely in cytoplasm (own DNA-dependent RNA polymerase).
• Envelope acquired from host Golgi or ER.
• Clinical spectrum: skin lesions (pustules, nodules).

• Key Members:
  • Variola virus (Smallpox) - eradicated.
  • Molluscum contagiosum virus (MCV) - benign skin nodules.
  • Vaccinia virus - smallpox vaccine, gene therapy vector.
  • Monkeypox virus - emerging zoonosis.
  • Orf virus - zoonotic, affects sheep/goats, causes skin lesions in humans.

⭐ Poxviruses are the only DNA viruses that replicate exclusively in the cytoplasm, possessing all necessary enzymes, including their own DNA-dependent RNA polymerase and DNA polymerase.

📌 Mnemonic: Pox in a Box (brick-shaped) & Cytoplasm (replication site).

Poxviruses - Smallpox & Molluscum Mayhem

• General:
  • Largest, brick-shaped, dsDNA, enveloped viruses.
  • Replicate in cytoplasm (unique for DNA viruses). 📌 Pox in a BoX, in cytoBOXplasm.
  • Inclusions: Guarnieri bodies (Variola, Vaccinia).
• Smallpox (Variola virus):
  • Eradicated globally (WHO 1980).
  • Transmission: Respiratory droplets, contact.
  • Clinical: Synchronous, centrifugal rash (macule → papule → vesicle → pustule → scab).
  • Vaccinia virus for vaccine (live attenuated).
• Molluscum Contagiosum (MCV):
  • Benign skin infection.
  • Transmission: Direct contact, fomites, autoinoculation.
  • Clinical: Pearly, dome-shaped, umbilicated papules.
  • Inclusions: Henderson-Paterson bodies.
  • Severe in immunocompromised (e.g., HIV).

⭐ Poxviruses are the only DNA viruses replicating entirely in the cytoplasm, using their own DNA-dependent RNA polymerase.

Adenoviruses - Adeno's Agile Attack

• Structure: Naked (non-enveloped), icosahedral capsid, linear dsDNA genome. Fibers at vertices for attachment.
• Replication: In nucleus. Uses host RNA polymerase, its own DNA polymerase.
  • Early genes (E1A, E1B): regulate viral/host genes, block apoptosis (E1B-p53, E1A-Rb).
  • Late genes: structural proteins.
• Transmission: Aerosol, fecal-oral, fomites, direct contact.
• Common Syndromes:
  • Pharyngoconjunctival fever (PCF)
  • Acute Respiratory Disease (ARD) (📌 Military recruits: Serotypes 4, 7)
  • Epidemic Keratoconjunctivitis (EKC)
  • Gastroenteritis (Types 40, 41)
  • Hemorrhagic cystitis

⭐ Adenovirus serotypes 4 and 7 are notorious for causing acute respiratory disease (ARD) outbreaks in military recruits; a live oral vaccine is available for these types.

Adenoviruses - Adeno's Ailment Array

• Naked icosahedral dsDNA viruses.
• 57 serotypes known; species A-G.
• Transmission: Aerosol, fecal-oral, fomites, direct contact (conjunctiva).
• Clinical Syndromes:
  • Pharyngitis, fever (esp. children).
  • Acute Respiratory Disease (ARD) in military recruits (serotypes 4, 7).
  • Pharyngoconjunctival fever (PCF) - swimming pool conjunctivitis (serotypes 3, 7).
  • Epidemic Keratoconjunctivitis (EKC) - shipyard eye (serotypes 8, 19, 37).
  • Hemorrhagic cystitis (children, esp. boys; serotypes 11, 21).
  • Gastroenteritis & intussusception (serotypes 40, 41).
  • Myocarditis, pneumonia in immunocompromised.
• Diagnosis: PCR, viral culture, serology.
• 📌 Mnemonic: "ADE"no = Acute febrile pharyngitis, DNA virus, EKC.

⭐ Adenoviruses are known for their characteristic basophilic intranuclear inclusions (smudge cells or Cowdry type B inclusions) in infected cells, which are a key histological finding, particularly in respiratory or urinary tract infections and in immunocompromised patients where they can cause disseminated disease. Live oral vaccine for serotypes 4 and 7 used in military recruits to prevent ARD (Acute Respiratory Disease).

High‑Yield Points - ⚡ Biggest Takeaways

• Poxviruses: Largest DNA viruses (brick-shaped); unique cytoplasmic replication; Guarnieri bodies (intracytoplasmic).
• Molluscum contagiosum (Poxvirus): Characteristic pearly, umbilicated skin lesions.
• Smallpox (Variola) eradicated; Vaccinia virus used for its vaccine.
• Adenoviruses: Naked icosahedral DNA viruses; cause pharyngoconjunctival fever, hemorrhagic cystitis, epidemic keratoconjunctivitis.
• Adenovirus serotypes 40 & 41 are key causes of infantile diarrhea.
• Adenoviruses show basophilic intranuclear inclusions; used as gene therapy vectors.