DNA & RNA Viruses: Structure, Transmission, and Prevention

Classification of DNA Viruses

• DNA viruses can be classified into several families based on their characteristics:
  • Parvovirus: small, non-enveloped, icosahedral, single-stranded DNA, e.g., B19 virus
  • Polyomavirus: small, non-enveloped, icosahedral, double-stranded DNA, e.g., JC virus, BK virus
  • Papillomavirus: small, non-enveloped, icosahedral, double-stranded DNA, e.g., human papilloma virus
  • Adenovirus: medium-sized, non-enveloped, icosahedral, double-stranded DNA, e.g., adenovirus
  • Hepadnavirus: enveloped, icosahedral, double-stranded DNA, e.g., hepatitis B virus
  • Herpesvirus: enveloped, icosahedral, double-stranded DNA, e.g., herpes simplex virus, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus
  • Poxvirus: large, enveloped, complex, double-stranded DNA, e.g., smallpox virus, molluscum contagiosum virus

Herpesviruses

• Herpesviruses can cause a range of diseases, including:
  • HSV-1: gingivostomatitis, herpes labialis, encephalitis, keratitis
  • HSV-2: herpes genitalis, perinatal disseminated disease
  • VZV: varicella, zoster
  • EBV: infectious mononucleosis, none (no recurrent infection)
  • CMV: congenital infection, mononucleosis in transfusion recipients, pneumonia and hepatitis in immunocompromised patients
  • HSV-8: Kaposi's sarcoma in AIDS patients

Adenovirus

• Adenovirus can cause:
  • Upper and lower respiratory tract disease (pharyngitis and pneumonia)
  • Enteric strains cause diarrhea
  • Transmitted by respiratory droplets, iatrogenic in eye disease, and fecal-oral with enteric strains
  • Live vaccine against types 3, 4, and 7 is used in the military to prevent pneumonia

Papillomavirus

• Papillomavirus can cause:
  • Papillomas (warts)
  • Condylomata acuminata (genital warts)
  • Carcinoma of the cervix and penis
  • Transmitted by direct contact of skin and genital lesions
  • Two early viral genes, E6 and E7, encode proteins that inhibit activity of proteins encoded by tumor suppressor genes, p53 gene and retinoblastoma gene, respectively
  • Vaccine containing capsid proteins of four HPV types (6, 11, 16, and 18) is available

Hepadnavirus: Hepatitis B Virus

• Hepatitis B virus can cause:
  • Hepatitis B and hepatocellular carcinoma
  • Transmitted by blood, during birth, and sexual intercourse
  • Hepatocellular injury due to immune attack by cytotoxic (CD8) T cells
  • Antigen-antibody complexes cause arthritis, rash, and glomerulonephritis
  • 5% of HBV infections result in a chronic carrier
  • Chronic hepatitis, cirrhosis, and hepatocellular carcinoma can occur (integration of part of viral DNA into hepatocyte DNA)

Laboratory Diagnosis of Hepatitis B Virus

• Three serologic tests are commonly used:
  • Surface antigen (HBsAg)
  • Surface antibody (HBsAb)
  • Core antibody (HBcAb)
• Detection of HbsAg ≥6 months chronic carrier
• Presence of e antigen infectious chronic carrier
• "Window" phase: HBV-infected person has neither detectable HBs antigen nor HBs antibody and is diagnosed by detecting HB core antibody

Treatment and Prevention of Hepatitis B Virus

• Alpha interferon and lamivudine reduce inflammation associated with chronic hepatitis B but does not cure carrier state
• Prevention:
  • Vaccine that contains HBsAg as immunogen
  • Hyperimmune serum globulins obtained from donors with high titers of HBsAb

Classification of RNA Viruses

• RNA viruses can be classified into several families based on their characteristics:
  • Picornavirus: small, non-enveloped, icosahedral, single-stranded RNA, positive polarity, e.g., poliovirus, rhinovirus, hepatitis A virus
  • Hepevirus: small, non-enveloped, icosahedral, single-stranded RNA, positive polarity, e.g., hepatitis E virus
  • Calicivirus: small, non-enveloped, icosahedral, single-stranded RNA, positive polarity, e.g., norwalk virus
  • Reovirus: small, non-enveloped, icosahedral, double-stranded RNA, e.g., rotavirus
  • Flavivirus: small, enveloped, icosahedral, single-stranded RNA, positive polarity, e.g., yellow fever virus, dengue virus, West Nile virus, hepatitis C virus
  • Togavirus: small, enveloped, icosahedral, single-stranded RNA, positive polarity, e.g., rubella virus
  • Retrovirus: enveloped, icosahedral, single-stranded RNA, positive polarity, e.g., HIV, human T-cell leukemia virus
  • Orthomyxovirus: small, enveloped, helical, single-stranded RNA, negative polarity, e.g., influenza virus
  • Paramyxovirus: small, enveloped, helical, single-stranded RNA, negative polarity, e.g., measles virus, mumps virus, respiratory syncytial virus
  • Rhabdovirus: small, enveloped, helical, single-stranded RNA, negative polarity, e.g., rabies virus
  • Filovirus: small, enveloped, helical, single-stranded RNA, negative polarity, e.g., Ebola virus, Marburg virus