PAPOVAVIRIDAE

• STRUCTURE: ds-DNA, circular. No envelope. Supercoiled double-stranded circles of DNA, wrapped around host histones to form a chromosome-like structure.

• HUMAN PAPILLOMAVIRUSES:

  • PATHOGENESIS: Papillomavirus replicates in host nucleus but it does not integrate as a provirus.

    • Virus is species-specific, and it is tissue-specific to epithelial cells only.

  • REPLICATION: Genome divided into Early region (early proteins) and late region (late proteins)

    • Early Proteins (E1-E8): Synthesized before DNA replication. The proteins are important in replication, transcription, and oncogenic transformation.

    • Late Proteins (L1-L2): Synthesized after DNA replication. Structural proteins.

  • DIAGNOSIS: Cytology, EM, or PCR. Does not grow well in culture.

  • MANIFESTATIONS:

    • Common Warts (verruca): HPV-2,4 Thickening of the epidermis, and hyperkeratosis.

      • Terminally differentiated surface epithelial cells are permissive, so the virus multiplies in those cells. These cells eventually die from lytic infection.

      • Basal Cells are non-permissive. Only the early genes are produced in these cells -- until they differentiate to epithelial cells.

        • Gene products of the early genes stimulate differentiation of the basal cells and growth of the wart.

      • Common in children. Lower incidence in adults may be because of acquired immunity.

    • Deep Plantar Warts: HPV-1,2

    • Genital Warts (Condylomata Acumulata): HPV-1,2,6,11,16,18

    • Cervical Carcinoma: HPV-16,18. It starts as cervical dysplasia, and not all forms progress to cancer.

  • TREATMENT:

    • Podophyllin, or salicylic acid with glutaraldehyde may be used. Or use alpha-IFN IM for severe genital warts or laryngeal papillomas.

• POLYOMAVIRUSES: They are asymptomatic in immunocompetent hosts. They are ubiquitous viruses. Both viruses are tumorigenic.

  • PATHOGENESIS: Polyoma can integrate into host DNA as a provirus.

  • DIAGNOSIS: It does grow well in culture.

  • JC VIRUS (JCV): Progressive Multifocal Leukoencephalopathy (PML), in immunocompromised host. It infects microglial cells in brain.

    • 5-10% of AIDS patients.

    • It is a slow virus disease.

  • BK VIRUS (BKV): Infects kidney and causes Ureteral Stenosis and Hemorrhagic Cystitis in immunocompromised host.

  • Simian Virus 40 (SV40): Formerly called vacuolating agent. Not associated with any disease in humans.

    • Resides in latent state in monkey kidney cells.

    • REPLICATION: Early and late proteins are formed. Large T-Antigen and small T-Antigen are formed respectively. dsDNA is duplicated in a semiconservative anti-parallel fashion, utilizing leading and lagging strand, and okazaki fragments.

Category: Microbiology Notes