ADENOVIRUSES

Important Properties –There are 41 known antigenic types; the fiber protein is the main type-specific antigen

• Types 3, 4, 7, and 21 cause respiratory disease
• Types 8 and 19 cause epidemic keratoconjunctivitis
• Types 11 and 21 cause hemorrhagic cystitis
• Types 40 and 41 cause infantile gastroenteritis

Summary of Replicative Cycle

• After attachment to the cell surface via its fiber, the virus penetrates and uncoats, and the viral DNA moves to the nucleus.
• Host cell DNA-dependent RNA polymerase transcribes the early genes, and splicing enzymes remove the RNA representing the introns, resulting in functional mRNA. (Note that introns and exons, which are common in eukaryotic DNA, were first described for adenovirus DNA.)
• Early mRNA is translated into nonstructural proteins in the cytoplasm.
• After viral DNA replication in the nucleus
• Late mRNA is transcribed and then translated into structural virion proteins.
• Viral assembly occurs in the nucleus, and the virus is released by lysis of the cell, not by budding.

Pathogenesis & Immunity- Virus preferentially infects epithelium of respiratory tract and eyes. Adenoviruses infect the mucosal epithelium of several organs (e.g., the respiratory tract [both upper and lower], the gastrointestinal tract, and the conjunctivas). Immunity based on neutralizing antibody is type-specific and lifelong.

In addition to acute infection leading to death of the cells, adenoviruses cause a latent infection, particularly in the adenoidal and tonsillar tissues of the throat.

PAPILLOMAVIRUSES

Important Properties –

Two of the early genes, E6 and E7, are implicated in carcinogenesis. They encode proteins that inactivate proteins encoded by tumor suppressor genes in human cells (e.g., the p53 gene and the retinoblastoma [RB] gene, respectively).

Inactivation of the p53 and RB proteins is an important step in the process by which a normal cell becomes a cancer cell.

Pathogenesis & Immunity

Papillomaviruses infect squamous epithelial cells and induce within those cells a characteristic cytoplasmic vacuole. These vacuolated cells, called koilocytes, are the hallmark of infection by these viruses. Most warts are benign and do not progress to malignancy. However, HPV infection is associated with carcinoma of the uterine cervix and penis

Both cell-mediated immunity and antibody are induced by viral infection and are involved in the spontaneous regression of warts. Immunosuppressed patients (e.g., AIDS patients) have more extensive warts, and women infected with HIV have a very high rate of carcinoma of the cervix.

PARVOVIRUSES

Summary of Replicative Cycle

• After adsorption to host cell receptors, the virion penetrates and moves to the nucleus, where replication occurs.
• The single-stranded genome DNA has “hairpin” loops at both of its ends that provide double-stranded areas for the cellular DNA polymerase to initiate the synthesis of the progeny genomes.
• The viral mRNA is synthesized by cellular RNA polymerase from the double-stranded DNA intermediate.
• The progeny virions are assembled in the nucleus. Released via cell lysis
• B19 virus replicates only when a cell is in S phase, which explains why the virus replicates in red cell precursors but not in mature red cells.

Pathogenesis – B19 virus infects primarily two types of cells: red blood cell precursors (erythroblasts) in the bone marrow, which accounts for the aplastic anemia, and endothelial cells in the blood vessels, which accounts, in part, for the rash associated with erythema infectiosum

Infection provides lifelong immunity against reinfection.