Rna

? brain, bone, lung tumors and non-Hodgkin's lymphoma

does not kill the host cell but instead changes its properties. ■ Kaposi's sarcoma, p. 752

The various interactions that viruses display with their hosts are illustrated in figure 14.15.

Retroviruses and Human Tumors

Although retroviruses are the main class of viruses causing tumors in animals, it was not until 1980 that a rare human leukemia was also shown to be caused by a retrovirus. It was named human T-cell lymphotrophic virus type 1 (HTLV-1), and this tumor is restricted to certain geographic areas. The virus causes tumors by a somewhat different mechanism than discussed thus far. The virus carries an oncogene that, when integrated into the host cell genome, codes for an activator protein that activates regulatory genes of the cell.

integration of viralDNA

integration of viralDNA

Virus is released by budding and cell usually survives.

Normal cells are transformed into tumor cells

Cell dies and virus is released . when cells lyse.

Normal cells are transformed into tumor cells

Latent infection

Cell dies and virus is released . when cells lyse.

Virus is released by budding and cell usually survives.

Normal cells are transformed into tumor cells

Persistent infection

Latent infection

Plasmid

Viral DNA present in cell as a plasmid without adverse effects; virus replicates as a plasmid.

Latent infection

Acute infection

Persistent infection

Figure 14.15 Various Effects of Animal Viruses on the Cells They Infect

Nester-Anderson-Roberts: I II. The Microbial World I 14. Viruses, Prions, and I I © The McGraw-Hill

Microbiology, A Human Viroids: Infectious Agents Companies, 2003

Perspective, Fourth Edition of Animals and Plants

14.7 Viral Host Range 361

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