Eucaryotic Viruses and Other Acellular Infectious Agents Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Chapter 18 Eucaryotic Viruses and Other Acellular Infectious Agents

Cytocidal Infections and Cell Damage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cytocidal Infections and Cell Damage An infection that results in cell death is a cytocidal infection Vertebrate viruses can harm their host cells in many ways; often this lead to cell death Microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues are referred to as cytopathic effects (CPEs).

Mechanisms of host cell damage and cell death Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mechanisms of host cell damage and cell death Many viruses can inhibit host DNA, RNA, and protein synthesis eg. Picornaviruses, herpesviruses and adenoviruses. Cell endosome may be damaged resulting in the cell destruction. causes release of hydrolytic enzymes into cell Can drastically alter plasma membrane can lead to attack of host cell by immune system HIV destroy helper T-cells (also called T4 or CD4+ cells )

Other mechanisms… High conc. Of viral proteins can have a direct toxic effect on cell and organism. Intracellular structure called inclusion bodies are formed during virus infection. These may results from the clustering of subunits of virions within the nucleous or cytoplasm. They also may contain cell components such as ribosomes or chromatin. These inclusion bodies can directly disrupt cell structure chromosomal disruptions result from herpesvirus and others transformation of host cell into malignant cell (Latin combination of "mal" meaning "bad" and "nascor" meaning "to be born"; malignant literally means "born to be bad.“)

Persistent, Latent, and Slow Virus Infections Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Persistent, Latent, and Slow Virus Infections acute infections rapid onset and relatively short duration (e.g. influenza) persistent infections can last many years

Types of persistent infections Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Types of persistent infections chronic virus infection virus almost always detectable clinical symptoms mild or absent for long periods (e.g. Hepatitis B virus and HIV) latent virus infection In this case, virus stops reproducing and remains dormant for a period before becoming active again) during latency, symptoms, antivirus-antibodies, and viruses are not detectable (e.g. Herpes simplex virus, varicella-zoster virus, cytomegalovirus)

Possible causes of persistent infections The virus genome may be integrated into host genome decrease in antigenicity of virus May mutate to less virulent and slower reproducing form

Types of Infections and Their Effects on Host Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Types of Infections and Their Effects on Host Cells Figure 18.13

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Slow virus diseases A small group of viruses causes extremely slow developing infections, often called slow virus disease or slow infection. Symptoms may take years to emerge. Measles virus occasionally produces a slow infection. HIV also cause slow disease

Viruses and Cancer Cancer is a class of diseases in which a cell, or a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues). Tumor (Latin tumere= to swell) growth or lump of tissue resulting from neoplasia (Greek= new growth) abnormal new cell growth and reproduction due to loss of regulation Anaplasia (to form backward). The unregulated proliferation and loss of differentition of tumor cells result in invasive growth that forms unorganized mass of cell It implies dedifferentiation, or loss of structural and functional differentiation of normal cells

Metastasis There are two major type of tumors with respect to over all form or growth pattern. If the tumor cells remain in place to form a compact mass, the tumor is benign. In contrast, cells from malignant or cancerous tumors can actively spread through the body in a processes known as Metastasis, often by floating in the blood and establishing secondary tumors.

Carcinogenesis complex, multistep process often involves oncogenes cancer-causing genes Carcinogenesis can be initiated by a chemical, usually a mutagen, but a cancer does not appear to develop until at least one more triggering event (possibly exposure to another chemical carcinigen or a virus) take place. At present, viruses have been implicated in the genesis of at least eight human cancers. With the exception of a few retroviruses, these viruses have dsDNA genomes.

Viruses implicated in human cancers Epstein-Barr virus Burkitt’s lymphoma nasopharyngeal carcinoma Hepatitis B virus liver cancer Hepatitis C virus Human herpesvirus 8 HIV Kaposi’s sarcoma human papillomavirus cervical cancer HTLV-1 (Human T-cell lymphotropic virus)and HTLV-2 leukemia

Possible mechanisms by which viruses cause cancer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Possible mechanisms by which viruses cause cancer carry oncogene into cell and insert it into host genome altered cell regulation due to changes in kinase activity or production of regulatory proteins insertion of promoter or enhancer next to cellular oncogene

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