Chapter Overview

Among microbial groups, viruses cause the majority of infections.
Viruses are extremely small parasites composed of a nucleic acid core surrounded by a protein capsid.
Viruses invade host cells by using specific receptors, and they induce the cell machinery to synthesize, assemble, and release new viruses.
Virus infections vary from mild to severe in effect, local to systemic in scope, and may have the potential for latency and oncogenicity.
DNA viruses of humans exist in the enveloped or naked state and can carry double-stranded or single-stranded DNA.
Poxviruses are large, complex DNA viruses that cause smallpox and molluscum contagiosum.
Herpesviruses are enveloped DNA viruses that are known for being latent in host cells after the initial infection.
Examples of common herpesvirus diseases are cold sores, genital herpes, chickenpox, shingles, mononucleosis, and roseola.
Herpesviruses also cause cancers such as lymphoma and sarcoma.
One cause of hepatitis is hepatitis B virus, an enveloped virus that damages the liver and may cause cancer.
Nonenveloped DNA viruses are the adenoviruses, one cause of colds, and papillomaviruses, the agents of common skin and genital warts.
Parvoviruses are single-stranded DNA viruses and are implicated in a respiratory infection of children.

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