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For medical purposes, viruses are most usefully described in terms of either their main site of infection, their mode of transmission, or the type of lesions and diseases they cause. Chapters 37 to 45 describe the clinically important viruses organized in this medically relevant manner. Several less prominent viruses are described in Chapter 46.

In this brief introduction, the clinically important viral pathogens are categorized into groups according to their main structural characteristics (i.e., DNA enveloped viruses, DNA nonenveloped1 viruses, RNA enveloped viruses, and RNA nonenveloped viruses) (see Table IV–1).

Table IV–1Major Viral Pathogens

1Nonenveloped viruses are also called naked nucleocapsid viruses.



These viruses are noted for their ability to cause latent infections. This family includes (1) herpes simplex virus types 1 and 2, which cause painful vesicles on the face and genitals, respectively; (2) varicella-zoster virus, which causes varicella (chickenpox) typically in children and, when it recurs, zoster (shingles); (3) cytomegalovirus, an important cause of congenital malformations; (4) Epstein–Barr virus, which causes infectious mononucleosis; and (5) human herpesvirus 8, which causes Kaposi’s sarcoma. (See Chapter 37.)

Hepatitis B Virus

This virus is one of the important causes of viral hepatitis. In contrast to hepatitis A virus (an RNA nucleocapsid virus), hepatitis B virus causes a more severe form of hepatitis, results more frequently in a chronic carrier state, and is implicated in the induction of hepatocellular carcinoma, the most common cancer worldwide. (See Chapter 41.)


Poxviruses are the largest and most complex of the viruses. The disease smallpox has been eradicated by effective use of the vaccine. Molluscum contagiosum virus is the only poxvirus that causes human disease in the United States at this time. (See Chapter 37.)



These viruses are best known for causing upper and lower respiratory tract infections, including pharyngitis and pneumonia. (See Chapter 38.)


These viruses cause papillomas on the skin and mucous membranes of many areas of the body. Some types are implicated as a cause of cancer ...

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