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A virus is one of the smallest microorganisms, consisting of only a nucleic acid core surrounded by a protein shell.1 Several types of viruses commonly infect human cells and are responsible for a diverse range of pathologies. Viral infections extend from relatively mild disorders such as the common cold to serious, life-threatening conditions such as AIDS. Viruses are somewhat unique in that they must rely totally on the metabolic processes of the host (human) cell to function.2 Hence, the pharmacological treatment of viral infections is complex, because it is often difficult to selectively destroy the virus without also destroying human cells.

This chapter describes the basic characteristics of viruses and the relatively limited number of drugs that can act selectively as antiviral agents. A brief discussion of methods of preventing viral infections (antiviral vaccines) follows. The chapter ends with a discussion of the current methods of treating a specific viral-induced disease—AIDS.

You will often treat patients who are in the active stages of a viral infection, as well as those suffering from the sequelae of viral disorders, such as gastroenteritis, encephalitis, and influenza. Such infections can be very debilitating, and you can play a role in maintaining and restoring the patient's strength and functional abilities during and after antiviral treatments. Certain viruses such as polioviruses can have devastating effects on neuromuscular function, and much of the historical basis of physical rehabilitation was developed during the polio epidemics of the 1940s and 1950s. Fortunately, antiviral drugs and vaccines have been instrumental in controlling or even eradicating certain viral infections. However, other viruses remain difficult to treat pharmacologically, and there is still a need for effective vaccines against many viruses, including HIV. Antiviral drug research is a very dynamic and rapidly changing area of pharmacology, and you should stay abreast of developments in this area to enrich your own knowledge and serve as a reliable source of information for your patients. Hence, you should understand pharmacotherapeutic treatment and prophylaxis of viral infections.


Classification of Viruses

Viruses are classified according to several criteria, including physical, biochemical, and pathogenic characteristics.1,2 The classifications of some of the more common viruses affecting humans, and their associated diseases, are listed in Table 34-1. The table shows that viruses can be divided into two categories, depending on the type of genetic material contained in the virus (DNA or RNA viruses). Families within each major subdivision are classified according to physical characteristics (e.g., configuration of the genetic material, shape of the virus capsule) and other functional criteria.


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