Viruses: genetic parasites--last major hurdle in conquest of infectious diseases.

VIRUSES GENEnC PARASITES LASTMAJOR HURDLE IN CONQUEST OF INFEcnOUS DISEASES The last time you had a COld, you probably cursed a microscopic entity called a virus. This confounding agent of disease breaks many biological rules. Scientists cannot even say for certain whether viruses are living, nonliving or somewhere in between. Although most viral infections are not very serious, some of these tiny particles wreak destruction far beyond the common cold. Many diseases, major and minor, are caused by viral infections: measles, mumps, polio, hepatitis, rabies, certain pneumonias, some cancers and, of course, flu and SOme intestinal upsets. Viruses also are believed to trigger AIDS (acquired immune deficiency syndrome). And the genital herpes simplex virus has disrupted the personal lives of millions of people. /n addition, viruses may playa role in a number of diseases thought to have other causes diseases such as multiple sclerosis, diabetes and Alzheimer's disease. Viruses are so elusive that the few available antiviral drugs combat only two or three viral diseases.At this point, there are more vaccines to prevent viral diseases than drugs to treat them. One of the most recent vaccines one for hepatitis B,a serious liver disease may become the first anticancer vaccine. The World Health Organization plans to test whether the vaccine will prevent a lethal form of liver cancer believed to be caused by hepatitis B. Some experts predict the vaccine will prevent as much as 95% of such cancer.