Since the 1940s, tremendous advances have occurred in the treatment of bacterial infections—but advances in the fight against virus-causing diseases only began to occur four decades later. What took so long? Bacteria and viruses are fundamentally different. Bacteria are self-sustaining in their ability to reproduce. Antibacterial drugs attack a process or element in the microbe that is either absent or not essential for the well being of the host (human or animal). Penicillin, for example, prevents susceptible bacteria from manufacturing a cell wall that is required for their survival but absent in animal cells.
By contrast, viruses use the host’s biochemical machinery to live and reproduce. Because of this intimate relationship, many drugs that are toxic to the virus also cause significant harm to the host. The challenge scientists face is finding those subtle differences that are unique to viruses.
One highly fruitful approach has involved studying the complex life cycle of viruses, from their attachment to and entry into the host’s cells, to their replication within the cells, to their release to infect new cells. Antiviral drugs have been developed that interfere with specific steps in this sequence.
PIONEER AGAINST VIRUSES. Acyclovir (also spelled aciclovir) prevents the virus from manufacturing DNA by interacting with two enzymes that are unique to these viruses. Just as penicillin started the antibiotic revolution, acyclovir was the first successful antiviral drug. It is effective against both the herpes simplex virus (HSV) and the varicella-zoster virus (VZV). HSV causes cold sores on the lips, conjunctivitis, and genital sores, whereas VZV can cause shingles and chickenpox. Acyclovir (Zovirax) reduces the time of healing of uncomfortable symptoms associated with these disorders.
Several important differences exist between antibiotics and antiviral drugs. Antibiotics are generally effective against multiple types of bacteria. By contrast, there are no all-purpose antiviral drugs, and existing drugs only act against a limited number of viruses. Antibiotics produce authentic cures of bacterial infections, while antiviral drugs only prevent viral reproduction and suppression of symptoms. When the drug is stopped, the virus returns, as does the disorder. Better antiviral drugs are vitally needed.
SEE ALSO Food and Drug Administration (1906), Salvarsan (1910), Penicillin (1928), AZT/Retrovir (1987).
Herpes simplex virus (HSV) particles consist of DNA genetic material covered by a protein coat (capsid), which is wrapped in a lipid layer, or envelope. Projections on the surface of the HSV particle bind to receptors on the white blood cell to create an opening through which the virus enters the cell.