A POSITIVE VIEW OF VIRUSES

            Looking at this beautiful tulip, one would never guess that it derives its pleasing appearance from a viral infection. It contains tulip mosaic virus, which affect the development of the plant cells and causes complex patterns of colors in the petals. Aside from this, the virus does not cause severe harm to the plants. Despite the reputation of viruses as cell killers, there is another side of viruses – that of being harmless, and in some cases, even beneficial.

            Although there is no agreement on the origins of viruses, it is highly likely that they have been in existence for billions of years. Virologists are convinced that viruses have been an important force in the evolution of living things. This is based on the fact that they interact with the genetic material of their host cells and that they carry genes from on host to another (transduction). It is convincing to imagine that viruses arose early in the history of cells as loose pieces of genetic material that became dependent nomads, moving from cell to cell. Viruses are also a significant factor in the functioning of many ecosystems because of the effects they have on their host cells. For example, it is documented that seawater can contain 10 millions viruses per milliliter. Since viruses are made of the same elements as living cells, it is estimated that the sum of viruses in the ocean represent 270 million metric tons of organic matter.

            Over the past several years, biomedical experts have been looking at viruses as vehicles to treat infections and disease. Viruses are already essential for production of vaccines to treat viral infections such as influenza, polio, and measles. Vaccine experts have also engineered new types of viruses by combining a less harmful virus such as vaccinia or adenovirus with some genetic material from a pathogen such HIV and herpes simplex. This technique creates a vaccine that provides immunity but does not expose the person to the intact pathogen. Several of these types of vaccines are currently in development.

            The “harmless virus” approach is also being used to treat genetic diseases such cystic fibrosis and sickle cell anemia. With gene therapy the normal gene is inserted into a retrovirus, such as the mouse leukemia virus, and the patient is infected with this altered virus. It is hoped that the virus will introduce the needed gene into the cells and correct the defect. Dozens of experimental trials are currently underway to develop potential cures for diseases, with some success.

            Virologists have also created mutant adenoviruses (ONYX) that target cancer or cells. These viruses cannot spread among normal cells, but when they enter cancer cells, they immediately cause the cells to self-destruct. One problem has been that infection with these mouse viruses has led to development of cancer in some patients.

            An older therapy getting a second chance involves use of bacteriophages to treat bacterial infections. This technique was tried in the past with mixed success, but was abandoned for more efficient antimicrobic drugs. The basis behind the therapy is that bacterial viruses would seek out only their specific host bacteria and would cause complete destruction of the bacterial cell. Newer experiments with animals have demonstrated that this method can control infections as well as traditional drugs. Some potential applications being considered are adding phage suspension to grafts to control skin infections and to intravenous fluids for blood infections.