Several members of IHV spend much of their time linking viruses to the cause of a disease, particularly viruses that cause cancer.
All classes or families of viruses have their own unique features, they are all fundamentally inanimate, simply genes surrounded by a protein shell, or coats. They all have their strategy, to reproduce themselves usually in a specific type of cell and to evade the host immune system. HIV is a retrovirus that is very uncommon in man but not unique. IHV Director Robert C. Gallo, MD and his colleagues discovered the first human retrovirus known as HTLV-1, which can cause leukemia of T cells in young adults as well as a fatal neurological disease similar to multiple sclerosis. Later, in 1982, Gallo and his colleagues discovered the second known human retrovirus known as HTLV-2, and in the 1983 to 1984 period they co-discovered HIV, the third known human retrovirus.
The strategy of HIV to reproduce itself is very complicated. However, it is sufficient to say, what makes a retrovirus unique is that it inserts its genetic information into the target cell DNA form, which occurs (within 1 or 2 days of exposure) if there is sufficient virus in the right location. The retrovirus will then last a lifetime in the individual, which is the very special problem of HIV. HIV targets critical cells of our immune system, what we call CD4+ T cells.
Today, some virus discoveries are coming out of genomics. But the older, more conventional and still very important approach for virus discovery is to start with an idea that a given disease may very well have a viral origin (one must have a rationale). Then, make your best guess as to what cell the virus is targeting (Gallo and his colleagues knew from clinicians that the T cells of AIDS patients were in trouble, so naturally they looked at T cells of AIDS patients). Next, one would attempt to grow such cells in culture with nutrient media. Of note, it was very difficult until the mid to late 1970’s to grow T cells until Gallo and his colleagues discovered a growth factor for T cells, which later became known as Interleukin 2 or IL-2 that scientists utilize today in cutting edge research such as culturing T cells from AIDS patients.
Following this process, one then examines the culture for tell-tale signs for viruses, of which there are multiple laboratory approaches to do so. For a retrovirus, one usually starts by looking for a certain kind of enzyme (protein) which has the unusual feature of catalyzing RNA into DNA because the retrovirus genome (genetic information) is in the form of RNA and must be converted into DNA upon infection of the cell. The enzyme that does this is special, and one can search for it, like Gallo and his colleagues did more than 30 years ago.
The next step in virus discovery would be to try to take a picture of the virus with a technique called electron microscopy. That is the beginning of the beginning, i.e. finding a virus is only one step. Then the viruses are characterized by immunological, biochemical and molecular techniques. Showing the cause of the disease involves a lot more additional steps which are based on much more technology, human data, and common sense.