Robert Gallo, M.D. (Founder, Institute of Human Virology (IHV)) gives expert video advice on: How do scientists learn about new viruses?; What makes a retrovirus more dangerous than a regular virus? and more...
Is a virus a living organism?
What you need to know is that all viruses have a common characteristic. They have genes; they have genetic information like we do, like every living thing does. Yet, they are not quite alive. So they have genes that are protected in a protein-coat layer that can be formed in multiple different ways and structure, and different viruses have different kind of structure that have different subtleties that way. These simple things that have no metabolism of their own, they really not living in a strict sense of the word. You like to see of something alive that has its own metabolism, that has its own biochemistry. This is sort of nothing, just genes and protein shells. And it uses us to reproduce, ‘us' meaning ourselves, from an animal, when we are talking about viruses infecting animals and humans. So, part of the definition that many scientists give to a virus is that it is an ‘obligate parasite'. What does that mean? It means it can not reproduce by itself. It reproduces only in a cell. This means that the virus can only reproduce itself by usurping our machinery, our cells' machinery. It has its genes that can make this or that protein to help it reproduce or to help it avoid the immune system. But it is greatly reliant on many things in our cells to reproduce itself. So outside the cell, virus can not even reproduce. So do you call that living? It always gets into its limit of what is living or what is not. No metabolism of its own, it can only replicate inside your cell. Period.
How do scientists learn about new viruses?
Fundamentally, we know about them because they cause disease. And often they only cause disease in the one species. So sometimes it's not possible to do a Koch's Postulate. Like I will inject a mouse and get the disease, because they don't infect the mouse. Or if they did infect the mouse, the mechanisms are completely different, and then the virus is very low. So very often, and the case of HIV is a good example, it doesn't affect anything virtually but man bar a small affect on the chimp species.
What is the difference between an RNA and DNA virus?
You can make viruses into two great categories: those that have RNA for their genetic information, ribonucleic acid; and those that have deoxyribonucleic acid, DNA, in their genetic information. HIV is an RNA virus. That too is not unique and wouldn't form the basis of a final definition for HIV, because many viruses have RNA as their genetic information. Influenza virus is an RNA virus. Polio is an RNA virus. We call the genetic information the genome of an organism, when it's the entire genetic information. The genome of HIV, packaged in the middle of the particle that we call a virus, is RNA.
What is an 'enveloped virus'?
Viruses that infect the cell and then destroy the cell and pop out when the cell bursts, these are not enveloped generally speaking. And so the virus particles come out without a fatty lipid layer around them. But other viruses like HIV bud from the cell membrane when they form. So here's the cell and the virus may bud off the cell membrane. They take with them the fatty lipid substance that surrounds our cells. The lipid called bylayer of the cell. And that becomes part of the virus.
What makes a retrovirus more dangerous than a regular virus?
The answer is there are some classes of viruses that form lifelong infections or what we call persisting infections. HIV is a retrovirus. When you get infected by a retrovirus it's always forever. It's always forever. Now scientists are not supposed to say always, so I should qualify. It's virtually always forever. Far as I know, it's so far been forever. It's true with herpes viruses, usually. It's true with some of the hepatitis viruses, usually. It's true with papilloma viruses, usually. And those viruses are mostly DNA viruses, some hepatitis viruses are not. But a retrovirus is the king of persisting infections, because quickly it inserts its genes into our DNA, into our chromosomal DNA, of the very cell that gets infected. It harbors the virus forever. You say, well, that cell will die someday. Yeah. Before it dies it usually divides, and its daughter cells will also contain the genes of HIV.