Understanding the Herpes Virus at the Cell Level
The word “herpes” conjures up different images for different people. Some see herpes as an ugly and annoying cold sore or blister that periodically appears on or around the lips. Others see herpes as a feared sexually transmitted disease that, once you have contracted, you have to suffer with for the rest of your life. Of course both of these images do represent the term “herpes” quite accurately for many people throughout the world, but medically speaking herpes is also appropriately applied to several lesser known afflictions. These conditions include herpes inside the mouth (herpes gingivostomatitis), herpes of the throat (herpes pharyngitis), herpes of the eye (herpes keratitis), herpes of the brain (herpes encephalitis), herpes transmitted to newborn infants (neonatal herpes), chickenpox (varicella-zoster), mono (mononucleosis) and shingles (herpes-zoster). All of these conditions are caused by one of the two closely related herpes viruses known as herpes simplex virus type 1 and herpes simplex virus type 2.
To truly understand the herpes virus it is helpful to first gain some knowledge about viruses in general. Viruses are the smallest known microbes, or infectious agents, that medical science has discovered to date. Most viruses consist of a nucleic acid surrounded by a protein coat known as a capsid; this nucleic acid-protein complex is referred to as a nucleocapsid. In more complex viruses, such as the herpes virus, the nucleocapsid is surrounded by a membrane-like structure containing carbohydrates, lipids and proteins. This membrane-like structure is referred to as an envelope. Each virus contains one of two large complex chemicals that contain the viruses genetic code which serves as a blueprint for making more viruses. This complex chemical code is either RNA (ribonucleic acid) or DNA (deozyribonucleic acid).
Unlike bacteria and more complex organisms, viruses do not carry all the equipment necessary to reproduce themselves. In order to multiply, a virus must enter a living cell, remove the cells protein coat and then use its RNA or DNA to redirect the cells synthesizing mechanism to make more copies of the virus. This process of making new viruses can actually destroy or injure the living or ‘host’ cell. If enough living host cells are injured or destroyed it results in a viral illness such as influenza (the flu), viral diarrhea or genital herpes. There are hundreds of known viruses and probably thousands of others not yet discovered. Each virus has adapted to infect a particular type of cell in a specific living organism which explains why there are so many types of viruses. Because they have become so specialized some viruses can only infect certain types of cells, for instance, liver cells or muscle cells or brain cells while leaving other cells alone. Likewise, many viruses are even limited to the type of species they can infect. In general, this usually means that viruses which infect cells in one type of animal, say a dog, can not be passed on to another type of animal, say a cat. Of course as with most rules, there are exceptions and some viruses can cause similar diseases in closely related species. Another exception is that sometimes viruses can cause also cause very different illnesses in the same species.