It’s the time of year when everyone is trying to stay healthy. Colds and the flu are going around, and it seems no one is immune. But have you ever wondered how a virus spreads? How does it know which cells to infect? And who is most at risk for getting sick? In this article, we will answer these questions and more!
What Is A Virus?
A virus is a minute infectious agent that can only reproduce inside the cells of a living host. Viruses are classified according to the type of host cell they infect: animal, plant, or bacterial. For example, animal viruses cause the common cold, flu, chickenpox, and AIDS; plant viruses cause tobacco mosaic disease, tomato spotted wilt disease, and bacterial viruses called bacteriophages. The structure of a virus particle (virion) consists of genetic material—either DNA or RNA—surrounded by a protein coat or capsid. Some virions also have an outer envelope composed of lipid molecules derived from the host cell membrane.
Our History With Viruses
Our history with viruses stretches back to the dawn of humanity. For most of that time, we coexisted with viruses in relative harmony. However, in recent centuries, as our societies have grown larger and more complex, the threat posed by viruses has increased exponentially. The 1918 flu pandemic, for example, killed an estimated 50 million people worldwide.
In the 21st century, we face the possibility of even more devastating pandemics as viruses mutate and spread more easily than ever before. To protect ourselves from these threats, we must understand our history with viruses and learn from past mistakes. Only then can we hope to avoid repeating them in the future.
How Viruses Work In Depth
While technically not alive, viruses exhibit some characteristics associated with living organisms. For example, they can evolve and mutate and be transmitted from one individual to another. However, unlike living organisms, they cannot reproduce on their own—they must use the machinery of a living cell to do so. Additionally, viruses are highly specialized—each type can only infect a limited range of host cells.
For example, the influenza virus can infect human cells, not bacterial ones. When a virus encounters a cell that it can infect, it attaches to the cell surface and injects its genetic material into it. The viral genome then hijacks the cellular machinery to directly synthesize new virions. Assembled virions are then released from the host cell, often causing the cell’s death. The release of virions may occur through budding (a process similar to cell division) or lysis (the destruction of the cell membrane).
In either case, the new virions can infect other cells. As a result, viruses are responsible for several serious diseases in humans, plants, and animals. However, viruses also play important roles in ecology and evolution. For example, certain bacteriophages prey on bacteria that cause human disease, making them an important tool in medicine. In addition, viruses are responsible for horizontal gene transfer—the exchange of DNA between different species—which is an important mechanism for evolution.