Virology

Virology is the scientific study of biological viruses. It is a specialized subfield of microbiology. Scientists in this field focus on many different things. They study how viruses are built and how they change over time. They also look at how viruses infect host cells to make copies of themselves. This includes studying how viruses interact with the immunity and physiology of a host organism. Virology is a broad subject. It connects to biology, health, animal welfare, agriculture, and ecology.

Viruses operate through a very specific biological mechanism. They are obligate intracellular parasites. This means they must be inside a living host cell to reproduce. To study them in a laboratory, scientists must provide these living cells. For animal viruses, researchers use laboratory cell cultures. For bacteriophages, which infect bacteria, scientists can use bacteria growing in test tubes. Plant virologists might use natural host plants or specific indicator plants. In the past, scientists used fertilized chicken eggs to grow viruses. This method was vital for the large-scale production of the polio vaccine.

When a virus infects a cell, it often causes visible changes. These changes are called cytopathic effects. For example, the herpes simplex virus can cause human fibroblasts to become round and balloon-like. Some viruses, such as the mumps virus, cause red blood cells to attach firmly to infected cells. This specific process is called haemadsorption. Other viruses produce localized lesions in cell layers known as plaques. These plaques are useful for scientists to perform quantitation assays. These assays help identify virus species through plaque reduction.

The history of virology began with the discovery of new pathogens. In 1884, Charles Chamberland invented the Chamberland filter. This device had pores small enough to remove all bacteria from a solution. In 1892, Dmitri Ivanovsky used this filter on tobacco plants. He found that the infection remained even after the bacteria were filtered out. In 1898, Martinus Beijerinck repeated these experiments. He concluded the agent was not a bacterium or a fungus. He called it a contagium vivum fluidum, meaning a contagious living fluid.

Early theories about the nature of viruses changed as technology improved. Beijerinck believed viruses were liquid in nature. However, Wendell Stanley later proved they were actually particulate. In 1935, Stanley found the tobacco mosaic virus was mostly made of protein. This virus was also the first to be crystallized. In 1955, Rosalind Franklin used X-ray crystallographic pictures to propose the full structure of the tobacco mosaic virus. Later that year, researchers showed that purified RNA and protein coats could assemble into functional viruses. This suggested how viruses are created inside host cells.

Visualizing these tiny particles required the invention of the electron microscope. German engineers Ernst Ruska and Max Knoll invented it in 1931. While light microscopes magnify up to 1,500 times, electron microscopes can reach 10,000,000 times. These tools use beams of electrons instead of light. One common technique is negative staining. Scientists suspend viruses in metal salts like uranium acetate. The metal atoms are opaque to electrons. This makes the viruses appear as if they are suspended in a dark background.

Modern virology uses even more advanced imaging techniques. Traditional electron microscopy can damage viruses through drying or the electron beam. To solve this, scientists use cryogenic electron microscopy. This method preserves the virus structure by embedding it in vitreous water. This allows researchers to see structures at near-atomic resolution. This technique is a powerful alternative to X-ray crystallography. Today, virology continues to expand. It helps us understand everything from the hepatitis B virus to the discovery of HIV in 1983.