Virology

Virology is the scientific study of biological viruses. It is a part of microbiology that looks at how viruses are made, how they change, and how they infect host cells to make more copies. The field also studies how viruses work with the body's immune system, the diseases they cause, and ways to study them in labs. Viruses are useful in research and medicine.

The field of virology began when Martinus Beijerinck discovered that a disease in tobacco plants was caused by something new — not a bacterial or fungal infection, but a tiny agent he called a "virus."

Studying viruses is important because they cause diseases in plants, animals, and humans. Scientists study how viruses cause disease and how strong those diseases can be. There are special areas of study just for viruses that infect plants (plant virology), animals (animal virology), and humans (medical virology).

Today, scientists have many tools to see and study viruses. Thousands of different viruses are now known, and virologists often focus on viruses that infect plants, microorganisms, or animals. Virology touches on many areas, including biology, health, animal welfare, farming, and ecology.

History

Main articles: History of virology and Social history of viruses

In the late 1800s, scientists began to find tiny germs too small to see with normal microscopes. One scientist, Martinus Beijerinck, found that a sickness in tobacco plants was caused by a special germ he called a virus. This started the science of virology.

Later, scientists learned how to grow viruses in labs using cells from animals and plants. They found many new viruses that can make animals and plants sick. Tools like the electron microscope helped scientists see viruses for the first time and learn about their shapes and looks.

Detecting viruses

Scientists have many ways to find viruses. One way is to look for tiny parts of the virus called antigens or for the virus’s genetic material. They also test whether a virus can still cause infection.

Electron microscopes help scientists see viruses. These microscopes use beams of electrons instead of light, so they can see much smaller objects than regular microscopes. A special method called negative staining makes viruses stand out against a dark background. Another method, cryogenic electron microscopy, keeps viruses safe in icy water so scientists can study their shapes very clearly.

To grow viruses in a lab, scientists use living cells from animals, bacteria in test tubes, or plants. When viruses grow in these cells, they can change the cells in ways that help scientists identify them. Scientists also use special tests with antibodies — proteins that recognize viruses — to study and detect them. One common test is called PCR, which looks for tiny bits of the virus’s genetic material. These tests are very good at finding viruses but need careful handling to avoid mistakes.

Quantitation and viral loads

Main article: Virus quantification

Counting viruses is very important in virology. We do this to help control some human infections. We measure something called the viral load. There are two main ways to count viruses. One way counts only the viruses that can infect cells. This is called infectivity assays. The other way counts all virus particles, even those that cannot infect.

Infectivity assays measure how many viruses can infect cells. They use live cells, plants, or lab-grown cells. Some tests give exact numbers. Others show the chance that a sample will cause infection. For bacteria viruses, called bacteriophages, scientists can count them by looking at holes they make in a layer of bacteria. Another method uses special stains to find infected cells.

Viral load assays count the total number of virus genes. These tests are useful for tracking diseases like HIV. They can also be used for viruses that affect plants. They often use a process called PCR to find and count the virus genes.

Main article: Viral load

Molecular biology

Molecular virology studies viruses at the level of their genetic material and proteins. Scientists use special tools to learn about viruses. Viruses are small and simple, which makes them great to study.

Viruses need to be cleaned and separated from other materials before scientists can study them. Machines called centrifuges can separate viruses from heavier substances. Another method uses electric charge to separate virus parts. This helps scientists see and understand them better.

Sequencing helps scientists read the genetic code of viruses. This is important for learning how viruses cause disease and how to fight them. By studying these codes, scientists can track how viruses change and spread. Special techniques let scientists make copies of virus parts without needing the actual virus. This is useful for creating tests and vaccines. Viruses that infect bacteria, called bacteriophages, have been helpful in research because they are easy to grow and study in labs.

Genetics

All viruses have genes. Scientists study these genes using special tools. One tool is called RNA silencing.

Scientists also study virus genes using a process called reassortment. This is when genes from different viruses mix. This happens in viruses with pieces of genetic material, like influenza viruses and rotaviruses. Another way scientists study genes is through recombination. This is when small pieces of DNA or RNA join together. Scientists can also use a technique called reverse genetics to make changed viruses for research.

Virus classification

Main article: Virus classification

Virus classification is an important part of virology, the study of viruses. Scientists sort viruses by features they share, not by the animals or plants they infect. In 1962, researchers André Lwoff, Robert Horne, and Paul Tournier made the first system to classify viruses. They used a method like how living things are grouped. This system looks at the type of genetic material viruses have.

Today, the International Committee on Taxonomy of Viruses (ICTV) manages virus classification. They use a system with many levels, from large groups called "realms" to specific types called "species." This helps scientists learn about the many kinds of viruses.

The Baltimore classification, named after scientist David Baltimore, groups viruses by how they make the molecules needed to build new viruses. This system divides viruses into seven groups based on whether their genetic material is DNA or RNA, and whether it is single-stranded or double-stranded. Examples include adenoviruses, coronaviruses, and retroviruses.