Viral

Viral refers to anything related to or caused by a virus. Viruses are small infectious agents that can only replicate inside the cells of another organism. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

Overview

Viruses are found in virtually every ecosystem on Earth and are the most numerous type of biological entity. The study of viruses is known as virology, a specialty within the field of microbiology. While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles, or virions.

Structure

Viruses display a wide diversity of shapes and sizes, called morphologies. Generally, viruses are much smaller than bacteria. Most viruses that have been studied have a diameter between 20 and 300 nanometres. Some filoviruses have a total length of up to 1400 nm; their diameters are only about 80 nm.

Classification

Viruses are classified into four groups based on their shape and whether they have an envelope. The four groups are the icosahedral, helical, enveloped, and complex viruses.

Replication

Viral populations do not grow through cell division, because they are acellular. Instead, they use the machinery and metabolism of a host cell to produce multiple copies of themselves, and they assemble in the cell.

Role in human disease

Viruses cause many human diseases, including the common cold, influenza, chickenpox, and cold sores. Many serious diseases such as Ebola, AIDS, avian influenza, and SARS are caused by viruses. The relative ability of viruses to cause disease is described in terms of virulence.

Prevention and treatment

Vaccines that produce immunity to viruses, antiviral drugs that can treat viral diseases, and antibiotics that kill bacteria, not viruses, are all part of the medical arsenal for dealing with viruses.

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