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A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. [1] Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. [2] [3] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.
A virus with this "viral envelope" uses it—along with specific receptors—to enter a new host cell. Viruses vary in shape from the simple helical and icosahedral to more complex structures. Viruses range in size from 20 to 300 nanometres; it would take 33,000 to 500,000 of them, side by side, to stretch to 1 centimetre (0.4 in).
Basic structural characteristics, such as genome type, virion shape and replication site, generally share the same features among virus species within the same family. [citation needed] Double-stranded DNA families: three are non-enveloped (Adenoviridae, Papillomaviridae and Polyomaviridae) and two are enveloped (Herpesviridae and Poxviridae).
Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms. Viruses are classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause.
Because the viruses share some common characteristics, including symptoms, test results are the only way to know exactly the type of virus involved in each case. But it also means that preventing ...
The kingdom contains three groups in the Baltimore classification system, which groups viruses together based on their manner of mRNA synthesis, and which is often used alongside standard virus taxonomy, which is based on evolutionary history. Those three groups are Group III: dsRNA viruses, Group IV: +ssRNA viruses, and Group V: -ssRNA viruses.
Viral disease is the sum of the effects of viral replication on the host and the host's subsequent immune response against the virus. [3] Viruses are able to initiate infection, disperse throughout the body, and replicate due to specific virulence factors. [2] There are several factors that affect pathogenesis.
There are some viruses that can maintain a persistent infection by infecting different cells of the body. Some viruses once acquired never leave the body. A typical example is the herpes virus, which tends to hide in nerves and become reactivated when specific circumstances arise. [25]