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A viral infection does not always cause disease. A viral infection simply involves viral replication in the host, but disease is the damage caused by viral multiplication. [5] An individual who has a viral infection but does not display disease symptoms is known as a carrier. [17] Mechanisms by which viruses cause damage and disease to host cells
The fourth step in the viral cycle is replication, which is defined by the rapid production of the viral genome. How a virus undergoes replication relies on the type of genetic material the virus possesses. Based on their genetic material, viruses will hijack the corresponding cellular machinery for said genetic material.
The resulting recombinant viruses may sometimes cause an outbreak of infection in humans. [ 25 ] Especially in coronaviruses, recombination may also occur even among distantly related evolutionary groups (subgenera), due to their characteristic transcription mechanism, that involves subgenomic mRNAs that are formed by template switching.
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Viral evolution is a subfield of evolutionary biology and virology concerned with the evolution of viruses. [1] [2] Viruses have short generation times, and many—in particular RNA viruses—have relatively high mutation rates (on the order of one point mutation or more per genome per round of replication).
Such viruses are called attenuated. Live vaccines can be dangerous when given to people with a weak immunity (who are described as immunocompromised), because in these people, the weakened virus can cause the original disease. [166] Biotechnology and genetic engineering techniques are used to produce subunit vaccines.
Rosalind Franklin proposed the full structure of the tobacco mosaic virus in 1955. One main motivation for the study of viruses is because they cause many infectious diseases of plants and animals. [1] The study of the manner in which viruses cause disease is viral pathogenesis. The degree to which a virus causes disease is its virulence. [2]
Koch formulated his postulates too early in the history of virology to recognize that many viruses do not cause illness in all infected individuals, a requirement of the first postulate. HIV/AIDS denialism includes claims that the viral spread of HIV/AIDS violates Koch's second postulate, despite that criticism being applicable to all viruses.