Typical virus

Amy Karger of the University of Minnesota Medical School recommends that people test themselves at three days and five days after exposure if possible.

Lab-developed tests are more sensitive than rapid tests so they should be able to pick up the virus by day three after exposure, if not earlier. The agency came under criticism for not requiring a negative test before leaving isolation, but even after tweaking the guidelines officials said that step should be optional. People with symptoms should stay isolated until they have been fever-free for at least 24 hours. Related content:. Note to readers: if you purchase something through one of our affiliate links we may earn a commission.

More than 30, different virus isolates are known today and grouped in more than 3, species, in genera and 71 families. Viral morphology provides the basis for grouping viruses into families. A virus family may consist of members that replicate only in vertebrates, only in invertebrates, only in plants, or only in bacteria.

Certain families contain viruses that replicate in more than one of these hosts. This section concerns only the 21 families and genera of medical importance. Besides physical properties, several factors pertaining to the mode of replication play a role in classification: the configuration of the nucleic acid ss or ds, linear or circular , whether the genome consists of one molecule of nucleic acid or is segmented, and whether the strand of ss RNA is sense or antisense.

Also considered in classification is the site of viral capsid assembly and, in enveloped viruses, the site of nucleocapsid envelopment. Table lists the major chemical and morphologic properties of the families of viruses that cause disease in humans. The use of Latinized names ending in -viridae for virus families and ending in -virus for viral genera has gained wide acceptance. The names of subfamilies end in -virinae. Vernacular names continue to be used to describe the viruses within a genus.

In this text, Latinized endings for families and subfamilies usually are not used. Table shows the current classification of medically significant viruses. In the early days of virology, viruses were named according to common pathogenic properties, e. From the early s until the mids, when many new viruses were being discovered, it was popular to compose virus names by using sigla abbreviations derived from a few or initial letters.

Thus the name Picornaviridae is derived from pico small and RNA; the name Reoviridae is derived from respiratory, enteric, and orphan viruses because the agents were found in both respiratory and enteric specimens and were not related to other classified viruses; Papovaviridae is from papilloma, polyoma, and vacuolating agent simian virus 40 [SV40] ; retrovirus is from reverse transcriptase; Hepadnaviridae is from the replication of the virus in hepatocytes and their DNA genomes, as seen in hepatitis B virus.

Hepatitis A virus is classified now in the family Picornaviridae, genus Hepatovirus. Although the current rules for nomenclature do not prohibit the introduction of new sigla, they require that the siglum be meaningful to workers in the field and be recognized by international study groups.

Several viruses of medical importance still remain unclassified. Some are difficult or impossible to propagate in standard laboratory host systems and thus cannot be obtained in sufficient quantity to permit more precise characterization. Hepatitis E virus, the Norwalk virus and similar agents see Ch. The fatal transmissible dementias in humans and other animals scrapie in sheep and goat; bovine spongiform encephalopathy in cattle, transmissible mink encephalopathy; Kuru, Creutzfeldt-Jakob disease, and Gerstmann-Straussler-Scheinker syndrome in humans see Ch.

The agents causing transmissible subacute spongiform encephalopathies have been linked to viroids or virinos i. Some of the transmissible amyloidoses show a familial pattern and can be explained by defined mutations which render a primary soluble glycoprotein insoluble, which in turn leads to the pathognomonic accumulation of amyloid fibers and plaques.

The pathogenesis of the sporadic amyloidoses, however, is still a matter of highly ambitious research. Turn recording back on. National Center for Biotechnology Information , U. Show details Baron S, editor. Search term. General Concepts Structure and Function Viruses are small obligate intracellular parasites, which by definition contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat. Classification of Viruses Morphology: Viruses are grouped on the basis of size and shape, chemical composition and structure of the genome, and mode of replication.

Nomenclature Aside from physical data, genome structure and mode of replication are criteria applied in the classification and nomenclature of viruses, including the chemical composition and configuration of the nucleic acid, whether the genome is monopartite or multipartite.

Structure and Function Viruses are inert outside the host cell. Classification of Viruses Viruses are classified on the basis of morphology, chemical composition, and mode of replication.

Morphology Helical Symmetry In the replication of viruses with helical symmetry, identical protein subunits protomers self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path. Figure The helical structure of the rigid tobacco mosaic virus rod. Figure Fragments of flexible helical nucleocapsids NC of Sendai virus, a paramyxovirus, are seen either within the protective envelope E or free, after rupture of the envelope.

Icosahedral Symmetry An icosahedron is a polyhedron having 20 equilateral triangular faces and 12 vertices Fig.

Figure Icosahedral models seen, left to right, on fivefold, threefold, and twofold axes of rotational symmetry. Figure Adenovirus after negative stain electron microscopy. Virus Core Structure Except in helical nucleocapsids, little is known about the packaging or organization of the viral genome within the core. Figure Two-dimensional diagram of HIV-1 correlating immuno- electron microscopic findings with the recent nomenclature for the structural components in a 2-letter code and with the molecular weights of the virus structural glyco- proteins.

Figure Schemes of 21 virus families infecting humans showing a number of distinctive criteria: presence of an envelope or double- capsid and internal nucleic acid genome.

Virus Classification On the basis of shared properties viruses are grouped at different hierarchical levels of order, family, subfamily, genus and species.

JB Lippincott, Philadelphia, Gajdusek DC. Unconventional viruses and the origin and disappearance of kuru. Gelderblom HR. Assembly and morphology of HIV: potential effect of structure on viral function. Mattern CFT: Symmetry in virus architecture. Marcel Dekker, New York, Raven Press, New York, Springer-Verlag, New York, Elsevier, Amsterdam, Structure and Classification of Viruses.

In: Baron S, editor. Chapter In this Page. Related information. PubMed Links to PubMed. RSV can be dangerous for some infants and young children. Help protect yourself and your loved ones from RSV infection.

Prevent RSV. VRS: lo que debe saber. Links with this icon indicate that you are leaving the CDC website.