Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people. Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin H and neuraminidase N. There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes H1 through H18 and N1 through N11, respectively. Reassortment can occur when two influenza viruses infect a host at the same time and swap genetic information.
This graphic shows the two types of influenza viruses A and B that cause most human illness and that are responsible for flu seasons each year. Both influenza A and B viruses can be further classified into clades and sub-clades which are sometimes called groups and sub-groups.
Note that this graphic is an example, and currently circulating influenza clades and subclades may differ from those presented here. Figure 1 — This is a picture of a phylogenetic tree.
Each sequence from a specific influenza virus has its own branch on the tree. The degree of genetic difference between viruses is represented by the length of the horizontal lines branches in the phylogenetic tree. The further apart viruses are on the horizontal axis of a phylogenetic tree, the more genetically different the viruses are to one another.
An influenza clade or group is a further subdivision of influenza viruses beyond subtypes or lineages based on the similarity of their HA gene sequences. See the Genome Sequencing and Genetic Characterization page for more information. Clades and subclades are shown on phylogenetic trees as groups of viruses that usually have similar genetic changes i. Dividing viruses into clades and subclades allows flu experts to track the proportion of viruses from different clades in circulation.
Note that clades and sub-clades that are genetically different from others are not necessarily antigenically different. These proteins act as antigens. Antigens are molecular structures on the surface of viruses that are recognized by the immune system and can trigger an immune response such as antibody production. Therefore, for antigenically different viruses, immunity developed against one of the viruses will not necessarily protect against the other virus as well.
Influenza A H3N2 viruses also change both genetically and antigenically. Early reports suggest the new virus is more contagious than the one causing SARS but less likely to cause severe symptoms. Coronaviruses CoVs are a family of viruses that cause respiratory and intestinal illnesses in humans and animals.
Since December , the world has been battling another coronavirus. Coronaviruses are relatively simple structures, and their form helps us to understand how they work. They are spherical and coated with spikes of protein. These spikes help the virus bind to and infect healthy cells. However, the same spikes are also what allows the immune system to 'see' the virus. Bits of the spike can be used in potential coronavirus vaccines to prompt the body to produce antibodies against this new virus.
Beneath these spikes is a layer of membrane. This membrane can be disrupted by detergents and alcohols, which is why soap and water and alcohol hand sanitiser gels are effective against the virus.
Whereas the genomes of some viruses like chickenpox and smallpox are made of DNA like humans, those of coronaviruses are made of the closely related RNA. RNA viruses have small genomes which are subject to constant change. These changes, called mutations, help the virus adapt to and infect new host species.
It is thought that the new COVID likely originated from bats but it is not yet known whether mutations allowed this jump from animals to humans. Even though there are many similarities between the new COVID and the virus that caused the SARS epidemic, there are also differences resulting from changes in their genomes.
For example, the three immunologically distinct viruses targeted by the trivalent poliovirus vaccine are considered to be the same species: human enterovirus C.
Selected representatives called type viruses may be used to illustrate the properties of a particular taxon. A number of virus families are assigned to higher-level orders, which are designated with the suffix -virales.
Examples are Herpesvirales, Mononegavirales, Picornavirales, and Nidovirales. Most families are unassigned to orders. In addition to biologic classification, viruses often are categorized according to their clinical presentation i. Box Respiratory route i. Fecal-oral route: polioviruses, coxsackieviruses, hepatitis A virus, rotavirus, astrovirus, norovirus. Parenteral route i. Vertical route e. Arthropod-borne route e.
Rodent-associated transmission: Lassa fever virus, sin nombre, and other hanta viruses e. Understanding virus classification can lead to important generalizations regarding the prevention and treatment of viral infection and insights into the distribution and evolution of viruses.
In addition, insights from viral taxonomy play key roles in preventing and staunching the spread of viral disease at the population level. All references are available online at www. National Center for Biotechnology Information , U. Principles and Practice of Pediatric Infectious Diseases. Published online Jul Robert David Siegel. Guest Editor s : Sarah S. Chief, Section of Infectious Diseases, St.
Christopher's Hospital for Children, Philadelphia, Pennsylvania. Guest Editor s : Charles G. Copyright and License information Disclaimer. All rights reserved. Elsevier hereby grants permission to make all its COVIDrelated research that is available on the COVID resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source.
TABLE Open in a separate window. Key References 5. Siegel R. Lipkin WI. The changing face of pathogen discovery and surveillance. Nat Rev Microbiol. Ho T, Tzanetakis IE. Development of a virus detection and discovery pipeline using next generation sequencing. References 1. Murphy FA. Virus taxonomy. Fields Virology. Lippincott-Raven Publishers; Philadelphia: Condit R.
Principles of virology. Fenner F. The classification and nomenclature of viruses: summary of results of meetings of the International Committee on Taxonomy of Viruses in Madrid, September J Gen Virol. Delwart EL. Viral metagenomics.
0コメント