Orthomyxoviridae Enveloped virions are 80 to nm in diameter, are to nm long, and may be filamentous. They consist of spike-shaped surface proteins, a partially host-derived lipid-rich envelope, and matrix M proteins surrounding a helical segmented nucleocapsid 6 to 8 segments. The family contains five genera, classified by variations in nucleoprotein NP and M antigens:
Clade 2 viruses were first identified in bird isolates from ChinaIndonesiaJapanand South Korea before spreading westward to the Middle EastEuropeand Africa. The clade 2 viruses have been primarily responsible for human H5N1 infections that have occurred during late andaccording to WHO. Genetic analysis has identified six subclades of clade 2, three of which have a distinct geographic distribution and have been implicated in human infections: Before our project, GenBank contained only 5 other complete genomes from Europe for the — period, and it contained no whole genomes from the Middle East or northern Africa.
Our analysis showed several new findings. First, all European, Middle Eastern, and African samples fall into a clade that is distinct from other contemporary Asian clades, all of which share common ancestry with the original Hong Kong strain. Phylogenetic trees built on each of the 8 segments show a consistent picture of 3 lineages, as illustrated by the HA tree shown in Figure 1.
Two of the clades contain exclusively Vietnamese isolates; the smaller of these, with 5 isolates, we label V1; the larger clade, with 9 isolates, is V2. The remaining 22 isolates all fall into a third, clearly distinct clade, labeled EMA, which comprises samples from Europe, the Middle East, and Africa.
Trees for the other 7 segments display a similar topology, with clades V1, V2, and EMA clearly separated in each case. A stands for the genus of influenza AB or C. N1 stands for the first of several known types of the protein neuraminidase.
The distinction concerns pathogenicity in poultry, not humans. Normally, a highly pathogenic avian virus is not highly pathogenic to either humans or nonpoultry birds.
This current deadly strain of H5N1 is unusual in being deadly to so many species, including some, like domestic cats, never previously susceptible to any influenza virus. HA codes for hemagglutininan antigenic glycoprotein found on the surface of the influenza viruses and is responsible for binding the virus to the cell that is being infected.
NA codes for neuraminidasean antigenic glycosylated enzyme found on the surface of the influenza viruses. It facilitates the release of progeny viruses from infected cells. HA and NA are also used as the basis for the naming of the different subtypes of influenza A viruses.
This is where the H and N come from in H5N1. Influenza A viruses are significant for their potential for disease and death in humans and other animals.
Influenza A virus subtypes that have been confirmed in humans, in order of the number of known human pandemic deaths that they have caused, include: H1N1which caused the flu pandemic "Spanish flu" and currently is causing seasonal human flu and the flu pandemic " swine flu " H2N2which caused "Asian flu" H3N2which caused "Hong Kong flu" and currently causes seasonal human flu H5N1" bird flu "which is noted for having a strain Asian-lineage HPAI H5N1 that kills over half the humans it infects, infecting and killing species that were never known to suffer from influenza viruses before e.
In most cases, it causes minor sickness or no noticeable signs of disease in birds. It is not known to affect humans at all. The only concern about it is that it is possible for it to be transmitted to poultry and in poultry mutate into a highly pathogenic strain.
Therefore, USDA now tracks these detections in wild birds, backyard flocks, commercial flocks and live bird markets.
The segmentation of its genome facilitates genetic recombination by segment reassortment in hosts infected with two different influenza viruses at the same time.
The ability of various influenza strains to show species-selectivity is largely due to variation in the hemagglutinin genes. Genetic mutations in the hemagglutinin gene that cause single amino acid substitutions can significantly alter the ability of viral hemagglutinin proteins to bind to receptors on the surface of host cells.
Such mutations in avian H5N1 viruses can change virus strains from being inefficient at infecting human cells to being as efficient in causing human infections as more common human influenza virus types. Influenza A virus subtype H3N2 is endemic in pigs in China, and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains.
The dominant strain of annual flu virus in January was H3N2which is now resistant to the standard antiviral drugs amantadine and rimantadine.Like the regular flu, swine flu can lead to more serious problems including pneumonia, a lung infection, and other breathing problems.
And it can make an illness like diabetes or asthma worse. A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of type A of subtype H5N1, is the highly pathogenic causative agent of H5N1 flu, commonly known as avian influenza ("bird flu").
Influenza virus type A is the most common subtype and is responsible for serious epidemics and pandemics throughout human history such as the (H1N1) ‘Spanish flu’, which was the most virulent virus in human history and caused an estimated 20–40 million deaths worldwide.
Influenza is an acute respiratory illness, caused by influenza A, B, and C viruses, that occurs in local outbreaks or seasonal epidemics. Clinical illness follows a short incubation period and presentation ranges from asymptomatic to fulminant, depending on the characteristics of .
Avian influenza A viruses are designated as highly pathogenic avian influenza (HPAI) or low pathogenicity avian influenza (LPAI) based on molecular characteristics of the virus and the ability of the virus to cause disease and mortality in chickens in a laboratory setting.
Nov 07, · Avian influenza, which is caused by influenza A viruses, can affect a variety of domestic and wild bird species. Infection can range from asymptomatic to severe, depending on the virulence of the virus and the susceptibility of the avian host.