The Structure Of The Influenza A Virus Virion Biology

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Influenza is a respiratory disease that occurs as a result of infection by influenza Virus. Influenza is one of the most main causes of illness and death today in all over the world. However, the history of the great epidemic which occurred in 1918 to 1919 and killed more than 40 million people around the world has prompted scientists to conduct more studies and research on these viral infections (Greenwood et al., 2002.p472). So far, the assets of strains of the influenza and the epidemiological behaviour are not fully understood. However, the inability to predict the new strains of flu represents a serious challenge to public health and programs that reduce the spread of such epidemics. There are three types of flu viruses infect humans are influenza A, influenza B and Influenza C (Collier and Oxford, 2006). Several studies show that influenza type A virus is the most common seen, which is the main cause of many serious epidemics and the pandemics. Influenza A infects humans, horses, goats, pigs, birds and some other animals. Based on studies conducted on flu pandemics that hit people in the past, all of these pandemics were caused by influenza A(Taubenberger and Morens, 2006). Influenza A identified in pigs in 1918, which coincided with a human flu pandemic 1918-1919.However, even though influenza A viruses have many similarities, but that is not mean they are same. Each influenza A viruses are genetically designed to infect that species. Genetic mutations may occur to some strains of influenza A virus with a different pathogenic dangerous and some of these mutations occur in the same species, but do not move to other species. On the other hand, some of the virus after mutation moves to other species, causing them serious pathogenic.


Group: Group V (-)ssRNA

Family: Myxoviridae

Sub-Family: Orthomyxoviridae

Genus: Influenza A


Influenza A viruses further classified into subtypes based upon the characteristics of the surface proteins Haemagglutinin (HA) and Neuraminidase (NA). There are at least 16 different HA and 9 different NA (Collier and Oxford, 2006). All 16 HA and 9 NA subtypes of type A viruses are maintained in aquatic birds. Widely circulating human influenza A viruses seem to have been limited to three H (H1, H2 and H3) and two neuraminidase (N1 and N2) subtypes. Recently, purely avian viruses including H5N1, H9N2 and H7N7 subtypes have been directly transmitted to humans (viralZone, 2009).

The virion:

Adopted from:(ViralZone,2009).

The virus reproduces only within the cells of living tissue and not affect by antibiotics such as penicillin that used to treat bacterial infections. Influenza virus is spherical and its size is equal to one thousandth of a millimetre, and genetic material of the virus consists of RNA, which contains 8 genes and the enzyme "polymerase" which plays a vital role in the proliferation of the virus. Influenza virus consists of an internal membrane made from protein surrounding the nuclear material of the virus. While, the outside membrane made from lipid, which project prominent glycoprotein spikes of two types:

Haemagglutinin (HA): which plays a key role in the ability of the virus to infect the cells of the respiratory tract by integration with cell's receptors and multiply inside the cell. This molecule is more parts of the virus's ability to stimulate the immune system, and the ability of body resistance measured by the level of Haemagglutinin resistance.

Neuraminidase (NA): works to spread out the virus after replication in respiratory system throughout the body (Gubarea et al., 2008).

The structure of the influenza A virus:

PB2: Transcriptase: cap binding

PB1:Transcriptase: elongation

PA : Transcriptase : protease activity

HA: Haemagglutinin

NP: Nucleoprotein: RNA binding; part of transcriptase complex; nuclear/ cytoplasmic transport of vRNA

NA: Neuraminidase: release of virus

M1: Matrix protein: major component of virion

M2: Intergral membrane protein-ion channel

NS1: Non-structural: nucleus; effects on cellular RNA transport, splicing, translation. Anti-iterferon protein.

NS2: Non-structural: nucleus+cytoplasm, function uknown


Influenza virus is a class of viruses that contain RNA as a genetic material. Influenza virus multiplies inside the host cell and uses the material of this cell to reproduce hundreds of copies of the virus. When the virus combined with cell membrane, the RNA of the virus enters inside the cell. Then the cell enzymes and ribosomes transcribe and translate the viral genes. In this way, virus multiplies inside the cell. Thus, the host cell produces hundreds of new virus particles, rather than the production of new cellular material. Therefore, the new virus particles excreted outside the host cells to infect new cells (Collier and oxford, 2006).

Drift and Shift:

Several studies indicate that, the influenza A viruses are continuously evolving, and

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