Antigenic Shift And Drift Of Influenza Virus Biology Essay

Influenza A virus is known in the worldwide as an ague contagious viral infective disease and respiratory piece of land disease that occur as a consequence of infection. Flu can do mild to severe illness, and can be lethal. Certain people, such as senior people and people with wellness conditions, are at a high hazard for serious jobs from the grippe virus. The grippe or the grippe is caused by RNA viruses which belong to Orthomyxoviridae household of viruses. There are three types of grippe viruses infect worlds are influenza A, grippe B and Influenza C. Influenza A viruses merely infect nonhuman hosts, and a reassortment of cistrons can go on between those subtypes.

Influenza is greatly contagious respiratory disease that spreads from individual to individual by sneezing and coughing. By comparison to the most viral respiratory infections, it is found that the symptoms of influenza infection are highly terrible. It is a seasonal infection ; the spread of infection is by and large in the winter ( Richman et al. , 2009 ) .Influenza A infects worlds, Equus caballuss, caprine animals, hogs, birds and some other animate beings.

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Based on surveies conducted on grippe pandemics that hit people in the yesteryear, all of these pandemics were caused by grippe A ( Taubenberger and Morens, 2006 ) .However, the history of the great epidemic which occurred in 1918 to 1919 and killed more than 40 million people around the universe has encouraged scientists to carry on more surveies and research on these viral infections ( Greenwood et al. , 2002 ) .Causative Agent:Influenza infection is caused by a member of viruses which belong to the household Orthomyxoviride, ( orthos in Grecian agencies consecutive and myxa in Grecian agencies mucous secretion ) .

There are three chief types: Influenza virus A, Influenza virus B, Influenza virus C. Influenza A is considered here which is besides known as avian grippe ( Collier et al. , 2006 ) .

Categorization:Group: Group V ( – ) ssRNAFamily: MyxoviridaeSub-Family: OrthomyxoviridaeGenus: Influenza AThe categorization of influenza virus A based on fluctuations on two proteins found on the virus surface. Hemagglutinin, a glycoprotein nowadays on the viral surface as bacillar projections, abbreviated HA and has 16 types. It has the ability to agglutinate red blood cells and heighten the fond regard and incursion of the virus to the receptor of the cells, the other type of glycoprotein is Neuraminidase, abbreviated NA and has 9 subtypes. About 80 % of them are HA and the ratio of HA to NA is about 4-5 to 1. The most important subtypes that can do extended eruptions in homo are H1N1, H1N2, and H3N2 viruses ( Richman et al. , 2009 )


The sub-types of viruses that cause avian grippe, which has infected human pandemic deceases:1 – 1918 ( H1N1 ) , which caused the Spanish grippe.2 – 1957 ( H2N2 ) , which has caused the Asian grippe.

3 – 1968 ( H3N2 ) , grippe, which has caused Hong Kong.4 – 1976 ( H1N1 ) , swine grippe episode5 – 1977 ( H1N1 ) , Russian grippe6 – 1997 ( H5N1 ) , South-East Asia, died 10s of 1000000s of birds caused by this strain.7 – 1999 ( H9N2 ) , bird grippe in Hong Kong.8 – 2003 ( H7N7 ) , bird grippe in Netherland9 – 2004 ( H5N1 ) , bird grippe in South-East Asia10 – 2009 ( H1N1 ) virus, which is a pandemic in our times ( H1 ) derived from the swine grippe of 1930 ( and related to the H1 of the great 1918 Spanish grippe ) and ( N1 ) from a virus that had been go arounding in the hogs of Europe and Asia since 1979 along with the M cistron from that virus ( Riel et al. , 2007 ) .The normal hosts for grippe A virus are the birds that live in H2O or they are called aquatic birds and the different mammals can be hosts for this virus like as worlds, Equus caballuss and hogs.

Structure ( Virion ) :The influenza virion is approximately spherical and enveloped virus ; the outer screen is prepared from the lipid membrane which is occupied from the host cell in which the viruses multiply. Then inserted into the lipid membrane are ‘spikes ‘ , which are proteins known as glycoprotein spikes, because they contain of protein linked to sugars called as:HA ( hemagglutinin ) and NA ( neuraminidase ) Figur 1: show Schematic of an grippe A virusHaemagglutinin ( HA ) : which plays a critical function in the ability of the virus to infect the cells of the respiratory piece of land by integrating with cell ‘s receptors and multiply in the cell. This molecule is more parts of the virus ‘s ability to excite the immune system, and the ability of organic structure opposition measured by the degree of Haemagglutinin opposition.

Neuraminidase ( NA ) : plants to distribute out the virus after reproduction in respiratory system throughout the organic structure ( Gubarea et al. , 2008 ) .


The grippe A virus contains eight-segmented, negative ( – ) RNA as its familial stuffs. It replicates by come ining the host cells ( surface assimilation ) and utilizing this cells as resources to bring forth 100s transcripts of viral RNA.After fond regard to the specific receptors on the surface of the host cells, the hemagglutinin ( HA ) binds to the sialic acid on the receptors surface and the virions enter into the cells by endocytosis. The neuraminidase plays a critical function in viral reproduction by taking sialic acid which besides known as neuraminic acid from the surface of cell.The messenger RNA synthesis and reproduction take topographic point in the karyon with aid of the viral RNA-dependent RNA polymerase.

The viral RNA polymerase uses the nucleocapsids as a templet and it does non necessitate a to the full uncoated nucleocapsids. Since this virus is a negative-strand RNA, RNA alteration enzymes and RNA polymerase are packaged in the virion. So the viral cistrons are transcribed and translated ( to give viral proteins ) by the cell ‘s enzymes and ribosome, that makes the viruses take over the cell productiveness and alternatively of bring forthing the cellular stuffs merely, the cell will bring forth 100s transcripts of viruses. These viruses will be released out from the host cell and they start occupying a new host cell by their ain ( Korteweg et al. , 2008 ) .

Antigenic displacement and impetus

Influenza type A viruses go through two sorts of alterations. One is a sequence of mutants that occur over clip and causes a slow development of the virus. This is known as Antigenic Drift. The other type of alteration is a sudden alteration in the hemagglutinin and/or the neuraminidase proteins. This is known as Antigenic Shift. A In this instance, a new subtype of the virus all of a sudden emerges. Type A viruses go through both sorts of alterations ( Schweiger et al. , 2002 ) .

Transmission:Influenza virus type A spread among the many animate beings, including ducks, poulets, hogs, giants, and Equus caballuss. Somehow, some minor species of the virus strains are limited to animate beings entirely, but in the progeny of birds and subjected to infection with all sorts of influenza virus A ( Richman et al. , 2009 ) .

Avian grippe type A can be transmitted to worlds in two ways: Directly from birds or contaminated environments to worlds and through an intermediary host such as hogs ( Collier et al. , 2006 ) .Most transmittal occurs in a short clip before or after the visual aspect of grippe symptoms on an septic individual. Furthermore, persons can be infected by inspiration of virus-laden aerosols. However, it can distribute quickly by sneezing and coughing particularly in medical scenes, schoolrooms and airdromes. Whereas, rhinal discharges ( droplets ) are the most common beginning of virus transmittal by contaminated stuffs or direct contact ( Brankston et al.

, 2007 )Epidemiology:Three pandemics of grippe occurred in the last century. In 1918, “ Spanish ” grippe ( H1N1 ) caused an estimated 40 million deceases in less than a twelvemonth ( Nicholson et al. , 2001 ) . While, In 1957, “ Asiatic ” grippe ( H2N2 ) caused an estimated 70,000 deceases in the US entirely and in 1968 more than 30,000 people were killed in the US by new subtypes of grippe A virus ( H3N2 ) .Harmonizing to The World Health Organization, the H1N1 virus affects younger age compared with seasonal grippes in all categories- those who are most often infected, necessitating intensive attention, hospitalized and deceasing ( WHO, 2009 ) .

It has been estimated that, 3-5 million of people worldwide are infected by grippe and 250 000 to 500 000 deceases annually due to influenza ( WHO, 2009 ) . Harmonizing to analyze published in December 30, 2009 by The New England Journal of Medicine, immature people who are under 18 old ages are more likely to catch grippe from an septic individual in their family than grownups ( ScienceDaily, 2009 ) .Pathogenesis:Virus is spread by contact from individual to individual through little atoms aerosols that can acquire in respiratory piece of land or through vehicles. The incubation clip is short, about 18 to 72 hours. Whereas, virus concentration in nasal and tracheal secernments stay long for 24 to 48 hours after symptoms begin.Influenza A virus infects the epithelial cells of the respiratory piece of land and taking cells die.

Cell decease at subsequently times may besides ensue from the action of cytotoxic T-cells. So, the efficiency of ciliary clearance is reduced, due to impaired map of the mucous secretion lift.The virulency and pathogencity of the influenza virus can be identified by two major factors which are host and viral factors.

Host factors:

Enzymes should be available in the cell host in order to assist the viral entry and reproduction.The mark receptors must be present on the surface of the host cell.Immunocompetence State of each host.Specific unsusceptibility against certain viral antigenic determinants in the host.Ability of the immune system to command the viral reproduction efficaciously without doing serious harm for the host by its inflammatory response ( Nagata et al. , 2008 ) .


Symptoms continue from 3-7 yearss, but in some instances, symptoms have persisted to 3 hebdomads:ConcernFever ( 38 -40 C )Sore pharynxFatigueAchesDry coughingNasal dischargeVomitingDiarrheaComplications of grippe A virus:PneumoniaOtitisToxic daze syndromeDiagnosis:Normally, clinician will diagnosis grippes based on patients symptoms, but other respiratory infections might hold similar symptoms. So, diagnostic is necessary by making multiple laboratory probe as showin this table 1:Treatment:In fact there is no effectual intervention for grippe A because, the antibiotics ( antiviral ) do non kill the viruses, but it may do the disease less terrible. There are four antiviral medicines have been approved for handling grippe A virus infections: Amantadine, Rimantadine, Zanamivir, and Oseltamivir ( Jefferson et al. , 2006 ) .Prevention and control:There are three possible ways to command or forestall influenza infection: inoculation, anti-viral and non-medical intercessions. The individual best manner to protect against grippe is to acquire inoculation. Besides infection can be prevented by disease control steps that to be followed by everyone during pandemic grippe or seasonal grippe ( Collier et al.

, 2006 ) .


Washing custodies by utilizing H2O and soap or intoxicant barter.Covering nose and oral cavity while coughing.Discard the tissue after usage in dust pin and wash custodies.Avoid close contact with people with grippe symptoms.Avoid being in ill ventilated and crowded topographic points for long clip.

In order to cut down the spread of grippe from animate beings:Quarantine the septic animate beings, and so kill it after that.Separation of carnal species during the engendering each species in isolation from the other type.Promote the people to inform approximately septic animate beings every bit shortly as possible.

Decision and future mentalityIt could be concluded that, influenza A virus is one of the most infective diseases that impacting worlds and a figure of animate beings. However, influenza A virus has led to several pandemics in the last century. Since the grippe virus is able to alter each clip, so it requires a new vaccinum in each clip of mutant. Novel influenza virus strains appear sporadically to which worlds have small unsusceptibility, follow-on upseting pandemics. There have been many accomplishments in the advancement of grippe vaccinums and antiviral medicines to forestall and handle grippe, and there are systems in topographic point to give early warning for the incidence of pandemic viruses.

There are batch betterments, based on recombinant DNA techniques and fresh accessory promise to alter the vaccinum therapy landscape against grippe and other infective diseases every bit good.In add-on to that, bettering immunisation protection will necessitate other health care professionals to educate their clients and equals about their susceptibleness to influenza and the badness of unwellness that grippe can do. World wellness organisation need to measure their clients ‘ beliefs, perceptual experiences and attitudes about grippe and the vaccinum and program intercessions to do the vaccinum and bringing of the influenza vaccinum attractive so the mortality and morbidity associated with grippe can be decreased.


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