Influenza A Evolution And Transmission Biology Essay

Influenza normally called grippe is an unwellness that caused by a virus that infects the respiratory piece of land, the olfactory organ, pharynx and bronchial tube and seldom besides the lungs.

It is caused by RNA viruses of the household orthomyxoviridae that affects birds and mammals. It besides has the ability to do pandemic infection in worlds.

Influenza A virus was the first to be isolated in 1933 by intranasal vaccination of the Mustela nigripes. Thereafter type B was isolated along with type Angstrom in cell civilization in 1940.

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One of the most outstanding characteristics of grippe viruses is their ability to alter antigenically either by antigenic displacement or antigenic impetus. Influenza virus it is non a cause of low febrility and snuffles that keeps you home in bed and it is non a GI disturbance ( stomach grippe ) .

Influenza A consequences in high mortality and morbidity rates in adult male in the winter months in temperature zone, but throughout the twelvemonth in more tropical climes. Since 1997, avian grippe has been a major job in the Far East, with strains from domestic domestic fowl on occasion infecting single straight, ensuing in high mortality rates ; virus could go altered to adult male. ( Greenwood et al. , 2002 )

Virus categorization

Influenza is an highly variable, fast mutating virus. There are three chief types, or genera Influenza A virus, B, and C though they are related each has different disease characteristic. Of the three type ‘s virus, influenza A mutates the fastest, and as a consequence it is classified into a figure of subtypes. Influenza B involves more easy but still has many strains. Influenza C is the most stable of the three viruses.

grippe A

Influenza A virus causes the most terrible signifier of grippe. It mutates 2-3 times faster than grippe B virus and is responsible for most big pandemics.

Influenza A virus categorization is based on fluctuation on two proteins found on the surface of the virus which is Hemaglutinine ( H ) has 16 subtypes and Neuraminidase ( N ) has 9 subtypes. The most important subtypes to homos are H1N1, H1N2, and H3N2 viruses.

Subtypes H1N1 is responsible for both the deathly 1918 Spanish grippe pandemic and 2009 swine grippe eruption. H5N1 subtypes associated with pandemic avian grippe.

Influenza A subtypes are farther divided into strains that are named after the location and twelvemonth of out interruptions they cause. For blink of an eye, the virus strain that caused a swine grippe out interruption among soldiers in new New Jersey in 1976 is called A new New Jersey 1976 ( H1N1 ) , the strain figure may besides be integrated into the strain name.

2. Influenza B

Influenza B can do decease in worlds, but is non known for doing world-wide pandemic. It can do spark epidemics but these are by and large less terrible than those that can do influenza A virus.

Influenza B virus does non travel through the sort of revolution that alterations in the surface protein of the virus as grippe A virus bash. It mutates though more easy than influenza A and has different strains.

3. Influenza C

Is the rarest and most stable of the three species of grippe, it normally mild unwellnesss though it can on occasion do more sever grippe Out interruptions are typically local and do non go big epidemics or planetary pandemics for illustration California.

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Virus construction

The grippe virus is approximately spherical and it is an enveloped virus, the outer bed is a lipid membrane which is taken from the host cell in which the virus multiplies. Alternatively into the lipid membrane are spikes, which are proteins for illustration, glycoprotein because they consist of protein linked to saccharify known as Hemaglutinine and Neuraminidase, these are the proteins that determine the types of grippe virus A, B or C and the subtypes for illustration A ( H1N1 ) , these proteins are of import in the immune response against the virus antibodies. ( )

Figure1 adopted from ( )

Embedded the lipid membrane is the M2 protein and beneath it is a viral protein called M1 or matrix protein. This protein gives strength and rigidness t the lipid envelope. Within the inside of the virion are the viral RNAs these are the familial stuff of the virus. Each RNA sections as they are called consist of RNA joined with several proteins shown in the figure1 ( B1, PB2, PA, NP ) . These RNA sections are the cistron of influenza virus. The inside of the virion besides contain a protein called NEP.

HA ( hemagglutinin ) protein: The HA protein is involved in fond regard and membrane merger in the endosome of the septic cell. The receptor adhering site on the virus is in a pocket that is non exposed to the immune system. The antigenic spheres are on the surface. These can be altered and the virus can thusA avoid a humoral response without impacting its ability to adhere to the receptor.

NA ( neuraminidase ) protein: The neuraminidase protein digests sialic acid ( neuraminic acid ) – which most cells have on their surface. Since sialic acid is portion of the virus receptor, when the virus binds to the cell, it will be internalized ( endocytosed ) . By late in infection, the sialic acid will hold been removed from the infected cell surface by the neuraminidase doing it is easier for the offspring virions to spread away one time they exit the cell. Neuraminidase is besides involved in incursion of the mucous secretion bed in the respiratory piece of land.

Antigenic impetus: Antigenic impetus is due to mutant. Antibodies to the HA protein are the most of import in protection, although those to NA besides play a function. Both proteins undergo antigenic impetus ( i.e. accumulate mutants ) and accumulate alterations such that an single immune to the original strain is non immune to the drifted 1. Antigenic impetus consequences in sporadic eruptions and limited epidemics.

Antigenic displacement: Antigenic displacement is due to reassortment. In the instance of grippe A, A antigenic displacement sporadically occurs. Apparently “ new ” HA and/or NA are found in the go arounding viral strains. There is small unsusceptibility ( peculiarly if both proteins change, or if new HA is present ) and an epidemic/pandemic is seen. ( )


Influenza virus may be transmitted in worlds in three ways ;

By direct contact with septic persons.

By contact with contaminated objects for illustration door grips.

By inspiration of virus loaded aerosols.

Influenza A virus is basically an avian virus that has late crossed into mammals ; birds have the most figure and rand of grippe strains.

Every 10-15 old ages a major new pandemic strain appears in adult male with a wholly new HA and sometimes a new NA every bit good ( antigenic displacement ) .

Over the subsequent old ages this strain undergoes minor alterations ( antigenic impetus ) every two to three old ages, perchance by selective antibody force per unit area in the population of worlds infected. . ( Greenwood et al. , 2002 )


Influenza was responsible for the most annihilating pestilence in human history. The Spanish grippe that swept around the universe killed about 675.000 people in the United Kingdom and an estimated 20-50 million people around the universe.

Influenza A Development

1874 — – ( H3N8 )

1890 — – ( H2N2 ) … … … … … … … … .Pandemic

1902 — – ( H3N2 )

1918 — – ( H1N1 ) … … … … … … … … ..Pandemic

1933 — – ( H1N1 ) … … … … … … … … ..First strains isolated

1947 — – ( H1N1 ) … … … … … … … … ..Variation detected

1957 — – ( H2N2 ) … … … … … … … … .. ” Asiatic ” Flu pandemic

1968 — – ( H3N2 ) … … … … … … … … .. ” Hong Kong ” Flu pandemic

1976 — – ( H1N1 ) … … … … … … … … .. ” Swine ” Flu, non-epidemic

1977 — – ( H1N1 ) + ( H3N2 ) … … … ” Russian ” Flu epidemic ( )

In late March and early April 2009, an eruption of H1N1 influenza A virus infection was detected in Mexico, with subsequent instances observed in many other countries.On June 11, 2009, the World Health Organization raised its pandemic watchful degree to the highest degree.

On 29 January 2010 the WHO reported that more than 209 states and abroad districts or communities have reported research lab confirmed instances of pandemic grippe H1N1 2009, including at least 14711 deceases. ( )


The pathogenicity and virulency of the grippe virus is determined by several interacting factors:

Host factors:

Presence of mark receptors on host cells

Handiness of enzymes in host cells which are indispensable for viral entry and reproduction

State of immunocompetence of the person host

Specific unsusceptibility against certain viral antigenic determinants in the single host and mark population

Ability of the immune system to command the viral reproduction efficaciously without doing serious indirect harm for the host by its inflammatory response

Viral factors:

Ability to adhere to host cells

Ability of virus casting

Restriction of cytopathogenic effects to let for an appropriate balance between viral reproduction and control by the host

Escape from immunosurveillance by development of antigenic fluctuation driven by selective force per unit area of the immune response

Escape from immunosurveillance by recombination with different virus strains from zoonotic disease

Transition of the immune response to rarefy effectual host defence mechanisms

The chief marks of the grippe virus are the columniform epithelial cells of the respiratory piece of land. In influenza infection, the receptor adhering site of viral hemagglutinin ( HA ) is required for adhering to galactose bound sialic acid on the surface of host cells. Certain countries of the adhering site of HA are extremely conserved between subtypes of the grippe virus. Hosts may forestall the fond regard by several mechanisms:

( 1 ) Specific immune response and secernment of specific IgA antibodies,

( 2 ) Unspecific mechanisms, such as mucociliary clearance or production of mucoproteins that able to adhere to viral hemagglutinin, and

( 3 ) Genetic variegation of the host receptor ( sialic acid ) , which is extremely conserved in the same species, but differs between avian and human receptors.

Once grippe has expeditiously infected respiratory epithelial cells, reproduction occurs within hours and legion virions are produced. Infectious atoms are preferentially released from the apical plasma membrane of epithelial cells into the air passages by a procedure called budding. This favors the fleet spread of the virus within the lungs due to the rapid infection of neighbouring cells. ( )

Immune response:

Influenza causes an acute infection of the host and initiates a cascade of immune reactions triping about all parts of the immune defence system. Most of the initial innate response, including cytokine release ( IFNI±/I? ) , inflow of neutrophil granulocytes or natural slayer cells, and cell activation, is responsible for the acute oncoming of the clinical symptoms. Innate unsusceptibility is an indispensable requirement for the adaptative immune response, foremost, to restrict the initial viral reproduction and antigen burden, and secondly, because the antigen-specific lymph cells of the adaptative immune response are activated by co-stimulatory molecules that are induced on cells of the innate immune system during their interaction with viruses ( Figure ) . Influenza viruses, nevertheless, encode in the non-structural protein1 ( NS1 ) mechanisms to hedge and antagonise the IFN I±/I? response. NS1 is likely to sequester viral dsRNA which prevents acknowledgment of this unsafe molecule by cellular detectors which would otherwise trip IFN I±/I? release

The adaptative immune response requires some yearss to be effectual but so helps to incorporate the viral spread, to eliminate the virus, and eventually to set up a memory response ensuing in a durable opposition to re-infection with homologous virus. Cross-protection within a subtype of grippe has merely seldom been observed and infections basically induce no protection across subtypes or between types A and B.

Influenza infection induces both systemic and local antibody ( humoral unsusceptibility ) , every bit good as cytotoxic T cell responses ( cellular unsusceptibility ) , each of which is of import in recovery from acute infection and opposition to reinfection. ( )

Incubation period of the virus:

The incubation period of influenza stopping points from 1 to 4 yearss, with 2 yearss being the norm. Persons become infective get downing 1 twenty-four hours before their symptoms being and remain infective through about 5 yearss after illness oncoming. Children can be infective for grater than 10 yearss, and immature kids can cast virus for up to 6 yearss before their unwellness oncoming. Badly immunocompromised individuals can cast virus for hebdomads or months.

Symptoms of grippe

When a individual is infected with influenza the following symptoms will look:

Fever which rise up to 38 and kids up to 40.

Headache, aching musculus and articulations pain

Tired and failing

Chills and sudating

Nasal congestion

Sore pharynx and dry cough

Loss of appetency

Diarrhea and purging ( these symptoms may impact kids more than grownups ) .

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Lab diagnosing

Virus Isolation – Throat swabs, NPA and rhinal lavations may be used for virus isolation. It is reported that rhinal lavations are the best specimens for virus isolation. The specimen may be inoculated in embryonated eggs or tissue civilization. 10-12 twenty-four hours embryonated eggs are used for virus isolation. The specimen is inoculated into the amnionic pit. The virus replicates in the cells of the amnionic membrane and big measures are released back into the amnionic fluid. After 2-3 yearss incubation, virus in the amnionic fluid can be detected by adding aliquots of harvested amnionic fluid to chick, guinea hog, or human red blood cells.

Rapid Diagnosis by Immunofluorescence – cells from pathological specimens may be examined for the presence of grippe A and B antigens by indirect immunofluorescence. , but EIA trials for the sensing of grippe A viral antigens are easier to construe than immunofluorescence. PCR assays for the sensing of influenza RNA can besides be used.

Serology – this is done by the presentation of a rise in serum antibody to the infecting virus. Complement fixative trial is the most common method used utilizing the type specific soluble antigen. ( )


Pneumonia is the major serious complication of grippe. It can develop about five yearss after viral grippe and about ever occurs in susceptible persons about five yearss after oncoming. This can be viral pneumonia, in which the grippe virus itself spreads into the lungs, or bacterial pneumonia, in which unrelated bacteriums ( such as Diplococcus pneumoniae ) . In both instances, the individual may hold a worsened cough, trouble external respiration, persistent or repeating febrility, and sometimes bloody phlegm. Pneumonia is more common in older people and in people with bosom or lung disease.

Children under 1 twelvemonth old have a really high hazard, non merely for pneumonia but besides for other complications, including meningitis and phrenitis ( rednesss in cardinal nervous system ) . The hazard diminutions after age one but is still elevated in kids aged three to five. ( Greenwood et al. , 2002 ) .


Amantadine and rimantadine are chemically related antiviral drugs active against grippe A viruses. After influenza A viruses enter cells, these drugs inhibit the uncoating of grippe A viruses by barricading the ion-channel activity of the viral M2 protein. Amantadine was approved in 1976 for intervention and prophylaxis of grippe type A infection in grownups and kids aged greater than or equal to 1 twelvemonth. Rimantadine was approved in 1993 for intervention and prophylaxis of grippe type A infection in grownups. For kids, rimantadine was approved merely for prophylaxis ; nevertheless, many experts consider rimantadine appropriate for intervention of grippe A in kids.

More late two neuraminidase inhibitors, zanamivir and oseltamivir they can cut down the continuance of symptoms by 1-3 yearss if given within 36 hours of illness oncoming. zanamivir is administrated by inspiration of a dry pulverization twice daily for five yearss.

Oseltamivir is given by mouth twice day-to-day dose for five to seven yearss, these has been used in those with normal nephritic map, but it should be used one time a twenty-four hours when nephritic map is impaired. ( ) .

Prevention and control

Influenza vaccinum increases a individual ‘s defences against the influenza virus. It works by presenting really little sums of viral constituents into the organic structure. These constituents are adequate to excite the production of antibodies ( cells designed to assail that peculiar virus ) , which will stay in the organic structure and ready to assail that same grippe virus in the hereafter.

Reasonably effectual ways to cut down the transmittal of influenza include good personal wellness and hygiene wonts such as: non touching your eyes, nose or mouth frequent manus rinsing ( with soap and H2O or with alcohol-based manus hang-ups ) covering coughs and sneezings ; avoiding close contact with ill people ; and remaining place yourself if you are ill. Avoiding expectoration is besides recommended

Although face masks might assist forestall transmittal when caring for patients. Since grippe spreads through both aerosols and contact with contaminated surfaces, surface sanitizing may assist forestall some infections. Alcohol is an effectual sanitizer against influenza viruses. ( )


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