Global Threat Of Influenza Virus Outbreak Biology Essay
In the yesteryear, avian grippe viruses were believed to be replicated ill in worlds and other mammals, as there was no convincing grounds of non avian infections by avian grippe virus. However, since 1997 there have been repeated instances of human infection by avian H9N2 and H5N1 influenza viruses in Southern China, Thailand Vietnam and Indonesia. Recently H1N1 ( swine grippe ) is added to the list of extremely infective grippe viruses doing eruptions in worlds [ 1 ] . Avian grippe virus has raised the concerns for public wellness non merely locally but besides posting a pandemic menace to the whole universe. Under the circumstance posted by avian grippe eruption, probes for all facets of influenza activity should be broadened and encouraged.
H5N1 influenza A infections have been reported in several mammalian species such as monkeys, mice, hogs, Mustela nigripess, domestic cats every bit good as Liberation Tigers of Tamil Eelams and Leopards [ 2 ] . In south China part, H5N1, H6N1 and H9N2 have become established in the domestic fowl population since mid-1990. Influenza virus is omnipresent among aquatic bird species. Phylogenetic surveies revealed that there are multiple line of descents of grippe A viruses co-circulating in shore birds in North America and other different geographical parts at the same clip. Sporadically, influenza A viruses are transmitted to other species and set up continual infections in those hosts [ 3 ] .
2. General debut of Structure of grippe virus
All avian grippe viruses belong to the Influenza virus A genus of the Orthomyxoviridae household and are enveloped, negative-strand, metameric RNA viruses. Virus atoms are normally spherical and about 100 nanometers in diameter [ 4 ] . The AIV genome consists of eight RNA sections that range in size from 890 to 2341 bases and codification for 11 known proteins [ 5 ] ( Table 1 ) ( Fig. 1 ) . Influenza viruses produce 11 viral proteins that can be divided into three chief classs: the surface proteins, the internal proteins, and nonstructural proteins that are non packaged in the virus atom [ 6 ] . The viral atom contains three surface proteins: the HA, neuraminidase ( NA ) , and matrix 2 ( M2 ) proteins The internal proteins include the three polymerase proteins, PA, PB1, and PB2, the nucleoprotein, the matrix 1 ( M1 ) , and the nonstructural protein 2 ( NS2 ) . The nonstructural protein 1 ( NS1 ) is the lone protein that is non packaged into the virus atom, although it is produced in big measures in septic cells [ 6 ] . The surface proteins are the lone antigens capable of bring oning neutralizing antibody and therefore a protective immune response [ 7 ] . Both the HA and NA proteins have high sequence and antigenic differences, and the cistrons have been separated into 16 different HA and nine different NA subtypes [ 8 ] . The different subtypes are characterized by antibody raised to one virus being able to neutralize other viruses of the same HA or NA subtype, but do non traverse neutralize viruses of different HA and NA subtypes. Influenza viruses, because of the fluctuation and the importance of the different subtypes, are normally characterized by the HA and NA subtypes [ 6 ] .
Life rhythm of grippe virus
During the infective rhythm, virus atoms, edge to cell surface sialic acid, are internalized by receptor-mediated endocytosis and viruses possessing cleaved HA undergo merger with the endosomal membrane [ 9 ] at low pH~5.0. Cleavage of HA is an absolute demand for infectivity and the nature of the HA cleavage site is an of import virulency determiner for grippe viruses [ 8 ] [ 6 ] . Cleavage efficiency of HA varies depending on the presence of individual or multiple basic residues at the cleavage site of HA1 and HA2 and the plasminogen adhering ability of NA [ 6 ] . Viruses incorporating HA with a individual positive charge at the cleavage site can be cleaved by specific enzymes such as tryptase Clara nowadays in the lungs, whereas HA incorporating multiple basic residues at the cleavage site are cleaved ubiquitously by peptidases [ 10 ] .
The M2 ion channel opens up in the acidic pH of the endosome, acidifies the internal virion nucleus, and thereby facilitates the release of vRNP from M1 into the cell cytol. M1-free vRNP is so imported into the karyon through atomic pores utilizing atomic conveyance signals of NP [ 11 ] . Inside the karyon, vRNP undergoes written text ( mRNA synthesis ) and reproduction ( complete positive-sense complementary RNA ( cRNA ) , vRNA subtraction strands, and vRNP synthesis. Progeny vRNPs, made inside the karyon, are exported out of the karyon into the cytol with the aid of M1 and NEP [ 12 ] . Finally, the envelope proteins ( HA, NA, M2 ) , matrix protein ( M1 ) and vRNP ( incorporating vRNAminus-strand, NP, 3P proteins, and NEP ) are transported to the assembly site on the plasma membrane where virus particles bud and are released into the outside environment [ 6 ]
3. Topological and chronological information about extremely infective avian grippe viruses ( HPAI )
Influenza A viruses can be divided into subtypes on the footing of the ownership of one of 16 antigenically distinguishable haemagglutinin ( HA ) antigens ( H1 to H16 ) and one of nine neuraminidase ( NA ) antigens ( NI to N9 ) [ 8 ] . Another manner of categorization is to split influenza viruses into two distinguishable groups on the footing of their ability to do disease. The really deadly viruses classified as extremely infective avian grippe ( HPAI ) , which may ensue in flock mortality every bit high as 100 % while other viruses cause a much milder disease dwelling chiefly of mild respiratory disease, depression and egg production jobs in puting birds are classified as low infective avian grippe ( LPAI ) [ 13 ] .
HPAI was considered a rare disease nevertheless, there has been an addition of the figure of LPAI and HPAI eruptions caused by H5, H7and H9 viruses in recent old ages. The ground for this addition in the figure of eruptions could be linked to the ecology of the virus every bit good as to the development of dumbly populated domestic fowl countries, in which biosecurity steps are hard to implement and retain. Some of these eruptions have had a great economic impact on the domestic fowl industry [ 13 ] .
The outgrowth of H5N1 viruses in Asia since 1996 was a cardinal determiner of the undermentioned epidemics. Highly infective avian grippe ( HPAI ) H5N1 has been reported in several Asiatic states including Cambodia, China, Indonesia, Japan, Korea, Laos, Pakistan, Taipei, Thailand and Vietnam [ 14 ] . The ruinous influenza pandemic of 1918, caused by an H1N1 virus, killed 20 to 40 million people. Pandemics caused by the Asian grippe A virus ( H2N2 ) in 1957 and the Hong Kong virus ( H3N2 ) in 1968 indicated that southern China is a conjectural grippe epicentre [ 15 ] .
5. Importance of Surveillance and epidemiological studies for possible planetary eruption
Influenza A did problem the whole universe from hot-humid Southeast Asia to cold-freezing Alaska and at least caused 3 terrible pandemics in the twentieth century [ 16 ] .
During the past few old ages, several subtypes of avian grippe A including H5N1, H7N7, H9N2, and perchance H7N3 have been reported to be capable of infecting worlds [ 17 ] . In 1997, the extremely infective avian grippe, H5N1 subtype was isolated from an septic homo in Hong Kong, showing direct transmittal of the avian grippe virus to worlds. A important re-emergence of extremely infective avian grippe ( HPAI ) H5N1 has been reported in several Asiatic states including Korea, Japan, Taipei, Cambodia, Laos, Pakistan, China, Indonesia, and Thailand, with to boot confirmed instances of human decease in Vietnam [ 18 ]
It can be postulated that H5N1 viruses will go on to go around in Asia and mutate, and the outgrowth of new reassortant H5N1 viruses can non be ruled out. However, the execution of effectual control steps, coupled with enhanced programmes for the surveillance and diagnosing of infection, will assist to cut down the hazards to animal and human wellness. Uninfected states will stay susceptible to the entry of disease from infected countries, and increased watchfulness, effectual biosecurity and quarantine controls must be maintained to cut down this hazard.
Continuous planetary surveillance of grippe is of cardinal importance. World Health organisation ( WHO ) has a web of 112 National Influenza Centers that proctors influenza activity and isolates influenza viruses in all continents. National Influenza Centers report the outgrowth of an & A ; acirc ; ˆ?unusual & A ; acirc ; ˆA? influenza virus instantly to the WHO Global Influenza Programme. Rapid sensing of unusual grippe eruptions, isolation of possible pandemic viruses and immediate qui vive to the WHO system by national governments is decisive for mounting a timely and efficient response to pandemics.
Fig 1 Structure of grippe A virus. ( A ) Diagram of the virion. Two types of surface glycoproteins are shown: HA predominates and is equally distributed over the virion, while NA occurs in spots. Inside the matrix nucleus are eight sections of individual stranded negative sense RNA encapsidated by NP in the signifier of RNP, which occurs in spiral ( modified from Webster, 2001 ) . ( B ) Electron micrograph of A/WSN/33 ( H1N1 ) . The virion appears spherical and possesses glycoprotein spikes on the surface [ 19 ]
Table.1 Gene merchandises of grippe virus
Gene merchandise ( s )
RNA written text
RNA written text and reproduction
Inactivate immune cells
Attachment and merger glycoprotein
Major nucleocapsid structural constituent
Receptor destructing enzyme
Membrane matrix protein
Membrane ion channel protein
Nuclear export of viral messenger RNA
Production of influenza viruses with integral RNA genome
*Gene sections are numbered in order of diminishing molecular weight.
**PB1-F2 is a fresh protein suggested by Chen et al. , 2001 [ 20 ] .