Artikel utama: Daftar subtipe virus influenza A Virus influenza A memiliki beberapa protein pada permukaannya, di antaranya protein hemaglutinin disingkat H atau HA serta protein neuraminidase disingkat NA atau N. Kombinasi jenis protein H dan protein N akan menentukan sifat dan penamaan subtipe virus influenza, misalnya H5N1. Saat ini telah ditemukan 18 jenis hemaglutinin H1 sampai H18 dan 11 jenis neuraminidase N1 sampai N11 ,  tetapi hanya subtipe H1-H16 dan N1-N9 yang diidentifikasi dari virus yang menginfeksi burung. Sebagian besar virus flu burung memiliki patogenisitas yang rendah LPAI. Namun, beberapa beberapa di antara mereka mengalami mutasi genetik sehingga berubah menjadi HPAI. Isolat virus influenza A subtipe H5 dapat dikelompokkan lebih lanjut menjadi beberapa klad bahasa Inggris: clade dan diberi nama berdasarkan sistem nomenklatur yang standar.
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Clade 2 viruses were first identified in bird isolates from China , Indonesia , Japan , and South Korea before spreading westward to the Middle East , Europe , and Africa. The clade 2 viruses have been primarily responsible for human H5N1 infections that have occurred during late and , according 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: Map Subclade 1, Indonesia Subclade 3, China"    A study focused on the EMA subclade has shed further light on the EMA mutations.
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. 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 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 hemagglutinin , an 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 neuraminidase , an 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: H1N1 , which caused the flu pandemic "Spanish flu" and the flu pandemic " swine flu " and is causing seasonal human flu H2N2 , which caused "Asian flu" H3N2 , which caused "Hong Kong flu" and 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 strains of 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 H3N2 , which is now resistant to the standard antiviral drugs amantadine and rimantadine. The possibility of H5N1 and H3N2 exchanging genes through reassortment is a major concern. Daniel R. Lucey , co-director of the Biohazardous Threats and Emerging Diseases graduate program at Georgetown University has made this point, "There is no H5N1 pandemic so there can be no pandemic vaccine ".
Further information: Influenza pandemic "The United States is collaborating closely with eight international organizations, including the World Health Organization WHO , the Food and Agriculture Organization of the United Nations FAO , the World Organization for Animal Health OIE , and 88 foreign governments to address the situation through planning, greater monitoring, and full transparency in reporting and investigating avian influenza occurrences.
The United States and these international partners have led global efforts to encourage countries to heighten surveillance for outbreaks in poultry and significant numbers of deaths in migratory birds and to rapidly introduce containment measures. The U. Department of State , the U. This drug has become a focus for some governments and organizations trying to prepare for a possible H5N1 pandemic. As for a vaccine , work cannot start on it until the emergence of a new virus, and we predict it would take six to nine months to develop it.
For the moment, we cannot by any means count on a potential vaccine to prevent the spread of a contagious influenza virus, whose various precedents in the past 90 years have been highly pathogenic".
In a study performed on mice in , "zanamivir was shown to be efficacious in treating avian influenza viruses H9N2, H6N1 , and H5N1 transmissible to mammals". Neither oseltamivir nor zanamivir can be manufactured in quantities that would be meaningful once efficient human transmission starts. This panzootic a disease affecting animals of many species, especially over a wide area outbreak was stopped by the killing of the entire domestic poultry population within the territory.
However, the disease has continued to spread; outbreaks were reported in Asia again in On December 21, the WHO announced a total of cases which resulted in the deaths of While H5N1 undergoes mutation and reassortment, creating variations which can infect species not previously known to carry the virus, not all of these variant forms can infect humans. H5N1 as an avian virus preferentially binds to a type of galactose receptors that populate the avian respiratory tract from the nose to the lungs and are virtually absent in humans, occurring only in and around the alveoli , structures deep in the lungs where oxygen is passed to the blood.
Therefore, the virus is not easily expelled by coughing and sneezing, the usual route of transmission. Humans with H5N1 have typically caught it from chickens, which were in turn infected by other poultry or waterfowl.
Migrating waterfowl wild ducks , geese and swans carry H5N1, often without becoming sick. The report stated the virus may sometimes stick to surfaces or get kicked up in fertilizer dust to infect people. Each specific known genetic variation is traceable to a virus isolate of a specific case of infection. Through antigenic drift , H5N1 has mutated into dozens of highly pathogenic varieties divided into genetic clades which are known from specific isolates, but all belong to genotype Z of avian influenza virus H5N1, now the dominant genotype.
In , new isolates of H5N1 were appearing within the bird population of Hong Kong. These new isolates caused acute disease, including severe neurological dysfunction and death in ducks. This was the first reported case of lethal influenza virus infection in wild aquatic birds since Mutations occurring within this genotype are increasing their pathogenicity.
Transmission and host range[ edit ] Transmission electron micrograph TEM of negatively stained Influenza A virus particles small and white attached to host cells large and irregular late passage.
Source: Dr. Other animals may become infected with the virus through direct contact with these bodily fluids or through contact with surfaces contaminated with them.
In Arctic temperatures, it does not degrade at all. Because migratory birds are among the carriers of the highly pathogenic H5N1 virus, it is spreading to all parts of the world. H5N1 is different from all previously known highly pathogenic avian flu viruses in its ability to be spread by animals other than poultry. In October , researchers discovered H5N1 is far more dangerous than was previously believed. Waterfowl were revealed to be directly spreading this highly pathogenic strain to chickens , crows , pigeons , and other birds, and the virus was increasing its ability to infect mammals, as well.
From this point on, avian flu experts increasingly referred to containment as a strategy that can delay, but not ultimately prevent, a future avian flu pandemic. They also found evidence of what doctors had long suspected—the virus not only affects the lungs, but also passes throughout the body into the gastrointestinal tract, the brain, liver, and blood cells.
Virus flu burung: China laporkan kasus virus H5N1 di provinsi Hunan
Kasus flu burung tersebut menjadi kasus pertama sejak terakhir ditemukan di Palembang pada silam. Tetapi baru dikenali dalam wabah besar yang melanda peternakan ayam di Amerika Serikat AS pada Saat itu flu burung masih menular di antara unggas dan belum terjadi penularan ke hewan lain. Pada Maret , flu burung dari subtipe H5N1 mulai menjangkiti peternakan ayam di Hongkong. Dua bulan kemudian, flu itu menular ke seorang anak laki-laki berusia tiga tahun. Saat itu obatnya belum ditemukan, sehingga anak tersebut meninggal.
Muncul di Palembang, Berikut Awal Mula Kasus Flu Burung
Sporadic human infections with Asian H5N1 virus have occurred in other countries, primarily in Asia and Africa. Most human infections with Asian H5N1 viruses in other countries have occurred after prolonged and close contact with infected sick or dead birds. The virus was first detected in in geese in China. Asian H5N1 was first detected in humans in during a poultry outbreak in Hong Kong and has since been detected in poultry and wild birds in more than 50 countries in Africa, Asia, Europe, and the Middle East. Since its widespread re-emergence in , rare, sporadic human infections with this virus have been reported in Asia, and later in Africa, Europe, and the Middle East. Human infections with Asian H5N1 viruses have been associated with severe disease and death.