1 epidemiology
1.1 contagiousness
1.2 virulence
1.3 transmission , host range
1.4 h5n1 transmission studies in ferrets (2011)
epidemiology
the earliest infections of humans h5n1 coincided epizootic (an epidemic in nonhumans) of h5n1 influenza in hong kong s poultry population in 1997. panzootic (a disease affecting animals of many species, on wide area) outbreak stopped killing of entire domestic poultry population within territory. however, disease has continued spread; outbreaks reported in asia again in 2003. on december 21, 2009 announced total of 447 cases resulted in deaths of 263.
contagiousness
highly pathogenic h5n1
h5n1 transmissible between birds, facilitating potential global spread of h5n1. while h5n1 undergoes mutation , reassortment, creating variations can infect species not known carry virus, not of these variant forms can infect humans. h5n1 avian virus preferentially binds type of galactose receptors populate avian respiratory tract nose lungs , virtually absent in humans, occurring in , around alveoli, structures deep in lungs oxygen passed blood. therefore, virus not expelled coughing , sneezing, usual route of transmission.
h5n1 spread domestic poultry, both through movements of infected birds , poultry products , through use of infected poultry manure fertilizer or feed. humans h5n1 have typically caught chickens, in turn infected other poultry or waterfowl. migrating waterfowl (wild ducks, geese , swans) carry h5n1, without becoming sick. many species of birds , mammals can infected hpai a(h5n1), role of animals other poultry , waterfowl disease-spreading hosts unknown.
according report world health organization, h5n1 may spread indirectly. report stated virus may stick surfaces or kicked in fertilizer dust infect people.
virulence
h5n1 has mutated variety of strains differing pathogenic profiles, pathogenic 1 species not others, pathogenic multiple species. each specific known genetic variation traceable virus isolate of specific case of infection. through antigenic drift, h5n1 has mutated dozens of highly pathogenic varieties divided genetic clades known specific isolates, belonging genotype z of avian influenza virus h5n1, dominant genotype. h5n1 isolates found in hong kong in 1997 , 2001 not consistently transmitted efficiently among birds , did not cause significant disease in these animals. in 2002, new isolates of h5n1 appearing within bird population of hong kong. these new isolates caused acute disease, including severe neurological dysfunction , death in ducks. first reported case of lethal influenza virus infection in wild aquatic birds since 1961. genotype z emerged in 2002 through reassortment earlier highly pathogenic genotypes of h5n1 first infected birds in china in 1996, , first infected humans in hong kong in 1997. genotype z endemic in birds in southeast asia, has created @ least 2 clades can infect humans, , spreading across globe in bird populations. mutations occurring within genotype increasing pathogenicity. birds able shed virus longer periods of time before death, increasing transmissibility of virus.
transmission , host range
transmission electron micrograph (tem) of negatively stained influenza virus particles (small , white) attached host cells (large , irregular) (late passage). (source: dr. erskine palmer, centers disease control , prevention public health image library)
infected birds transmit h5n1 through saliva, nasal secretions, feces , blood. other animals may become infected virus through direct contact these bodily fluids or through contact surfaces contaminated them. h5n1 remains infectious after on 30 days @ 0 °c ( 32.0 °f) (over 1 month @ freezing temperature) or 6 days @ 37 °c ( 98.6 °f) (one week @ human body temperature); @ ordinary temperatures lasts in environment weeks. in arctic temperatures, not degrade @ all.
because migratory birds among carriers of highly pathogenic h5n1 virus, spreading parts of world. h5n1 different known highly pathogenic avian flu viruses in ability spread animals other poultry.
in october 2004, researchers discovered h5n1 far more dangerous believed. waterfowl revealed directly spreading highly pathogenic strain chickens, crows, pigeons, , other birds, , virus increasing ability infect mammals, well. point on, avian flu experts increasingly referred containment strategy can delay, not prevent, future avian flu pandemic.
since 1997, studies of influenza (h5n1) indicate these viruses continue evolve, changes in antigenicity , internal gene constellations; expanded host range in avian species , ability infect felids; enhanced pathogenicity in experimentally infected mice , ferrets, in cause systemic infections; , increased environmental stability.
the new york times, in article on transmission of h5n1 through smuggled birds, reports wade hagemeijer of wetlands international stating, believe spread both bird migration , trade, trade, particularly illegal trade, more important .
on september 27, 2007 researchers reported h5n1 bird flu virus can pass through pregnant woman s placenta infect fetus. found evidence of doctors had long suspected — virus not affects lungs, passes throughout body gastrointestinal tract, brain, liver, , blood cells.
in may 2013, north korea confirmed h5n1 bird flu outbreak forced authorities kill on 160,000 ducks in pyongyang.
h5n1 transmission studies in ferrets (2011)
novel, contagious strains of h5n1 created ron fouchier of erasmus medical center in rotterdam, netherlands, first presented work public @ influenza conference in malta in september 2011. 3 mutations introduced h5n1 virus genome, , virus passed noses of infected ferrets noses of uninfected ones, repeated 10 times. after these 10 passages h5n1 virus had acquired ability of transmission between ferrets via aerosols or respiratory droplets.
after fouchier offered article describing work leading academic journal science, national science advisory board biosecurity (nsabb) recommended against publication of full details of study, , 1 submitted nature yoshihiro kawaoka of university of wisconsin describing related work. however, after additional consultations @ world health organization , nsabb, nsabb reversed position , recommended publication of revised versions of 2 papers. however, dutch government declared type of manuscripts required fouchier apply export permit in light of eu directive 428/2009 on dual use goods. after controversy surrounding publishing of research, fouchier complied (under formal protest) dutch government demands obtain special permit submitting manuscript, , research appeared in special issue of journal science devoted h5n1. papers fouchier , kawaoka conclude entirely possible natural chain of mutations lead h5n1 virus acquiring capability of airborne transmission between mammals, , h5n1 influenza pandemic not impossible.
in may 2013, reported scientists @ harbin veterinary research institute in harbin, china had created h5n1 strains passed between guinea pigs.
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