Contagion of the New Millennium: H5N1, Surviving the Avian Flu Virus

Contagion of the New Millennium: H5N1 - Surviving the Avian Flu Virus by Victor Chase () [Victor Chase] on leondumoulin.nl *FREE* shipping on.
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Seven of them died. It's not clear exactly how this happened. Family members likely had similar contacts with infected birds. They may also have shared genes that made them particularly susceptible to the virus. However, casual contact does not seem to be involved. During the fall of , researchers from Erasmus Medical Center in the Netherlands made a stunning announcement.

They had taught H5N1 the nasty trick of going airborne and spreading among ferrets. Nearly all human flu bugs spread easily among ferrets. They are commonly used in studies of human flu viruses. Both research teams were funded by the U. National Institute of Health. In a statement, the NIH says the research shows "that the H5N1 virus has greater potential than previously believed to gain a dangerous capacity to be transmitted among mammals, including perhaps humans.

The NIH funded the research because it felt there was a need for more information on how H5N1 might learn to spread among humans. National Science Advisory Board for Biosecurity asked the study authors not to publish crucial information about the creation of the mutant viruses. The details will be made available only to qualified researchers.

But the studies remain extremely controversial. Some senior scientists have said the mutant viruses should never have been created. They note that while the mutant viruses are housed in state-of-the-art containment facilities, the risk of escape is not zero. It's also not unprecedented. This so-called "Russian flu" led to widespread epidemics. Although officials denied it, many scientists believe the virus had escaped from a laboratory. The H5N1 virus found in a wild bird in Washington state in late is slightly different from the Asian-origin avian H5N1 virus that made humans sick.

Various strains of bird flu pop up in U. When they do, all affected poultry flocks are culled.

Pandemic influenza – including a risk assessment of H5N1

For example, in a highly dangerous bird flu strain appeared in a Texas chicken flock. The outbreak involved an H5N2 virus not the H5N1 bird flu. By April , the outbreak had been eradicated. No human infections were detected. If you are a seller for this product, would you like to suggest updates through seller support? Learn more about Amazon Prime. Product details Mass Market Paperback Publisher: View shipping rates and policies Average Customer Review: Related Video Shorts 0 Upload your video.

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Pandemic influenza – including a risk assessment of H5N1

Write a customer review. There was a problem filtering reviews right now. Please try again later. A great precursor before reading all of the apocalypse books concerning the bird flu. Because the post H1N1 strains did not replace the previously circulating H3N2 strains, co-circulation of influenza viruses of both subtypes has continued up to the present time , and co-infection with both subtypes has been reported 62 , together with the circulation of reassortant H1N2 viruses 20 , As noted above, a major problem in the interpretation of the historical evidence of past pandemics is the possibility that significant information may have been either not recorded or not yet identified.

For example, what are we to make of the year interval between and in which there was much evidence of major influenza activity, including Europe-wide and Western Hemispheric epidemics of influenza-like illness, sometimes associated with high mortality, but little evidence for pandemic activity?

It is difficult to decide whether true pandemics may have been missed during this long era, or whether this interval represented a prolonged period of seasonal influenza, analogous to our current year interval in which moderately severe influenza outbreaks associated with directional global spread have not been recognised since i. Additional historical research may shed light on these uncertainties. At the time of the influenza pandemic, no one suspected that the cause of human influenza was derived from an avian infectious agent capable of infecting multiple mammalian species.

Additional avian influenza A viruses were identified in the s Webster and colleagues proposed in that pandemic influenza viruses might be related to avian influenza viruses Given that pigs can be infected with both avian and human strains of influenza, and that various influenza virus reassortants have been isolated from this species, pigs have been proposed to be an intermediary in the process of viral reassortment This outbreak was thought to pose a significant threat for the development of a pandemic.

Public health officials in the USA initiated a large-scale vaccination programme, but no further spread occurred In , an avian-like H1N1 virus began infecting swine in northern Europe and established a stable novel H1N1 viral lineage 41 that was unrelated to the swine H1N1 lineage descended from the virus. Until there was little evidence that a wholly avian influenza virus could similarly infect humans directly; in that year eighteen people were infected with avian H5N1 influenza viruses in Hong Kong and six died of complications 8 , Although these viruses were very poorly transmissible, if at all 28 , between humans, their detection reinforces the knowledge that under poorly understood circumstances humans and other mammals can be infected with wholly avian influenza strains of either high or low pathogenicity for poultry.

Since there have been documented human infections with H5N1 viruses, associated with deaths as of January 27, ; [ 80 ]; see below. Therefore, it may be unnecessary to invoke pigs as the intermediary in the formation of a pandemic strain because reassortment could conceivably take place directly in humans or other mammals.

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The occurrence of three influenza pandemics in the 19th Century 47 and another three in the 20th Century has led some experts to conclude that pandemics occur in cycles, and that we are currently overdue Belief in influenza cyclicity can be traced to epidemiological efforts in the midth Century. Following the pandemic, interest was renewed in examining the recurrence patterns of influenza By the s, cumulative historical information 14 , 27 , 47 , 71 , 72 appeared to suggest that pandemics appear in regular cycles. This seemed to make biological sense: It was becoming clear at about the same time that high population immunity led post-pandemic viruses to drift antigenically, and that genes encoding surface proteins could potentially mix with other HA and NA genes to which humans lacked immunity It was reasonable to assume that such an intimate viral—immunological relationship would have a predictable life span.

Around the time of the and pandemics, the prevailing view was that pandemics tended to recur as frequently as every 10 to 11 years, an idea that was first proposed in the s. The swine influenza outbreak in see above further strengthened this hypothesis 18 , Influenza expert Edwin Kilbourne has recently concluded that: Without pandemic cycles there can be little basis for predicting pandemic emergence. It now appears likely that pandemic emergence can result from at least two very different mechanisms: The possibility that a pandemic could result from viral acquisition of a novel NA alone, or from a distinctive HA that is of the same serotype as a circulating virus but antigenically remote from it, has not been disproven.

There is no reason to suppose that the two different known pandemic mechanisms should be capable of producing the same cyclic intervals, or that other competing mechanisms of adaptation, such as reassortment with closely related HAs 25 , or changing population immunity induced by increasing use of immunologically complex vaccines, could not disrupt cycles that might otherwise occur.

It has also become clear that despite a large catalogue of naturally occurring genes for influenza surface protein that are theoretically capable of causing new pandemics by reassorting themselves into human-adapted strains, only three of the sixteen known HAs H1, H2 and H3 and two of the nine NAs N1 and N2 are known to have done so in the past years 44 , Because scientific evidence of viral identity only extends backwards for years, it will take many future generations to fully evaluate Hilleman's hypothesis. Historical evidence of pandemic occurrence provides no obvious cyclic patterns over the past three centuries Presumably, mutable viruses that induce high population immunity will eventually drive their own evolutionary changes; however, if pandemic cycles do occur they must be so irregular as to confound predictability.

H5N1 HPAI viruses initially caused a poultry epizootic in southern China, followed within a year by an epizootic in Hong Kong that produced 18 human cases and six deaths. H5N1 strains continued to circulate thereafter in China, and they reappeared in epizootic form in, and spread widely after, This geographical extension was accompanied by the appearance and spread of genetically and antigenically different H5N1 HPAI strains Some of these epizootics have featured human infections and, rarely, human deaths 1.

Since the mids, strains of H9N2 LPAI viruses have become enzootic in domestic poultry populations on several continents 1 , 6 , leading to a small number of human infections. Like those of H5N1, different genetic lineages of H9N2 have been established, some of which share with H5N1 viruses closely related gene segments that encode internal proteins. Some H9N2 viruses have even acquired enhanced specificity for the human form of the HA receptor Before the epizootic was contained, at least 86 poultry workers and three of their contacts had become infected and developed conjunctivitis with or without an influenza-like illness; one of them died Do these unique features of epizootic H5N1 viruses predict an impending pandemic?

There is little consensus among experts.

Your Bird Flu FAQs

Despite significant research, fundamental questions about how influenza A viruses switch hosts from wild avian species to domestic poultry and mammals, and subsequently to human hosts, remain unanswered. Also incompletely understood are the viral genetic changes that underlie human adaptation; even less well understood are those genetic changes that would allow human-to-human transmissibility, and the viral, host, or environmental cofactors that may contribute to human pathogenesis Given the potential for high morbidity and mortality, an approximation of the risk of the H5N1 virus becoming adapted to efficient human-to-human transmission would be extremely helpful for pandemic preparedness planning.

In this regard, even though historical observations support the inevitability of future pandemics, data accumulated over the past decade may not strongly point to emergence of an H5N1 influenza pandemic. Examination of current and historical information leads us to the following reflections.

Evidence suggests that H5N1 viruses are evolving rapidly; however, the direction of this evolution, which is driven by incompletely understood selection pressures, is unclear. While current strains of Southeast Asian H5N1 HPAI viruses are descendants of the Chinese epizootic virus, significant genetic and antigenic evolution has since occurred, involving drift in the H5 HA, mutations in other genes, and reassortment with other avian influenza viruses 5.

It is not yet clear which of these many changes are associated with lethality in wild birds, or with pathogenicity and transmissibility in poultry or other species.


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At the same time, adaptation of H5N1 HPAI strains associated with asymptomatic, endemic infection of domestic ducks is probably contributing to continuing spill-over into poultry, leading to the maintenance of a pool of pathogenic viruses to which humans will be continually exposed Nevertheless, there are limited data relating to whether or not any H5N1 influenza strain is evolving in the direction of human adaptation. Given that only H5 and H7 viruses have been shown to acquire the requisite polybasic insertional mutation at the HA cleavage site that makes them highly pathogenic to poultry, the last three human pandemic viruses, which contained avian-like HA genes of H1, H2, and H3 subtypes, were by definition not HPAI viruses.

Neither is there evidence that a human pandemic or even an epidemic has been caused by any of the many other HPAI viruses. Furthermore, while HPAI outbreaks have been described in poultry for over years, none of the last three pandemics is known to have been temporally associated with an epizootic in poultry or wild birds, leaving no historical data to support the possibility that poultry are capable of serving as intermediate hosts in the development of a pandemic.

The role of virulence and pathogenicity in evolutionary virus—host relationships is therefore unclear; pandemic viruses of comparatively low e. To cause a pandemic, an avian virus would have to adapt at least to human HA receptors and separately acquire human transmissibility properties.

This appears to be a difficult challenge that is rarely met by influenza A viruses.

Kundrecensioner

Despite the likelihood that humans and other mammals have been exposed to countless avian viruses over many centuries, the last two pandemics have resulted from reassortment of pre-existing human-adapted viruses with imported genes derived from avian influenza viruses, not from de novo adaptation of avian viruses to humans.

When genes from a H5N1 virus were experimentally reassorted in various combinations with those from a human H3N2 virus, some reassortant combinations resulted in viral replication in ferrets, but none was efficiently transmitted between animals 43 , prompting critical questions about whether H5N1 viruses may be limited in their potential to adapt to, and be transmitted between, humans. The mutational changes that are associated with the binding of H5N1 viruses to receptors in different hosts are proving to be complex Experiments suggest that only two mutations in the receptor-binding site converted the H1, H2, and H3 HAs of the past three influenza pandemic viruses from avian receptor-binding patterns to human receptor-binding patterns.

Several mutations have been reported to enhance the binding of H5 to the human form of the receptor; however, none has been reported to induce a complete switch in specificity. While it is possible that additional unknown mutations could result in such a complete switch, there is no evidence that this has happened after at least 11 years of exposure of thousands of humans to H5N1, and no evidence that this has happened after human exposure to other HPAI or LPAI viruses of the H5 subtype over many decades. Changes in HA receptor binding during host adaptation must therefore be extremely complex, and must differ from subtype to subtype.

The H5 viruses and other subtypes may well face unappreciated biological barriers in achieving efficient binding to human receptors. While concern over the emergence of an H5N1 pandemic is clearly warranted, if for no other reason than its current high case fatality rate, many other possibilities for pandemic emergence must also be anticipated and planned for. The majority of the world's population those under the age of 41 has no protective immunity to the H2 subtype-bearing influenza viruses that circulated between and Isolates of H2N2 viruses from that era are still maintained in countless freezers, while circulating human-adapted H3N2 viruses presumably remain susceptible to importation of avian H2 by reassortment; this suggests obvious potential origins of future pandemics.

Current H9N2 viruses, some with the ability to bind to human receptors, and already capable of causing human disease, are another potential source of a future pandemic. Since , H1N1 and H3N2 viruses have co-circulated globally to produce seasonal epidemics, which cause approximately 36, deaths annually in the USA. Moreover, recent data have made it clear that evolution of circulating human influenza viruses occurs not just by gradual antigenic drift but also by intra-clade reassortment resulting in the importation of new HAs to which there is a lesser degree of population immunity, and which creates, at the same time, novel constellations of viral gene segments It is unclear whether continued co-circulation and accelerated evolution of different post-pandemic viruses, coupled with the growing use of influenza vaccines against them, will increase or decrease pandemic risk or influence the HA or NA subtype of the next pandemic virus.

The co-circulation of post-pandemic H1 and H3 viruses for three consecutive decades seems to be unprecedented over the past to years. If only H1, H2, or H3 viruses have pandemic potential, the question arises whether such co-circulation limits, in the near future, the next pandemic to only H2 viruses. At present there are no data to answer such a question; however, over the past several decades the dogma regarding pandemics has been so radically overturned that it is now important to rethink and restudy all aspects of this issue.

The past decade has demonstrated how difficult it is to contain HPAI outbreaks, given high intensity poultry production and the movement of poultry between countries. The H5N1 viruses are likely to remain enzootic in domestic bird populations in many countries indefinitely. This poses numerous agricultural and economic problems. While it might provide an opportunity for H5N1 viruses to acquire efficient human-to-human transmission if such a change is in fact possible , it might, on the other hand, provide a better opportunity for viruses to adapt to poultry and wild birds, the chief spill-over hosts.

Frequently Asked Questions About Bird Flu

The use of antiviral drugs in agricultural settings has made many H5N1 viruses resistant to adamantanes, while there has also been evidence for H5N1 resistance to neuraminidase inhibitors The evolution of H5N1 into antigenically distinct clades, probably driven in part by the use of poultry vaccines, greatly complicates the situation and makes it more difficult to predict where H5N1 evolution is going, what to expect next, and how to plan for it Understanding and predicting pandemic emergence is a difficult challenge that we are far from being able to meet in As our understanding of influenza viruses has increased dramatically in recent decades, we have moved ever further from certainty about the determinants of, and possibilities for, pandemic emergence.

Planning efforts must consider a range of possibilities that cannot yet be prioritised in terms of their likelihood, and must also deal with unpredictable ranges of pandemic morbidity and mortality impacts. As a prescient editorial noted more than 75 years ago 12 , it is still not possible to make any scientifically based prediction about the emergence of future pandemics. National Center for Biotechnology Information , U. Author manuscript; available in PMC Oct 1.

See other articles in PMC that cite the published article. Summary Influenza pandemics and epidemics have apparently occurred since at least the Middle Ages. Epidemiology, History, Influenza A virus, Pandemic. Introduction Major influenza epidemics have apparently occurred since at least the Middle Ages, if not since ancient times Past influenza pandemics Pandemic 1: Unanswered questions and conclusions Interpandemic events: Avian and swine influenza At the time of the influenza pandemic, no one suspected that the cause of human influenza was derived from an avian infectious agent capable of infecting multiple mammalian species.

The origins of pandemic influenza viruses The occurrence of three influenza pandemics in the 19th Century 47 and another three in the 20th Century has led some experts to conclude that pandemics occur in cycles, and that we are currently overdue An overview of the epidemiology of avian influenza. Beitrag zu dem durch Kerzen filtrierbaren Virus Fowl plague.

Report on the candle filterable virus.

Avian Influenza / Emo Virus And Its Treatment

Properties and dissemination of H5N1 viruses isolated during an influenza outbreak in migratory waterfowl in western China. Establishment of multiple sublineages of H5N1 influenza virus in Asia: Continuing evolution of H9N2 influenza viruses in Southeastern China. Influenza including its infection among pigs. Cox NJ, Subbarao K. Global epidemiology of influenza: A history of epidemics in Great Britain from AD to the extinction of plague.