Avian influenza infection in human
Mohan, M.; Fernandez, Trevor Francis and Feroz Mohammed, M.S. (2008) Avian influenza infection in human. Veterinary World, 1 (4). pp. 122-125. ISSN 0972-8988
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Outbreaks caused by the H5N1 strain are presently of the greatest concern for human health. In assessing risks to human health, it is important to know exactly which avian virus strains are causing the outbreaks in birds. All available evidence points to an increased risk of transmission to humans when outbreaks of highly pathogenic avian H5N1 influenza are widespread in poultry. There is mounting evidence that this strain has a unique capacity to jump the species barrier and cause severe disease, with high mortality, in humans. There is no evidence, to date that efficient human to human transmission of H5N1 strain has occurred and very often. Efficient transmission among humans is a key property of pandemic strains and a property that the avian H5N1 and H9N2 viruses apparently lacked. The biological and molecular basis for effective aerosol transmission among humans is not known. The virus can improve its transmissibility among humans via two principal mechanisms. The first is a “reassortment” event, in which genetic material is exchanged between human and avian viruses during co-infection of a human or pig. Reassortment could result in a fully transmissible pandemic virus, announced by a sudden surge of cases with explosive spread. The second mechanism is a more gradual process of adaptive mutation, whereby the capability of the virus to bind to human cells increases during subsequent infections of humans. Adaptive mutation, expressed initially as small clusters of human cases with some evidence of human-to-human transmission, would probably give the world some time to take defensive action, if detected sufficiently early. As the number of human infections grows, the risk increases that a new virus subtype could emerge, triggering an influenza pandemic. Humans as well as swine must now be considered a potential mixing vessel for the generation of such a virus. This link between widespread infection in poultry and increased risk of human infection is being demonstrated right now in Asia. However, urgent control of all outbreaks of avian influenza in birds - even when caused by a strain of low pathogenicity - is of utmost importance. Research has shown that certain, avian influenza virus strains, usually of low pathogenicity can rapidly mutate (within 6 to 9 months) into a highly pathogenic strain if allowed to circulate in poultry populations. Altogether, more than half of the laboratory-confirmed cases have been fatal. H5N1 avian influenza in humans is still a rare disease, but a severe one that must be closely watched and studied, particularly because of the potential of this virus to evolve in ways that could start a pandemic. The challenge for all of us is to gain an under-standing of how just 10 or 11 proteins of these viruses to replicate and be transmitted not only bet-ween hosts of one species but also between species.
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