Bird flu is a major concern and currently there are human cases of H5N1. How is H5N1 different from other seasonal cases of influenza? Is there evidence of human to human spread of H5N1?
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An avann influenza virus of type HISNI has recently evolved a "high pathogenicity" (hp) strain that causes severe illiness in most wild birus (except ducks) as well as in dorncstic poultry. A few bumans have becn infected. The World Health Oryanization (WHO) currently inspects every human case with particular attention to how the putictits contracted the virus. Why is this virus a cause for concems, and why are WHO officials so intentested in cach paticnt's source of infection?
H5N1 avian flu virus has spread from Asia to Africa and Europe. Is it likely that human air travel could have spread this virus?
Ian S.
Vaccines are generated against new strains of the Influenza virus almost every year to prevent widespread flu epidemics. This is because the virus can evolve to change some of the proteins in the virus coat to evade human immune systems. In order to create new vaccines for upcoming flu seasons, scientists forecast, or predict, which mutant virus strains will come to prevail and cause possible flu epidemics. This is not a perfect approach because occasionally their predictions will not be quite right and a vaccine will be produced that is only partially active. The flu virus actually has two mechanisms for evolution: a slow mechanism called antigenic drift and a rapid mechanism called antigenic shift. The slow antigenic drift mechanism is due to minor genetic changes resulting in amino acid changes in two particular coat proteins, whereas antigenic shift is due to reassortment of entire regions of the Influenza virus genome leading to the exchange of entire genes, or sets of genes, between related viruses. You can read more about the Influenza virus in this World Health Organization's short article: http://www.who.int/biologicals/vaccines/influenza/en/. The Influenza virus is divided into several categories, type A, type B, type C, and so on. Type A is the major virus type responsible for infection in humans and for infection in several other organisms including pigs and birds. This is a major worry for physicians and scientists because Influenza strains that originally evolved in birds or pigs occasionally undergo antigenic shift and transfer some information from the bird or pig strain to type A strains more likely to infect humans. Antigenic shift is believed to be the mechanism that created strains of Influenza virus responsible for the famous "Spanish" flu pandemic (1918-1920), the "Asian" flu pandemic (1956-1958), the "Hong Kong" flu pandemic (1968-1969), and the "Swine" flu pandemic (2009). Hundreds of thousands to tens of millions of people died in each of those pandemics, depending on the strain of Influenza virus. The Influenza virus is an RNA virus and replicates its RNA genome by making RNA copies using an RNA-dependent-RNA-polymerase. Unlike DNA polymerase, the RNA-dependent-RNA-polymerase encoded by the Influenza virus genome has no 3´-to-5´ or 5´-to-3´ exonuclease activity. Since type A Influenza viruses can infect birds, pigs, and humans, it is possible that two type A subtypes could simultaneously infect a single organism. For example, it is possible for pigs to be infected with type A influenza viruses that originated from birds and from humans at the same time. 1. Create a hypothesis that would explain the mechanism for Influenza virus antigenic drift. Please be detailed and explain why antigenic drift results in amino acid changes rather than reassortment of the viral genome. 2. The rapid evolution of type A influenza virus by antigenic shift has serious implications for the human population. For example, the type A Influenza virus strain H5N1, sometimes found in domestic poultry, rarely infects humans but when infected, Avian H5N1 kills about 60% of the infected humans. Create a hypothesis that would mechanistically explain antigenic shift and how antigenic shift could possibly create a "hybrid" H5N1 Influenza virus that would be highly infectious and highly lethal for humans.
Adi S.
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