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The potential threat for a pandemic or global epidemic of influenza is from a new or “novel” virus,one that has not previously infected humans. The novel virus influenza currently circulating in birds is Influenza A subtype H5N1 virus. This avian virus, most commonly found in chickens, first jumped from birds to humans in Hong Kong in 1997, infecting 18 people and causing 6 deaths. In late 2003, the virus began sweeping poultry flocks in East Asia and as of October 24, 2005, has infected 121 humans, and killed 62. The virus circulating in Asia has expanded its host range to include cats, tigers, and leopards, which generally have not been considered susceptible to influenza A. Migratory birds have been linked to the spreading of the virus between countries. In recent months, the disease has spread from chicken flocks in Vietnam and Thailand to flocks in China, Indonesia, Russia, Turkey, Romania and Croatia. Although, there has been no evidence that the virus is genetically mutating to allow human-to-human transmission, response plans are geared toward this potential event.
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