Word: strains
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...markets, and culling 80,000 birds from farms near the outbreak's locus. York said Tuesday that there were no reports of humans sickened by the virus, and that the government had not yet determined whether the birds were infected with the potentially lethal H5N1 or a less virulent strain of influenza. (See pictures of the bird...
...shot is the only vaccination that is continually updated, because influenza is a rare type of virus that is constantly changing. There are three types of the flu - Influenza A, B and C - each one with its own viral strain that replicates and changes independently from the other types. Seasonal strains of human influenza change constantly, which is why people can catch the flu multiple times. (See the Year in Health, from...
...there many other subtypes of influenza to which humans are immune. They reside mostly in birds, although every once in a while a strain will suddenly develop the ability to infect people. "A virus like that gives people no time to develop protection or immunity, so almost everyone is susceptible," says Dr. Carolyn Bridges, an influenza expert at the CDC. "When that happens, we have a pandemic...
...hundred years, although it's hard track outbreaks that occurred before the 18th century due to incomplete medical records. The disease hits big cities first - because that's where people generally travel - and then spreads to surrounding areas. The last major pandemic occurred in 1918 when an Influenza A strain jumped from birds to humans and killed an estimated 20-40 million people (3% of the world's population). The pandemic struck during World War I and warring nations worried that the enemy might use the virus to its advantage, so most news reports of the outbreak were censored. Spain...
...outbreaks among its poultry population since the mid-1990s, the largest outbreak occurring in 1997 when eighteen people in Hong Kong came down with the virus. Outbreaks also occurred in 2001 and 2002, leading to the culling and destruction of millions of possibly-infected fowl. By 2003, the strain had spread to much of Asia's bird population. "It remains a serious pandemic threat," says Bridges. "It has a 100% mortality rate among poultry, but so far we are not seeing the type of molecular changes required to jump to humans...