Why are experts concerned
The current strain of bird flu infecting poultry flocks in Asia-H5N1-is highly contagious among birds and has resulted in the death or destruction of over 150 million birds. The outbreaks are the most widespread and severe on record. Infected birds often die within two days. As of early 2007 birds in at least 30 countries have been affected.
Because such viruses rarely infect people, however, scientists fear we may have little or no immunity to them, making us particularly susceptible to illness should H5N1 undergo the mutations necessary to spread among humans. 31
High mortality rate in humans
Since 2003, there have been over 261 documented cases of human infection with H5N15 among people working in close contact with infected domesticated birds in Asia, Europe and other parts of the world.34
According to the World Health Organisation, in the first 258 cases of bird-to-human transmission of H5N1, there were 157 deaths.34 In other words, more than half of those infected have died. This mortality rate of roughly 60% is one reason public health authorities worldwide are so concerned.
Person-to-person spread unconfirmed21
Thus far, it seems difficult for humans to acquire the virus from birds and even more difficult for the virus to spread among people. In fact, no suspected cases of person-to-person transmission have been confirmed. This indicates that the species barrier is still fairly strong.
However, given how devastating H5N1 has been both for birds and the small number of humans it has infected, health experts are concerned that further mutations of H5N1 could change the virus into a form easily transmitted from person-to-person, resulting in a worldwide outbreak of the disease, or "pandemic."
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