H5N1 is a particular subtype of the avianinfluenzaavirus, and is the current cause of bird flu in a number of countries.
H5N1是禽流感A型病毒的一个特殊亚种，目前是许多国家禽流感的元凶。
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It is an infection caused by the avianinfluenzaavirus, thought to originate from wild water-birds who can carry the virus without showing any symptoms of sickness.