Medical Definition of H5N1
1: a virus that is a subtype (H5N1) of the orthomyxovirus (species Influenza A virus of the genus Influenzavirus A) causing influenza A, that infects mainly birds and is highly contagious among birds, and that sporadically infects humans often causing serious illness and death Indonesians have hidden their birds when government agents have come to kill sick chickens and domestic ducks, common conduits of H5N1 to humans.—Delthia Ricks, Discover, December 2009—often used before another noun The H5N1 strain raging across east Asia has a mutation that blocks the two antiviral drugs that are off-patent and cheap.—Debora MacKenzie, New Scientist, 28 Feb. 2004 ◆The subtype H5N1 is distinguished by a mutation of hemagglutinin (H5) that affects the ability of the virus to infect cells, and a mutation of a neuraminidase (N1) that enables the release of the replicated virus from cells.
2: influenza caused by the H5N1 virus; especially : bird flu—often used before another noun … public health authorities had focused on the threat of avian H5N1 influenza, and a signal feature among recognized cases of H5N1 influenza in humans was mortality exceeding 50%.—Harvey V. Fineberg, The New England Journal of Medicine, 3 Apr. 2014
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