The victims are varied, from thousands of sea lions off the coast of Peru to mink farmed for fur in Spain to grizzly bears in Montana and harbor seals in Maine. For months, the avian influenza virus that has been decimating birds across the world (see story, p. 24) has also sickened and killed a menagerie of mammals, raising fears it might evolve to spread more efficiently between these animals, and ultimately between people. For that nightmare to unfold, however, the virus, a subtype known as H5N1, would have to undergo a major transformation, changing from a pathogen efficient at infecting cells in the guts of birds and spreading through feces-contaminated water into one adept at infecting human lung tissue and spreading through the air. So far, that has not happened. None of the few people who have caught the virus currently wiping out birds, called clade 2.3.4.4b, seems to have passed it on to other people.
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