Alpacas at a small farm in Idaho have tested positive for H5N1 bird flu, according to state and federal officials, adding them to a growing list of mammals being infected with avian influenza. The Animal and Plant Health Inspection Service at the U.S. Department of Agriculture reported Wednesday that four alpacas tested positive at a backyard poultry premises in Jerome County, Idaho. The agency said the discovery was not entirely unexpected, citing the “high amount of virus in the environment” after infected poultry was culled at the site earlier this month and the co-mingling of multiple anim…