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USDA Avian Influenza Fact Sheet

Summary

There are two types of avian influenza (AI) that are identified as H5N1. A difference exists in the virus classification; one is low pathogenic (LPAI) and the other is highly pathogenic (HPAI). Pathogenicity refers to the ability of the virus to produce disease. HPAI H5N1, often referred to as the “Asian” H5N1, is the type causing worldwide concern. LPAI H5N1, often referred to as the “North American” H5N1, is of less concern.