Bird flu cases are rising in the Northern Hemisphere, and outbreaks are likely to continue testing farmers and public health authorities determined to curb the spread this winter. The current circulating "clade" of H5N1, which is mainly carried by birds, is highly pathogenic, meaning it can cause severe avian influenza (or bird flu). Though H5N1 was first detected in the mid-1990s, outbreaks have only occurred annually since 2020. H5N1 is now present on every continent, including Antarctica,