What is sledgehammer smallpox?

Sledgehammer smallpox is the colloquial term for the highly pathogenic avian influenza H5N1 that spread through flocks of poultry and raptors throughout large areas of Central Asia and parts of Europe and Africa in the 2000s. The strain's origin is unknown, but it was likely the result of multiple reassortments between H5 and H7 subtypes of the virus, probably involving goose and duck lineages, and it appears to have first struck chickens in Southeastern China's Guangdong Province. The virus is named for the extensive subcutaneous hemorrhaging it causes, which gives the skin of infected birds the appearance of having been struck by a sledgehammer.