Hemorrhagic smallpox, sometimes called bloody pox, fulminant smallpox, and blackpox, is a severe and rare form of smallpox and is usually fatal. Like all forms of smallpox it is caused by the variola virus. It is characterized by an incubation period of 7 to 14 days. It has two stages, the first begins with fever, headache, chills, nausea, vomiting and severe muscle aches. The skin flushes in a deep-purple, uneven pattern across the face. The early stage is often mistaken for measles. The late stage is characterized by the appearance of small blisters resembling a severe form of chickenpox. These small blisters then flatten until they are even with the skin, and change into reddish lesions similar to those seen in measles. The skin then turns a deep purple. Lesions appear inside the mouth and active bleeding from oral and nasal mucous membranes is common. This is followed by active bleeding in the gastrointestinal tract, and blood appears in the stool and urine. Blood studies resemble the clinical values of disseminated intravascular coagulation.
^Fenner et al., 1988: Fenner F. , Henderson D.A. , Arita I. , Jezek Z. , Ladnyi I.D. Chapter 1: The clinical features of smallpox. 1 - 68 . In: Smallpox and its eradication 1988 . World Health Organization (WHO)