 Individuals with congenital erythropoietic porphyria do not crave blood.The enzyme (hematin) necessary to alleviate symptoms is not absorbed intact on oral ingestion, and drinking blood would have no beneficial effect on the sufferer.Finally, and most important, the fact that vampire reports were literally rampant in the 18th century, and that congenital erythropoietic porphyria is an extremely rare manifestation of a rare disease, makes it an unlikely explanation of the folkloric vampire.