Xeroderma Pigmentosum and Porphyria
Genetic diseases, caused by the crippling of chromosomes before birth. The skin develops no melanine so that there is no protection from UV light and its agressive rays. The person suffering from these deseases easily get burned in the sun up to 3rd degree or produce skin cancer after spending only minutes in the day/sunlight. As bad as this might be for them, it has nothing to do with vampirism. Vampires can go out during the day but mostly avoid it as it is not their natural time, therefore uncomfortable and weakening.
There are some interesting facts that should be take into consideration when comparing vampirism to this genetic malfunction.
First, those suffering from any of those diseases are also easily burnt by artificial light and are forced to spend a life in nearly total darkness. Second, they don´t crave for blood or any other kind of energy. Third, they are all born with this genetic defect Porphyria and XP are not infective.
A thesis of some researchers, why they are related to vampirism as well, is that due to the incestive attitude of some European regions during the earlier centuries and also the aristocratic families, this disease may have occured extremely often in some regions of the world, therefore was more present and watchable for the normal population. And everyone can easily imagine what a Romanian farmer of the 18th century might have thought when he watched someone being slowly burnt by the sun.
Plagues and moving corpses
During the 18th century, the German military collected datas of an enourmous spread of TB in the east of Europe. This development caused a vampire hunt that searches its equal in history. TB is a highly infective disease of the lung spread by contact with those who suffer from it and even by contact to corpses died of this disease decades ago. Some of the symptoms let the infected persons hallucinate about ghosts attacking them and choking them to death while shaken by high fever.
The fact that eastern Europeans commonly have a strong belief in mythological vampires and felt the need to exhume the TB victims after death again when the infection started to kill other members of the same family led to another phenomenon that added to the hystery infecting half of Europe.
In this century, nearly nothing was known about the decomposing process of corpses. Corpses were burried often less than two feet below the surface of earth. When the process stated, the corpses started to swell because of gases developing in the interior, the skin peeled off and showed a reddish layer below, blood colored water soundfully exited from the corpses mouth and nose. The corpse sometimes even moved a bit. This all in addition to the fact that most of the family members of the first victim and also people who have had physical contact to the corpse died led to the belief that this corpse was a vampire, feeding on the lifes of the others for an indeed very long time. Essays were written by the meds of the German military who were sent to survey the phenomenon, mass exhuminations followed during the course of which the dead body was staked to the ground, decaptivated and humiliated in several other ways.
The knowledge of this plague nowadays led to the conclusion that the mystery about vampirism has been revealed. How could they know...
In the 15th century, a Carpathian count called Vlad Tepes - The Impaler - became famous for the tactic of Burned Earth and other reffective of simply scaring his enemies out of his country. When the Turcs endangered his home country, nowadays Romania, by invasion, he left burned villages on their way towards the center of his country and staked every and any dead or captured Turc soldier, alltogether approximately 20.000 persons. The large wooden stakes with the corpses on it became famous as the "Wood of the Impaled" and didn´t fail as a method to simply scare his enemies out of the country. Vlad Dracul - as his real name was - won the war. Rumors were spread that he dipped bread in the blood of his dead enemys and ate this. He ended locked up for 17 years regained his title later and died under mysterious circumstances. Nobody knows for real where he is burried.
His name was revived when an author named Abraham Stoker made researches for the hero of his planned book and found out that the life of this count was interesting enough to create a vampire that should become the most famous ever in history - Dracula.
I wonder what Vlad Tepes - a convinced Christian - would tell us about his thoughts on this if he was still alive...
Elizabeth Bathory and other serial killers
The "Blood Countess", known for her habit of bathing in the blood of animals and young females that were slain for her in masses. She had the idea that this blood would keep her young and beautiful. When she was finally arrested, the corpses of more than 150 young women were found that had to die for this. In contradicion to general belief, she did not drink the blood and also never claimed to be a vampire. The term serial killer would fit better if a description of this kind of person was searched. Several cases of mass murders have become known ever since, due to the greed for great stories. Among those "The Butcher of Hamburg", Fritz Haarmann who was found guilty for having bitten several young boys to death. Blood was never drawn. He was sentenced to death in the 20s of this century. Interestingly he was decaptivated. The picture painted of the folkloristic vampire often seduced to be compared to perverts, serial killers or other persons who actually never had anything to do with vampirism, as there was either blood or biting involved. Indeed, it makes a nice header in the boulevard news, and the general "bloodthirst" of the masses is fed. In cases like this it never mattered that the term "vampirism" was totally misconcepted. Those people whom I call "Folkloristic vampires" add a great deal to this misconception.
The habits of "Folk vampires"
The aforementioned "Folkloristic vampires" are a group of psychologically instable persons who develop both the need to act like vampires (in the way they believe vampires act) and certain habits that often lead them directly to jail or security lock up in mandatories.
Those persons have gathered their amount of habits from sources of "information" they tend to consume, among those fictional literature and films of a great amount. So come most of them react to garlic, holy symbols and sun in a very specific way. Some of them even claim to be able to fly. They often stick to dress codes including black suits and capes and sleep in coffins. How mythology added those characteristics is sometimes doubtable, but can be guessed when regarding the whole context.
Vampires are mythologically regarded as companions of the devil. Therefore it would be logical in relation to the Christian concept that anything holy has to be avoided. General belief mentions holy water, crosses and blessed rosaries as unbeatable weapons when hunting those "foul creatures". Ouch! I should take off my necklace...
Garlic is mentioned in context to eastern European belief. Exhumed corpses were often declared vampires. They were defeated by being staked to the ground of their graves and houses were protected from them with garlic girlands. This is due to the concept that everything has to be defeated with something equal. Corpses smell, garlic as well. Therefore it was regarded protective. The tradition of using stakes was founded much earlier. Several cultures tried to prevent the dead rising from their graves in order to hunt the living by fixing them to their graves by wodden stakes or iron poles. This tradition transformed to exhuming suspected vampires, staking and decaptivating, often also burning them in order to kill them again.
Sunlight might weaken a real vampire, but noone who can claim to be able to gather his senses would believe to burn to ashes. This aspect of mythology can be related to the significance of darkness. Vampires are dwelling in the darkness, the "Day"-time of all that is evil. When the sun rises, all evil fades with the darkness, due to common belief, originated in the fear of darkness and everything unseen.
But why should a vampire be able to fly?
Easy to answer. Bats are related to vampires. Actually, in south America, there are even two kinds of vampire bats existing. Bats are also creatures of darkness and also related to the devil. (Slowly the circle closes, doesn´t it?) Vampires are said to be able to assume bat shape and bats can fly. Any questions?!
As a conclusive statement let me say that all those mythological explanations are only suggestive. But one could at least always say that those observations make it even more funny to watch those people who want to be oh so big bad vampires only work hand in hand with superstition, Christian belief and the result of dramaturgic experments.