Vampirism is not a single disease, but instead many–each type coming with its own perks and downfalls. As legend goes, Daedric Prince Molag Bal infamously did not get along with Arkay, the God of life and death. As a result of one of their feuds, Molag Bal captured one of Arkay’s devoted followers, Lamae Beolfag, and turned her into the first vampire. In this sense, Molag Bal is the father of all vampires. The cause for the different strains of vampirism is due to the different bloodlines, or due to the different people that made deals with Molag Bal and were subsequently turned.
Noxiphilic Sanguivoria: The most common form of vampirism in the Second Era, Noxiphilic Sanguivoria, is classified by a vampire’s ability to withstand the forces of the sun. All vampires of this bloodline are descended from the original vampire, Lamae Beolfag. Other talents include increased abilities and strengths during the nighttime hours and spectacular regenerative powers. In order to become this type of vampire, one must be exsanguinated by a vampire and then ingest his or her blood in return.
Porphyric Hemophilia: Common to both Cyrodiil and Morrowind, this particular strain of vampirism is known for being the most ill-affected by sunlight. This disease in contracted through direct contact with vampires and once acquired must be left unchecked for three days before the victim will turn into a vampire. There are four stages to this strain of vampirism, each achieved by consecutive days gone without feeding: with each day more, greater advantages and skills are gained like invisibility and night eye. Known vampires of the third era include prominent members of society such as Janus Hassildor: the Count of Skingrad, Vicente Valtieri, and Springheel Jack.
Sanguinare Vampiris: All vampires of this particular strain are descended from Lord Harkon of Castle Volkihar and are commonly referred to as the Sons and Daughters of Coldharbour. These vampires have the most complex and diverse abilities, resulting from the Vampire Lord effect, which is unique to this breed. Powers include special spells: vampire’s seduction, embrace of shadows, and vampiric drain–all of which help vampires ensnare and fight their victims. Volkihar vampires are not directly hurt by sunlight, but severely weakened, being unable to regenerate health, stamina, and magicka in direct daylight.
There are many other types and strains of vampirism throughout all of Tamriel, but the above are the most common. For more information, check Immortal Blood, Vampires of the Iliac Bay, and Vampires of Vvardenfell.