There are only three ways to acquire this disease. The first is fighting with vampires and contracting it as with other diseases. The second way is through the Dark Brotherhood. After reaching a certain rank, Vicente Valtieri offers the chance to become a vampire. If the offer is declined, it is possible to ask again later. The offer only extends until Valtieri dies during "The Purification". The third is by eating the beating heart in the Mehrunes' Razor add-on.