The V-virus is a retrovirus that causes mutations in human DNA which result in the carriers exhibiting vampire-like characteristics, most notably pronounced canines and a thirst for blood. However, they are not vampires in the classic sense as they do not exhibit many of the characteristics traditionally associated with vampires. Nonetheless, they were regarded as such by the rest of humanity. The origins of the V-virus have not been made clear, but Type-V mutants, as these carriers are more properly known as, have existed throughout human history. Only in the late 20th century did advances in biology reveal that vampires were humans who had been infected with the V-virus.