Vampires & Killing Kits.

There is a genetic disease that causes the victim to seek the dark, & their skin will burn if they go out in daylight. Also there is a disease that can be transmitted by bats, so it is easy to see how the Vampire stories began.

http://meeg-toomuchinformation.blogspot.com.au/2009/05/in-age-of-vampires.html

http://www.fvza.org/science1.html