Bacillus Vampiris is a fictional disease in the 1954 novel, I Am Legend.
Vampiris is a bacillus form of anaerobic bacteria, that can infect humans and bats as well as dogs. Outside of its hosts, the bacteria sporulates into dust and escapes into the air. Thus, if a vampire is cut deep enough, the bacteria will escape into the air, reducing its former host to powder.
Vampiris is spread through small cuts in the skin from the dust storms. It can also be spread through mosquito bites. It infects the living host and it can regenerate a dead host.
The symptoms of Vampiris are very similar to those of vampirism. Infected hosts develop a craving for blood, and become extremely sensitive to UV radiation, as UV rays destroy the bacilli. Vampiris also causes hysterical blindness near mirrors, a severe allergy to the smell of garlic (due to garlic's severe allergic reaction to the bacilli), as well as over-development of the canines, causing them to grow to the size of fangs. Hosts also develop a strong, bulletproof adhesive that can only be penetrated by large, powerful weapons such as stakes.
When deprived of food, Vampiris creates its own proteins, and can thus infect and turn corpses as well as living hosts. While the living hosts of Vampiris will retain most of their human levels of intelligence despite their vampiric characteristics, the dead hosts - corpses infected and reanimated by Vampiris - will exhibit zombie-like behaviour. These undead hosts will mindlessly seek out blood to drink, and will even resort to feeding off the weaker of their own kind.
A pill containing dehydrated blood and a fusion inhibitor can treat, but not cure, Vampiris to the point that it allows those infected with Vampiris who take it to spent short periods of time in broad daylight. It is also shown that if a human is bitten and infected by an infected bat, they will develop an immunity to Vampiris.