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Major spoilers below!

Strain worms, also known as Bloodworms, are a parasitic species that mainly produces the pathogen that infect and mutates human hosts into Vampires.


As the vector to spread vampirism, these worms acted as Vampires' means of reproduction, carrying incurable and fast-acting, mutagenic virus to rewrite its host's DNA. The vampire doesn't necessarily have to infect the host via. feeding — exposing the potential host with at least a single worm should do the trick as in the case of Kelly Goodweather. The latter trait was exploited by Thomas Eichhorst at horrific effect in "Gone But Not Forgotten" through sending two suicide bomber strigois who blow themselves up with C4 to expose everyone within with their worms.

In addition of being the vector to spread vampirism, these worms bound its host to the Ancients' hive mind and control.

As with ordinary parasitic worms, bloodworms multiplies within the host and their survival depends on its condition — if their vampire host dies, the worms will lose its source of sustenance and die with it as well.

Crimson Worms[]

Main article: Crimson Worm

The progenitor of bloodworms are crimson worms. In addition of producing lesser bloodworms, crimson worms carry the consciousness or rather, soul of very Seven Ancients, effectively making them the Ancients' true form.

Bloodworm Solution[]

"Well, you can't ingest them orally. I discovered I needed to, uh, absorb them in solution through the eyes. Did you ever see this number on my arm? Did it not make you wonder about my age? I was a prisoner in a German death camp in 1944. I'm 94 years old. I need this to keep living. I've made my choice. It may be wicked, it may mean I go to a fiery and horrible place when I die, but it's too late to stop now. I will not stop. I'm going to win or die confronting the Master. I will not fade away as a weak old man."
― Setrakian about Bloodworm solution [src]

In TV series, as demonstrated by Setrakian, bloodworms can be boiled into a special solution that endows the recipient enhanced senses, longevity, strength, and durability of a Strigoi without the risk of turning him/her into one, since the worms' mutagenic viruses has been sterilized by the process. The completed solution then administered through the recipient's eye like eye drops. In addition of giving himself a leverage against strigois, Setrakian uses it to stay in the fight against The Master for as long as he can.