system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] Would it be possible to engineer a virus to infect and kill Tyranids?

Alternatively why have the Tyranids not encountered a virus that could wipe them out on any of the countless planets they have consumed?
gpt
There have been many viruses, naturally occurring as well as manufactured and deployed in plague bombs, that killed a lot of Tyranids.

The next generation of Tyranids develops a resistance, the next generation develops an immunity, then they devour and recycle the biomass from all of the dead Tyranids in the first attack. Then the next generation develops a gland that spits the same virus back out with gobs of corrosive mucus.

So, yes, but it only works the first time you use it. The HIVE MIND, which can transmit genetic information through the warp, can propagate a resistance to any disease faster than the disease itself can possibly spread.