I'm not aware of any rules for this but I'm inclined to think these horribly rare ordnance would be rather effective v tyranids and their bio ships?

I'm thinking that these should damage the ships structure itself in addition to their normal effect on its contents what with everything being effectively alive.

It would make the pestilaans light cruiser the ultimate answer to the Tyranid threat - oh the irony

Oh and on a not unrelated matter - are servitors affected by disease?

Yeah virus weapons should do horrific damage to 'nids, but probably wont kill of the entire fleet. Also there have been reports of carnifexes that survived Exterminatus weapons! (they had burrowed deep into the planet's crust) Almso I'd rule that since splinter fleets are subtily different: a viral strain that works well against one, might not be as effective against another.

About the servitors: It would need to be something hideously powerfull like Nurgle's rot to affect a servitor. Anything that would cause massive physical dsicomfort in a human will just be ignored by a servitor I guess they are still carriers for the disease - wich might be a good triçk to infect stuff.)

Enginser: "****, whats wrong with that servitor? it's covered in bruises and pustules and it's leaking pus out of it's ears."

Techpriest: "The flesh is weak. Ignore it."

Chaos saboteur: "Nurgle be praised! My plan works! soon the infected servitor will spread grandfather's gifts to the whole hive!"

The trick is hitting a hive ship with the torpedo. The spore clouds defending the hive ship will take out a whole spread of torpedoes normally. And, taking out anything less than a hive ship won't really slow the fleet down much. Well, there's the narwhal, but that can probably be replaced quickly.

Are servitors still alive then or just techno zombies?

For things like the Skull servitors is there a brain inside that skull being immersed in some life sustaining solution + oxygen feed or is it literally a skull crammed with electronics?

Things like the Charron pattern servitors - are these just lobotomised cybernetically enhanced humans and thus still technically alive? Do you use Medicae or Tech use to heal them?

Are Servitor crews affected by de-pressurisation of a module?

There's actually a codex story (or might be BFG.. hum.) of an Imperial shooting a virus torpedo into a hive ship as a desperate measure. It succeeded in killing the hive ship before being driven off by other vessels. A year later, a hive-ship appeared in the next system firing spores filled with the same virus back at the imperial ships.

Are servitors still alive then or just techno zombies?

For things like the Skull servitors is there a brain inside that skull being immersed in some life sustaining solution + oxygen feed or is it literally a skull crammed with electronics?

Things like the Charron pattern servitors - are these just lobotomised cybernetically enhanced humans and thus still technically alive? Do you use Medicae or Tech use to heal them?

Are Servitor crews affected by de-pressurisation of a module?