Virusen and Bacterias are covered under the poisonframework since they work in a similiar way. Most Bacteria even produce some kind of poison that makes them that dangerous.
Also: Intelligent parasites = Goa'uld?
Parasites dont have to be animals at all. Many lichens and fungy can be parasites as well. There is a Fungy that feeds on and controls ants. This picture shows a infected Ant.
Since this is df we can go even to a rediculus variant - living Crystals that feed of the your flesh and form a stationary orgasm on your corpse. Being explosive in nature they propagate themselvs by launching theyr own shards into anything living that passes by.
I've actually seen an X-Files episode similar to what you described in that last sentence. IIRC It was called
Fire Walker.
A parasite that grows in your dwarf's cranium and than explodes releasing its spawn on those around it would be fun. Imagine if it slowly harms your dwarf and pops out in the hospital, after a great goblin siege.
Got anymore real life examples?
Google "bot fly". Now, since DF has giant versions of a lot of vermin type things, imagine a Giant Bot Fly. Pretty much your chestburster right there.
We have the chestburster idea down, but after reviewing what everyone else said. It sounds so dull now. Also, I'd imagine the giant bot fly to the size of a cat.
"O.K., the whole leech off the host is still there. The problem is, it's traditional and just boring to me. There are other types of parasites that alter the behavior of hosts and even types that can be symbiotic with their host!
Not saying don't do it. I am saying a Parasite system should include all types of parasites rather then the only ones you included.
Also yes the virus/poison system could also work excellently for some paracites.
Perhaps the virus/poison should be the by products (poop) of certain parasites. No reason why we should make new stuff up.
Hmm... the wikipedia article on parasitoids used the alternate term "necrotroph"...
I just like the sound of having your dwarves fall victim to a host of necrotrophs.
In fact, it's just plain so DF to have something like those parasitic mushrooms.
Those mushrooms that are popping out of the ant's head? Yeah, it grows by eating the brain of the ant. And conrolling the ant zombie-style to move to a place where it will be just upwind of many other ants. Then the mushroom bursts out of the head of the ant, and the spores fly out, to infect more ants.
Having mushroom zombie spores that potentially infect entire fortresses with funguses that cause dwarves' heads to explode... Yeah, that's DF, allright.
You've actually given me a better idea.
Digging deeper will cause the release of new parasites into your dwarfs. The first few waves should be held off by having well feed healthy dwarfs but when you dig too deep. Clown deep, you should hit some very FUN parasites associated with what is even deeper than those. You never know what kinds of things you'll dig up i.e. randomly generated.