- last post: 01.01.0001 12:00 AM PDT
Its already been established that infected grunts and jackals turn in to carrrier forms, along with other inadequate hosts like damaged combat forms. Most likely, this also includes drones, because of their diminutive size.
Hunters cannot be infected, because of their biological composition. All hunters are a colony of worm-like creatures working together and shaped by their armor. A Flood cannot infect a worm smaller than it.
As for brutes, we don't know why we haven't seen many infected versions of them, but here are some possible reasons:
1) Brutes have hard, leatherlike skin. It may be difficult for an infection form to penetrate that skin.
2) Brutes are a relatively new memebr of the covenant, thus meaning that their contact with the Flood has been limited. It may take some time to turn a being in to a combat form, and there may not have been any brutes exposed to the flood for that long to be infected.
3) Brutes may have some natural immunity to infection, like Johnson.
The prophets can most likely be infected, as an infection form is seen burrowing in to Mercy. However, prophets do not look like adequate hsots, and would most likely becoem carriers instead of combat forms. Also, there has only been one known contact between the Flood and a prophet (Mercy), so there may not have been time for a Prophet to be infected.
That leaves Humans and Elites, who can be infected. I believe all races have been covered.
EDIT: Your idea on Gravemind teleporting is certainly plausable. However, the teleportation system is known to work only within a certain network. It worked in Halo 2 because they were right next to Delta Halo. Unless Earth has a hidden teleportation system, i don't think Gravemind could teleport down.
[Edited on 7/1/2006]